Articles de revues : « High energy astrophysics, GRB, upper limits »

1

Albert, A., M. André, M. Anghinolfi, G. Anton, M. Ardid, J.-J. Aubert, J. Aublin et al. « Constraining the contribution of Gamma-Ray Bursts to the high-energy diffuse neutrino flux with 10 yr of ANTARES data ». Monthly Notices of the Royal Astronomical Society 500, n^o 4 (25 novembre 2020) : 5614–28. http://dx.doi.org/10.1093/mnras/staa3503.

Texte intégral

Résumé :

ABSTRACT Addressing the origin of the astrophysical neutrino flux observed by IceCube is of paramount importance. Gamma-Ray Bursts (GRBs) are among the few astrophysical sources capable of achieving the required energy to contribute to such neutrino flux through pγ interactions. In this work, ANTARES data have been used to search for upward going muon neutrinos in spatial and temporal coincidence with 784 GRBs occurred from 2007 to 2017. For each GRB, the expected neutrino flux has been calculated in the framework of the internal shock model and the impact of the lack of knowledge on the majority of source redshifts and on other intrinsic parameters of the emission mechanism has been quantified. It is found that the model parameters that set the radial distance where shock collisions occur have the largest impact on neutrino flux expectations. In particular, the bulk Lorentz factor of the source ejecta and the minimum variability time-scale are found to contribute significantly to the GRB-neutrino flux uncertainty. For the selected sources, ANTARES data have been analysed by maximizing the discovery probability of the stacking sample through an extended maximum-likelihood strategy. Since no neutrino event passed the quality cuts set by the optimization procedure, 90 per cent confidence level upper limits (with their uncertainty) on the total expected diffuse neutrino flux have been derived, according to the model. The GRB contribution to the observed diffuse astrophysical neutrino flux around 100 TeV is constrained to be less than 10 per cent.

Styles APA, Harvard, Vancouver, ISO, etc.

2

Albert, A., R. Alfaro, C. Alvarez, J. C. Arteaga-Velázquez, K. P. Arunbabu, D. Avila Rojas, H. A. Ayala Solares et al. « Constraints on the Very High Energy Gamma-Ray Emission from Short GRBs with HAWC ». Astrophysical Journal 936, n^o 2 (1 septembre 2022) : 126. http://dx.doi.org/10.3847/1538-4357/ac880e.

Texte intégral

Résumé :

Abstract Many gamma-ray bursts (GRBs) have been observed from radio wavelengths, and a few at very high energies (VHEs, >100 GeV). The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is well suited to study transient phenomena at VHEs owing to its large field of view and duty cycle. These features allow for searches of VHE emission and can probe different model assumptions of duration and spectra. In this paper, we use data collected by HAWC between 2014 December and 2020 May to search for emission in the energy range from 80 to 800 GeV coming from a sample of 47 short GRBs that triggered the Fermi, Swift, and Konus satellites during this period. This analysis is optimized to search for delayed and extended VHE emission within the first 20 s of each burst. We find no evidence of VHE emission, either simultaneous or delayed, with respect to the prompt emission. Upper limits (90% confidence level) derived on the GRB fluence are used to constrain the synchrotron self-Compton forward-shock model. Constraints for the interstellar density as low as 10−2 cm−3 are obtained when assuming z = 0.3 for bursts with the highest keV fluences such as GRB 170206A and GRB 181222841. Such a low density makes observing VHE emission mainly from the fast-cooling regime challenging.

Styles APA, Harvard, Vancouver, ISO, etc.

3

Abdalla, H., F. Aharonian, F. Ait Benkhali, E. O. Angüner, H. Ashkar, M. Backes, V. Baghmanyan et al. « H.E.S.S. Follow-up Observations of Binary Black Hole Coalescence Events during the Second and Third Gravitational-wave Observing Runs of Advanced LIGO and Advanced Virgo ». Astrophysical Journal 923, n^o 1 (1 décembre 2021) : 109. http://dx.doi.org/10.3847/1538-4357/ac2e04.

Texte intégral

Résumé :

Abstract We report on the observations of four well-localized binary black hole (BBH) mergers by the High Energy Stereoscopic System (H.E.S.S.) during the second and third observing runs of Advanced LIGO and Advanced Virgo, O2 and O3. H.E.S.S. can observe 20 deg2 of the sky at a time and follows up gravitational-wave (GW) events by “tiling” localization regions to maximize the covered localization probability. During O2 and O3, H.E.S.S. observed large portions of the localization regions, between 35% and 75%, for four BBH mergers (GW170814, GW190512_180714, GW190728_064510, and S200224ca). For these four GW events, we find no significant signal from a pointlike source in any of the observations, and we set upper limits on the very high energy (>100 GeV) γ-ray emission. The 1–10 TeV isotropic luminosity of these GW events is below 1045 erg s−1 at the times of the H.E.S.S. observations, around the level of the low-luminosity GRB 190829A. Assuming no changes are made to how follow-up observations are conducted, H.E.S.S. can expect to observe over 60 GW events per year in the fourth GW observing run, O4, of which eight would be observable with minimal latency.

Styles APA, Harvard, Vancouver, ISO, etc.

4

Laskar, Tanmoy, Alicia Rouco Escorial, Genevieve Schroeder, Wen-fai Fong, Edo Berger, Péter Veres, Shivani Bhandari et al. « The First Short GRB Millimeter Afterglow : The Wide-angled Jet of the Extremely Energetic SGRB 211106A ». Astrophysical Journal Letters 935, n^o 1 (1 août 2022) : L11. http://dx.doi.org/10.3847/2041-8213/ac8421.

Texte intégral

Résumé :

Abstract We present the discovery of the first millimeter afterglow of a short-duration γ-ray burst (SGRB) and the first confirmed afterglow of an SGRB localized by the GUANO system on Swift. Our Atacama Large Millimeter/Sub-millimeter Array (ALMA) detection of SGRB 211106A establishes an origin in a faint host galaxy detected in Hubble Space Telescope imaging at 0.7 ≲ z ≲ 1.4. From the lack of a detectable optical afterglow, coupled with the bright millimeter counterpart, we infer a high extinction, A V ≳ 2.6 mag along the line of sight, making this one of the most highly dust-extincted SGRBs known to date. The millimeter-band light curve captures the passage of the synchrotron peak from the afterglow forward shock and reveals a jet break at t jet = 29.2 − 4.0 + 4.5 days. For a presumed redshift of z = 1, we infer an opening angle, θ jet = (15.°5 ± 1.°4), and beaming-corrected kinetic energy of log ( E K / erg ) = 51.8 ± 0.3 , making this one of the widest and most energetic SGRB jets known to date. Combining all published millimeter-band upper limits in conjunction with the energetics for a large sample of SGRBs, we find that energetic outflows in high-density environments are more likely to have detectable millimeter counterparts. Concerted afterglow searches with ALMA should yield detection fractions of 24%–40% on timescales of ≳2 days at rates of ≈0.8–1.6 per year, outpacing the historical discovery rate of SGRB centimeter-band afterglows.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Aglietta, M., E. D. Alyea, P. Antonioli, G. Badino, G. Bari, M. Basile, V. S. Berezinsky et al. « Upper limits to low energy $\bar\nu_\mathrm{e}$ flux from GRB 990705 ». Astronomy & ; Astrophysics 366, n^o 2 (février 2001) : 573–77. http://dx.doi.org/10.1051/0004-6361:20000233.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

6

Stecker, F. W., et O. C. de Jager. « New Upper Limits on Intergalactic Infrared Radiation from High-Energy Astrophysics ». Astrophysical Journal 415 (octobre 1993) : L71. http://dx.doi.org/10.1086/187035.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

7

Murase, Kohta, Mainak Mukhopadhyay, Ali Kheirandish, Shigeo S. Kimura et Ke Fang. « Neutrinos from the Brightest Gamma-Ray Burst ? » Astrophysical Journal Letters 941, n^o 1 (1 décembre 2022) : L10. http://dx.doi.org/10.3847/2041-8213/aca3ae.

Texte intégral

Résumé :

Abstract We discuss implications that can be obtained by searches for neutrinos from the brightest gamma-ray burst (GRB), GRB 221009A. We derive constraints on GRB model parameters such as the cosmic-ray loading factor and dissipation radius, taking into account both neutrino spectra and effective areas. The results are strong enough to constrain proton acceleration near the photosphere, and we find that the single burst limits are comparable to those from stacking analysis. Quasi-thermal neutrinos from subphotospheres and ultra-high-energy neutrinos from external shocks are not yet constrained. We show that GeV–TeV neutrinos originating from neutron collisions are detectable, and urge dedicated analysis on these neutrinos with DeepCore and IceCube as well as ORCA and KM3NeT.

Styles APA, Harvard, Vancouver, ISO, etc.

8

Ai, Shunke, et He Gao. « Model Constraints Based on the IceCube Neutrino Nondetection of GRB 221009A ». Astrophysical Journal 944, n^o 2 (1 février 2023) : 115. http://dx.doi.org/10.3847/1538-4357/acb3bf.

Texte intégral

Résumé :

Abstract GRB 221009A is a bright gamma-ray burst (GRB) with isotropic energy larger than 1054 erg. Its fairly low redshift makes it a promising candidate for high-energy neutrino detection. However, a neutrino search for this GRB reported by the IceCube collaboration yielded a null result. In this paper, we utilize the upper limit from the IceCube observation to test different GRB prompt emission models. We find that, at least for this specific burst, the dissipative photosphere model could be ruled out in a large parameter space. The internal-shock model can survive only with a large bulk motion Lorentz factor Γ, where the most stringent and conservative constraints are Γ > ∼ 450 and Γ > ∼ 200, respectively. Also, the ratio of the total dissipated energy that goes into the protons and electrons (ϵ p /ϵ e ) can be constrained with a given Γ. For Γ < 400, ϵ p /ϵ e < 10 is required. For the Internal-collision-induced Magnetic Reconnection and Turbulence (ICMART) model, the constraint from GRB 221009A is modest. Under the ICMART model, only for extreme situations when most dissipated energy deposit into protons and all accelerated protons are suitable for producing neutrinos, a slightly large bulk motion (Γ > ∼ 250) is required.

Styles APA, Harvard, Vancouver, ISO, etc.

9

Yassine, M., F. Piron, R. Mochkovitch et F. Daigne. « Time evolution of the spectral break in the high-energy extra component of GRB 090926A ». Astronomy & ; Astrophysics 606 (octobre 2017) : A93. http://dx.doi.org/10.1051/0004-6361/201630353.

Texte intégral

Résumé :

Aims. The prompt light curve of the long GRB 090926A reveals a short pulse ~10 s after the beginning of the burst emission, which has been observed by the Fermi observatory from the keV to the GeV energy domain. During this bright spike, the high-energy emission from GRB 090926A underwent a sudden hardening above 10 MeV in the form of an additional power-law component exhibiting a spectral attenuation at a few hundreds of MeV. This high-energy break has been previously interpreted in terms of gamma-ray opacity to pair creation and has been used to estimate the bulk Lorentz factor of the outflow. In this article, we report on a new time-resolved analysis of the GRB 090926A broadband spectrum during its prompt phase and on its interpretation in the framework of prompt emission models. Methods. We characterized the emission from GRB 090926A at the highest energies with Pass 8 data from the Fermi Large Area Telescope (LAT), which offer a greater sensitivity than any data set used in previous studies of this burst, particularly in the 30−100 MeV energy band. Then, we combined the LAT data with the Fermi Gamma-ray Burst Monitor (GBM) in joint spectral fits to characterize the time evolution of the broadband spectrum from keV to GeV energies. We paid careful attention to the systematic effects that arise from the uncertainties on the LAT response. Finally, we performed a temporal analysis of the light curves and we computed the variability timescales from keV to GeV energies during and after the bright spike. Results. Our analysis confirms and better constrains the spectral break, which has been previously reported during the bright spike. Furthermore, it reveals that the spectral attenuation persists at later times with an increase of the break characteristic energy up to the GeV domain until the end of the prompt phase. We discuss these results in terms of keV−MeV synchroton radiation of electrons accelerated during the dissipation of the jet energy and inverse Compton emission at higher energies. We interpret the high-energy spectral break as caused by photon opacity to pair creation. Requiring that all emissions are produced above the photosphere of GRB 090926A, we compute the bulk Lorentz factor of the outflow, Γ. The latter decreases from 230 during the spike to 100 at the end of the prompt emission. Assuming, instead, that the spectral break reflects the natural curvature of the inverse Compton spectrum, lower limits corresponding to larger values of Γ are also derived. Combined with the extreme temporal variability of GRB 090926A, these Lorentz factors lead to emission radii R ~ 1014 cm, which are consistent with an internal origin of both the keV−MeV and GeV prompt emissions.

Styles APA, Harvard, Vancouver, ISO, etc.

10

BESSON, D., S. RAZZAQUE, J. ADAMS et P. HARRIS. « Limits on the transient ultra-high energy neutrino flux from gamma-ray bursts (GRB) derived from RICE data ». Astroparticle Physics 26, n^o 6 (janvier 2007) : 367–77. http://dx.doi.org/10.1016/j.astropartphys.2006.07.008.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

11

Ronchi, M., F. Fumagalli, M. E. Ravasio, G. Oganesyan, M. Toffano, O. S. Salafia, L. Nava, S. Ascenzi, G. Ghirlanda et G. Ghisellini. « Rise and fall of the high-energy afterglow emission of GRB 180720B ». Astronomy & ; Astrophysics 636 (avril 2020) : A55. http://dx.doi.org/10.1051/0004-6361/201936765.

Texte intégral

Résumé :

The gamma-ray burst (GRB) 180720B is one of the brightest events detected by the Fermi satellite and the first GRB detected by the H.E.S.S. telescope above 100 GeV, at around ten hours after the trigger time. We analysed the Fermi (GBM and LAT) and Swift (XRT and BAT) data and describe the evolution of the burst spectral energy distribution in the 0.5 keV–10 GeV energy range over the first 500 s of emission. We reveal a smooth transition from the prompt phase, dominated by synchrotron emission in a moderately fast cooling regime, to the afterglow phase whose emission has been observed from the radio to the gigaelectronvolts energy range. The LAT (0.1–100 GeV) light curve initially rises (FLAT ∝ t2.4), peaks at ∼78 s, and falls steeply (FLAT ∝ t−2.2) afterwards. The peak, which we interpret as the onset of the fireball deceleration, allows us to estimate the bulk Lorentz factor Γ0 ∼ 150 (300) under the assumption of a circum-burst medium with a wind-like (homogeneous) density profile. We derive a flux upper limit in the LAT energy range at the time of H.E.S.S. detection, but this does not allow us to unveil the nature of the high-energy component observed by H.E.S.S. We fit the prompt spectrum with a physical model of synchrotron emission from a non-thermal population of electrons. The 0–35 s spectrum after its EF(E) peak (at 1–2 MeV) is a steep power law extending to hundreds of megaelectronvolts. We derive a steep slope of the injected electron energy distribution N(γ) ∝ γ−5. Our fit parameters point towards a very low magnetic field (B′ ∼ 1 G) in the emission region.

Styles APA, Harvard, Vancouver, ISO, etc.

12

Dichiara, S., E. Troja, V. Lipunov, R. Ricci, S. R. Oates, N. R. Butler, E. Liuzzo et al. « The early afterglow of GRB 190829A ». Monthly Notices of the Royal Astronomical Society 512, n^o 2 (18 février 2022) : 2337–49. http://dx.doi.org/10.1093/mnras/stac454.

Texte intégral

Résumé :

ABSTRACT GRB 190829A at z = 0.0785 is the fourth closest long GRB ever detected by the Neil Gehrels Swift observatory, and the third confirmed case with a very high-energy component. We present our multiwavelength analysis of this rare event, focusing on its early stages of evolution, and including data from Swift, the MASTER global network of optical telescopes, ALMA, and ATCA. We report sensitive limits on the linear polarization of the optical emission, disfavouring models of off-axis jets to explain the delayed afterglow peak. The study of the multiwavelength light curves and broad-band spectra supports a model with at least two emission components: a bright reverse shock emission, visible at early times in the optical and X-rays and, later, in the radio band; and a forward shock component dominating at later times and lower radio frequencies. A combined study of the prompt and afterglow properties shows many similarities with cosmological long GRBs, suggesting that GRB 190829A is an example of classical GRBs in the nearby universe.

Styles APA, Harvard, Vancouver, ISO, etc.

13

Greiner, J., J. Bolmer, M. Wieringa, A. J. van der Horst, D. Petry, S. Schulze, F. Knust et al. « Large-amplitude late-time radio variability in GRB 151027B ». Astronomy & ; Astrophysics 614 (juin 2018) : A29. http://dx.doi.org/10.1051/0004-6361/201731755.

Texte intégral

Résumé :

Context. Deriving physical parameters from gamma-ray burst (GRB) afterglow observations remains a challenge, even 20 years after the discovery of afterglows. The main reason for the lack of progress is that the peak of the synchrotron emission is in the sub-mm range, thus requiring radio observations in conjunction with X-ray/optical/near-infrared data in order to measure the corresponding spectral slopes and consequently remove the ambiguity with respect to slow vs. fast cooling and the ordering of the characteristic frequencies. Aims. We have embarked on a multifrequency, multi-epoch observing campaign to obtain sufficient data for a given GRB that allows us to test the simplest version of the fireball afterglow model. Methods. We observed GRB 151027B, the 1000th Swift-detected GRB, with GROND in the optical–near-IR, ALMA in the sub-millimeter, ATCA in the radio band; we combined this with public Swift/XRT X-ray data. Results. While some observations at crucial times only return upper limits or surprising features, the fireball model is narrowly constrained by our data set, and allows us to draw a consistent picture with a fully determined parameter set. Surprisingly, we find rapid, large-amplitude flux density variations in the radio band which are extreme not only for GRBs, but generally for any radio source. We interpret them as scintillation effects, though their extreme nature requires the scattering screen to be at a much smaller distance than usually assumed, multiple screens, or a combination of the two. Conclusions. The data are consistent with the simplest fireball scenario for a blast wave moving into a constant-density medium, and slow-cooling electrons. All fireball parameters are constrained at or better than a factor of 2, except for the density and the fraction of the energy in the magnetic field which has a factor of 10 uncertainty in both directions.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Bolmer, J., C. Ledoux, P. Wiseman, A. De Cia, J. Selsing, P. Schady, J. Greiner et al. « Evidence for diffuse molecular gas and dust in the hearts of gamma-ray burst host galaxies ». Astronomy & ; Astrophysics 623 (mars 2019) : A43. http://dx.doi.org/10.1051/0004-6361/201834422.

Texte intégral

Résumé :

Context. Damped Lyman-α (DLA) absorption-line systems at the redshifts of gamma-ray burst (GRB) afterglows offer a unique way to probe the physical conditions within star-forming galaxies in the early Universe. Aims. Here we built up a large sample of 22 GRBs at redshifts z > 2 observed with VLT/X-shooter in order to determine the abundances of hydrogen, metals, dust, and molecular species. This allows us to study the metallicity and dust depletion effects in the neutral interstellar medium at high redshift and to answer the question of whether (and why) there might be a lack of H2 in GRB-DLAs. Methods. We developed new methods based on the Bayesian inference package, PyMC, to FIT absorption lines and measure the column densities of different metal species as well as atomic and molecular hydrogen. The derived relative abundances are used to FIT dust depletion sequences and determine the dust-to-metals ratio and the host-galaxy intrinsic visual extinction. Additionally, we searched for the absorption signatures of vibrationally-excited H2 and carbon monoxide. Results. We find that there is no lack of H2-bearing GRB-DLAs. We detect absorption lines from molecular hydrogen in 6 out of 22 GRB afterglow spectra, with molecular fractions ranging between f ≃ 5 × 10−5 and f ≃ 0.04, and claim tentative detections in three additional cases. For the remainder of the sample, we measure, depending on S/N, spectral coverage and instrumental resolution, more or less stringent upper limits. The GRB-DLAs in our sample have on average low metallicities, [X/H]¯ ≈ −1.3, comparable to the population of extremely-strong QSO-DLAs (log N(H I) > 21.5). Furthermore, H2-bearing GRB-DLAs are found to be associated with significant dust extinction, AV > 0.1 mag, and dust-to-metals ratios DTM > 0.4, confirming the importance of dust grains for the production of molecules. All these systems exhibit neutral hydrogen column densities log N(H I) > 21.7. The overall fraction of H2 detections in GRB-DLAs is ≥ 27% (41% including tentative detections), which is three to four times larger than in the general QSO-DLA population. For 2 < z < 4, and considering column densities log N(H I) > 21.7, the H2 detection fraction is 60–80% in GRB-DLAs and in extremely strong QSO-DLAs. This is likely due to the fact that both GRB- and QSO-DLAs with high neutral hydrogen column densities are probed by sight-lines with small impact parameters, indicating that the absorbing gas is associated with the inner regions of the absorbing galaxy, where the gas pressure is higher and the conversion of H I to H2 takes place. In the case of GRB hosts, this diffuse molecular gas is located at distances ≳ 500 pc from the GRB and hence is unrelated to the star-forming region where the event occurred.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Ranjan, A., P. Noterdaeme, J. K. Krogager, P. Petitjean, R. Srianand, S. A. Balashev, N. Gupta et C. Ledoux. « Chemical enrichment and host galaxies of extremely strong intervening DLAs towards quasars ». Astronomy & ; Astrophysics 633 (janvier 2020) : A125. http://dx.doi.org/10.1051/0004-6361/201936078.

Texte intégral

Résumé :

We present the results from VLT/X-shooter spectroscopic observations of 11 extremely strong intervening damped Lyman-α absorbers (ESDLAs) that were initially selected as high N(H I) (i.e. ≥5 × 1021 cm−2) candidates from the Sloan Digital Sky Survey (SDSS). We confirm the high H I column densities, which we measure to be in the range log N(H I) = 21.6 − 22.4. Molecular hydrogen is detected with high column densities (N(H2)≥1018 cm−2) in 5 out of 11 systems, 3 of which are reported here for the first time, and we obtain conservative upper limits on N(H2) for the remaining 6 systems. We also measure the column density of various metal species (Zn II, Fe II, Si II, Cr II, and C I), quantify the absorption-line kinematics (Δv90), and estimate the extinction of the background quasar light (AV) by dust in the absorbing gas. We compare the chemical properties of this sample of ESDLAs, supplemented with literature measurements, to that of DLAs located at the redshift of long-duration γ-ray bursts (GRB-DLAs). We confirm that the two populations are almost indistinguishable in terms of chemical enrichment and gas kinematics. In addition, we find no marked differences in the incidence of H2. All this suggests that ESDLAs and GRB-DLAs probe similar galactic environments. We search for the galaxy counterparts of ESDLAs and find associated emission lines in 3 out of 11 systems, 2 of which are reported here for the first time (at zabs = 2.304 and 2.323 towards the quasars SDSS J002503.03+114547.80 and SDSS J114347.21+142021.60, respectively). The measured separations between the quasar sightlines and the emission associated with the ESDLA galaxy (for a total of five sightlines) are all very small (ρ < 3 kpc). Because our observations are complete up to ρ ∼ 7 kpc, we argue that the emission counterparts of the remaining systems are more likely below the detection limit than outside the search area. While the small impact parameters are similar to what is observed for GRB-DLAs, the associated star formation rates are on average lower than for GRB host galaxies. This is explained by long-duration GRBs being associated with the death of massive stars and therefore pinpointing regions of active star formation in the GRB host galaxies. Our observations support the suggestion from the literature that ESDLAs could act as blind analogues of GRB-DLAs, probing neutral gas with high column density in the heart of high-redshift galaxies, without any prior on the instantaneous star formation rate.

Styles APA, Harvard, Vancouver, ISO, etc.

16

do E. S. Pedreira, A. C. Caligula, N. Fraija, A. Galvan-Gamez, B. Betancourt Kamenetskaia, P. Veres, M. G. Dainotti, S. Dichiara et R. L. Becerra. « Afterglow Polarization from Off-axis Gamma-Ray Burst Jets ». Astrophysical Journal 942, n^o 2 (1 janvier 2023) : 81. http://dx.doi.org/10.3847/1538-4357/aca019.

Texte intégral

Résumé :

Abstract As we further our studies on gamma-ray bursts (GRBs), via both theoretical models and observational tools, more and more options begin to open for exploration of its physical properties. As GRBs are transient events primarily dominated by synchrotron radiation, it is expected that the synchrotron photons emitted by GRBs should present some degree of polarization throughout the evolution of the burst. Whereas observing this polarization can still be challenging due to the constraints on observational tools, especially for short GRBs, it is paramount that the groundwork is laid for the day we have abundant data. In this work, we present a polarization model linked with an off-axis spreading top-hat jet synchrotron scenario in a stratified environment with a density profile n(r) ∝ r −k . We present this model's expected temporal polarization evolution for a realistic set of afterglow parameters constrained within the values observed in the GRB literature for four degrees of stratification k = 0, 1, 1.5, and 2 and two magnetic field configurations with high extreme anisotropy. We apply this model and predict polarization from a set of GRBs exhibiting off-axis afterglow emission. In particular, for GRB 170817A, we use the available polarimetric upper limits to rule out the possibility of an extremely anisotropic configuration for the magnetic field.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Albert, J., E. Aliu, H. Anderhub, P. Antoranz, A. Armada, C. Baixeras, J. A. Barrio et al. « MAGIC Upper Limits on the Very High Energy Emission from Gamma‐Ray Bursts ». Astrophysical Journal 667, n^o 1 (20 septembre 2007) : 358–66. http://dx.doi.org/10.1086/520761.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

18

Reimer, O., M. Pohl, P. Sreekumar et J. R. Mattox. « EGRET Upper Limits on the High‐Energy Gamma‐Ray Emission of Galaxy Clusters ». Astrophysical Journal 588, n^o 1 (mai 2003) : 155–64. http://dx.doi.org/10.1086/374046.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

19

RAUE, MARTIN. « THE EXTRAGALACTIC BACKGROUND LIGHT : LOWER VERSUS UPPER LIMITS ». International Journal of Modern Physics D 18, n^o 10 (octobre 2009) : 1633–37. http://dx.doi.org/10.1142/s0218271809015588.

Texte intégral

Résumé :

The discovery of distant sources of very high energy (VHE) γ-rays with hard energy spectra enabled to derive strong upper limits on the density of the extragalactic background light (EBL). These limits are close to the lower limits derived from deep source counts. A recent re-dertemination of the EBL contribution from resolved sources at 3.6 μm finds a higher EBL density, which is claimed to be in conflict with the assumptions utilized to derive the EBL upper limits from VHE spectra. Here, it is shown that is possible to recover the canonical Γ ~ 1.5 intrinsic spectra for such a higher EBL density.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Abdalla, H., F. Aharonian, F. Ait Benkhali, E. O. Angüner, M. Arakawa, C. Arcaro, C. Armand et al. « Upper limits on very-high-energy gamma-ray emission from core-collapse supernovae observed with H.E.S.S. » Astronomy & ; Astrophysics 626 (juin 2019) : A57. http://dx.doi.org/10.1051/0004-6361/201935242.

Texte intégral

Résumé :

Young core-collapse supernovae with dense-wind progenitors may be able to accelerate cosmic-ray hadrons beyond the knee of the cosmic-ray spectrum, and this may result in measurable gamma-ray emission. We searched for gamma-ray emission from ten supernovae observed with the High Energy Stereoscopic System (H.E.S.S.) within a year of the supernova event. Nine supernovae were observed serendipitously in the H.E.S.S. data collected between December 2003 and December 2014, with exposure times ranging from 1.4 to 53 h. In addition we observed SN 2016adj as a target of opportunity in February 2016 for 13 h. No significant gamma-ray emission has been detected for any of the objects, and upper limits on the >1 TeV gamma-ray flux of the order of ~10−13 cm−2s−1 are established, corresponding to upper limits on the luminosities in the range ~2 × 1039 to ~1 × 1042 erg s−1. These values are used to place model-dependent constraints on the mass-loss rates of the progenitor stars, implying upper limits between ~2 × 10−5 and ~2 × 10−3 M⊙ yr−1 under reasonable assumptions on the particle acceleration parameters.

Styles APA, Harvard, Vancouver, ISO, etc.

21

Ndiyavala-Davids, Hambeleleni, Christo Venter, Andreas Kopp et Michael Backes. « Assessing uncertainties in the predicted very high energy flux of globular clusters in the Cherenkov Telescope Array era ». Monthly Notices of the Royal Astronomical Society 500, n^o 4 (19 novembre 2020) : 4827–36. http://dx.doi.org/10.1093/mnras/staa3588.

Texte intégral

Résumé :

ABSTRACT Terzan 5 is the only Galactic globular cluster that has plausibly been detected in the very high energy range. Stacking upper limits by High-Energy Stereoscopic System on the integral γ-ray flux of a population of other globular clusters are very constraining for leptonic cluster emission models. We demonstrate that uncertainty in model parameters leads to a large spread in the predicted flux, and there are indeed regions in parameter space for which the stringent stacking upper limits are satisfied. We conduct two more case studies: we study the uncertainties in differential TeV flux for M15, showing that our model can satisfy the stringent MAGIC upper limits for this cluster, for typical cluster parameters. We also calculate the differential flux at TeV energies for ω Cen, from which five pulsars have recently been detected at radio energies. It is thus important to increase measurement accuracy on key model parameters in order to improve predictions of cluster fluxes so as to better guide the observational strategy of the Cherenkov Telescope Array.

Styles APA, Harvard, Vancouver, ISO, etc.

22

Yang, Liu, Kai Zhu, Yong-Sheng Zhu et Hao Cai. « Combining upper limits with a Bayesian approach ». Chinese Physics C 39, n^o 12 (décembre 2015) : 123001. http://dx.doi.org/10.1088/1674-1137/39/12/123001.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

23

Abbasi, R., M. Ackermann, J. Adams, J. A. Aguilar, M. Ahlers, M. Ahrens, J. M. Alameddine et al. « Searching for High-energy Neutrino Emission from Galaxy Clusters with IceCube ». Astrophysical Journal Letters 938, n^o 2 (1 octobre 2022) : L11. http://dx.doi.org/10.3847/2041-8213/ac966b.

Texte intégral

Résumé :

Abstract Galaxy clusters have the potential to accelerate cosmic rays (CRs) to ultrahigh energies via accretion shocks or embedded CR acceleration sites. The CRs with energies below the Hillas condition will be confined within the cluster and eventually interact with the intracluster medium gas to produce secondary neutrinos and gamma rays. Using 9.5 yr of muon neutrino track events from the IceCube Neutrino Observatory, we report the results of a stacking analysis of 1094 galaxy clusters with masses ≳1014 M ⊙ and redshifts between 0.01 and ∼1 detected by the Planck mission via the Sunyaev–Zel’dovich effect. We find no evidence for significant neutrino emission and report upper limits on the cumulative unresolved neutrino flux from massive galaxy clusters after accounting for the completeness of the catalog up to a redshift of 2, assuming three different weighting scenarios for the stacking and three different power-law spectra. Weighting the sources according to mass and distance, we set upper limits at a 90% confidence level that constrain the flux of neutrinos from massive galaxy clusters (≳1014 M ⊙) to be no more than 4.6% of the diffuse IceCube observations at 100 TeV, assuming an unbroken E −2.5 power-law spectrum.

Styles APA, Harvard, Vancouver, ISO, etc.

24

Abbasi, R. U., M. Abe, T. Abu-Zayyad, M. Allen, R. Azuma, E. Barcikowski, J. W. Belz et al. « Search for point sources of ultra-high-energy photons with the Telescope Array surface detector ». Monthly Notices of the Royal Astronomical Society 492, n^o 3 (3 février 2020) : 3984–93. http://dx.doi.org/10.1093/mnras/stz3618.

Texte intégral

Résumé :

ABSTRACT The surface detector (SD) of the Telescope Array (TA) experiment allows us to detect indirectly photons with energies of the order of 1018 eV and higher, and to separate photons from the cosmic ray background. In this paper, we present the results of a blind search for point sources of ultra-high-energy (UHE) photons in the Northern sky using the TA SD data. The photon-induced extensive air showers are separated from the hadron-induced extensive air shower background by means of a multivariate classifier based upon 16 parameters that characterize the air shower events. No significant evidence for the photon point sources is found. The upper limits are set on the flux of photons from each particular direction in the sky within the TA field of view, according to the experiment’s angular resolution for photons. The average 95 per cent confidence level upper-limits for the point-source flux of photons with energies greater than 1018, 1018.5, 1019, 1019.5 and 1020 eV are 0.094, 0.029, 0.010, 0.0073 and 0.0058 km−2yr−1, respectively. For energies higher than 1018.5 eV, the photon point-source limits are set for the first time. Numerical results for each given direction in each energy range are provided as a supplement to this paper.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Abdalla, H., A. Abramowski, F. Aharonian, F. Ait Benkhali, A. G. Akhperjanian, T. Andersson, E. O. Angüner et al. « Systematic search for very-high-energy gamma-ray emission from bow shocks of runaway stars ». Astronomy & ; Astrophysics 612 (avril 2018) : A12. http://dx.doi.org/10.1051/0004-6361/201630151.

Texte intégral

Résumé :

Context. Runaway stars form bow shocks by ploughing through the interstellar medium at supersonic speeds and are promising sources of non-thermal emission of photons. One of these objects has been found to emit non-thermal radiation in the radio band. This triggered the development of theoretical models predicting non-thermal photons from radio up to very-high-energy (VHE, E ≥ 0.1 TeV) gamma rays. Subsequently, one bow shock was also detected in X-ray observations. However, the data did not allow discrimination between a hot thermal and a non-thermal origin. Further observations of different candidates at X-ray energies showed no evidence for emission at the position of the bow shocks either. A systematic search in the Fermi-LAT energy regime resulted in flux upper limits for 27 candidates listed in the E-BOSS catalogue.Aim. Here we perform the first systematic search for VHE gamma-ray emission from bow shocks of runaway stars.Methods. Using all available archival H.E.S.S. data we search for very-high-energy gamma-ray emission at the positions of bow shock candidates listed in the second E-BOSS catalogue release. Out of the 73 bow shock candidates in this catalogue, 32 have been observed with H.E.S.S.Results. None of the observed 32 bow shock candidates in this population study show significant emission in the H.E.S.S. energy range. Therefore, flux upper limits are calculated in five energy bins and the fraction of the kinetic wind power that is converted into VHE gamma rays is constrained.Conclusions. Emission from stellar bow shocks is not detected in the energy range between 0.14 and 18 TeV.The resulting upper limits constrain the level of VHE gamma-ray emission from these objects down to 0.1–1% of the kinetic wind energy.

Styles APA, Harvard, Vancouver, ISO, etc.

26

Ahnen, Max L. « On Integral Upper Limits Assuming Power-law Spectra and the Sensitivity in High-energy Astronomy ». Astrophysical Journal 836, n^o 2 (21 février 2017) : 196. http://dx.doi.org/10.3847/1538-4357/aa5b97.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

27

Coelho, Jaziel G., Luana N. Padilha, Rita C. dos Anjos, Cynthia V. Ventura et Geanderson A. Carvalho. « An updated view and perspectives on high-energy gamma-ray emission from SGR J1935+2154 and its environment ». Journal of Cosmology and Astroparticle Physics 2022, n^o 10 (1 octobre 2022) : 041. http://dx.doi.org/10.1088/1475-7516/2022/10/041.

Texte intégral

Résumé :

Abstract SGR J1935+2154 was discovered in 2016 and is currently one of the most burst-active Soft Gamma-ray Repeaters (SGR), having emitted many X-ray bursts in recent years. In one of our previous articles, we investigated the contribution to high-energy and very high-energy gamma-ray emission (VHE, E > 100 GeV) due to cosmic-ray acceleration of SNR G57.2+0.8 hosting SGR J1935+2154 using the GALPROP propagation code. However, follow-up observations of SGR 1935+2154 were made for 2 hours on April 28, 2020, using the High Energy Stereoscopic System (H.E.S.S.). The observations coincide with X-ray bursts detected by INTEGRAL and Fermi/Gamma-ray Burst Monitor (GBM). These are the first high-energy gamma-ray observations of an SGR in a flaring state, and upper limits on sustained and transient emission have been derived. Now that new H.E.S.S. observations have been made, it is interesting to update our model with respect to these new upper limits. We extend our previous results to a more general situation using the new version of GALPROP. We obtain a hadronic model that confirms the results discussed by H.E.S.S. . This leads to an optimistic prospect that cosmic ray gamma rays from SGR J1935+2154 can contribute to the overall gamma energy density distribution and in particular to the diffusion gamma rays from the Galactic center.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Andreoni, I., J. Cooke, S. Webb, A. Rest, T. Pritchard, M. Caleb, S.-W. Chang et al. « Probing the extragalactic fast transient sky at minute time-scales with DECam ». Monthly Notices of the Royal Astronomical Society 491, n^o 4 (4 décembre 2019) : 5852–66. http://dx.doi.org/10.1093/mnras/stz3381.

Texte intégral

Résumé :

ABSTRACT Searches for optical transients are usually performed with a cadence of days to weeks, optimized for supernova discovery. The optical fast transient sky is still largely unexplored, with only a few surveys to date having placed meaningful constraints on the detection of extragalactic transients evolving at sub-hour time-scales. Here, we present the results of deep searches for dim, minute-time-scale extragalactic fast transients using the Dark Energy Camera, a core facility of our all-wavelength and all-messenger Deeper, Wider, Faster programme. We used continuous 20 s exposures to systematically probe time-scales down to 1.17 min at magnitude limits g > 23 (AB), detecting hundreds of transient and variable sources. Nine candidates passed our strict criteria on duration and non-stellarity, all of which could be classified as flare stars based on deep multiband imaging. Searches for fast radio burst and gamma-ray counterparts during simultaneous multifacility observations yielded no counterparts to the optical transients. Also, no long-term variability was detected with pre-imaging and follow-up observations using the SkyMapper optical telescope. We place upper limits for minute-time-scale fast optical transient rates for a range of depths and time-scales. Finally, we demonstrate that optical g-band light-curve behaviour alone cannot discriminate between confirmed extragalactic fast transients such as prompt GRB flashes and Galactic stellar flares.

Styles APA, Harvard, Vancouver, ISO, etc.

29

del Palacio, S., F. García, D. Altamirano, R. H. Barbá, V. Bosch-Ramon, M. Corcoran, M. De Becker et al. « The high-energy emission from HD 93129A near periastron ». Monthly Notices of the Royal Astronomical Society 494, n^o 4 (5 mai 2020) : 6043–52. http://dx.doi.org/10.1093/mnras/staa1156.

Texte intégral

Résumé :

ABSTRACT We conducted an observational campaign towards one of the most massive and luminous colliding wind binaries in the Galaxy, HD 93129A, close to its periastron passage in 2018. During this time the source was predicted to be in its maximum of high-energy emission. Here we present our data analysis from the X-ray satellites Chandra and NuSTAR and the γ-ray satellite AGILE. High-energy emission coincident with HD 93129A was detected in the X-ray band up to ∼18 keV, whereas in the γ-ray band only upper limits were obtained. We interpret the derived fluxes using a non-thermal radiative model for the wind-collision region. We establish a conservative upper limit for the fraction of the wind kinetic power that is converted into relativistic electron acceleration, fNT,e < 0.02. In addition, we set a lower limit for the magnetic field in the wind-collision region as BWCR > 0.3 G. We also argue a putative interpretation of the emission from which we estimate fNT,e ≈ 0.006 and BWCR ≈ 0.5 G. We conclude that multiwavelength, dedicated observing campaigns during carefully selected epochs are a powerful tool for characterizing the relativistic particle content and magnetic field intensity in colliding wind binaries.

Styles APA, Harvard, Vancouver, ISO, etc.

30

Schwartz, Daniel A. « The High-energy emission of jetted AGN ». Proceedings of the International Astronomical Union 14, A30 (août 2018) : 53–60. http://dx.doi.org/10.1017/s1743921319003454.

Texte intégral

Résumé :

AbstractQuasars with flat radio spectra and one-sided, arc-second scale, ≈ 100 mJy GHz radio jets are found to have similar scale X-ray jets in about 60% of such objects, even in short 5 to 10 ks Chandra observations. Jets emit in the GHz band via synchrotron radiation, as known from polarization measurements. The X-ray emission is explained most simply, i.e. with the fewest additional parameters, as inverse Compton (iC) scattering of cosmic microwave background (cmb) photons by the relativistic electrons in the jet. With physics based assumptions, one can estimate enthalpy fluxes upwards of 1046 erg s−1, sufficient to reverse cooling flows in clusters of galaxies, and play a significant role in the feedback process which correlates the masses of black holes and their host galaxy bulges. On a quasar-by-quasar basis, we can show that the total energy to power these jets can be supplied by the rotational energy of black holes with spin parameters as low as a = 0.3. For a few bright jets at redshifts less than 1, the Fermi gamma ray observatory shows upper limits at 10 Gev which fall below the fluxes predicted by the iC/cmb mechanism, proving the existence of multiple relativistic particle populations. At large redshifts, the cmb energy density is enhanced by a factor (1+z)4, so that iC/cmb must be the dominant mechanism for relativistic jets unless their rest frame magnetic field strength is hundreds of micro-Gauss.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Acero, F., F. Aharonian, A. G. Akhperjanian, G. Anton, U. Barres de Almeida, A. R. Bazer-Bachi, Y. Becherini et al. « HESS upper limits on very high energy gamma-ray emission from the microquasar GRS 1915+105 ». Astronomy & ; Astrophysics 508, n^o 3 (4 novembre 2009) : 1135–40. http://dx.doi.org/10.1051/0004-6361/200913389.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

32

Abbasi, R., M. Ackermann, J. Adams, J. A. Aguilar, M. Ahlers, M. Ahrens, C. Alispach et al. « Search for High-energy Neutrinos from Ultraluminous Infrared Galaxies with IceCube ». Astrophysical Journal 926, n^o 1 (1 février 2022) : 59. http://dx.doi.org/10.3847/1538-4357/ac3cb6.

Texte intégral

Résumé :

Abstract Ultraluminous infrared galaxies (ULIRGs) have infrared luminosities L IR ≥ 1012 L ⊙, making them the most luminous objects in the infrared sky. These dusty objects are generally powered by starbursts with star formation rates that exceed 100 M ⊙ yr−1, possibly combined with a contribution from an active galactic nucleus. Such environments make ULIRGs plausible sources of astrophysical high-energy neutrinos, which can be observed by the IceCube Neutrino Observatory at the South Pole. We present a stacking search for high-energy neutrinos from a representative sample of 75 ULIRGs with redshift z ≤ 0.13 using 7.5 yr of IceCube data. The results are consistent with a background-only observation, yielding upper limits on the neutrino flux from these 75 ULIRGs. For an unbroken E −2.5 power-law spectrum, we report an upper limit on the stacked flux Φ ν μ + ν ¯ μ 90 % = 3.24 × 10 − 14 TeV − 1 cm − 2 s − 1 ( E / 10 TeV ) − 2.5 at 90% confidence level. In addition, we constrain the contribution of the ULIRG source population to the observed diffuse astrophysical neutrino flux as well as model predictions.

Styles APA, Harvard, Vancouver, ISO, etc.

33

NOVIKOV, V. A., L. B. OKUN et M. I. VYSOTSKY. « DO PRESENT LEP DATA PROVIDE EVIDENCE FOR ELECTROWEAK CORRECTIONS ? » Modern Physics Letters A 08, n^o 27 (7 septembre 1993) : 2529–38. http://dx.doi.org/10.1142/s0217732393002889.

Texte intégral

Résumé :

The Born approximation, based on [Formula: see text] instead of α, reproduces all electroweak precision measurements within their (1σ) accuracy. The low upper limits for the genuinely electroweak corrections constitute one of the major achievements of LEP. The astonishing smallness of these corrections results from the cancellation of a large positive contribution from the heavy top quark and large negative contributions from all other virtual particles. It is precisely the non-observation of electroweak radiative corrections that places stringent upper and lower limits on the top mass.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Zakeri, Mohammadreza, et Yu-Feng Zhou. « Constraining time dependent dark matter signals from the Sun ». Journal of Cosmology and Astroparticle Physics 2022, n^o 04 (1 avril 2022) : 026. http://dx.doi.org/10.1088/1475-7516/2022/04/026.

Texte intégral

Résumé :

Abstract Dark matter (DM) particles captured by the Sun can produce high-energy electrons outside the Sun through annihilating into meta-stable mediators. The corresponding cosmic-ray electron signals observed by the space-based experiments will be time dependent due to the orbital motion of the space-based detectors. The shape of this time dependence is predictable given the orbital information of the detectors. Since the high-energy CR electron (with energy E > 100 GeV) fluxes are expected to be constant in time, non-observation of such time variation can be used to place upper limits on the DM annihilation cross section. We analyze the time dependence of dark matter cosmic-ray signals in three space-based experiments: AMS-02, DAMPE and CALET. Under the assumption that no time dependent signal is observed, we derive the 95% C.L. exclusion limits on the signal strength from the current data. We map our limits onto the parameter space of the dark photon model and find that the constraints are comparable with that derived from the supernova SN1987A.

Styles APA, Harvard, Vancouver, ISO, etc.

35

DREINER, HERBERT. « b→sγ IN SUPERSTRING INSPIRED MODELS ». Modern Physics Letters A 03, n^o 09 (août 1988) : 867–75. http://dx.doi.org/10.1142/s0217732388001033.

Texte intégral

Résumé :

Superstring inspired models contain, in general, extra quarks per family beyond those of the standard model. These quarks may give considerable contributions to b→sγ. Limits on their masses and couplings may be extracted from the presently available upper limits on this rare decay.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Giacomelli, G., et A. Margiotta. « The MACRO Experiment ». Modern Physics Letters A 18, n^o 29 (21 septembre 2003) : 2001–18. http://dx.doi.org/10.1142/s0217732303011654.

Texte intégral

Résumé :

In this paper we describe the main results obtained by the MACRO experiment: final stringent upper limits on GUT magnetic monopoles and nuclearites, results on atmospheric neutrino oscillations, high energy muon neutrino astronomy, searches for WIMPs, search for low energy stellar gravitational collapse neutrinos, several studies with high energy downgoing muons and determination of the primary cosmic ray composition at knee energies.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Schroedter, M. « Upper Limits on the Extragalactic Background Light from the Very High Energy Gamma‐Ray Spectra of Blazars ». Astrophysical Journal 628, n^o 2 (août 2005) : 617–28. http://dx.doi.org/10.1086/431173.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

38

Abdalla, H., A. Abramowski, F. Aharonian, F. Ait Benkhali, E. O. Angüner, M. Arakawa, M. Arrieta et al. « Population study of Galactic supernova remnants at very high γ-ray energies with H.E.S.S. » Astronomy & ; Astrophysics 612 (avril 2018) : A3. http://dx.doi.org/10.1051/0004-6361/201732125.

Texte intégral

Résumé :

Shell-type supernova remnants (SNRs) are considered prime candidates for the acceleration of Galactic cosmic rays (CRs) up to the knee of the CR spectrum at E ≈ 3 × 1015 eV. Our Milky Way galaxy hosts more than 350 SNRs discovered at radio wavelengths and at high energies, of which 220 fall into the H.E.S.S. Galactic Plane Survey (HGPS) region. Of those, only 50 SNRs are coincident with a H.E.S.S source and in 8 cases the very high-energy (VHE) emission is firmly identified as an SNR. The H.E.S.S. GPS provides us with a legacy for SNR population study in VHE γ-rays and we use this rich data set to extract VHE flux upper limits from all undetected SNRs. Overall, the derived flux upper limits are not in contradiction with the canonical CR paradigm. Assuming this paradigm holds true, we can constrain typical ambient density values around shell-type SNRs to n ≤ 7 cm−3 and electron-to-proton energy fractions above 10 TeV to ϵep ≤ 5 × 10−3. Furthermore, comparisons of VHE with radio luminosities in non-interacting SNRs reveal a behaviour that is in agreement with the theory of magnetic field amplification at shell-type SNRs.

Styles APA, Harvard, Vancouver, ISO, etc.

39

Dhital, N., P. Homola, D. Alvarez-Castillo, D. Góra, H. Wilczyński, K. Almeida Cheminant, B. Poncyljusz et al. « Cosmic ray ensembles as signatures of ultra-high energy photons interacting with the solar magnetic field ». Journal of Cosmology and Astroparticle Physics 2022, n^o 03 (1 mars 2022) : 038. http://dx.doi.org/10.1088/1475-7516/2022/03/038.

Texte intégral

Résumé :

Abstract Propagation of ultra-high energy photons in the solar magnetosphere gives rise to cascades comprising thousands of photons. We study the cascade development using Monte Carlo simulations and find that the photons in the cascades are spatially extended over millions of kilometers on the plane distant from the Sun by 1 AU. We estimate the chance of detection considering upper limits from current cosmic rays observatories in order to provide an optimistic estimate rate of 0.002 events per year from a chosen ring-shaped region around the Sun. We compare results from simulations which use two models of the solar magnetic field, and show that although signatures of such cascades are different for the models used, for practical detection purpose in the ground-based detectors, they are similar.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Zhang, H., I. M. Christie, M. Petropoulou, J. M. Rueda-Becerril et D. Giannios. « Inverse Compton signatures of gamma-ray burst afterglows ». Monthly Notices of the Royal Astronomical Society 496, n^o 1 (5 juin 2020) : 974–86. http://dx.doi.org/10.1093/mnras/staa1583.

Texte intégral

Résumé :

ABSTRACT The afterglow emission from gamma-ray bursts (GRBs) is believed to originate from a relativistic blast wave driven into the circumburst medium. Although the afterglow emission from radio up to X-ray frequencies is thought to originate from synchrotron radiation emitted by relativistic, non-thermal electrons accelerated by the blast wave, the origin of the emission at high energies (HE; ≳GeV) remains uncertain. The recent detection of sub-TeV emission from GRB 190114C by the Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC) raises further debate on what powers the very high energy (VHE; ≳300 GeV) emission. Here, we explore the inverse Compton scenario as a candidate for the HE and VHE emissions, considering two sources of seed photons for scattering: synchrotron photons from the blast wave (synchrotron self-Compton or SSC) and isotropic photon fields external to the blast wave (external Compton). For each case, we compute the multiwavelength afterglow spectra and light curves. We find that SSC will dominate particle cooling and the GeV emission, unless a dense ambient infrared photon field, typical of star-forming regions, is present. Additionally, considering the extragalactic background light attenuation, we discuss the detectability of VHE afterglows by existing and future gamma-ray instruments for a wide range of model parameters. Studying GRB 190114C, we find that its afterglow emission in the Fermi-Large Area Telescope (LAT) band is synchrotron dominated. The late-time Fermi-LAT measurement (i.e. t ∼ 104 s), and the MAGIC observation also set an upper limit on the energy density of a putative external infrared photon field (i.e. ${\lesssim} 3\times 10^{-9}\, {\rm erg\, cm^{-3}}$), making the inverse Compton dominant in the sub-TeV energies.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Deng, Xue-Mei, et Yi Xie. « New upper limits of a braneworld model with recent Solar System tests ». Modern Physics Letters A 31, n^o 05 (5 février 2016) : 1650021. http://dx.doi.org/10.1142/s0217732316500218.

Texte intégral

Résumé :

As an extension of previous works on classical tests of a braneworld model which is called as the Dadhich, Maartens, Papadopoulos and Rezania (DMPR) solution, and as an attempt to find more stringent constraints on this model, we investigate its effects on physical experiments and astronomical observations conducted in the Solar System by modeling new observable effects and adopting new datasets. First, we investigate gravitational time delay at inferior conjunction (IC) caused by the braneworld model, which was not considered in previous works, because these measurements are not affected by the solar corona noise. Second, the Cassini superior conjunction (SC) experiment is, for the first time, used to test the DMPR model. Third, compared to previous works, we refine the model, which confronts the perihelion shift induced by the braneworld model with modern Solar System ephemerides INPOP10a (IMCCE, France) and EPM2011 (IAA RAS, Russia). The correction of DMPR solution to Einstein’s general relativity (GR) in the four-dimensional spacetime can be characterized by a constant bulk “tidal charge” parameter [Formula: see text], which is confined in the present work. We find that time delay experiment at IC is independent of [Formula: see text] and not suitable for testing the braneworld model. However, the Cassini SC experiment and modern Solar System ephemerides can give better upper bounds on [Formula: see text]: (1) [Formula: see text] by Cassini, and (2) [Formula: see text] based on the supplementary advances of the perihelia provided by INPOP10a and [Formula: see text] based on the ones of EPM2011. The latter upper bounds are improved to be tighter than the ones of previous works by at least two orders of magnitude. Besides, the stronger constraints on the brane tension are given by the modern ephemerides, which are [Formula: see text] for INPOP10a and [Formula: see text] for EPM2011. These improved upper bounds mean that the Solar System tests can serve as a good testbed for high dimensional theories.

Styles APA, Harvard, Vancouver, ISO, etc.

42

Hirashita, Hiroyuki, Denis Burgarella et Rychard J. Bouwens. « Dust mass and dust production efficiencies on the redshift frontier ». Proceedings of the International Astronomical Union 15, S341 (novembre 2019) : 216–20. http://dx.doi.org/10.1017/s1743921319002096.

Texte intégral

Résumé :

AbstractIn order to clarify the dust production in the early Universe, we constrain the dust mass in high-redshift (z ≳ 5) galaxies using the upper limits obtained by ALMA. We perform fitting to the rest-frame UV–far-infrared spectral energy distribution (SED) of a giant Lyα emitter, Himiko, at z = 6.6 and a composite SED of z > 5 Lyman break galaxies (LBGs). For Himiko, we obtain a high dust temperature > 70 K. This high dust temperature puts a strong upper limit on the total dust mass Md ≲ 2 × 106 M⊙, and the dust mass produced per supernova (SN) md,SN ≲ 0.1 M⊙. Such a low md,SN suggests significant loss of dust by reverse shock destruction or outflow. For the LBG sample, we only obtain an upper limit for md,SN as ∼2 M⊙. This clarifies the importance of observing UV-bright objects (like Himiko) to constrain the dust production by SNe.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Michelson, P. F., D. L. Bertsch, K. Brazier, J. Chiang, B. L. Dingus, C. E. Fichtel, J. Fierro et al. « EGRET upper limits to the high-energy gamma-ray emission from the millisecond pulsars in nearby globular clusters ». Astrophysical Journal 435 (novembre 1994) : 218. http://dx.doi.org/10.1086/174808.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

44

Abdalla, H., R. Adam, F. Aharonian, F. Ait Benkhali, E. O. Angüner, M. Arakawa, C. Arcaro et al. « Very high energy γ-ray emission from two blazars of unknown redshift and upper limits on their distance ». Monthly Notices of the Royal Astronomical Society 494, n^o 4 (23 avril 2020) : 5590–602. http://dx.doi.org/10.1093/mnras/staa999.

Texte intégral

Résumé :

ABSTRACT We report on the detection of very high energy (VHE; E > 100 GeV) γ-ray emission from the BL Lac objects KUV 00311−1938 and PKS 1440−389 with the High Energy Stereoscopic System (H.E.S.S.). H.E.S.S. observations were accompanied or preceded by multiwavelength observations with Fermi/LAT, XRT and UVOT onboard the Swift satellite, and ATOM. Based on an extrapolation of the Fermi/LAT spectrum towards the VHE γ-ray regime, we deduce a 95 per cent confidence level upper limit on the unknown redshift of KUV 00311−1938 of $z$ < 0.98 and of PKS 1440−389 of $z$ < 0.53. When combined with previous spectroscopy results, the redshift of KUV 00311−1938 is constrained to 0.51 ≤ $z$ < 0.98 and of PKS 1440−389 to 0.14 ⪅ $z$ < 0.53.

Styles APA, Harvard, Vancouver, ISO, etc.

45

RIZZO, THOMAS G. « UPPER LIMITS ON THE TOP QUARK MASS IN MODELS WITH NEW GAUGE BOSONS ». Modern Physics Letters A 05, n^o 02 (20 janvier 1990) : 115–23. http://dx.doi.org/10.1142/s0217732390000159.

Texte intégral

Résumé :

The experimental value of the ρ parameter is used to obtain an upper limit on the top-quark mass (mt) in models with extended gauge sectors. This limit is found to be generally stronger than that obtained from similar considerations in the Standard Model (SM). This bound, however, is shown to depend strongly on the particular extension of the usual SM gauge sector under consideration. Improved experimental lower limits on mt can also be used to rule out large regions of the parameter space of extended electroweak models.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Ghirlanda, G., F. Nappo, G. Ghisellini, A. Melandri, G. Marcarini, L. Nava, O. S. Salafia, S. Campana et R. Salvaterra. « Bulk Lorentz factors of gamma-ray bursts ». Astronomy & ; Astrophysics 609 (janvier 2018) : A112. http://dx.doi.org/10.1051/0004-6361/201731598.

Texte intégral

Résumé :

Knowledge of the bulk Lorentz factor Γ0 of gamma-ray bursts (GRBs) allows us to compute their comoving frame properties shedding light on their physics. Upon collisions with the circumburst matter, the fireball of a GRB starts to decelerate, producing a peak or a break (depending on the circumburst density profile) in the light curve of the afterglow. Considering all bursts with known redshift and with an early coverage of their emission, we find 67 GRBs (including one short event) with a peak in their optical or GeV light curves at a time tp. For another 106 GRBs we set an upper limit tpUL. The measure of tp provides the bulk Lorentz factor Γ0 of the fireball before deceleration. We show that tp is due to the dynamics of the fireball deceleration and not to the passage of a characteristic frequency of the synchrotron spectrum across the optical band. Considering the tp of 66 long GRBs and the 85 most constraining upper limits, we estimate Γ0 or a lower limit Γ0LL. Using censored data analysis methods, we reconstruct the most likely distribution of tp. All tp are larger than the time Tp,γ when the prompt γ-ray emission peaks, and are much larger than the time Tph when the fireball becomes transparent, that is, tp>Tp,γ>Tph. The reconstructed distribution of Γ0 has median value ~300 (150) for a uniform (wind) circumburst density profile. In the comoving frame, long GRBs have typical isotropic energy, luminosity, and peak energy ⟨ Eiso ⟩ = 3(8) × 1050 erg, ⟨ Liso ⟩ = 3(15) × 1047 erg s-1, and ⟨ Epeak ⟩ = 1(2) keV in the homogeneous (wind) case. We confirm that the significant correlations between Γ0 and the rest frame isotropic energy (Eiso), luminosity (Liso), and peak energy (Ep) are not due to selection effects. When combined, they lead to the observed Ep−Eiso and Ep−Liso correlations. Finally, assuming a typical opening angle of 5 degrees, we derive the distribution of the jet baryon loading which is centered around a few 10-6M⊙.

Styles APA, Harvard, Vancouver, ISO, etc.

47

BRAU, FABIAN. « UPPER AND LOWER LIMITS ON THE EIGENVALUES OF THE SPINLESS SALPETER EQUATION ». International Journal of Modern Physics A 20, n^o 30 (10 décembre 2005) : 7277–84. http://dx.doi.org/10.1142/s0217751x05022883.

Texte intégral

Résumé :

In the context of relativistic quantum mechanics, we obtain a nonlinear first order differential equation for the energy as a function of the coupling constant of a central potential. This differential equation is only exact for power law and logarithmic potentials in the massless limit. For other potentials, we discuss under which conditions the differential equation yields rigorous upper and lower limits on the value of energy levels. These results are applied to the Cornell potential used in meson spectroscopy. We also show that the method applies to noncentral potentials.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Abbasi, R., M. Ackermann, J. Adams, J. A. Aguilar, M. Ahlers, M. Ahrens, J. M. Alameddine et al. « Searches for Neutrinos from Gamma-Ray Bursts Using the IceCube Neutrino Observatory ». Astrophysical Journal 939, n^o 2 (1 novembre 2022) : 116. http://dx.doi.org/10.3847/1538-4357/ac9785.

Texte intégral

Résumé :

Abstract Gamma-ray bursts (GRBs) are considered as promising sources of ultra-high-energy cosmic rays (UHECRs) due to their large power output. Observing a neutrino flux from GRBs would offer evidence that GRBs are hadronic accelerators of UHECRs. Previous IceCube analyses, which primarily focused on neutrinos arriving in temporal coincidence with the prompt gamma-rays, found no significant neutrino excess. The four analyses presented in this paper extend the region of interest to 14 days before and after the prompt phase, including generic extended time windows and targeted precursor searches. GRBs were selected between 2011 May and 2018 October to align with the data set of candidate muon-neutrino events observed by IceCube. No evidence of correlation between neutrino events and GRBs was found in these analyses. Limits are set to constrain the contribution of the cosmic GRB population to the diffuse astrophysical neutrino flux observed by IceCube. Prompt neutrino emission from GRBs is limited to ≲1% of the observed diffuse neutrino flux, and emission on timescales up to 104 s is constrained to 24% of the total diffuse flux.

Styles APA, Harvard, Vancouver, ISO, etc.

49

MASPERI, LUIS, et GALILEO VIOLINI. « LIMITS SET BY ANALYTICITY AND CURRENT ALGEBRA ON THE EXISTENCE OF A HEAVY NUCLEON ». Modern Physics Letters A 05, n^o 02 (20 janvier 1990) : 101–6. http://dx.doi.org/10.1142/s0217732390000135.

Texte intégral

Résumé :

We estimate through the analysis of dispersion relations and current algebra sum rules that the experimentally searched excited state of nucleon with mass below pion-nucleon threshold must have a coupling one order of magnitude smaller than the normal pion-nucleon one [Formula: see text] as an upper bound.

Styles APA, Harvard, Vancouver, ISO, etc.

50

ILTAN, E. O. « LEPTON FLAVOR VIOLATING li→ljγγ DECAYS INDUCED BY SCALAR UNPARTICLE ». Modern Physics Letters A 23, n^o 39 (21 décembre 2008) : 3331–39. http://dx.doi.org/10.1142/s021773230802714x.

Texte intégral

Résumé :

We study the radiative lepton flavor violating li→ljγγ decays in the case that the lepton flavor violation is induced by the scalar unparticle mediation. We restrict the scaling dimension du and the scalar unparticle–photon–photon coupling by using the experimental upper limit of the branching ratio of the decay μ→eγγ. Furthermore, we predict the BRs of the other radiative decays by using the restrictions we get. We observe that the measurements of upper limits of BRs of these decays ensure considerable information for testing the possible signals coming from unparticle physics.

Styles APA, Harvard, Vancouver, ISO, etc.

Articles de revues sur le sujet « High energy astrophysics, GRB, upper limits »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres