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1
Krivonos, Roman, Daniel Wik, Brian Grefenstette, Kristin Madsen, Kerstin Perez, Steven Rossland, Sergey Sazonov und Andreas Zoglauer. „NuSTAR measurement of the cosmic X-ray background in the 3–20 keV energy band“. Monthly Notices of the Royal Astronomical Society 502, Nr. 3 (04.02.2021): 3966–75. http://dx.doi.org/10.1093/mnras/stab209.
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ABSTRACT We present measurements of the intensity of the cosmic X-ray background (CXB) with the Nuclear Spectroscopic Telescope Array (NuSTAR) telescope in the 3–20 keV energy range. Our method uses spatial modulation of the CXB signal on the NuSTAR detectors through the telescope’s side aperture. Based on the NuSTAR observations of selected extragalactic fields with a total exposure of 7 Ms, we have estimated the CXB 3–20 keV flux to be 2.8 × 10−11 erg s−1 cm−2 deg−2, which is $\sim \! 8{{\ \rm per\ cent}}$ higher than that measured with HEAO-1 and consistent with the INTEGRAL measurement. The inferred CXB spectral shape in the 3–20 keV energy band is consistent with the canonical model of Gruber et al. We demonstrate that the spatially modulated CXB signal measured by NuSTAR is not contaminated by systematic noise and is limited by photon statistics. The measured relative scatter of the CXB intensity between different sky directions is compatible with cosmic variance, which opens new possibilities for studying CXB anisotropy over the whole sky with NuSTAR.
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Brejnholt, Nicolai F., Finn E. Christensen, Charles J. Hailey, Nicolas M. Barrière, William W. Craig, Brian Grefenstette, Jason Koglin et al. „The Rainwater Memorial Calibration Facility for X-Ray Optics“. X-Ray Optics and Instrumentation 2011 (21.09.2011): 1–9. http://dx.doi.org/10.1155/2011/285079.
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The Nuclear Spectroscopic Telescope ARray (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing hard X-ray (5–80 keV) telescope to orbit. The ground calibration of the optics posed a challenge as the need to suppress finite source distance effects over the full optic and the energy range of interest were unique requirements not met by any existing facility. In this paper we present the requirements for the NuSTAR optics ground calibration, and how the Rainwater Memorial Calibration Facility, RaMCaF, is designed to meet the calibration requirements. The nearly 175 m long beamline sports a 48 cm diameter 5–100 keV X-ray beam and is capable of carrying out detailed studies of large diameter optic elements, such as the NuSTAR optics, as well as flat multilayer-coated Silicon wafers.
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Hailey, Charles J. „First results from the NuSTAR “mini-survey” of the Galactic center region“. Proceedings of the International Astronomical Union 9, S303 (Oktober 2013): 439–43. http://dx.doi.org/10.1017/s1743921314001094.
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AbstractOne of the major science objectives of the Nuclear Spectroscopic Telescope Array (NuSTAR) observatory is to perform the first sub-arcminute, hard X-ray survey of several square degrees of the Galactic plane, centered on a region near the Galactic center. As a prelude to the full survey, which began in July 2013, NuSTAR conducted a ∼500 ks, 0.3 × 0.4° “mini-survey” focused on Sgr A* and its environs. We present analysis of several candidate pulsar wind nebulae and filaments, which are revealed to be intense sources of X-ray emission at >10 keV.
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Islam, Nazma, Robin H. D. Corbet, Joel B. Coley, Katja Pottschmidt und Felix Fuerst. „Investigating the Superorbital Modulations in 4U 1909 + 07, IGR J16418-4532, and IGR J16479-4514 with Swift XRT, BAT, and NuSTAR Observations“. Astrophysical Journal 948, Nr. 1 (01.05.2023): 45. http://dx.doi.org/10.3847/1538-4357/acbc19.
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Abstract A puzzling variety of superorbital modulations has been discovered in several supergiant high mass X-ray binaries (sgHMXBs). To investigate the mechanisms driving these superorbital modulations, we have analyzed long-term Neil Gehrels Swift Observatory (Swift) Burst Alert Telescope (BAT) observations of three sgHMXBs: 4U 1909 + 07, IGR J16418–4532, and IGR J16479–4514, and constructed their dynamic power spectra and superorbital intensity profiles. These Swift BAT observations are complemented by pointed Swift X-ray Telescope (XRT) and Nuclear Spectroscopic Telescope Array (NuSTAR) observations performed near the predicted maximum and minimum phase of a single superorbital cycle for each of these sources. The BAT dynamic power spectra show changes in the strength of the superorbital modulation on timescales of years, with either the peak at the fundamental frequency and/or the second harmonic present at different times for all three sources. The pointed Swift XRT and NuSTAR observations show no significant differences between the pulse profiles and spectral parameters at the superorbital maximum and minimum phase. This is likely due to the fact the superorbital modulation had weakened significantly during the times when the NuSTAR observations were carried out for all three sources. The results from the Swift XRT, BAT, and NuSTAR analysis indicate the possible presence of multiple corotating interaction regions (CIRs) in the stellar winds of the supergiant stars, although a structured stellar wind from the supergiant star due to tidal oscillations cannot be ruled out.
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Pandey, Ashwani. „NuSTAR View of TeV Blazar Mrk 501“. Galaxies 8, Nr. 3 (25.07.2020): 55. http://dx.doi.org/10.3390/galaxies8030055.
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We report the results of flux and spectral variability studies of all seven Nuclear Spectroscopic Telescope Array (NuSTAR) observations of TeV γ-ray emitting blazar Markarian (or Mrk) 501. We found strong evidence of intraday variability in 3–79 keV X-ray light curves (LCs) of Mrk 501 during four out of these seven observations. We examined spectral variability using a model-independent hardness-ratio analysis and found a general “harder-when-brighter” behaviour in two observations. We also investigated the nature of 3–79 keV X-ray spectra of TeV blazar Mrk 501 and found that five out of seven spectra are well described by the curved log-parabola models with photon indices (at 10 keV) α∼ 2.12–2.32 and a curvature β∼ 0.15–0.28. The two other spectra are somewhat better represented by simple power-law models with photon indices 2.70 and 2.75. We briefly discuss available physical models to explain our results.
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Torres-Albà, N., S. Marchesi, X. Zhao, M. Ajello, R. Silver, T. T. Ananna, M. Baloković et al. „Compton-thick AGN in the NuSTAR Era VI: The Observed Compton-thick Fraction in the Local Universe“. Astrophysical Journal 922, Nr. 2 (01.12.2021): 252. http://dx.doi.org/10.3847/1538-4357/ac1c73.
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Abstract We present the analysis of simultaneous Nuclear Spectroscopic Telescope Array (NuSTAR) and XMM-Newton data of eight Compton-thick active galactic nuclei (CT-AGN) candidates selected in the Swift-BAT 100 month catalog. This work is part of an ongoing effort to find and characterize all CT-AGN in the Local (z ≤ 0.05) Universe. We used two physically motivated models, MYTorus and borus02, to characterize the sources in the sample, finding five of them to be confirmed CT-AGN. These results represent an increase of ∼19% over the previous NuSTAR-confirmed, BAT-selected CT-AGN at z ≤ 0.05, bringing the total number to 32. This corresponds to an observed fraction of ∼8% of all AGN within this volume-limited sample, although it increases to 20% ± 5% when limiting the sample to z ≤ 0.01. Out of a sample of 48 CT-AGN candidates, selected using BAT and soft (0.3−10 keV) X-ray data, only 24 are confirmed as CT-AGN with the addition of the NuSTAR data. This highlights the importance of NuSTAR when classifying local obscured AGN. We also note that most of the sources in our full sample of 48 Seyfert 2 galaxies with NuSTAR data have significantly different lines of sight and average torus column densities, favoring a patchy torus scenario.
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Chatterjee, Debjit, Arghajit Jana, Kaushik Chatterjee, Riya Bhowmick, Sujoy Kumar Nath, Sandip K. Chakrabarti, A. Mangalam und Dipak Debnath. „Properties of Faint X-ray Activity of XTE J1908+094 in 2019“. Galaxies 9, Nr. 2 (16.04.2021): 25. http://dx.doi.org/10.3390/galaxies9020025.
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We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe Kα emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be 6.5−0.7+0.5M⊙, with 90% confidence.
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Cooper, Kristopher, Iain G. Hannah, Brian W. Grefenstette, Lindsay Glesener, Säm Krucker, Hugh S. Hudson, Stephen M. White, David M. Smith und Jessie Duncan. „NuSTAR observations of a repeatedly microflaring active region“. Monthly Notices of the Royal Astronomical Society 507, Nr. 3 (19.08.2021): 3936–51. http://dx.doi.org/10.1093/mnras/stab2283.
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ABSTRACT We investigate the spatial, temporal, and spectral properties of 10 microflares from AR12721 on 2018 September 9 and 10 observed in X-rays using the Nuclear Spectroscopic Telescope ARray and the Solar Dynamic Observatory’s Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager. We find GOES sub-A class equivalent microflare energies of 1026–1028 erg reaching temperatures up to 10 MK with consistent quiescent or hot active region (AR) core plasma temperatures of 3–4 MK. One microflare (SOL2018-09-09T10:33), with an equivalent GOES class of A0.1, has non-thermal hard X-ray emission during its impulsive phase (of non-thermal power ∼7 × 1024 erg s−1) making it one of the faintest X-ray microflares to have direct evidence for accelerated electrons. In 4 of the 10 microflares, we find that the X-ray time profile matches fainter and more transient sources in the extreme-ultraviolet, highlighting the need for observations sensitive to only the hottest material that reaches temperatures higher than those of the AR core (>5 MK). Evidence for corresponding photospheric magnetic flux cancellation/emergence present at the footpoints of eight microflares is also observed.
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Mondal, Santanu, und C. S. Stalin. „Changing Accretion Geometry of Seyfert 1 Mrk 335 with NuSTAR: A Comparative Study“. Galaxies 9, Nr. 2 (25.03.2021): 21. http://dx.doi.org/10.3390/galaxies9020021.
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We present a detailed spectral study of the narrow-line Seyfert 1 galaxy, Markarian 335, using eight epoch observations made between 2013 and 2020 with the Nuclear Spectroscopic Telescope Array. The source was variable during this period both in spectral flux and flow geometry. We estimated the height of the Compton cloud from the model fitted parameters for the whole observation period. This allowed us to investigate the underlying physical processes that drive the variability in X-rays. Our model fitted mass varies in a narrow range, between (2.44±0.45−3.04±0.56)×107M⊙, however, given the large error bars, it is consistent with being constant and is in agreement with that known from optical reverberation mapping observations. The disk mass accretion rate reached a maximum of 10% of the Eddington rate during June 2013. Our study sheds light on mass outflows from the system and also compares different aspects of accretion with X-ray binaries.
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Hare, Jeremy, Igor Volkov, George G. Pavlov, Oleg Kargaltsev und Simon Johnston. „Precise Timing and Phase-resolved Spectroscopy of the Young Pulsar J1617–5055 with NuSTAR“. Astrophysical Journal 923, Nr. 2 (01.12.2021): 249. http://dx.doi.org/10.3847/1538-4357/ac30e2.
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Abstract We report on a Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the young, energetic pulsar PSR J1617–5055. Parkes Observatory 3 GHz radio observations of the pulsar (taken about 7 yr before the NuSTAR observations) are also reported here. NuSTAR detected pulsations at a frequency of f ≈ 14.4 Hz (P ≈ 69.44 ms) and, in addition, the observation was long enough to measure the source’s frequency derivative, f ̇ ≈ − 2.8 × 10 − 11 Hz s−1. We find that the pulsar shows one peak per period at both hard X-ray and radio wavelengths, but that the hard X-ray pulse is broader (having a duty cycle of ∼0.7), than the radio pulse (having a duty cycle of ∼0.08). Additionally, the radio pulse is strongly linearly polarized. J1617's phase-integrated hard X-ray spectrum is well fit by an absorbed power-law model, with a photon index Γ = 1.59 ± 0.02. The hard X-ray pulsations are well described by three Fourier harmonics, and have a pulsed fraction that increases with energy. We also fit the phase-resolved NuSTAR spectra with an absorbed power-law model in five phase bins and find that the photon index varies with phase from Γ = 1.52 ± 0.03 at phases around the flux maximum to Γ = 1.79 ± 0.06 around the flux minimum. Last, we compare our results with other pulsars whose magnetospheric emission is detected at hard X-ray energies and find that, similar to previous studies, J1617's hard X-ray properties are more similar to the MeV pulsars than the GeV pulsars.
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Panagiotou, C., und R. Walter. „The environment of the wind–wind collision region of η Carinae“. Astronomy & Astrophysics 610 (Februar 2018): A37. http://dx.doi.org/10.1051/0004-6361/201731841.
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Context. η Carinae is a colliding wind binary hosting two of the most massive stars and featuring the strongest wind collision mechanical luminosity. The wind collision region of this system is detected in X-rays and γ-rays and offers a unique laboratory for the study of particle acceleration and wind magneto-hydrodynamics. Aim. Our main goal is to use X-ray observations of η Carinae around periastron to constrain the wind collision zone geometry and understand the reasons for its variability. Methods. We analysed 10 Nuclear Spectroscopic Telescope Array (NuSTAR) observations, which were obtained around the 2014 periastron. The NuSTAR array monitored the source from 3 to 30 keV, which allowed us to grasp the continuum and absorption parameters with very good accuracy. We were able to identify several physical components and probe their variability. Results. The X-ray flux varied in a similar way as observed during previous periastrons and largely as expected if generated in the wind collision region. The flux detected within ~10 days of periastron is lower than expected, suggesting a partial disruption of the central region of the wind collision zone. The Fe Kα line is likely broadened by the electrons heated along the complex shock fronts. The variability of its equivalent width indicates that the fluorescence region has a complex geometry and that the source obscuration varies quickly with the line of sight.
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Pike, Sean N., Mutsumi Sugizaki, Jakob van den Eijnden, Benjamin Coughenour, Amruta D. Jaodand, Tatehiro Mihara, Sara E. Motta et al. „Accretion Spin-up and a Strong Magnetic Field in the Slow-spinning Be X-Ray Binary MAXI J0655-013“. Astrophysical Journal 954, Nr. 1 (22.08.2023): 48. http://dx.doi.org/10.3847/1538-4357/ace696.
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Abstract We present Monitor of All-sky X-ray Image (MAXI) and Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the Be X-ray binary, MAXI J0655−013, in outburst. NuSTAR observed the source once early in the outburst, when spectral analysis yields a bolometric (0.1–100 keV), unabsorbed source luminosity of L bol = 5.6 × 1036 erg s−1, and a second time 54 days later, by which time the luminosity had dropped to L bol = 4 × 1034 erg s−1 after first undergoing a dramatic increase. Timing analysis of the NuSTAR data reveals a neutron star spin period of 1129.09 ± 0.04 s during the first observation, which decreased to 1085 ± 1 s by the time of the second observation, indicating spin-up due to accretion throughout the outburst. Furthermore, during the first NuSTAR observation, we observed quasi-periodic oscillations (QPOs) with centroid frequency ν 0 = 89 ± 1 mHz, which exhibited a second harmonic feature. By combining the MAXI and NuSTAR data with pulse period measurements reported by Fermi/GBM, we are able to show that apparent flaring behavior in the MAXI light curve is an artifact introduced by uneven sampling of the pulse profile, which has a large pulsed fraction. Finally, we estimate the magnetic field strength at the neutron star surface via three independent methods, invoking a tentative cyclotron resonance scattering feature at 44 keV, QPO production at the inner edge of the accretion disk, and spin-up via interaction of the neutron star magnetic field with accreting material. Each of these result in a significantly different value. We discuss the strengths and weaknesses of each method and infer that MAXI J0655−013 is likely to have a high surface magnetic field strength, B s > 1013 G.
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Sanna, A., C. Ferrigno, P. S. Ray, L. Ducci, G. K. Jaisawal, T. Enoto, E. Bozzo et al. „NuSTAR and NICER reveal IGR J17591–2342 as a new accreting millisecond X-ray pulsar“. Astronomy & Astrophysics 617 (September 2018): L8. http://dx.doi.org/10.1051/0004-6361/201834160.
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We report the discovery by the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) of the accreting millisecond X-ray pulsar IGR J17591–2342. Coherent X-ray pulsations around 527.4 Hz (1.9 ms) with a clear Doppler modulation were detected. This implies an orbital period of ∼8.8 h and a projected semi-major axis of ∼1.23 lt-s. With the binary mass function, we estimate a minimum companion mass of 0.42 M⊙, obtained assuming a neutron star mass of 1.4 M⊙ and an inclination angle lower than 60°, as suggested by the absence of eclipses or dips in the light curve of the source. The broad-band energy spectrum, obtained by combining NuSTAR, swift and INTEGRAL observations, is dominated by Comptonisation of soft thermal seed photons with a temperature of ∼0.7 keV by electrons heated to 21 keV. We also detect black-body-like thermal direct emission that is compatible with an emission region of a few kilometers and a temperature compatible with the seed source of Comptonisation. A weak Gaussian line centred on the iron Kα complex can be interpreted as a signature of disc reflection. A similar spectrum characterises the NICER spectra, which was measured when the outburst faded.
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Kabiraj, Sanhita, und Biswajit Paul. „Broad-band X-ray characteristics of the transient pulsar GRO J2058+42“. Monthly Notices of the Royal Astronomical Society 497, Nr. 1 (16.07.2020): 1059–65. http://dx.doi.org/10.1093/mnras/staa2079.
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ABSTRACT The Be X-ray binary GRO J2058+42 recently went through a Type-II outburst during 2019 March–April lasting for about 50 d. This outburst was detected with the operating all sky X-ray monitors like the Fermi-GBM, Swift-BAT, and MAXI-GSC. Two Nuclear Spectroscopic Telescope Array(NuSTAR) observations were also made, one during the rise and other during the decay of the outburst. It gave us the unique opportunity to analyse the broad-band characteristics of the pulsar for the first time and accretion torque characteristics of the pulsar over a range of X-ray luminosity. The pulse profiles are strongly energy-dependent, with at least four different pulse components at low energy (< 20 keV), which evolves to a single-peaked profile at high energy (> 30 keV). In each of the narrow energy bands, the pulse profiles are nearly identical in the two NuSTAR observations. The spectra from both the observations are fitted well to a power-law with a Fermi–Dirac-type high-energy cutoff. We ruled out presence of a cyclotron line in the pulse phase averaged X-ray spectrum in the NuSTAR band with an optical depth greater than 0.15. An iron emission line is detected in both the NuSTAR spectra with an equivalent width of about 125 eV. We looked at the dependence of the spin-up rate on the luminosity and estimated the magnetic field strength from that, which came out to be much higher compared to other known BeXRB pulsars. Lastly, we discussed the inadequacy of the torque–luminosity relation for determination of magnetic field strength of neutron stars.
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Duncan, Jessie, Reed B. Masek, Albert Y. Shih, Lindsay Glesener, Will Barnes, Katharine K. Reeves, Yixian Zhang, Iain G. Hannah und Brian W. Grefenstette. „Thermal Evolution of an Active Region Through Quiet and Flaring Phases as Observed by NuSTAR, XRT, and AIA“. Astrophysical Journal 966, Nr. 2 (01.05.2024): 197. http://dx.doi.org/10.3847/1538-4357/ad37f7.
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Abstract Solar active regions (ARs) contain a broad range of temperatures, with the thermal plasma distribution often observed to peak in the few millions of kelvin. Differential emission measure (DEM) analysis can allow instruments with diverse temperature responses to be used in concert to estimate this distribution. Nuclear Spectroscopic Telescope ARray (NuSTAR) hard X-ray (HXR) observations are uniquely sensitive to the highest-temperature components of the corona, and thus extremely powerful for examining signatures of reconnection-driven heating. Here, we use NuSTAR diagnostics in combination with extreme-ultraviolet and soft X-ray observations (from the Solar Dynamics Observatory/Atmospheric Imaging Assembly and Hinode/X-Ray Telescope) to construct DEMs over 170 distinct time intervals during a 5 hr observation of an alternately flaring and quiet active region (NOAA designation AR 12712). This represents the first HXR study to examine the time evolution of the distribution of thermal plasma in an AR. During microflares, we find that the initial microflare-associated plasma heating is predominantly heating of material that is already relatively hot, followed later on by broader heating of initially cooler material. During quiescent times, we show that the amount of extremely hot (>10 MK) material in this region is significantly (∼2–4 orders of magnitude) less than that found in the quiescent AR observed in HXRs by FOXSI-2. This result implies there can be radically different high-temperature thermal distributions in different ARs, and strongly motivates future HXR DEM studies covering a large number of these regions.
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Sharma, Prince, Rahul Sharma, Chetana Jain und Anjan Dutta. „Timing and spectral analysis of HMXB OAO 1657-415 with NuSTAR“. Monthly Notices of the Royal Astronomical Society 509, Nr. 4 (27.11.2021): 5747–55. http://dx.doi.org/10.1093/mnras/stab3436.
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ABSTRACT This work presents a comprehensive timing and spectral analysis of high-mass X-ray binary pulsar, OAO 1657-415 by using the observation made with Nuclear Spectroscopic Telescope Array on 2019 June. During this observation, OAO 1657-415 exhibited X-ray variability by a factor of about 3. X-ray pulsations at 37.03322(14) s were observed up to 70 keV. OAO 1657-415 was undergoing a spin-down phase with $\dot{P} = 9(1) \times 10^{-8}$ s s−1. This is an order of about 100 larger than the long-term spin-up rate. The pulse profile evolved marginally during the observation. We have discussed the long-term pulse period history of the source spanning a time-base of 43 yr, including the latest Fermi/GBM data. The 3–70 keV source spectrum is described by a partially covered cut-off power law, an Fe Kα line at 6.4 keV and a Compton shoulder at 6.3 keV. We report the presence of a cyclotron absorption feature around 40 keV, which is indicative of a surface magnetic field strength of 3.59 ± 0.06 (1 + $z$) × 1012 and $3.29_{-0.22}^{+0.23} \ (1 + z) \times 10^{12}$ G. This work shows the first robust presence of cyclotron absorption feature in the source.
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Fabian, A. C., D. J. Buisson, P. Kosec, C. S. Reynolds, D. R. Wilkins, J. A. Tomsick, D. J. Walton et al. „The soft state of the black hole transient source MAXI J1820+070: emission from the edge of the plunge region?“ Monthly Notices of the Royal Astronomical Society 493, Nr. 4 (27.02.2020): 5389–96. http://dx.doi.org/10.1093/mnras/staa564.
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ABSTRACT The Galactic black hole X-ray binary MAXI J1820+070 had a bright outburst in 2018 when it became the second brightest X-ray source in the sky. It was too bright for X-ray CCD instruments such as XMM–Newton and Chandra, but was well observed by photon-counting instruments such as Neutron star Inner Composition Explorer (NICER) and Nuclear Spectroscopic Telescope Array(NuSTAR). We report here on the discovery of an excess-emission component during the soft state. It is best modelled with a blackbody spectrum in addition to the regular disc emission, modelled as either diskbb or kerrbb. Its temperature varies from about 0.9 to 1.1 keV, which is about 30–80 per cent higher than the inner disc temperature of diskbb. Its flux varies between 4 and 12 per cent of the disc flux. Simulations of magnetized accretion discs have predicted the possibility of excess emission associated with a non-zero torque at the innermost stable circular orbit (ISCO) about the black hole, which, from other NuSTAR studies, lies at about 5 gravitational radii or about 60 km (for a black hole, mass is $8\, {\rm M}_{\odot }$). In this case, the emitting region at the ISCO has a width varying between 1.3 and 4.6 km and would encompass the start of the plunge region where matter begins to fall freely into the black hole.
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Barua, Samuzal, V. Jithesh, Ranjeev Misra, Gulab C. Dewangan, Rathin Sarma und Amit Pathak. „NuSTAR observation of Ark 564 reveals the variation of coronal temperature with flux“. Monthly Notices of the Royal Astronomical Society 492, Nr. 2 (10.01.2020): 3041–46. http://dx.doi.org/10.1093/mnras/staa067.
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ABSTRACT The hard X-ray spectral index of some active galactic nuclei (AGN) has been observed to steepen with the source flux. This has been interpreted in a Comptonization scenario, where an increase in the soft flux decreases the temperature of the corona, leading to steepening of the photon index. However, the variation of the coronal temperature with flux has been difficult to measure due to the presence of complex reflection component in the hard X-rays and the lack of high-quality data at that energy band. Recently, a 200 ks Nuclear Spectroscopic Telescope Array(NuSTAR) observation of Ark 564 in 3–50 keV band revealed the presence of one of the coolest coronae with temperature kTe ∼ 15 keV in the time-averaged spectrum. Here, we reanalyse the data and examined the spectra in four flux levels. Our analysis shows that the coronal temperature decreased from ∼17 to ∼14 keV as the flux increased. The high energy photon index Γ ∼ 2.3 varied by less than 0.1, implying that the optical depth of the corona increased by about 10 per cent as the flux increased. This first reporting of coronal temperature variation with flux shows that further long observation by NuSTAR of this and other sources would shed light on the geometry and dynamics of the inner regions of the accretion flow.
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Jana, Arghajit, Arka Chatterjee, Neeraj Kumari, Prantik Nandi, Sachindra Naik und Dusmanta Patra. „Probing the nuclear and circumnuclear properties of NGC 6300 using X-ray observations“. Monthly Notices of the Royal Astronomical Society 499, Nr. 4 (05.11.2020): 5396–409. http://dx.doi.org/10.1093/mnras/staa2552.
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ABSTRACT We present the results obtained from a detailed X-ray timing and spectral analysis of the Seyfert 2 galaxy NGC 6300 by using observations from the Suzaku observatory, theChandra X-ray Observatory and the Nuclear Spectroscopic Telescope Array(NuSTAR) mission between 2007 and 2016. We calculate the variance and the rms fractional variability of the source in different energy bands and we find variabilities in various energy bands. Spectral properties of the source are studied by using various phenomenological and physical models. The properties of the Compton clouds, reflection, Fe Kα line emission and soft X-ray excess are studied in detail. Several physical parameters of the source are extracted and investigated to establish the presence/absence of any correlation between them. We also investigate the nature of the circumnuclear ‘torus’ and we find that the torus is not uniform, but clumpy. The observed changes in the line-of-sight column density can be explained in terms of transiting clouds. The iron line-emitting region is found to be different in the different epochs of observations. We also observe that the torus and the nucleus independently evolve over the years.
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Jana, Arghajit, Sachindra Naik, Debjit Chatterjee und Gaurava K. Jaisawal. „NuSTAR and Swift observations of the extragalactic black hole X-ray binaries“. Monthly Notices of the Royal Astronomical Society 507, Nr. 4 (28.08.2021): 4779–87. http://dx.doi.org/10.1093/mnras/stab2448.
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ABSTRACT We present the results obtained from detailed spectral and timing studies of extragalactic black hole X-ray binaries LMC X–1 and LMC X–3, using simultaneous observations with Nuclear Spectroscopic Telescope Array (NuSTAR) and Neil Gehrels Swift observatories. The combined spectra in the 0.5–30 keV energy range, obtained between 2014 and 2019, are investigated for both sources. We do not find any noticeable variability in 0.5–30 keV light curves, with 0.1–10 Hz fractional rms estimated to be <2 per cent. No evidence of quasi-periodic oscillations is found in the power density spectra. The sources are found to be in the high soft state during the observations with disc temperature Tin ∼ 1 keV, photon index, Γ > 2.5 and thermal emission fraction, fdisc > 80 per cent. An Fe Kα emission line is detected in the spectra of LMC X–1, though no such feature is observed in the spectra of LMC X–3. From the spectral modelling, the spins of the black holes in LMC X–1 and LMC X–3 are estimated to be in the range of 0.92–0.95 and 0.19−0.29, respectively. The accretion efficiency is found to be, η ∼ 0.13 and η ∼ 0.04 for LMC X–1 and LMC X–3, respectively.
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Ezhikode, Savithri H., Gulab C. Dewangan, Ranjeev Misra und Ninan Sajeeth Philip. „Correlation between relativistic reflection fraction and photon index in NuSTAR sample of Seyfert 1 AGN“. Monthly Notices of the Royal Astronomical Society 495, Nr. 3 (Januar 2020): 3373–86. http://dx.doi.org/10.1093/mnras/staa1288.
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ABSTRACT The primary X-ray emission from active galactic nuclei (AGNs), described by a power-law, irradiates the accretion disc producing reflection features in the spectrum. The reflection features arising from the inner regions of the disc can be significantly modified by the relativistic effects near the black hole. We investigate the relationship between the relativistic reflection fraction Rf, defined as the ratio of the coronal intensity that illuminates the accretion disc to the coronal intensity observed directly, and the hard X-ray photon index Γ of a Nuclear Spectroscopic Telescope Array (NuSTAR) sample of Seyfert 1 galaxies. The X-ray spectra are modelled using relxill code that helps to directly obtain the reflection fraction of a relativistically smeared reflection component. The parameter Rf depends on the amount of Comptonized X-ray emission intercepted by the inner accretion disc. We found a positive correlation between Γ and Rf in our sample. Seed photons from a larger area of an accretion disc entering the corona will result in increased cooling of the coronal plasma, giving rise to steeper X-ray spectrum. The corona irradiating the larger area of the disc will result in higher reflection fraction. Thus, the observed Rf –Γ relation is most likely related to the variations in the disc–corona geometry of AGNs.
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Annuar, A., D. M. Alexander, P. Gandhi, G. B. Lansbury, D. Asmus, M. Baloković, D. R. Ballantyne et al. „NuSTAR observations of four nearby X-ray faint AGNs: low luminosity or heavy obscuration?“ Monthly Notices of the Royal Astronomical Society 497, Nr. 1 (27.06.2020): 229–45. http://dx.doi.org/10.1093/mnras/staa1820.
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ABSTRACT We present NuSTAR (Nuclear Spectroscopic Telescope Array) observations of four active galactic nuclei (AGNs) located within 15 Mpc. These AGNs, namely ESO 121-G6, NGC 660, NGC 3486, and NGC 5195, have observed X-ray luminosities of L2–10 keV,obs ≲ 1039 erg s−1, classifying them as low-luminosity AGN (LLAGN). We perform broad-band X-ray spectral analysis for the AGN by combining our NuSTAR data with Chandra or XMM–Newton observations to directly measure their column densities (NH) and infer their intrinsic power. We complement our X-ray data with archival and new high-angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured (NH > 1023 cm−2; L2–10 keV,int ∼ 1041 erg s−1), and NGC 660 may be Compton thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with L2–10 keV,int < 1039 erg s−1, i.e. genuine LLAGN. Both of the heavily obscured AGNs have Lbol > 1041 erg s−1 and λEdd ≳ 10−3, and are detected in high-angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486, however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN.
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Victoria-Ceballos, César Ivan, Omaira González-Martín, Josefa Masegosa, Anna Lia Longinotti, Donaji Esparza-Arredondo und Natalia Osorio-Clavijo. „Testing Physical Scenarios for the Reflection Features of Type-1 AGNs using XMM-Newton and NuSTAR Simultaneous Observations“. Astrophysical Journal 954, Nr. 1 (25.08.2023): 96. http://dx.doi.org/10.3847/1538-4357/ace785.
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Abstract Above ∼3 keV, the X-ray spectrum of active galactic nuclei (AGNs) is characterized by the intrinsic continuum and Compton reflection features. For type-1 AGNs, several regions may contribute to the reflection. To investigate the nature of the reflecting medium, we perform a systematic analysis of the reflector using XMM-Newton and Nuclear Spectroscopic Telescope Array observations of a sample of 22 type-1 AGNs. We create a baseline model that includes Galactic absorption and an intrinsically absorbed power law, plus a reflection model. We test a set of nine reflection models in a subsample of five objects. Based on these results, we select three models to be tested on the entire sample, accounting for distinct physical scenarios: neutral/distant reflection, ionized/relativistic reflection, and neutral/distant+ionized/relativistic reflection, namely, a hybrid model. We find that 18 sources require the reflection component to fit their spectra. Among them, 67% prefer the hybrid model. Neutral and ionized models are equally preferred by three sources. We conclude that both the neutral/distant reflector most probably associated with the inner edges of the torus and the ionized/relativistic reflector associated with the accretion disk are required to describe the reflection in type-1 AGNs.
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Jana, Arghajit, Claudio Ricci, Sachindra Naik, Atsushi Tanimoto, Neeraj Kumari, Hsiang-Kuang Chang, Prantik Nandi, Arka Chatterjee und Samar Safi-Harb. „Absorption variability of the highly obscured active galactic nucleus NGC 4507“. Monthly Notices of the Royal Astronomical Society 512, Nr. 4 (25.03.2022): 5942–59. http://dx.doi.org/10.1093/mnras/stac799.
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ABSTRACT We present a detailed study of the highly obscured active galaxy NGC 4507, performed using four Nuclear Spectroscopic Telescope Array (NuSTAR) observations carried out between May and August in 2015 (∼130 ks in total). Using various phenomenological and physically motivated torus models, we explore the properties of the X-ray source and those of the obscuring material. The primary X-ray emission is found to be non-variable, indicating a stable accretion during the period of the observations. We find the equatorial column density of the obscuring materials to be ∼2 × 1024 cm−2 while the line-of-sight column density to be ∼7–8 × 1023 cm−2. The source is found to be deeply buried with the torus covering factor of ∼0.85. We observe variability in the line-of-sight column density on a time-scale of <35 d. The covering factor of the Compton-Thick material is found to be ∼0.35 in agreement with the results of recent X-ray surveys. From the variability of the line-of-sight column density, we estimate that the variable absorbing material is likely located either in the BLR or in the torus.
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Rajguru, Garima, L. Marcotulli, M. Ajello und A. Tramacere. „XMM–NuSTAR Observation and Multiwavelength Spectral Energy Distribution Modeling of Blazar 4FGL J1520.8–0348“. Astrophysical Journal 965, Nr. 2 (01.04.2024): 112. http://dx.doi.org/10.3847/1538-4357/ad3236.
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Abstract Active galactic nuclei (AGNs) can power relativistic jets, which are called blazars when pointed close to our line of sight. Depending on the presence or absence of emission lines in their optical spectra, blazars are categorized into flat spectrum radio quasars (FSRQs) or BL Lacertae (BL Lac) objects. According to the “blazar sequence,” as synchrotron peak frequency ( ν pk sy ) shifts to higher energies, the synchrotron peak luminosity decreases. This means that BL Lac objects as luminous as FSRQs, and with synchrotron peak frequencies ν pk sy > 10 15 Hz, should not exist. Detected as a high-synchrotron peak (HSP; ν pk sy > 10 15 Hz) BL Lac object, 4FGL J1520.8-0348 shows high γ-ray luminosity (L γ > 1046 erg s−1), being at a high redshift of z = 1.46. Since it is an outlier in the “blazar sequence,” the process of its jet acceleration and power may be different from bona fide BL Lac objects. In this work, we constrain its spectral energy distribution (SED) by modeling the multiwavelength data from infrared to γ-ray regime. Simultaneous X-ray data were obtained from X-ray Multi-Mirror Mission and Nuclear Spectroscopic Telescope Array to constrain the synchrotron emission and underlying electron distribution. On undertaking the SED modeling of the source, including the effect of extragalactic background light, we conclude that the source is more likely to be a “blue FSRQ” or “masquerading BL Lac” where the BL Lac object is actually an FSRQ in disguise.
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Tümer, Ayşegül, Daniel R. Wik, Xiaoyuan Zhang, Duy N. Hoang, Massimo Gaspari, Reinout J. van Weeren, Lawrence Rudnick et al. „The NuSTAR and Chandra View of CL 0217+70 and Its Tell-tale Radio Halo“. Astrophysical Journal 942, Nr. 2 (01.01.2023): 79. http://dx.doi.org/10.3847/1538-4357/aca1b5.
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Abstract Mergers of galaxy clusters are the most energetic events in the universe, driving shock and cold fronts, generating turbulence, and accelerating particles that create radio halos and relics. The galaxy cluster CL 0217+70 is a remarkable late-stage merger, with a double peripheral radio relic and a giant radio halo. Chandra detects surface brightness (SB) edges that correspond to radio features within the halo. In this work, we present a study of this cluster with Nuclear Spectroscopic Telescope Array and Chandra data using spectro-imaging methods. The global temperature is found to be kT = 9.1 keV. We set an upper limit for the inverse Compton (IC) flux of ∼2.7 × 10−12 erg s−1 cm−2, and a lower limit to the magnetic field of 0.08 μG. Our local IC search revealed a possibility that IC emission may have a significant contribution at the outskirts of the radio halo emission and on/near shock regions within ∼0.6 r 500 of clusters. We detected a “hot spot” feature in our temperature map coincident with an SB edge, but our investigation on its origin is inconclusive. If the “hot spot” is the downstream of a shock, we set a lower limit of kT > 21 keV to the plasma that corresponds to ∼2. We found three shock fronts within 0.5 r 500. Multiple weak shocks within the cluster center hint at an ongoing merger activity and continued feeding of the giant radio halo. CL 0217+70 is the only example hosting these secondary shocks in multiple form.
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Agarwal, Aditi, Priyanka Rani, Raj Prince, C. S. Stalin, G. C. Anupama und Vipul Agrawal. „A Possible Quasi-Periodic Oscillation in the X-ray Emission of 3C 120“. Galaxies 9, Nr. 2 (25.03.2021): 20. http://dx.doi.org/10.3390/galaxies9020020.
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We present here the detection of a possible quasi-periodic oscillation (QPO) signal in the X-ray light curve of the active galactic nucleus 3C 120, a broad line radio galaxy at z = 0.033. The hint of a QPO at the 3σ level at 7.1 × 10−6 Hz (∼1.65 days) was detected based on the analysis of X-ray data acquired in the 3–79 keV band by the Nuclear Spectroscopic Telescope Array (NuSTAR). The data, when processed separately in the soft (3–10 keV), hard (10–79 keV) and the total (3–79 keV) bands using four different techniques, namely discrete correlation function, Lomb Scargle periodogram, structure–function, and power spectral density indicated the presence of a QPO. 3C 120 very well fits in the negative correlation in the frequency of the QPO versus the black hole mass (FQPO versus MBH) diagram known for stellar-mass and supermassive black hole sources. Considering the observed signs of QPO to represent the innermost stable orbit of the accretion disk, we found a black hole mass of 1.9×109 M⊙ for a Kerr black hole and 3.04×108 M⊙ for a Schwarzschild black hole. This deduced black hole mass from QPO measurement is a few times larger than the black hole mass obtained from reverberation mapping observations.
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Grimani, Catia. „Clues from 4U 0142+61 on supernova fallback disc formation and precession“. Monthly Notices of the Royal Astronomical Society 507, Nr. 1 (21.07.2021): 261–66. http://dx.doi.org/10.1093/mnras/stab2078.
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ABSTRACT The Nuclear Spectroscopic Telescope Array (NuSTAR) experiment detected a hard X-ray emission (10–70 keV) with a period of 8.68917 s and a pulse-phase modulation at 55 ks, or half this value, from the anomalous X-ray pulsar (AXP) 4U 0142+61. It is shown here that this evidence is naturally explained by the precession of a Keplerian supernova fallback disc surrounding this AXP. It is also found that the precession of discs formed around young neutron stars at distances larger than those considered in the past, may constitute almost neglected sources of gravitational waves with frequencies belonging to the sensitivity bands of the future space interferometers: Laser Interferometer Space Antenna (LISA), Advanced Laser Interferometer Antenna (ALIA), DECi-hertz Interferometer Gravitational wave Observatory (DECIGO), and Big Bang Observer (BBO). In this work, the gravitational wave emission from precessing fallback discs possibly formed around young pulsars such as Crab in a region extending beyond 8 × 107 m from the pulsar surface is estimated. It is also evaluated the role that infrared radiation emission from circumpulsar discs may play in contributing to inverse Compton scattering of TeV energy positrons and electrons. Extensive observational campaigns of disc formation around young and middle-aged pulsars may also contribute to solve the long-standing problem of a pulsar origin for the excess of positrons in cosmic rays observed near the Earth above 7 GeV. In the near future the James Webb Space Telescope, with unprecedented near- and mid-infrared observation capabilities, may provide direct evidence of a large sample of supernova fallback discs.
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Cattell, Cynthia, Lindsay Glesener, Benjamin Leiran, John Dombeck, Keith Goetz, Juan Carlos Martínez Oliveros, Samuel T. Badman, Marc Pulupa und Stuart D. Bale. „Periodicities in an active region correlated with Type III radio bursts observed by Parker Solar Probe“. Astronomy & Astrophysics 650 (Juni 2021): A6. http://dx.doi.org/10.1051/0004-6361/202039510.
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Context. Periodicities have frequently been reported across many wavelengths in the solar corona. Correlated periods of ~5 min, comparable to solar p-modes, are suggestive of coupling between the photosphere and the corona. Aims. Our study investigates whether there are correlations in the periodic behavior of Type III radio bursts which are indicative of nonthermal electron acceleration processes, and coronal extreme ultraviolet (EUV) emission used to assess heating and cooling in an active region when there are no large flares. Methods. We used coordinated observations of Type III radio bursts from the FIELDS instrument on Parker Solar Probe (PSP), of EUV emissions by the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and white light observations by SDO Helioseismic and Magnetic Image (HMI), and of solar flare X-rays by Nuclear Spectroscopic Telescope Array (NuSTAR) on April 12, 2019. Several methods for assessing periodicities are utilized and compared to validate periods obtained. Results. Periodicities of ~5 min in the EUV in several areas of an active region are well correlated with the repetition rate of the Type III radio bursts observed on both PSP and Wind. Detrended 211 and 171 Å light curves show periodic profiles in multiple locations, with 171 Å peaks sometimes lagging those seen in 211 Å. This is suggestive of impulsive events that result in heating and then cooling in the lower corona. NuSTAR X-rays provide evidence for at least one microflare during the interval of Type III bursts, but there is not a one-to-one correspondence between the X-rays and the Type III bursts. Our study provides evidence for periodic acceleration of nonthermal electrons (required to generate Type III radio bursts) when there were no observable flares either in the X-ray data or the EUV. The acceleration process, therefore, must be associated with small impulsive events, perhaps nanoflares.
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Pike, Sean N., Hitoshi Negoro, John A. Tomsick, Matteo Bachetti, McKinley Brumback, Riley M. T. Connors, Javier A. García et al. „MAXI and NuSTAR Observations of the Faint X-Ray Transient MAXI J1848-015 in the GLIMPSE-C01 Cluster“. Astrophysical Journal 927, Nr. 2 (01.03.2022): 190. http://dx.doi.org/10.3847/1538-4357/ac5258.
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Abstract We present the results of Monitor of All-sky X-ray Image (MAXI) monitoring and two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the recently discovered faint X-ray transient MAXI J1848015. Analysis of the MAXI light curve shows that the source underwent a rapid flux increase beginning on 2020 December 20, followed by a rapid decrease in flux after only ∼5 days. NuSTAR observations reveal that the source transitioned from a bright soft state with unabsorbed, bolometric (0.1–100 keV) flux F = 6.9 ± 0.1 × 10−10 erg cm−2 s−1, to a low hard state with flux F = 2.85 ± 0.04 × 10−10 erg cm−2 s−1. Given a distance of 3.3 kpc, inferred via association of the source with the GLIMPSE-C01 cluster, these fluxes correspond to an Eddington fraction of the order of 10−3 for an accreting neutron star (NS) of mass M = 1.4M ⊙, or even lower for a more massive accretor. However, the source spectra exhibit strong relativistic reflection features, indicating the presence of an accretion disk that extends close to the accretor, for which we measure a high spin, a = 0.967 ± 0.013. In addition to a change in flux and spectral shape, we find evidence for other changes between the soft and hard states, including moderate disk truncation with the inner disk radius increasing from R in ≈ 3 R g to R in ≈ 8 R g, narrow Fe emission whose centroid decreases from 6.8 ± 0.1 keV to 6.3 ± 0.1 keV, and an increase in low-frequency (10−3–10−1 Hz) variability. Due to the high spin, we conclude that the source is likely to be a black hole rather than an NS, and we discuss physical interpretations of the low apparent luminosity as well as the narrow Fe emission.
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Jana, Arghajit, Neeraj Kumari, Prantik Nandi, Sachindra Naik, Arka Chatterjee, Gaurava K. Jaisawal, Kimitake Hayasaki und Claudio Ricci. „Broad-band X-ray observations of the 2018 outburst of the changing-look active galactic nucleus NGC 1566“. Monthly Notices of the Royal Astronomical Society 507, Nr. 1 (29.07.2021): 687–703. http://dx.doi.org/10.1093/mnras/stab2155.
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ABSTRACT We study the nature of the changing-look active galactic nucleus NGC 1566 during its 2018 June outburst. During the outburst, the X-ray intensity of the source rises up to ∼25–30 times compared to its quiescent state intensity. We perform timing and spectral analysis of the source during pre-outburst, outburst, and post-outburst epochs using semisimultaneous observations with the XMM–Newton, Nuclear Spectroscopic Telescope Array(NuSTAR), and Neil Gehrels Swift Observatories. We calculate variance, normalized variance, and fractional rms amplitude in different energy bands to study the variability. The broad-band 0.5–70 keV spectra are fitted with phenomenological models, as well as physical models. A strong soft X-ray excess is detected in the spectra during the outburst. The soft-excess emission is found to be complex and could originate in the warm Comptonizing region in the inner accretion disc. We find that the increase in the accretion rate is responsible for the sudden rise in luminosity. This is supported by the ‘q’-shape of the hardness-intensity diagram that is generally found in outbursting black hole X-ray binaries. From our analysis, we find that NGC 1566 most likely harbours a low-spinning black hole with the spin parameter a* ∼ 0.2. We also discuss a scenario where the central core of NGC 1566 could be a merging supermassive black hole.
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Yamada, Satoshi, Yoshihiro Ueda, Atsushi Tanimoto, Masatoshi Imanishi, Yoshiki Toba, Claudio Ricci und George C. Privon. „Comprehensive Broadband X-Ray and Multiwavelength Study of Active Galactic Nuclei in 57 Local Luminous and Ultraluminous Infrared Galaxies Observed with NuSTAR and/or Swift/BAT“. Astrophysical Journal Supplement Series 257, Nr. 2 (01.12.2021): 61. http://dx.doi.org/10.3847/1538-4365/ac17f5.
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Abstract We perform a systematic X-ray spectroscopic analysis of 57 local luminous and ultraluminous infrared galaxy systems (containing 84 individual galaxies) observed with the Nuclear Spectroscopic Telescope Array and/or Swift/BAT. Combining soft X-ray data obtained with Chandra, XMM-Newton, Suzaku, and/or Swift/XRT, we identify 40 hard (>10 keV) X-ray–detected active galactic nuclei (AGNs) and constrain their torus parameters with the X-ray clumpy torus model XCLUMPY. Among the AGNs at z < 0.03, for which sample biases are minimized, the fraction of Compton-thick (N H ≥ 1024 cm−2) AGNs reaches 64 − 15 + 14 % (6/9 sources) in late mergers, while it is 24 − 10 + 12 % (3/14 sources) in early mergers, consistent with the tendency reported by Ricci et al. We find that the bolometric AGN luminosities derived from the infrared data increase but the X-ray to bolometric luminosity ratios decrease with merger stage. The X-ray-weak AGNs in late mergers ubiquitously show massive outflows at subparsec to kiloparsec scales. Among them, the most luminous AGNs (L bol,AGN ∼ 1046 erg s−1) have relatively small column densities of ≲1023 cm−2 and almost super-Eddington ratios (λ Edd ∼ 1.0). Their torus covering factors (C T (22) ∼ 0.6) are larger than those of Swift/BAT-selected AGNs with similarly high Eddington ratios. These results suggest a scenario where, in the final stage of mergers, multiphase strong outflows are produced due to chaotic quasi-spherical inflows, and the AGN becomes extremely X-ray weak and deeply buried due to obscuration by inflowing and/or outflowing material.
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Zhang, Tianyi, und Yongquan Xue. „The <i>NuSTAR</i> Extragalactic Surveys: Source Catalogs from the Extended <i>Chandra</i> Deep Field-South and the <i>Chandra</i> Deep Field-North“. JUSTC 53 (2023): 1. http://dx.doi.org/10.52396/justc-2023-0032.
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We present a routinized and reliable method to obtain source catalogs from the <i>Nuclear Spectroscopic Telescope Array</i> (<i>NuSTAR</i>) extragalactic surveys of the Extended <i>Chandra</i> Deep Field-South (E-CDF-S) and <i>Chandra</i> Deep Field-North (CDF-N). The <i>NuSTAR</i> E-CDF-S survey covers a sky area of <inline-formula><tex-math id="M1">\begin{document}$ \approx30'\times30' $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0032_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0032_M1.png"/></alternatives></inline-formula> to a maximum depth of <inline-formula><tex-math id="M2">\begin{document}$ \sim $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0032_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0032_M2.png"/></alternatives></inline-formula> 230 ks corrected for vignetting in the 3–24 keV band, with a total of 58 sources detected in our E-CDF-S catalog; the <i>NuSTAR</i> CDF-N survey covers a sky area of <inline-formula><tex-math id="M3">\begin{document}$ \approx7'\times10' $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0032_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0032_M3.png"/></alternatives></inline-formula> to a maximum depth of <inline-formula><tex-math id="M4">\begin{document}$ \sim $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0032_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="JUSTC-2023-0032_M4.png"/></alternatives></inline-formula> 440 ks corrected for vignetting in the 3–24 keV band, with a total of 42 sources detected in our CDF-N catalog that is produced for the first time. We verify the reliability of our two catalogs by crossmatching them with the relevant catalogs from the <i>Chandra</i> X-ray observatory, and find that the fluxes of our <i>NuSTAR</i> sources are generally consistent with that of their <i>Chandra</i> counterparts. Our two catalogs are produced following the exactly same method and made publicly available, thereby providing a uniform platform that facilitates further studies involving these two fields. Our source-detection method provides a systematic approach for source cataloging in other <i>NuSTAR</i> extragalactic surveys.
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LaMassa, Stephanie M., Tahir Yaqoob, Panayiotis Tzanavaris, Poshak Gandhi, Timothy Heckman, George Lansbury und Aneta Siemiginowska. „The Complex X-Ray Obscuration Environment in the Radio-loud Type 2 Quasar 3C 223“. Astrophysical Journal 944, Nr. 2 (01.02.2023): 152. http://dx.doi.org/10.3847/1538-4357/acb3bb.
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Abstract 3C 223 is a radio-loud, Type 2 quasar at z = 0.1365 with an intriguing X-ray Multi-mirror Mission (XMM)-Newton spectrum that implicated it as a rare, Compton-thick (N H ≳ 1.25 × 1024 cm−2) active galactic nucleus (AGN). We obtained contemporaneous XMM-Newton and Nuclear Spectroscopic Telescope Array (NuSTAR) spectra to fit the broadband X-ray spectrum with the physically motivated MYTorus and borus02 models. We confirm earlier results that the obscuring gas is patchy with both high (though not Compton-thick) levels of obscuration (N H > 1023 cm−2) and gas clouds with column densities up to an order of magnitude lower. The spectral fitting results indicate additional physical processes beyond those modeled in the spectral grids of MYTorus and borus02 impact the emergent spectrum: the Compton-scattering region may be extended beyond the putative torus; a ring of heavy Compton-thick material blocks most X-ray emission along the line of sight; or the radio jet is beamed, boosting the production of Fe Kα line photons in the global medium compared with what is observed along the line of sight. We revisit a recent claim that no radio-loud Compton-thick AGN have yet been conclusively shown to exist, finding three reported cases of radio-loud AGN with global average (but not line-of-sight) column densities that are Compton thick. Now that it is possible to separately determine line-of-sight and global column densities, inhomogeneity in the obscuring medium has consequences for how we interpet the spectrum and classify an AGN as “Compton thick.”
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Dutta, Anirban, und Vikram Rana. „A broad-band X-ray study of the asynchronous polar CD Ind“. Monthly Notices of the Royal Astronomical Society 511, Nr. 4 (03.03.2022): 4981–90. http://dx.doi.org/10.1093/mnras/stac296.
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ABSTRACT We present a simultaneous broad-band analysis of X-ray data obtained with the XMM–Newton and the Nuclear Spectroscopic Telescope Array (NuSTAR) for the asynchronous polar source, CD Ind. The spin-folded light curve in the soft 0.3–3.0 keV band shows a single broad hump-like structure superimposed with occasional narrow dips, indicating a single-pole accretion model with a complex intrinsic absorber. Lack of strong modulation in the folded light curve above 3 keV reveals that emission from the corresponding zone of the post-shock region (PSR) remains in view throughout the spin phase. The broad-band spectrum is modelled with a three-component absorbed plasma emission model and absorbed isobaric cooling flow model, both of which fit the data well with similar statistical significance. The presence of a partial covering absorber is evident in the spectra with equivalent column density ${\sim}7\times 10^{22}\, \text{cm}^{-2}$ and a covering fraction of ~25 per cent. Strong ionized oxygen Kα line emission is detected in the spectra. We notice spectral variability during the spin phase 0.75–1.05, when there is a considerable increase in the column density of the overall absorber (from ${\sim}1 \times 10^{20}\, \text{cm}^{-2}$ to ${\sim}9 \times 10^{20}\, \text{cm}^{-2}$). We required at least three plasma temperatures to describe the multitemperature nature of the PSR. The shock temperature ${\sim}43.3_{-3.4}^{+3.8}$ keV, represented by the upper temperature of the cooling flow model, implies a white dwarf mass of ${\sim}0.87^{+0.04}_{-0.03}\, \mathrm{M}_{\odot }$. The iron Kα line complex show strong He-like and weak neutral fluorescence lines. We could not unambiguously detect the presence of Compton reflection in the spectra, which is probably very small and signifies a tall shock height.
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Athulya, M. P., und Anuj Nandi. „Multimission view of the low-luminosity ‘obscured’ phase of GRS 1915+105“. Monthly Notices of the Royal Astronomical Society 525, Nr. 1 (09.08.2023): 489–507. http://dx.doi.org/10.1093/mnras/stad2072.
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ABSTRACT GRS 1915+105 has been observed in an ‘obscured’ phase since 2019 May, exhibiting steady and low X-ray luminosities with sporadic re-brightenings. In this paper, we perform a comprehensive and wide-band analysis of the spectral and timing properties of the source during the period 2019–2021 using observations from AstroSat (SXT: 0.5–8 keV; LAXPC: 3–60 keV), the Neutron star Interior Composition Explorer (NICER) (0.5–12 keV), and the Nuclear Spectroscopic Telescope Array (NuSTAR) (3–60 keV). Spectral analysis reveals the presence of a highly variable obscurer ($N_{\rm H_{\rm 1}}\sim$ 1022–1024 atoms cm−2) throughout the observation period. The source is detected in the low/hard state for most of the time, with the spectra being described by a Comptonized component (Γ ∼ 1.16–1.79, kTe ∼ 2–31 keV). The source spectra steepen (Γ ∼ 2.5), indicating a softening of the spectrum, during the rise of the re-brightenings. Various emission and absorption lines corresponding to the neutral Fe Kα, Fe xxv Kα, Fe xxvi Kα, and the Ni xxviii Kα were detected, with the equivalent widths varying in the range 70 eV–3.5 keV. The column density of the absorbing plasma varied in the range 1016–1018 atoms cm−2 at a distance ≤2 × 1010 cm. Interestingly, the source is also seen to exhibit various variability classes (ρ, λ, δ, χ) at relatively low luminosities (∼0.01 LEdd) during the re-brightening phases. Different variability classes show the signature of quasi-periodic oscillations (νQPO: 20–180 mHz, rmsQPO: 7.5 per cent–16 per cent). The source showed a maximum bolometric luminosity (Lbol) of ∼0.01 LEdd (re-brightening phases) and a minimum Lbol of 0.004 LEdd (quiet phase) during the period. We discuss the possible disc dynamics around the black hole during this low-luminosity ‘obscured’ phase.
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Harrison, Fiona A., William W. Craig, Finn E. Christensen, Charles J. Hailey, William W. Zhang, Steven E. Boggs, Daniel Stern et al. „THENUCLEAR SPECTROSCOPIC TELESCOPE ARRAY(NuSTAR) HIGH-ENERGY X-RAY MISSION“. Astrophysical Journal 770, Nr. 2 (30.05.2013): 103. http://dx.doi.org/10.1088/0004-637x/770/2/103.
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38
Kargaltsev, Oleg, Jeremy Hare, Igor Volkov und Alexander Lange. „A Lack of 9 s Periodicity in the Follow-up NuSTAR Observation of LS 5039“. Astrophysical Journal 958, Nr. 1 (01.11.2023): 79. http://dx.doi.org/10.3847/1538-4357/ad022d.
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Abstract The Nuclear Spectroscopic Array (NuSTAR) observed the gamma-ray binary LS 5039 for a second time in order to check for the presence of a periodic signal candidate found in the data from the previous NuSTAR observation. We do not detect the candidate signal in the vicinity of its previously reported frequency, assuming the same orbital ephemeris as in our previous paper. This implies that the previously reported periodic signal candidate was a noise fluctuation. We also perform a comparison of the lightcurves from the two NuSTAR observations and the joint spectral fitting. Our spectral analysis confirms the phase dependence found from a single NuSTAR observation at a higher significance level.
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Madsen, Kristin K., Finn E. Christensen, William W. Craig, Karl W. Forster, Brian W. Grefenstette, Fiona A. Harrison, Hiromasa Miyasaka und Vikram Rana. „Observational artifacts of Nuclear Spectroscopic Telescope Array: ghost rays and stray light“. Journal of Astronomical Telescopes, Instruments, and Systems 3, Nr. 04 (27.10.2017): 1. http://dx.doi.org/10.1117/1.jatis.3.4.044003.
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40
Liebe, Carl Christian. „Calibration and alignment of metrology system for the Nuclear Spectroscopic Telescope Array mission“. Optical Engineering 51, Nr. 4 (16.04.2012): 043605. http://dx.doi.org/10.1117/1.oe.51.4.043605.
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41
Molina, M., A. Malizia, N. Masetti, L. Bassani, A. Bazzano, A. J. Bird, M. Fiocchi, E. Palazzi und P. Ubertini. „Investigating the true nature of three hard X-ray sources“. Monthly Notices of the Royal Astronomical Society 507, Nr. 3 (19.08.2021): 3423–33. http://dx.doi.org/10.1093/mnras/stab2370.
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ABSTRACT Many of the new high energy sources discovered both by INTEGRAL/IBIS and Swift/BAT have been characterized thanks to extensive, multiband follow-up campaigns, but there are still objects whose nature remains to be asserted. In this paper, we investigate the true nature of three high energy sources, IGR J12134−6015, IGR J16058−7253, and Swift J2037.2+4151, employing multiwavelength data from the near-infrared to the X-rays. Through Gaia and ESO-VLT measurements and through Swift/XRT X-ray spectral analysis, we re-evaluate the classification for IGR J12134−6015, arguing that the source is a Galactic object and in particular a cataclysmic variable. We were able to confirm, thanks toNuclear Spectroscopic Telescope Array(NuSTAR) observations, that the hard X-ray emission detected by INTEGRAL/IBIS and Swift/BAT from IGR J16058−7253 is coming from two Seyfert 2 galaxies which are both counterparts for this source. Through optical and X-ray spectral analysis of SwiftJ2037.2+4151 we find that this source is likely part of the rare and peculiar class of symbiotic X-ray binaries and displays flux and spectral variability as well as interesting spectral features, such as a blending of several emission lines around the iron line complex.
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Di Marco, Alessandro, Fabio La Monaca, Juri Poutanen, Thomas D. Russell, Alessio Anitra, Ruben Farinelli, Guglielmo Mastroserio et al. „First Detection of X-Ray Polarization from the Accreting Neutron Star 4U 1820−303“. Astrophysical Journal Letters 953, Nr. 2 (01.08.2023): L22. http://dx.doi.org/10.3847/2041-8213/acec6e.
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Abstract This paper reports the first detection of polarization in the X-rays for atoll-source 4U 1820−303, obtained with the Imaging X-ray Polarimetry Explorer (IXPE) at 99.999% confidence level (CL). Simultaneous polarimetric measurements were also performed in the radio with the Australia Telescope Compact Array. The IXPE observations of 4U 1820−303 were coordinated with Swift X-ray Telescope, Neutron Star Interior Composition Explorer, and Nuclear Spectroscopic Telescope Array aiming to obtain an accurate X-ray spectral model covering a broad energy interval. The source shows a significant polarization above 4 keV, with a polarization degree of 2.0% ± 0.5% and a polarization angle of −55° ± 7° in the 4–7 keV energy range, and a polarization degree of 10% ± 2% and a polarization angle of −67° ± 7° in the 7–8 keV energy bin. This polarization also shows a clear energy trend with polarization degree increasing with energy and a hint for a position-angle change of ≃90° at 96% CL around 4 keV. The spectro-polarimetric fit indicates that the accretion disk is polarized orthogonally to the hard spectral component, which is presumably produced in the boundary/spreading layer. We do not detect linear polarization from the radio counterpart, with a 3σ upper limit of 50% at 7.25 GHz.
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O’Connor, B., E. Göğüş, D. Huppenkothen, C. Kouveliotou, N. Gorgone, L. J. Townsend, A. Calamida et al. „Identification of an X-Ray Pulsar in the BeXRB System IGR J18219−1347“. Astrophysical Journal 927, Nr. 2 (01.03.2022): 139. http://dx.doi.org/10.3847/1538-4357/ac5032.
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Abstract We report on observations of the candidate Be/X-ray binary (BeXRB) IGR J18219−1347 with the Swift/X-ray Telescope, the Nuclear Spectroscopic Telescope ARray, and the Neutron Star Interior Composition Explorer during Type-I outbursts in 2020 March and June. Our timing analysis revealed the spin period of a neutron star with P spin = 52.46 s. This periodicity, combined with the known orbital period of 72.4 days, indicates that the system is a BeXRB. Furthermore, by comparing the spectral energy distribution of the infrared counterpart to that of known BeXRBs, we confirm this classification and set a distance of approximately 10–15 kpc for the source. The broadband X-ray spectrum (1.5–50 keV) of the source is described by an absorbed power law with a photon index Γ ∼ 0.5 and a cutoff energy at ∼13 keV.
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Kawamuro, Taiki, Claudio Ricci, Satoshi Yamada, Hirofumi Noda, Ruancun Li, Matthew J. Temple und Alessia Tortosa. „Coevolution and Nuclear Structure in the Dwarf Galaxy POX 52 Studied by Multiwavelength Data from Radio to X-Ray“. Astrophysical Journal 960, Nr. 1 (19.12.2023): 15. http://dx.doi.org/10.3847/1538-4357/ad0972.
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Abstract The nearby dwarf galaxy POX 52 at z = 0.021 hosts an active galactic nucleus (AGN) with a black hole (BH) mass of M BH ∼ 105–6 M ⊙ and an Eddington ratio of ∼0.1–1. This object provides the rare opportunity to study both AGN and host-galaxy properties in a low-mass highly accreting system. To do so, we collected its multiwavelength data from X-ray to radio. First, we construct a spectral energy distribution, and by fitting it with AGN and host-galaxy components, we constrain AGN-disk and dust-torus components. Then, while considering the AGN-disk emission, we decompose optical Hubble Space Telescope images. As a result, it is found that a classical bulge component is probably present, and its mass (M bulge) is consistent with an expected value from a local relation. Lastly, we analyze new quasi-simultaneous X-ray (0.2–30 keV) data obtained by the Nuclear Spectroscopic Telescope Array and XMM-Newton. The X-ray spectrum can be reproduced by multicolor blackbody, warm and hot coronae, and disk and torus reflection components. Based on this, the spin is estimated to be a spin = 0.998−0.814, which could suggest that most of the current BH mass was achieved by prolonged mass accretion. Given the presence of the bulge, POX 52 would have undergone a galaxy merger, while the M BH–M bulge relation and the inferred prolonged accretion could suggest that AGN feedback occurred. Regarding the AGN structure, the spectral slope of the hot corona, its relative strength to the bolometric emission, and the torus structure are found to be consistent with Eddington-ratio dependencies found for nearby AGNs.
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Abdelmaguid, Moaz, Joseph D. Gelfand, Eric Gotthelf und Samayra Straal. „Broadband X-Ray Spectroscopy of the Pulsar Wind Nebula in HESS J1640-465“. Astrophysical Journal 946, Nr. 1 (01.03.2023): 40. http://dx.doi.org/10.3847/1538-4357/acbd30.
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Abstract We present updated measurements of the X-ray properties of the pulsar wind nebula associated with the TeV γ-ray source HESS J1640-465 derived from Chandra and Nuclear Spectroscopic Telescope Array data. We report a high N H value along the line of sight, consistent with previous work, which led us to incorporate the effects of dust scattering in our spectral analysis. Due to uncertainties in the dust scattering, we report a range of values for the PWN properties (photon index and unabsorbed flux). In addition, we fit the broadband spectrum of this source and found evidence for spectral softening and decreasing unasborbed flux as we go to higher photon energies. We then used a one-zone time-dependent evolutionary model to reproduce the dynamical and multiwavelength spectral properties of our source. Our model suggests a short spin-down timescale, a relatively higher than average magnetized pulsar wind, a strong pulsar wind nebula magnetic field and maximum electron energy up to PeV, suggesting HESS J1640-465 could be a PeVatron candidate.
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Yamada, Satoshi, Yoshihiro Ueda, Martín Herrera-Endoqui, Yoshiki Toba, Takamitsu Miyaji, Shoji Ogawa, Ryosuke Uematsu, Atsushi Tanimoto, Masatoshi Imanishi und Claudio Ricci. „Hard X-Ray to Radio Multiwavelength SED Analysis of Local U/LIRGs in the GOALS Sample with a Self-consistent AGN Model including a Polar-dust Component“. Astrophysical Journal Supplement Series 265, Nr. 2 (21.03.2023): 37. http://dx.doi.org/10.3847/1538-4365/acb349.
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Abstract We conduct hard X-ray to radio multiwavelength spectral energy distribution (SED) decomposition for 57 local luminous and ultraluminous infrared galaxies observed with the Nuclear Spectroscopic Telescope Array and/or Swift/Burst Alert Telescope in the GOALS sample. We modify the latest SED-fitting code X-CIGALE by implementing the infrared (IR) CLUMPY model, allowing us to conduct the multiwavelength study with the X-ray torus model XCLUMPY self-consistently. Adopting the torus parameters obtained by the X-ray fitting, we estimate the properties of the host galaxies, active galactic nucleus (AGN) tori, and polar dust. The star formation rates (SFRs) become larger with merger stage and most of them are above the main sequence. The SFRs are correlated with radio luminosity, indicating starburst emission is dominant in the radio band. Although polar-dust extinction is much smaller than torus extinction, the UV-to-IR (mainly IR) polar dust luminosities are ∼2 times larger than the torus ones. The polar-dust temperature decreases while the physical size, estimated by the temperature and dust sublimation radius, increases with AGN luminosity from a few tens of parsec (early mergers) to kiloparsec scales (late mergers), where the polar dust likely comes from expanding (i.e., evolving) dusty outflows. A comparison between the SFRs and intrinsic AGN luminosities suggests that starbursts occur first and AGNs arise later, and overall their growth rates follow the simultaneous coevolution local galaxy–SMBH mass relation. We confirm the coexistence of intense starbursts, AGNs, and large-scale outflows in late mergers, supporting a standard AGN feedback scenario.
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Riaz, Shafqat, Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi, Haiyang Wang und Zhibo Yu. „Reflection Spectra of Accretion Disks Illuminated by Disk-like Coronae“. Astrophysical Journal 925, Nr. 1 (01.01.2022): 51. http://dx.doi.org/10.3847/1538-4357/ac3827.
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Abstract Relativistic reflection features in the X-ray spectra of black hole binaries and active galactic nuclei are thought to be produced through illumination of a cold accretion disk by a hot corona. In this work, we assume that the corona has the shape of an infinitesimally thin disk with its central axis the same as the rotational axis of the black hole. The corona can either be static or corotate with the accretion disk. We calculate the disk’s emissivity profiles and iron line shapes for a set of coronal radii and heights. We incorporate these emissivity profiles into relxill_nk and we simulate some observations of a black hole binary with the Nuclear Spectroscopic Telescope Array to study the impact of a disk-like coronal geometry on the measurement of the properties of the system, and in particular, on the possibility of testing the Kerr nature of the source. We find that, in general, the astrophysical properties of the accretion disk are recovered well even if we fit the data with a model employing a broken power law or a lamppost emissivity profile, while it is more challenging to constrain the geometric properties of the black hole spacetime.
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Chase, Owen, Felicia McBride, Andrea Gokus, Matteo Lucchini, Haocheng Zhang, Roopesh Ojha und Derek B. Fox. „The Peculiar Variable X-Ray Spectrum of the Active Galactic Nucleus PKS 2005–489“. Astrophysical Journal 948, Nr. 1 (27.04.2023): 2. http://dx.doi.org/10.3847/1538-4357/acc575.
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Abstract PKS 2005−489 is a well-known, bright southern BL Lac object that has been detected up to TeV energies. In a low-flux state it exhibits the expected multiwavelength double-peaked spectrum in the radio−γ-ray band. The high-flux state shows extreme flux variations in the X-ray band with a hardening as well as a peculiar curved feature in the spectrum. Thus far, PKS 2005−489 is the only source to exhibit such a feature. To study the X-ray variability further, we obtained the first hard X-ray spectrum of the source with the Nuclear Spectroscopic Telescope Array. We compare quasi-simultaneous radio, optical, UV, soft and hard X-ray, and γ-ray data of PKS 2005−489 to archival data in order to study its broadband behavior. We find a very consistent quiet state in the spectral energy distribution, with little variation in spectral shape or flux between the 2012 and 2020 data. A possible explanation for the peculiar X-ray spectrum in the flaring state is an additional component in the jet, possibly accelerated via magnetic reconnection, that is not co-spatial to the low-flux state emission region.
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You, Bei, Yanting Dong, Zhen Yan, Zhu Liu, Youli Tuo, Yuanle Yao und Xinwu Cao. „X-Ray Spectral Correlations in a Sample of Low-mass Black Hole X-Ray Binaries in the Hard State“. Astrophysical Journal 945, Nr. 1 (01.03.2023): 65. http://dx.doi.org/10.3847/1538-4357/acba11.
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Abstract The power-law emission and reflection component provide valuable insights into the accretion process around a black hole. In this work, thanks to the broadband spectra coverage of the Nuclear Spectroscopic Telescope Array, we study the spectral properties for a sample of low-mass black hole X-ray binaries (BHXRBs). We find that there is a positive correlation between the photon index Γ and the reflection fraction R (the ratio of the coronal intensity that illuminates the disk to the coronal intensity that reaches the observer), consistent with previous studies, but except for MAXI J1820+070. It is quite interesting that this source also deviates from the well-known “V”-shaped correlation between the photon index Γ and the X-ray luminosity log L X , when it is in the bright hard state. More specifically, the Λ-shaped correlation between Γ and logL X is observed, as the luminosity decreases by a factor of 3 in a narrow range from ∼1038 to 1037.5 erg s−1. Furthermore, we discover a strong positive correlation between R and the X-ray luminosity for BHXRBs in the hard state, which puts a constraint on the disk-corona coupling and the evolution.
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Balman, Şölen, Eric M. Schlegel und Patrick Godon. „Characterizing the Advective Hot Flows of Nova-like Cataclysmic Variables in the X-Rays: The Case of BZ Cam and V592 Cas“. Astrophysical Journal 932, Nr. 1 (01.06.2022): 33. http://dx.doi.org/10.3847/1538-4357/ac6616.
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Abstract We present a joint spectral analysis of ROSAT PSPC, Swift X-ray Telescope, and Nuclear Spectroscopic Telescope Array Focal Plane Module A/B (FPMA/B) data of the nova-like (NL) cataclysmic variables (CVs) BZ Cam and V592 Cas in the 0.1–78.0 keV band. Plasma models of collisional equilibrium fail to model the 6.0–7.0 iron line complex and continuum with χ ν 2 larger than 2.0. Our results show nonequilibrium ionization (NEI) conditions in the X-ray plasma with temperatures of 8.2–9.4 keV and 10.0–12.9 keV for BZ Cam and V592 Cas, respectively. The centroids of He-like and H-like iron ionization lines are not at their equilibrium values as expected from NEI conditions. We find power-law spectral components that reveal the existence of scattering and Comptonization with a photon index of 1.50–1.87. We detect a P Cygni profile in the H-like iron line of BZ Cam translating to outflows of 4500–8700 km s−1 consistent with the fast winds in the optical and UV. This is the first time such a fast collimated outflow is detected in the X-rays from an accreting CV. An iron Kα line around 6.2–6.5 keV is found revealing the existence of reflection effects in both sources. We study the broadband noise and find that the optically thick disk truncates in BZ Cam and V592 Cas consistent with transition to an advective hot flow structure. V592 Cas also exhibits a quasiperiodic oscillation at 1.4 − 0.3 + 2.6 mHz. In general, we find that the two NLs portray spectral and noise characteristics as expected from advective hot accretion flows at low radiative efficiency.