Artículos de revistas sobre el tema "Galactic emissions"
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1
Grimaldi, Claudio. "Demography of galactic technosignatures". Monthly Notices of the Royal Astronomical Society 500, n.º 2 (7 de noviembre de 2020): 2278–88. http://dx.doi.org/10.1093/mnras/staa3450.
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ABSTRACT Probabilistic arguments about the existence of technological life beyond Earth traditionally refer to the Drake equation to draw possible estimates of the number of technologically advanced civilizations releasing, either intentionally or not, electromagnetic emissions in the Milky Way. Here, we introduce other indicators than Drake’s number ND to develop a demography of artificial emissions populating the Galaxy. We focus on three main categories of statistically independent signals (isotropic, narrow beams, and rotating beacons) to calculate the average number NG of emission processes present in the Galaxy and the average number of them crossing Earth, $\bar{k}$, which is a quantity amenable to statistical estimation from direct observations. We show that $\bar{k}$ coincides with ND only for isotropic emissions, while $\bar{k}$ can be orders of magnitude smaller than ND in the case of highly directional signals. We further show that while ND gives the number of emissions being released at the present time, NG considers also the signals from no longer active emitters but whose emissions still occupy the Galaxy. We find that as long as the average longevity of the emissions is shorter than about 105 yr, NG is fully determined by the rate of emissions alone, in contrast to ND and $\bar{k}$ which depend also on the emission longevity. Finally, using analytic formulas of NG, ND, and $\bar{k}$ determined for each type of emission processes here considered, we provide a comprehensive overview of the values these quantities can possibly achieve as functions of the emission birthrates, longevities, and directionality.
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Okuda, H., T. Nakagawa, H. Shibai, Y. Doi, K. Mochizuki, Y. Yamashita-Yui, M. Yui, T. Nishimura y F. J. Low. "Diffuse [CII] Emission in the Galaxy". Symposium - International Astronomical Union 169 (1996): 497–98. http://dx.doi.org/10.1017/s0074180900230143.
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An extensive survey of [C II] line emission at 158 microns using the balloon borne telescope (BICE) has provided a complete map of the emission intensity distribution in the first and the fourth quadrants of the galactic plane (280° < l < 80°, −5° < b < 5°: Okuda et al. 1993). The emission is very extended throughout the galactic plane in which three intensity maxima are seen towards the tangential directions of the Scutum and the Norma arms as well as in the Galactic center region. However the Galactic center maximum is much less prominent compared with the two other distributions, unlike the case of far infrared continuum and CO emissions.
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Sofue, Yoshiaki. "4.1. Radio continuum and molecular gas in the Galactic center: large-scale structures". Symposium - International Astronomical Union 184 (1998): 161–68. http://dx.doi.org/10.1017/s0074180900084473.
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The radio emission from the Galactic Center is a mixture of thermal (free-free) and non-thermal (synchrotron) emissions (Fig. 1a). However, the spectral index in the central 3° region is flat almost everywhere (Sofue 1985), even in regions where strong linear polarization is detected. Therefore, a flat spectrum observed near the galactic center can no longer be taken as an indicator of thermal emission.
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Abbasi, R., M. Ackermann, J. Adams, N. Aggarwal, J. A. Aguilar, M. Ahlers, J. M. Alameddine et al. "Searches for Neutrinos from Large High Altitude Air Shower Observatory Ultra-high-energy γ-Ray Sources Using the IceCube Neutrino Observatory". Astrophysical Journal Letters 945, n.º 1 (1 de marzo de 2023): L8. http://dx.doi.org/10.3847/2041-8213/acb933.
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Abstract Galactic PeV cosmic-ray accelerators (PeVatrons) are Galactic sources theorized to accelerate cosmic rays up to PeV in energy. The accelerated cosmic rays are expected to interact hadronically with nearby ambient gas or the interstellar medium, resulting in γ-rays and neutrinos. Recently, the Large High Altitude Air Shower Observatory (LHAASO) identified 12 γ-ray sources with emissions above 100 TeV, making them candidates for PeVatrons. While at these high energies the Klein–Nishina effect exponentially suppresses leptonic emission from Galactic sources, evidence for neutrino emission would unequivocally confirm hadronic acceleration. Here, we present the results of a search for neutrinos from these γ-ray sources and stacking searches testing for excess neutrino emission from all 12 sources as well as their subcatalogs of supernova remnants and pulsar wind nebulae with 11 yr of track events from the IceCube Neutrino Observatory. No significant emissions were found. Based on the resulting limits, we place constraints on the fraction of γ-ray flux originating from the hadronic processes in the Crab Nebula and LHAASO J2226+6057.
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Miroshnichenko, Anatoly S. "MWC 314 – A new galactic B[e] supergiant". Symposium - International Astronomical Union 162 (1994): 396–97. http://dx.doi.org/10.1017/s0074180900215489.
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We present a new study of MWC 314 = BD +14°3887 – a poorly investigated object with strong emission lines and IR excesses. Merrill (1927) payed attention to it because of the presence of hydrogen and Fe II emissions in its spectrum. Swensson (1942) also detected interstellar lines H and K CaII and 4430 Å band, Balmer emissions from Hα to H8, NaI 5890 and 5896 Å emissions and estimated its spectral type as gG2-3 or dG4-5 from the SED in continuum, and B2 from the excitation degree. Photospheric lines and spectral features of late-type stars were not observed. Allen (1973) noted that the object's SED corresponds to that of a late-type star but it might be a symbiotic system or a reddened normal star. The IRAS fluxes were obtained only at 12 and 25 μm. The object is unknown as a radio source. From this we can conclude that this system consists of, at least, a hot star surrounded by a gaseous envelope.
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Macías-Pérez, J. F., R. D. Davies, R. Watson, C. M. Gutierrez y R. Rebolo. "A Characterization of the Diffuse Galactic Emissions at Large Angular Scales Using the Tenerife Data". Advances in Astronomy 2013 (2013): 1–15. http://dx.doi.org/10.1155/2013/780407.
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The anomalous microwave emission (AME) has been proved to be an important component of the galactic diffuse emission in the range from 20 to 60 GHz. To discriminate between different models of AME, low frequency microwave data from 10 to 20 GHz are needed. We present here a reanalysis of published and unpublished Tenerife data from 10 to 33 GHz at large angular scales (from 5 to 15 degrees). We cross-correlate the Tenerife data to templates of the main galactic diffuse emissions: synchrotron, free-free, and thermal dust. We find evidence of dust-correlated emission in the Tenerife data that could be explained as spinning dust grain emission.
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Giard, Martin y Guilaine Lagache. "Galactic emissions: seeing through the Galaxy". Comptes Rendus Physique 4, n.º 8 (octubre de 2003): 901–8. http://dx.doi.org/10.1016/j.crhy.2003.09.009.
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Desai, Abhishek, Justin Vandenbroucke, Samalka Anandagoda, Jessie Thwaites y M. J. Romfoe. "Constraints on the Origins of the Galactic Neutrino Flux Detected by IceCube". Astrophysical Journal 966, n.º 1 (23 de abril de 2024): 23. http://dx.doi.org/10.3847/1538-4357/ad2a5e.
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Abstract Galactic and extragalactic objects in the Universe are sources of high-energy neutrinos that may contribute to the astrophysical neutrino signal seen by IceCube. Recently, a study done using cascade-like events seen by IceCube reported neutrino emission from the Galactic plane with >4σ significance. In this work, we put a lower limit on the number of Galactic sources required to explain this emission. To achieve this, we use a simulation package created to simulate point sources in the Galaxy along with the neutrino and gamma-ray flux emissions originating from them. Along with using past IceCube discovery potential curves, we also account for Eddington bias effects due to Poisson fluctuations in the number of detected neutrino events. We present a toy Monte Carlo simulation to show that there must be at least eight sources, each with luminosity less than 1.6 × 1035 erg s−1, responsible for the Galactic neutrino emission. Our results constrain the number of individual point-like emission regions, which apply both to discrete astrophysical sources and to individual points of diffuse emission.
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Yamauchi, S. "Hot Plasma in the Galaxy". Symposium - International Astronomical Union 188 (1998): 47–50. http://dx.doi.org/10.1017/s0074180900114408.
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In the X-ray band, we can see weak and extended X-rays along the Galactic plane and near the Galactic Bulge region, although these regions are dominated by many point sources (e.g., Warwick et al. 1985). The Tenma satellite discovered conspicuous emission lines from selected regions near the Galactic plane (Koyama et al. 1986). These lines are identified with K-shell line from He-like Fe, hence the extended emission is attributable to optically thin hot plasmas with temperatures of several keV. The origin of the thin hot plasmas, however, have been debatable, because no class of X-ray objects shows such high temperature plasma emissions. To investigate the origin of the extended X-rays, we are currently observing the Galactic plane regions with the ASCA satellite. In this paper, we report on the ASCA results: the hard X-ray imaging and spectroscopy of the hot plasma in the Galaxy.
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Fauvet, L., J. F. Macías-Pérez, S. R. Hildebrandt y F. X. Désert. "A Characterization of the Diffuse Galactic Emissions in the Anticenter of the Galaxy". Advances in Astronomy 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/746020.
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Using the Archeops and WMAP data, we perform a study of the anticenter Galactic diffuse emissions—thermal dust, synchrotron, free-free, and anomalous emissions—at degree scales. The high-frequency data are used to infer the thermal dust electromagnetic spectrum and spatial distribution allowing us to precisely subtract this component at lower frequencies. After subtraction of the thermal dust component, a mixture of standard synchrotron and free-free emissions does not account for the residuals at these low frequencies. Including the all-sky 408 MHz Haslam data we find evidence for anomalous emission with a spectral index of −2.5 in units. However, we are not able to provide coclusion regarding the nature of this anomalous emission in this region. For this purpose, data between 408 MHz and 20 GHz covering the same sky region are needed.
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Shaban, Ahmed, Rongmon Bordoloi, John Chisholm, Soniya Sharma, Keren Sharon, Jane R. Rigby, Michael G. Gladders et al. "A 30 kpc Spatially Extended Clumpy and Asymmetric Galactic Outflow at z ∼ 1.7". Astrophysical Journal 936, n.º 1 (1 de septiembre de 2022): 77. http://dx.doi.org/10.3847/1538-4357/ac7c65.
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Abstract We image the spatial extent of a cool galactic outflow with fine-structure Fe ii* emission and resonant Mg ii emission in a gravitationally lensed star-forming galaxy at z = 1.70347. The Fe ii* and Mg ii (continuum-subtracted) emissions span out to radial distances of ∼14.33 and 26.5 kpc, respectively, with maximum spatial extents of ∼21 kpc for Fe ii* emission and ∼30 kpc for Mg ii emission. Mg ii emission is patchy and covers a total area of ∼184 kpc2, constraining the minimum area covered by the outflowing gas to be ∼13% of the total area. Mg ii emission is asymmetric and shows ∼21% more extended emission along the decl. direction. We constrain the covering fractions of the Fe ii* and Mg ii emission as a function of radial distance and characterize them with a power-law model. The Mg ii 2803 emission line shows two kinematically distinct emission components and may correspond to two distinct shells of outflowing gas with a velocity separation of Δv ∼ 400 km s−1. By using multiple images with different magnifications of the galaxy in the image plane, we trace the Fe ii* and Mg ii emissions around three individual star-forming regions. In all cases, both the Fe ii* and Mg ii emissions are more spatially extended compared to the star-forming regions traced by the [O ii] emission. These findings provide robust constraints on the spatial extent of the outflowing gas and, combined with outflow velocity and column density measurements, will give stringent constraints on mass-outflow rates of the galaxy.
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Manconi, Silvia, Francesca Calore y Fiorenza Donato. "Dissecting the inner Galaxy with gamma-ray pixel count statistics". Journal of Physics: Conference Series 2156, n.º 1 (1 de diciembre de 2021): 012093. http://dx.doi.org/10.1088/1742-6596/2156/1/012093.
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Abstract The nature of the GeV gamma-ray Galactic center excess (GCE) in the data of Fermi-LAT is still under investigation. Different techniques, such as template fitting and photon-count statistical methods, have been applied in the past few years in order to disentangle between a GCE coming from sub-threshold point sources or rather from diffuse emissions, such as the dark matter annihilation in the Galactic halo. A major limit to all these studies is the modeling of the Galactic diffuse foreground, and the impact of residual mis-modeled emission on the results’ robustness. We combine for the first time adaptive template fitting and pixel count statistical methods in order to assess the role of sub-threshold point sources to the GCE, while minimizing the mis-modelling of diffuse emission components. We reconstruct the flux distribution of point sources in the inner Galaxy well below the Fermi-LAT detection threshold, and measure their radial and longitudinal profiles. We find that point sources and diffuse emission from the Galactic bulge each contributes about 10% of the total emission therein, disclosing a potential sub-threshold point-source contribution to the GCE.
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Pan, Zeyang, Zhijie Qu, Joel N. Bregman y Jifeng Liu. "The XMM-Newton Line Emission Analysis Program (X-LEAP). I. Emission-line Survey of O vii, O viii, and Fe L-shell Transitions". Astrophysical Journal Supplement Series 271, n.º 2 (1 de abril de 2024): 62. http://dx.doi.org/10.3847/1538-4365/ad2ea0.
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Abstract The XMM-Newton Line Emission Analysis Program (X-LEAP) is designed to study diffuse X-ray emissions from the Milky Way (MW) hot gas, as well as emissions from the foreground solar wind charge exchange (SWCX). This paper presents an all-sky survey of spectral feature intensities corresponding to the O vii, O viii, and iron L-shell (Fe-L) emissions. These intensities are derived from 5418 selected XMM-Newton observations with long exposure times and minimal contamination from point or extended sources. For 90% of the measured intensities, the values are within ≈2–18 photons cm−2 s−1 sr−1 (line unit (LU)), ≈0–8 LU, and ≈0–9 LU, respectively. We report long-term variations in O vii and O viii intensities over 22 yr, closely correlating with the solar cycle and attributed to SWCX emissions. These variations contribute ∼30% and ∼20% to the observed intensities on average and peak at ≈4 and ≈1 LU during solar maxima. We also find evidence of short-term and spatial variations in SWCX, indicating the need for a more refined SWCX model in future studies. In addition, we present SWCX- and absorption-corrected all-sky maps for a better view of the MW hot gas emission. These maps show a gradual decrease in oxygen intensity moving away from the Galactic center and a concentration of Fe-L intensity in the Galactic bubbles and disk.
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Dundovic, A., C. Evoli, D. Gaggero y D. Grasso. "Simulating the Galactic multi-messenger emissions with HERMES". Astronomy & Astrophysics 653 (septiembre de 2021): A18. http://dx.doi.org/10.1051/0004-6361/202140801.
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Context. The study of nonthermal processes such as synchrotron emission, inverse Compton scattering, bremsstrahlung, and pion production is crucial to understanding the properties of the Galactic cosmic-ray population, to shed light on their origin and confinement mechanisms, and to assess the significance of exotic signals possibly associated to new physics. Aims. We present a public code called HERMES which is designed generate sky maps associated to a variety of multi-messenger and multi-wavelength radiative processes, spanning from the radio domain all the way up to high-energy gamma-ray and neutrino production. Methods. We describe the physical processes under consideration, the code concept and structure, and the user interface, with particular focus on the python-based interactive mode. In particular, present the modular and flexible design that allows the user to easily extend the numerical package according to their needs. Results. In order to demonstrate the capabilities of the code, we describe the details of a comprehensive set of sky maps and spectra associated to all physical processes included in the code. We comment in particular on the radio, gamma-ray, and neutrino maps, and mention the possibility of studying signals stemming from dark matter annihilation. Conclusions. HERMES can be successfully applied to constrain the properties of the Galactic cosmic-ray population, improve our understanding of the diffuse Galactic radio, gamma-ray, and neutrino emission, and search for signals associated to particle dark matter annihilation or decay.
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Wu, Yuanwei, Bo Zhang, Jingjing Li y Xing-Wu Zheng. "Water-maser survey towards off-plane O-rich AGBs around the orbital plane of the Sagittarius stellar stream". Monthly Notices of the Royal Astronomical Society 516, n.º 2 (9 de septiembre de 2022): 1881–93. http://dx.doi.org/10.1093/mnras/stac1971.
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ABSTRACT A 22 GHz water-maser survey was conducted towards 178 O-rich asymptotic giant branch (AGB) stars with the aim of identifying maser emission associated with the Sagittarius stellar stream. In this survey, maser emissions were detected in 21 targets, 20 of which were new detections. We studied the Galactic distributions of H2O- and SiO-maser-traced AGBs towards the Sgr orbital plane, and found an elongated structure towards the (l, b) ∼ (340°, 40°) direction. In order to verify its association with the Sagittarius tidal stream, we further studied the 3D motion of these sources, but found that, kinematically, these maser-traced AGBs are still Galactic disc sources rather than stream debris. In addition, we found a remarkable outward motion, ∼50 km s−1 away from the Galactic Centre of these maser-traced AGBs, but with no systermatic lag of rotational speed as reported in 2000 for solar-neighbourhood Miras.
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Iwashita, Ryoji, Jun Kataoka y Yoshiaki Sofue. "Broadband Radio Study of the North Polar Spur: Origin of the Spectral Turnover with Insights into the X-Ray and Gamma-Ray Spectra". Astrophysical Journal 958, n.º 1 (1 de noviembre de 2023): 83. http://dx.doi.org/10.3847/1538-4357/ad0374.
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Abstract The North Polar Spur (NPS) is a giant structure that is clearly visible in both radio and X-ray all-sky maps. We analyzed broadband radio observations covering a range between 22 MHz and 70 GHz to systematically analyze the thermal/nonthermal emissions associated with the NPS. We demonstrate that the radio emission of the NPS comprises synchrotron, free–free, and dust emission; however, synchrotron emissions dominate over other emissions, especially at high Galactic latitudes. Moreover, the synchrotron spectra exhibit a power-law behavior with N(γ) ∝ γ −s (s ≃ 1.8–2.4) up to a few GHz moderated by a turnover at ν brk ≃ 1 GHz, above which the spectral index s decreases by one. Assuming that the turnover is due to the electrons being cooled by synchrotron radiation before escaping (or advecting) from the emission region, the magnetic field strength can be estimated to be B ∼ 8 μG if the NPS is a distant structure that is near the Galactic center (GC). However, an unreasonably strong B ∼ 114 μG is required if the NPS is near the local supernova remnant (SNR). The corresponding nonthermal energy stored in the NPS is E n/th ≃ 4.4 × 1055 erg in the GC scenario, whereas E n/th ≃ 4.1 × 1052 erg is difficult to explain with a single local SNR. We also estimated the gamma-ray emission associated with the NPS through inverse Comptonization of the cosmic microwave background, which peaks at 100–1000 keV with a flux of ν F ν ∼ 10−9 erg cm−2 s−1 sr−1 in the GC model, and may be a good candidate for detection by future X-ray/gamma-ray observatories.
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WANG, WEI. "GALACTIC Al 1.8 MeV GAMMA-RAY SURVEYS WITH INTEGRAL". International Journal of Modern Physics: Conference Series 23 (enero de 2013): 48–53. http://dx.doi.org/10.1142/s2010194513011069.
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26 Al is a long-life radioactive isotope with a half lifetime of near 1 Myr. The origin of Galactic 26 Al is dominated by massive stars and their core-collapse supernovae. Detections of 1809 keV emission from 26 Al provide direct evidence that nucleosynthesis is ongoing in the Galaxy. The gamma-ray line shapes reflect the dynamics of the ejected isotopes in the interstellar medium and then probe properties of ISM and Galactic rotation effect. Gamma-ray emissions of 26 Al in the Galaxy are studied with the high spectral resolution INTEGRAL spectrometer (SPI). We carry out the first spectral survey of 26 Al gamma-ray line emission along the Galactic plane. The 26 Al line energy shifts reflect the large-scale Galactic rotation. The 26 Al intensity is brighter in the 4th than in the 1st quadrant (ratio ~ 1.3); the 26 Al line toward the direction of the Aquila region appears somewhat broadened; a latitudinal scale height of [Formula: see text] pc for 26 Al in the inner Galaxy is determined. Strong 26 Al emission signal is detected in the nearby star-formation regions Sco-Cen and Cygnus. The 26 Al line shapes in star-formation regions provide a clue to constrain the kinematic properties of ISM. In addition, we derive the flux ratio of 60 Fe /26 Al ~ 15% which can be directly compared with theoretical predictions. More theoretical work on nuclear reactions, massive star evolution models deserves improvements.
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Hu, Yue, A. Lazarian y Q. Daniel Wang. "Multiscale magnetic fields in the central molecular zone: inference from the gradient technique". Monthly Notices of the Royal Astronomical Society 511, n.º 1 (28 de enero de 2022): 829–42. http://dx.doi.org/10.1093/mnras/stac159.
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ABSTRACT The central molecular zone (CMZ) plays an essential role in regulating the nuclear ecosystem of our Galaxy. To get an insight into magnetic fields of the CMZ, we employ the gradient technique (GT), which is rooted in the anisotropy of magnetohydrodynamic turbulence. Our analysis is based on the data of multiple wavelengths, including molecular emission lines, radio 1.4 GHz continuum image, and Herschel $70\, {\mu }{\rm m}$ image, as well as ionized [Ne ii] and Paschen-alpha emissions. The results are compared with the observations of Planck 353 GHz and High-resolution Airborne Wideband Camera Plus (HWAC+) $53\, {\mu }{\rm m}$ polarized dust emissions. We map the magnetic fields orientation at multiple wavelength across the central molecular zone, including close-ups of the Radio Arc and Sagittarius A West regions, on multiscales from ∼0.1 pc to 10 pc. The magnetic fields towards the central molecular zone traced by the GT are globally compatible with the polarization measurements, accounting for the contribution from the galactic foreground and background. This correspondence suggests that the magnetic field and turbulence are dynamically crucial in the galactic center. We find that the magnetic fields associated with the Arched filaments and the thermal components of the Radio Arc are in good agree with the HAWC+ polarization. Our measurement towards the non-thermal Radio Arc reveals the poloidal magnetic field components in the galactic center. For Sagittarius A West region, we find a great agreement between the GT measurement using [Ne ii] emission and HWAC+ $53\, {\mu }{\rm m}$ observation. We use the GT to predict the magnetic fields associated with ionized Paschen-alpha gas down to scales of 0.1 pc.
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Smoot, G. F. "Of Cosmic Background Anisotropies". Symposium - International Astronomical Union 168 (1996): 31–44. http://dx.doi.org/10.1017/s007418090010991x.
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Observations of the Cosmic Microwave Background (CMB) Radiation have put the standard model of cosmology, the Big Bang, on firm footing and provide tests of various ideas of large scale structure formation. CMB observations now let us test the role of gravity and General Relativity in cosmology including the geometry, topology, and dynamics of the Universe. Foreground galactic emissions, dust thermal emission and emission from energetic electrons, provide a serious limit to observations. Nevertheless, observations may determine if the evolution of the Universe can be understood from fundamental physical principles.
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Liu, Ru-liang, Li-hong Cao, Jun-han You y Fu-zhen Ckeng. "The X and UV emissions of active galactic nuclei". Chinese Astronomy and Astrophysics 11, n.º 2 (junio de 1987): 94–99. http://dx.doi.org/10.1016/0275-1062(87)90030-0.
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Wang, Jiaxin, Tess Jaffe, Torsten Ensslin y Joe Taylor. "hammurabi X: a C++ package for simulating Galactic emissions". Journal of Open Source Software 5, n.º 47 (6 de marzo de 2020): 1889. http://dx.doi.org/10.21105/joss.01889.
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Chian, Abraham C. L. "Order and Chaos in Accretion Disks of Active Galactic Nuclei". International Astronomical Union Colloquium 163 (1997): 663–66. http://dx.doi.org/10.1017/s0252921100043359.
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AbstractLangmuir turbulence plays an important role in electron heating and generation of plasma emission in accretion disks of active galactic nuclei. The nonlinear dynamical behavior of Langmuir turbulence and its relevance in the interpretation of AGN variability is discussed. In particular, we study nonlinear saturation of the Langmuir stimulated modulational instability, for which the low-frequency mode is a resonant ion-acoustic wave. The nonlinear system of coupled wave equations is shown to undergo transition from order to chaos via the route of quasiperiodicity. The periodic, quasiperiodic and chaotic variabilities in AGN emissions may be the electromagnetic signatures of the ordered and chaotic states of Langmuir turbulence in accretion disks or jets of AGN.
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Baan, Willem A., Edo Loenen y Xiaoli Lian. "Diagnostics of the ISM in star formation regions". Proceedings of the International Astronomical Union 8, S292 (agosto de 2012): 215–18. http://dx.doi.org/10.1017/s1743921313001129.
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AbstractLine emissions of high- and low-density molecular tracers serve as powerful diagnostic tools for the ISM in both Galactic and extragalactic star formation environments. The emission line strengths and line ratios may be interpreted using detailed modeling of both the dominant physics and the chemistry of the molecular constituents. Observed molecular line ratios will thus reveal the signatures of dominant UV, X-ray, and CR radiation fields and of mechanical heating and feedback from the star formation process. In addition, certain line ratios reflect the physical and chemical changes resulting from the time-evolution of a star formation region. In this paper, we present results of Galactic sources and extragalactic starbursts covering a large range of FIR luminosities and illustrate the similarities between the diagnostics of these environments.
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Fesen, Robert A., Jack M. M. Neustadt, Thomas G. How y Christine S. Black. "Detection of extensive optical emission from the extremely radio faint Galactic supernova remnant G182.4+4.3". Monthly Notices of the Royal Astronomical Society 486, n.º 4 (27 de abril de 2019): 4701–9. http://dx.doi.org/10.1093/mnras/stz1140.
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Abstract Wide-field H α images of the radio faint Galactic supernova remnant G182.4+4.2 reveal a surprisingly extensive and complex emission structure, with an unusual series of broad and diffuse filaments along the remnant’s south-western limb. Deep [O iii] 5007 Å images reveal no appreciable remnant emission with the exception of a single filament coincident with the westernmost of the broad south-west filaments. The near total absence of [O iii] emission suggests the majority of the remnant’s optical emission arises from relatively slow shocks (≤70 km s−1), consistent with little or no associated X-ray emission. Low-dispersion optical spectra of several regions in the remnant’s main emission structure confirm a lack of appreciable [O iii] emission and indicate [S ii]/Hα line ratios of 0.73–1.03, consistent with a shock-heated origin. We find G182.4+4.2 to be a relatively large (d ∼ 50 pc at 4 kpc) and much older (age ∼ 40 kyr) supernova remnant than previously estimated, whose weak radio and X-ray emissions are related to its age, low shock velocity, and location in a low-density region some 12 kpc out from the Galactic Centre.
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Ozaki, M. y K. Koyama. "Thermal and Non-Thermal X-Rays from SN 1006 and IC 443". Symposium - International Astronomical Union 188 (1998): 256–57. http://dx.doi.org/10.1017/s0074180900115013.
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From many Galactic supernova remnants (SNRs), X-ray emissions consisting of non-equilibrium ionization (NEI) plasma and additional hard component are detected. The hard emission have been usually interpreted as a high temperature plasma of = 10 keV. However, the recent observation with ASCA made it clear that the hard components of some SNRs are of non-thermal origin. Here we report the ASCA results of SN 1006 and IC 443 observations as an example of such SNRs.
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Witt, Adolf N., Jayant Murthy, Bo Å. S. Gustafson, W. Jack Baggaley, Eli Dwek, Anny-Chantal Levasseur-Regourd, Ingrid Mann, Kalevi Mattila y Jun-ichi Watanabe. "COMMISSION 21: LIGHT OF THE NIGHT SKY". Proceedings of the International Astronomical Union 4, T27A (diciembre de 2008): 171–73. http://dx.doi.org/10.1017/s174392130802543x.
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Commission 21 consists of IAU members and consultants with expertise and interest in the study of the light of the night sky and its various diffuse components, at all accessible electromagnetic frequencies. In cosmic distance scales, the subjects of Commission 21 range from airglow and tropospheric scattering in Earth's atmosphere, through zodiacal light in the solar system, including thermal emission from interplanetary dust, integrated starlight in the Milky Way galaxy, diffuse galactic light due to dust scattering in the galactic diffuse interstellar medium, thermal emissions from interstellar dust and free free emission from ionized interstellar gas, to various diffuse extragalactic background sources, including the cosmologically important cosmic microwave background (CMB). Observations of the diffuse night sky brightness at any frequency typically include signals from several of these sources, and it has been the historic mandate of Commission 21 to foster the necessary collaboration of experts from the different astronomical sub-disciplines involved.
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ITO, HIROTAKA, MOTOKI KINO, NOZOMU KAWAKATU y SHOICHI YAMADA. "NONTHERMAL EMISSIONS FROM SHOCKED SHELLS DRIVEN BY POWERFUL AGN JETS". International Journal of Modern Physics D 19, n.º 06 (junio de 2010): 893–99. http://dx.doi.org/10.1142/s0218271810017111.
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We explore the emissions by accelerated electrons in shocked shells driven by jets in active galactic nuclei (AGNs). Focusing on powerful sources which host luminous quasars, the synchrotron radiation and inverse-Compton (IC) scattering of various photons that are mainly produced in the core are considered as radiation processes. We show that the radiative output is dominated by the IC emission for compact sources (≲ 30 kpc), whereas the synchrotron radiation is more important for larger sources. It is predicted that, for powerful sources (L j ~ 1047 ergs s -1), GeV – TeV gamma-rays produced via the IC emissions can be detected by the Fermi satellite and modern Cherenkov telescopes such as MAGIC, HESS and VERITAS if the source is compact.
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Hauser, Michael G. "The COBE DIRBE Search for the Cosmic Infrared Background". Symposium - International Astronomical Union 168 (1996): 99–108. http://dx.doi.org/10.1017/s0074180900109982.
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The Diffuse Infrared Background Experiment (DIRBE) on the Cosmic Background Explorer (COBE) satellite is designed to conduct a sensitive search for isotropic cosmic infrared background radiation over the spectral range from 1.25 to 240 μm. The cumulative emissions of pregalactic, protogalactic, and evolving galactic systems are expected to be recorded in this background. The DIRBE instrument has mapped the full sky with high redundancy at solar elongation angles ranging from 64°to 124°to facilitate separation of interplanetary, Galactic, and extragalactic sources of emission. Conservative limits on the isotropic infrared background are given by the minimum observed sky brightnesses in each DIRBE spectral band during the 10 months of cryogenic operation. Extensive modeling of the foregrounds is under way to isolate or strongly limit the extragalactic infrared component. The current approach to these modeling efforts is described and representative present residuals are reported.
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Zhang, Xiao, Yang Chen, Hui Li y Xin Zhou. "On the hadronic γ-ray emission from Tycho's Supernova Remnant". Proceedings of the International Astronomical Union 9, S296 (enero de 2013): 358–59. http://dx.doi.org/10.1017/s1743921313009812.
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AbstractTycho is one of nearly a dozen Galactic supernova remnants which are suggested to emit hadronic γ-ray emission. Among them, however, it is the only one in which the hadronic emission is proposed to arise from the interaction with low-density ambient medium. Based on the multi-band observations, we suggest that Tycho is encountering dense cloud at the northeastern boundary. The γ-ray emissions can be explained by hadronic process with self-consistent parameters, such as a modest energy conversion efficiency. In this SNR-cloud association scenario, the distance can be estimated as ~2.5 kpc.
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Liu, Hao. "Fingerprint of Galactic Loop I on polarized microwave foregrounds". Astronomy & Astrophysics 617 (septiembre de 2018): A90. http://dx.doi.org/10.1051/0004-6361/201833471.
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Context. Currently, detection of the primordial gravitational waves using the B-mode of cosmic microwave background (CMB) is primarily limited by our knowledge of the polarized microwave foreground emissions. Improvements of the foreground analysis are therefore necessary. As we revealed in an earlier paper, the E-mode and B-mode of the polarized foreground have noticeably different properties, both in morphology and frequency spectrum, suggesting that they arise from different physicalprocesses, and need to be studied separately. Aims. I study the polarized emission from Galactic loops, especially Loop I, and mainly focus on the following questions: Does the polarized loop emission contribute predominantly to the E-mode or B-mode? In which frequency bands and in which sky regions can the polarized loop emission be identified? Methods. Based on a well known result concerning the magnetic field alignment in supernova explosions, a theoretical expectation is established that the loop polarizations should be predominantly E-mode. In particular, the expected polarization angles of Loop I are compared with those from the real microwave band data of WMAP and Planck. Results and conclusions. The comparison between model and data shows remarkable consistency between the data and our expectations at all bands and for a large area of the sky. This result suggests that the polarized emission of Galactic Loop I is a major polarized component in all microwave bands from 23 to 353 GHz, and a considerable part of the polarized foreground likely originates from a local bubble associated with Loop I, instead of the far more distant Galactic emission. This result also provides a possible way to explain the E-to-B excess problem by contribution of the loops. Finally, this work may also provide the first geometrical evidence that the Earth was hit by a supernova explosion.
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Qaiyum, Abdul. "Millimeter and Submillimeter Emissions from Galactic and Extragalactic Photodissociation Regions". Astrophysics and Space Science 305, n.º 1 (13 de junio de 2006): 1–10. http://dx.doi.org/10.1007/s10509-005-9017-4.
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Choudhury, M. y A. R. Rao. "The Radio X-Ray Correlation in Cygnus X-3 and Other Galactic Microquasars". International Astronomical Union Colloquium 194 (2004): 203. http://dx.doi.org/10.1017/s0252921100152492.
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Cygnus X-3, a Galactic X-ray binary, shows the presence of outflows in the form of radio jets. The SED in the X-ray band shows a complicated structure and evolution. We review some recent results of the long-term correlation of the radio and X-ray emissions, chiefly in the low (hard) states of the source. Comparing the results with those of other Galactic microquasars, we attempt to provide a consistent picture of the accretion — ejection mechanism in these sources.
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Liao, Mai, Minfeng Gu, Minhua Zhou y Liang Chen. "The X-ray emission in young radio active galactic nuclei". Monthly Notices of the Royal Astronomical Society 497, n.º 1 (4 de junio de 2020): 482–97. http://dx.doi.org/10.1093/mnras/staa1559.
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ABSTRACT In this work, we investigated the X-ray emission for a sample of young radio active galactic nuclei (AGNs) by combining data from Chandra/XMM–Newton with data for other wavebands. We find strong correlations between the X-ray luminosity LX at 2–10 keV and the radio luminosities LR at 5 GHz for the VLBI radio-core, VLA radio-core and Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) component, indicating that both parsec- and kiloparsec-scale radio emissions are strongly correlated with X-ray emission in these sources. We find an approximately linear dependence of the radio on the X-ray luminosity in the sources with radiatively efficient accretion flows (i.e. the Eddington ratio Redd ≳ 10−3), with b ∼ 1 ($L_{\rm R}\, \propto \, L_{\rm X} ^{b}$) and $\xi _{\rm RX}\, \sim$ 1 in the fundamental plane using the VLBI data. The dependence is consistent with the re-analysed results of a previous study of Fan and Bai at Redd ≳ 10−3, but is significantly different from the theoretical prediction of accretion flow as the origin of X-ray emission. In contrast to the case for radio-quiet quasars, there is no significant correlation between Γ and the Eddington ratio. Our results seem to indicate that the X-ray emission of high-accretion young radio AGNs may be from the jet. We constructed the spectral energy distributions (SEDs) for 18 sources (most of which are in radiatively efficient accretion), namely nine galaxies and nine quasars with high-quality X-ray data, and find that the X-ray emission of most quasars is more luminous than that of normal radio-quiet quasars. This is clearly seen from the quasar composite SED, in which the X-ray emission is apparently higher than that of radio-quiet quasars, probably supporting jet-related X-ray emission in young radio AGNs. The possibility that the X-ray emission is from self-synchrotron Compton is discussed.
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Tagawa, Hiromichi, Shigeo S. Kimura y Zoltán Haiman. "High-energy Electromagnetic, Neutrino, and Cosmic-Ray Emission by Stellar-mass Black Holes in Disks of Active Galactic Nuclei". Astrophysical Journal 955, n.º 1 (1 de septiembre de 2023): 23. http://dx.doi.org/10.3847/1538-4357/ace71d.
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Abstract Some Seyfert galaxies are detected in high-energy gamma rays, but the mechanism and site of gamma-ray emission are unknown. Also, the origins of the cosmic high-energy neutrino and MeV gamma-ray backgrounds have been veiled in mystery since their discoveries. We propose emission from stellar-mass BHs (sBHs) embedded in disks of active galactic nuclei as their possible sources. These sBHs are predicted to launch jets due to the Blandford–Znajek mechanism, which can produce intense electromagnetic, neutrino, and cosmic-ray emissions. We investigate whether these emissions can be the sources of cosmic high-energy particles. We find that emission from internal shocks in the jets can explain gamma rays from nearby radio-quiet Seyfert galaxies including NGC 1068, if the Lorentz factor of the jets (Γj) is high. On the other hand, for moderate Γj, the emission can significantly contribute to the background gamma-ray and neutrino intensities in the ~MeV and ≲PeV bands, respectively. Furthermore, for moderate Γj with efficient amplification of the magnetic field and cosmic-ray acceleration, the neutrino emission from NGC 1068 and the ultrahigh-energy cosmic rays can be explained. These results suggest that the neutrino flux from NGC 1068 as well as the background intensities of MeV gamma rays, neutrinos, and the ultrahigh-energy cosmic rays can be explained by a unified model. Future MeV gamma-ray satellites will test our scenario for neutrino emission.
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Yuan, Chengchao, Kohta Murase, Dafne Guetta, Asaf Pe’er, Imre Bartos y Péter Mészáros. "GeV Signatures of Short Gamma-Ray Bursts in Active Galactic Nuclei". Astrophysical Journal 932, n.º 2 (1 de junio de 2022): 80. http://dx.doi.org/10.3847/1538-4357/ac6ddf.
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Abstract The joint detection of gravitational waves and the gamma-ray counterpart of a binary neutron star merger event, GW170817, unambiguously validates the connection between short gamma-ray bursts and compact binary object (CBO) mergers. We focus on a special scenario where short gamma-ray bursts produced by CBO mergers are embedded in disks of active galactic nuclei (AGNs), and we investigate the γ-ray emission produced in the internal dissipation region via synchrotron, synchrotron self-Compton, and external inverse Compton (EIC) processes. In this scenario, isotropic thermal photons from the AGN disks contribute to the EIC component. We show that a low-density cavity can be formed in the migration traps, leading to the embedded mergers producing successful GRB jets. We find that the EIC component would dominate the GeV emission for typical CBO mergers with an isotropic-equivalent luminosity of L j,iso = 1048.5 erg s−1 that are located close to the central supermassive black hole. Considering a long-lasting jet of duration T dur ∼ 102–103 s, we find that the future Cherenkov Telescope Array (CTA) will be able to detect its 25–100 GeV emission out to a redshift z = 1.0. In the optimistic case, it is possible to detect the on-axis extended emission simultaneously with GWs within one decade using MAGIC, H.E.S.S., VERITAS, CTA, and LHAASO-WCDA. Early diagnosis of prompt emissions with Fermi-GBM and HAWC can provide valuable directional information for the follow-up observations.
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Wasleske, Erik J. y Vivienne F. Baldassare. "X-Ray Emission of Ultraviolet Variable Active Galactic Nucleus Candidates". Astronomical Journal 166, n.º 2 (17 de julio de 2023): 64. http://dx.doi.org/10.3847/1538-3881/ace16b.
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Abstract We analyze the X-ray properties of a sample of 23 high-probability active galactic nucleus (AGN) candidates with ultraviolet variability identified in Wasleske et al. Using data from the Chandra X-ray Observatory and XMM-Newton Observatory, we that find 11/23 nuclei are X-ray detected. We use spectral energy distribution modeling to compute star formation rates and show that the X-ray luminosities are typically in excess of the X-ray emission expected from star formation by at least an order of magnitude. Interestingly, this sample shows a diversity of optical spectroscopic properties. We explore possible reasons for why some objects lack optical spectroscopic signatures of black hole activity while still being UV-variable and X-ray bright. We find that host galaxy stellar emission and obscuration from gas and dust are potential factors. We study where this sample falls on relationships such as α OX − L 2500 and L X − L IR and find that some of the sample falls outside the typical scatter for these relations, indicating that they differ from the standard quasar population. With the diversity of optical spectroscopic signatures and varying impacts of dust and stellar emissions on our sample, these results emphasize the strength of variability in selecting the most complete set of AGN, regardless of other host galaxy properties.
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Papavasileiou, Theodora, Odysseas Kosmas y Ioannis Sinatkas. "Studying the Spectral Energy Distributions Emanating from Regular Galactic XRBs". Universe 9, n.º 7 (28 de junio de 2023): 312. http://dx.doi.org/10.3390/universe9070312.
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X-ray binary systems (XRBs) exhibit similar dynamics and multimessenger emission mechanisms to active galactic nuclei (AGNs) with the benefit of shorter time scaling. Those systems produce rich spectral energy distributions (SEDs) ranging from the radio band to the very high energy gamma rays. The emission origin varies between the system’s accretion disk (X-rays) to the corona and, most notably, to the two twin plasma ejections (jets) that often meet the interstellar medium forming highly observable radio lobes. Modeling of the jets offers an excellent opportunity to understand the intrinsic mechanisms and the jet particles, such as electrons, positrons, and protons. In this work, we employ a lepto-hadronic jet model that assumes particle acceleration through shock waves over separate zonal regions of the jet. The hadronic models consider proton–proton collisions that end up in gamma-ray photons through neutral pion decays. The main leptonic mechanisms involve synchrotron radiation (from both electrons and protons) and inverse Compton scattering of ambient photons (coming from the disk, the corona, and the companion star) on jet electrons. The emissions from the disk, the corona, and the donor star are also included in the SED calculations, along with the photon absorption effects due to their interaction with higher-energy jet photons. We apply the model on a 10M⊙ black hole accreting at the Eddington rate out of a 20M⊙ companion star. One of our goals is to investigate and determine an optimal frame concerning the values for the free parameters that enter our calculations to produce higher integral fluxes.
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Kimura, Shigeo S. "High-energy emissions from neutron star mergers". EPJ Web of Conferences 210 (2019): 03001. http://dx.doi.org/10.1051/epjconf/201921003001.
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In 2017, LIGO-Virgo collaborations reported detection of the first neutron star merger event, GW170817, which is accompanied by electromagnetic counterparts from radio to gamma rays. Although high-energy neutrinos were not detected from this event, mergers of neutron stars are expected to produce such high-energy particles. Relativistic jets are launched when neutron stars merge. If the jets contain protons, they can emit high-energy neutrinos through photomeson production. In addition, neutron star mergers produce massive and fast ejecta, which can be a source of Galactic high-energy cosmic rays above the knee. We briefly review what we learned from the multi-messenger event, GW170817, and discuss prospects for multi-messenger detections and hadronic cosmic-ray production related to the neutron star mergers.
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Yang, Xiaolong y Ziwei Ou. "The Core Starbursts of the Galaxy NGC 3628: Radio Very Long Baseline Interferometry and X-Ray Studies". Astrophysical Journal 952, n.º 1 (1 de julio de 2023): 27. http://dx.doi.org/10.3847/1538-4357/acd765.
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Abstract We present radio very long baseline interferometry (VLBI) and X-ray studies of the starburst galaxy NGC 3628. The VLBI observation at 1.5 GHz reveals seven compact (0.7−7 pc) radio sources in the central ∼250 pc region of NGC 3628. Based on their morphology, high radio-brightness temperatures (105–107 K), and steep radio spectra, none of these seven sources can be associated with active galactic nuclei (AGNs); instead, they can be identified as supernova remnants (SNRs), with three of them appearing consistent with partial shells. Notably, one of them (W2) is likely a nascent radio supernova (SN) and appears to be consistent with the star formation rate of NGC 3628 when assuming a canonical initial mass function. The VLBI observation provides the first precise measurement of the diameter of the radio sources in NGC 3628, which allow us to fit a well-constrained radio surface brightness—diameter (Σ–D) correlation by including the detected SNRs. Furthermore, future VLBI observations can be conducted to measure the expansion velocity of the detected SNRs. In addition to our radio VLBI study, we analyze Chandra and XMM-Newton spectra of NGC 3628. The spectral fitting indicates that the SNR activities could well account for the observed X-ray emissions. Along with the Chandra X-ray image, it further reveals that the X-ray emission is likely maintained by the galactic-scale outflow triggered by SN activities. These results provide strong evidence that SN-triggered activities play a critical role in generating both radio and X-ray emissions in NGC 3628.
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Fesen, Robert A., Kathryn E. Weil, John C. Raymond, Laurent Huet, Martin Rusterholz, Dennis di Cicco, David Mittelman, Sean Walker, Marcel Drechsler y Sheldon Faworski. "G107.0+9.0: a new large optically bright, radio, and X-Ray faint galactic supernova remnant in Cepheus". Monthly Notices of the Royal Astronomical Society 498, n.º 4 (11 de septiembre de 2020): 5194–206. http://dx.doi.org/10.1093/mnras/staa2765.
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ABSTRACT Wide-field H α images of the Galactic plane have revealed a new supernova remnant (SNR) nearly 3 deg in diameter centred at l = 107.0, b = +9.0. Deep and higher resolution H α and [O iii] 5007 Å images show dozens of H α filaments along the remnant’s northern, western, and southwestern limbs, but few [O iii] bright filaments. The nebula is well detected in the H α Virginia Tech Spectral-Line Survey images, with many of its brighter filaments even visible on Digital Sky Survey images. Low-dispersion spectra of several filaments show either Balmer dominated, non-radiative filaments, or the more common SNR radiative filaments with [S II]/H α ratios above 0.5, consistent with shock-heated line emission. Emission line ratios suggest shock velocities ranging from ≤70 km s−1 along its western limb to ≃ 100 km s−1 along its northwestern boundary. While no associated X-ray emission is seen in ROSAT images, faint 1420 MHz radio emission appears coincident with its western and northern limbs. Based on an analysis of the remnant’s spatially resolved H α and [O iii] emissions, we estimate the remnant’s distance at ∼1.5−2.0 kpc implying a physically large (dia. = 75−100 pc) and old (90−110 × 103 yr) SNR in its post-Sedov radiative phase of evolution expanding into a low-density interstellar medium (n0 = 0.05−0.2 cm−3) and lying some 250−300 pc above the Galactic plane.
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Rahman, Fazlu, Pravabati Chingangbam y Tuhin Ghosh. "Statistical properties of galactic synchrotron temperature and polarization maps — a multi-frequency comparison". Journal of Cosmology and Astroparticle Physics 2024, n.º 01 (1 de enero de 2024): 036. http://dx.doi.org/10.1088/1475-7516/2024/01/036.
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Abstract Understanding the statistical properties of synchrotron emission from our Galaxy is valuable from the perspective of observations targeting signals of cosmological origin, as well as for understanding physical processes in our Galaxy. In this work, we extend the analysis of Rahman et al. [1] to — (a) all-sky observed maps of total foreground emissions at different frequencies provided by WMAP, Planck and Stockert-Villa, (b) component separated synchrotron temperature maps provided by WMAP, Planck and BeyondPlanck, and (c) component separated polarization maps provided by WMAP and Planck. The tools we use are Minkowski functionals and tensors. Our main goals are twofold. First, we determine the variation of morphological properties of the total foreground maps with observing frequency and compare with simulations. This study elucidates how the morphology varies with frequency due to the relative dominance of different foreground components at different frequencies. Secondly, we determine the nature of non-Gaussianity and statistical isotropy of synchrotron fluctuations towards smaller scales using various component separated synchrotron temperature and polarization maps. We find that all maps exhibit kurtosis-type non-Gaussianity, in agreement with the Haslam map. This result can be an important input for the modelling of small-scale synchrotron fluctuations for component separation pipelines. This also suggests that residual synchrotron contamination in CMB will manifest as kurtosis and will not be captured by three-point statistics. From a comparison of the different component separated maps, we find that BeyondPlanck and WMAP MCMC-e agree well with Haslam at all scales. The other maps show differences of varying statistical significance. Our analysis suggests a combination of residual AME and/or free-free emissions and point sources as contributing to these differences, and underscores the need for further improvement of the pipelines.
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Suchkov, Sergey I., Irina V. Arkhangelskaja, Andrey I. Arkhangelskiy, Aleksey V. Bakaldin, Irina V. Chernysheva, Arkady M. Galper, Oleg D. Dalkarov et al. "The Upcoming GAMMA-400 Experiment". Universe 9, n.º 8 (14 de agosto de 2023): 369. http://dx.doi.org/10.3390/universe9080369.
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The upcoming GAMMA-400 experiment will be implemented aboard the Russian astrophysical space observatory, which will be operating in a highly elliptical orbit over a period of 7 years to provide new data on gamma-ray emissions and cosmic-ray electron + positron fluxes, mainly from the galactic plane, the Galactic Center, and the Sun. The main observation mode will be a continuous point-source mode, with a duration of up to ~100 days. The GAMMA-400 gamma-ray telescope will study high-energy gamma-ray emissions of up to several TeV and cosmic-ray electrons + positrons up to 20 TeV. The GAMMA-400 telescope will have a high angular resolution, high energy and time resolutions, and a very good separation efficiency for separating gamma rays from the cosmic-ray background and the electrons + positrons from protons. A distinctive feature of the GAMMA-400 gamma-ray telescope is its wonderful angular resolution for energies of >30 GeV (0.01° for Eγ = 100 GeV), which exceeds the resolutions of space-based and ground-based gamma-ray telescopes by a factor of 5–10. GAMMA-400 studies can reveal gamma-ray emissions from dark matter particles’ annihilation or decay, identify many unassociated, discrete sources, explore the extended sources’ structures, and improve the cosmic-ray electron + positron spectra data for energies of >30 GeV.
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Lee, Yong-Hyun, Bon-Chul Koo y Jae-Joon Lee. "Supernova Remnants in the UWISH2 and UWIFE Surveys". Proceedings of the International Astronomical Union 9, S296 (enero de 2013): 370–71. http://dx.doi.org/10.1017/s1743921313009873.
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AbstractWe report the preliminary results for the detection of H2 and [Fe II] line features around the Galactic supernova remnants (SNRs) from the UWISH2 and UWIFE surveys that cover the first galactic quadrant of 7°<l<65° and |b|<1.3°. By this time, we have found a total of 17 H2-emitting and 14 [Fe II]-emitting SNRs in the coverage, and more than a half of them are detected in both H2 and [Fe II] emissions, which implies that the environment of these SNRs might be complex and composed of multi-phase medium. In this paper, we present our identification strategy and some preliminary results including H2 and [Fe II] luminosity distributions.
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You Jun-han, Cheng Fu-zhen, Gong Rui-sheng y Liu Ru-liang. "An analysis of the X and UV emissions of active galactic nuclei". Chinese Astronomy and Astrophysics 11, n.º 3 (septiembre de 1987): 263–68. http://dx.doi.org/10.1016/0275-1062(87)90012-9.
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Fauvet, L., J. F. Macías-Pérez y F. X. Désert. "Model of the polarized foreground diffuse Galactic emissions from 33 to 353GHz". Astroparticle Physics 36, n.º 1 (agosto de 2012): 57–63. http://dx.doi.org/10.1016/j.astropartphys.2012.04.013.
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Parajuli, Resha y Dieter H. Hartmann. "Tidal disruption events in galactic centers". Proceedings of the International Astronomical Union 9, S303 (octubre de 2013): 427–28. http://dx.doi.org/10.1017/s1743921314001069.
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Supermassive black holes (106–109 M⊙) are now known to be present at the centers of most galaxies, but they are also found to have a close correlation with the host galaxy they live in. The masses of the supermasssive black holes (SMBHs) have been rigorously calculated using stellar dynamics (e.g., Gillessen et al. 2009) for the Milky Way, gas dynamics (e.g., Davis et al. 2013) for NGC 4526, water maser emissions, reverberation mapping, etc. In comparison, the mass of the SMBH seems to be tightly correlated with the galactic bulge it resides in. The tight correlation between the mass of the BH and the velocity dispersion of the stars in the bulge, known as the M-σ relation, (Ferrarese & Merritt, 2000; Tremaine et al. 2002), and the 2:1000 mass of BH - mass of bulge ratio suggests some sort of co-evolution process. A feedback driven coevolution process would suggest that the BH directly controls galaxy properties via energy and momentum feedback (Kormendy & Ho, 2013). However, since correlation does not necessarily imply causation, the evolution may be a non-causal process that occurs in tandem, where the BH and bulge grow independently. In such a process, star formation in the bulge and growth of SMBH occur in separate periods and are self regulating (Cen, 2012).
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Bhatta, Gopal. "Blazar Jets as Possible Sources of Ultra-High Energy Photons: A Short Review". Universe 8, n.º 10 (1 de octubre de 2022): 513. http://dx.doi.org/10.3390/universe8100513.
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In this paper, I present a qualitative discussion on the prospect of production of ultra-high photons in blazars. The sources are a subclass of active galactic nuclei which host supermassive black holes and fire relativistic jets into the intergalactic medium. The kpc-scale jets are believed to be dominated by Poynting flux and constitute one of the most efficient cosmic particle accelerators, that potentially are capable of accelerating the particles up to EeV energies. Recent IceCube detection of astrophysical neutrino emissions, in coincidence with the enhanced gamma-ray from Tev blazar TXS 0506 + 056, further supports hadronic models of blazar emissions in which particle acceleration processes, such as relativistic shocks, magnetic re-connection, and relativistic turbulence, could energize hadrons, e.g., protons, up to energies equivalent to billions of Lorentz factors. The ensuing photo-pionic processes may then result in gamma-rays accompanied by neutrino flux. Furthermore, the fact that blazars are the dominant source of observed TeV emission encourages search for signatures of acceleration scenarios that would lead to the creation of ultra-high-energy photons.
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Alexa, Petr, Petra Količová y Radim Uhlář. "Gamma Radioactivity Of The January 2013 Rainfall In Ostrava / Gama Radioaktivita Deště V Lednu 2013 V Ostravě". GeoScience Engineering 60, n.º 2 (1 de julio de 2014): 25–29. http://dx.doi.org/10.2478/gse-2014-0010.
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Abstract Gamma radioactivity of an 8 mm thick ice layer formed after a modest rain on 21 January 2013 in the VŠB-Technical University of Ostrava campus was analyzed and gamma-ray emissions from primordial 40K have been found. Cosmogenic 7Be produced mainly in galactic cosmic-ray spallation processes on atmospheric nitrogen and oxygen and 226Ra, 235U and 137Cs have been also observed.
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Abdalla, H., A. Abramowski, F. Aharonian, F. Ait Benkhali, E. O. Angüner, M. Arakawa, C. Armand et al. "Detection of variable VHE γ-ray emission from the extra-galactic γ-ray binary LMC P3". Astronomy & Astrophysics 610 (febrero de 2018): L17. http://dx.doi.org/10.1051/0004-6361/201732426.
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Context. Recently, the high-energy (HE, 0.1–100 GeV) γ-ray emission from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered to be modulated with a 10.3-day period, making it the first extra-galactic γ-ray binary. Aim. This work aims at the detection of very-high-energy (VHE, >100 GeV) γ-ray emission and the search for modulation of the VHE signal with the orbital period of the binary system. Methods. LMC P3 has been observed with the High Energy Stereoscopic System (H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has been folded with the known orbital period of the system in order to test for variability of the emission. Results. VHE γ-ray emission is detected with a statistical significance of 6.4 σ. The data clearly show variability which is phase-locked to the orbital period of the system. Periodicity cannot be deduced from the H.E.S.S. data set alone. The orbit-averaged luminosity in the 1–10 TeV energy range is (1.4 ± 0.2) × 1035 erg s−1. A luminosity of (5 ± 1) × 1035 erg s−1 is reached during 20% of the orbit. HE and VHE γ-ray emissions are anti-correlated. LMC P3 is the most luminous γ-ray binary known so far.
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Gladstone, G. Randall, Wayne R. Pryor, Doyle T. Hall, Joshua A. Kammer, Darrell F. Strobel, Harold A. Weaver, John R. Spencer et al. "New Horizons Detection of the Local Galactic Lyman-α Background". Astronomical Journal 162, n.º 6 (15 de noviembre de 2021): 241. http://dx.doi.org/10.3847/1538-3881/ac23cd.
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Abstract Since 2007 the Alice spectrograph on the New Horizons (NH) spacecraft has been used to periodically observe the Lyman-α (Lyα) emissions of the interplanetary medium (IPM), which mostly result from resonant scattering of solar Lyα emissions by interstellar hydrogen atoms passing through the solar system. Three observations of IPM Lyα along a single great circle were made during the NH cruise to Pluto, and these have been supplemented by observations along six great circles (spread over the sky at 30° intervals), acquired one month before and one day after the NH flyby of Pluto, and on a further five occasions since then, out to just over 47 au from the Sun. These data indicate a distant Lyα background of 43 ± 3 Rayleigh brightness (equivalent to 56 ± 4 nW m−2 sr−1), which is present in all directions (i.e., not only in the upstream direction, as previously reported). This result is found independently by: (1) the falloff with distance from the Sun of the IPM Lyα brightness observed by NH–Alice in several directions on the sky, and (2) the residual between the observed brightness and a model brightness accounting for the resonantly scattered solar Lyα component alone. The repeated observations show that this distant Lyα background is constant and uniform over the sky, and represents the local Galactic Lyα background. The observations show no strong correlation with the cloud structure of the local IPM. The observed brightness constrains the absorption coefficient of interstellar dust at Lyα to 0.2 ± 0.01 kpc−1.