共查询到20条相似文献，搜索用时 15 毫秒
1.
If X-ray flashes (XRFs) and X-ray rich Gamma-ray Bursts (XRRGs) have the same origin as the Gamma-ray bursts (GRBs) but are viewed off-center from structured jets,their early afterglows may differ from those of GRBs,and when the ultra-relativistic outflow inter-acts with the surrounding medium,there are two shocks formed,a forward shock (FS),and a reverse shock (RS). We calculate numerically the early afterglow powered by uniform jets,Gaussian jets and power-law jets in the forward-reverse shock scenario. A set of differen-tial equations govern the dynamical evolution. The synchrotron self-Compton effect has been taken into account in the calculation. In the uniform jets,the very early afterglows of XRRGs and XRFs are significantly lower than the GRBs and the observed peak times of RS emission are later in the interstellar medium environment. The RS components in XRRGs and XRFs are difficult to detect,but in the stellar wind environment,the reduction of the very early flux and the delay of the RS peak time are not so remarkable. In nonuniform jets (Gaussian and power-law jets),where there are emission materials on the line of sight,the very early light curve resembles equivalent isotropic ejecta in general although the RS flux decay index shows notable deviations if the RS is relativistic (in stellar wind). 相似文献
2.
It is widely accepted that many gamma-ray bursts (GRBs) are produced by relativistic jets. Previous studies on the beaming effects in GRBs are mainly based on the conical geometry. However, some observations of the relativistic jets in radio galaxies, active galactic nuclei, and “micro-quasars” have shown that many of these outflows are cylindrical, but not conical. In this study, we assume that the jets that produce GRBs are cylindrical, and that the circum-burst environment is dense and optically thick. In the prompt burst phase, the strong X-ray emission can sublimate the circum-burst medium to form an optically thin channel, from which the optical photons are allowed to escape. As a result, the optical afterglows can be observed only for the observers who are positioned on the axes of jets. It is shown that the observed optical afterglows usually decay very rapidly (in the form of Sv oc t^v^l1 where p is the index of electron power-law distribution), due to the joint effect of the lateral expansion of the cylindrical jet and the absorption of optical photons by the dust outside the channel. Our model provides a possible explanation for the dark gamma-ray bursts. 相似文献
3.
Frank M. Rieger Valentí Bosch-Ramon Peter Duffy 《Astrophysics and Space Science》2007,309(1-4):119-125
We consider the acceleration of energetic particles by Fermi processes (i.e., diffusive shock acceleration, second order Fermi
acceleration, and gradual shear acceleration) in relativistic astrophysical jets, with particular attention given to recent
progress in the field of viscous shear acceleration. We analyze the associated acceleration timescales and the resulting particle
distributions, and discuss the relevance of these processes for the acceleration of charged particles in the jets of AGN,
GRBs and microquasars, showing that multi-component powerlaw-type particle distributions are likely to occur. 相似文献
4.
We give a new theoretical basis for examination of the presence of the Kerr black hole (KBH) or the Kerr naked singularity
(KNS) in the central engine of different astrophysical objects around which astrophysical jets are typically formed: X-ray
binary systems, gamma ray bursts (GRBs), active galactic nuclei (AGN), etc. 相似文献
5.
Yong-feng Huang Chang-yi Tan Zi-gao Dai Tan Lu 《Chinese Astronomy and Astrophysics》2002,26(4):1744-423
Afterglows from most gamma-ray bursts, such as GRBs 970228, 970508, 971214, 980329 and 980703, decay slowly and steadily. These bursts are widely believed to be due to isotropic fireballs. However, they in fact can also be well fitted by a cylindrical jet model. It is proposed that these bursts are probably generated by cylindrical jets, and not necessarily by isotropic fireballs. 相似文献
6.
7.
M. Modjaz 《Astronomische Nachrichten》2011,332(5):434-447
Long‐duration gamma‐ray bursts (GRBs) and type Ib/c supernovae (SNe Ib/c) are amongst nature's most magnificent explosions. While GRBs launch relativistic jets, SNe Ib/c are core‐collapse explosions whose progenitors have been stripped of their hydrogen and helium envelopes. Yet for over a decade, one of the key outstanding questions is what conditions lead to each kind of explosion in massive stars. Determining the fates of massive stars is not only a vibrant topic in itself, but also impacts using GRBs as star formation indicators over distances up to 13 billion light‐years and for mapping the chemical enrichment history of the universe. This article reviews a number of comprehensive observational studies that probe the progenitor environments, their metallicities and the explosion geometries of SN with and without GRBs, as well as the emerging field of SN environmental studies. Furthermore, it discusses SN2008D/XRT 080109 which was discovered serendipitously with the Swift satellite via its X‐ray emission from shock breakout and which generated great interest amongst both observers and theorists while illustrating a novel technique for stellar forensics. The article concludes with an outlook on how the most promising venues of research – with the many existing and upcoming large‐scale surveys such as PTF and LSST – will shed new light on the diverse deaths of massive stars (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
Ghirlanda G. Salvaterra R. Toffano M. Ronchini S. Guidorzi C. Oganesyan G. Ascenzi S. Bernardini M. G. Camisasca A. E. Mereghetti S. Nava L. Ravasio M. E. Branchesi M. Castro-Tirado A. Amati L. Blain A. Bozzo E. O’Brien P. Götz D. Le Floch E. Osborne J. P. Rosati P. Stratta G. Tanvir N. Bogomazov A. I. D’Avanzo P. Hafizi M. Mandhai S. Melandri A. Peer A. Topinka M. Vergani S. D. Zane S. 《Experimental Astronomy》2021,52(3):277-308
Gamma-ray Bursts (GRBs) are the most powerful transients in the Universe, over–shining for a few seconds all other γ-ray sky sources. Their emission is produced within narrowly collimated relativistic jets launched after the core–collapse of massive stars or the merger of compact binaries. THESEUS will open a new window for the use of GRBs as cosmological tools by securing a statistically significant sample of high-z GRBs, as well as by providing a large number of GRBs at low–intermediate redshifts extending the current samples to low luminosities. The wide energy band and unprecedented sensitivity of the Soft X-ray Imager (SXI) and X-Gamma rays Imaging Spectrometer (XGIS) instruments provide us a new route to unveil the nature of the prompt emission. For the first time, a full characterisation of the prompt emission spectrum from 0.3 keV to 10 MeV with unprecedented large count statistics will be possible revealing the signatures of synchrotron emission. SXI spectra, extending down to 0.3 keV, will constrain the local metal absorption and, for the brightest events, the progenitors’ ejecta composition. Investigation of the nature of the internal energy dissipation mechanisms will be obtained through the systematic study with XGIS of the sub-second variability unexplored so far over such a wide energy range. THESEUS will follow the spectral evolution of the prompt emission down to the soft X–ray band during the early steep decay and through the plateau phase with the unique ability of extending above 10 keV the spectral study of these early afterglow emission phases.
相似文献9.
Gamma jets (GJ) at MeV energies may be produced in galactic halos by Inverse Compton Scattering (ICS) of collinear ultrarelativistic electron beams (at GeV energies) onto thermal photons. These electron jets are emitted by neutron star jets (NSJ) or black holes (BH) while the target thermal photons are generated by a nearby binary stellarlike companion (or by a relic accreting disk). The GJ precesses in a conical shape as a lighthouse (with a characteristic Keplerian binary period) forced by the NSJ magnetic lines interaction with the stellar companion ones. The sudden blazing of the GJ, once the observer is into the beam cone direction, is detected as a GRB. Our predicted GRB spectra fit the GRB observed ones; GRB luminosity, variability and counts are well explained if the GJ sources are located in an extended and an evaporating galactic halo as the one recently required in the fast running away NS model. Observed jets such as SS433, the Great Annihilator, superluminal sources such as the last GRS1758-258, GRS1915+105 are the ideal candidates for NSJ as well as GJ. The SGRs are the lower energy and wider beamed version of this GJ model so they are linked to classical GRBs. The last mysterious presence of the twin rings near SN1987A (as well as the ring traces near NGC6543) are the spectacular signature of such (double sided) conical jet precession projected onto the red giant relic spherical shell. The tiny but very puzzling offaxis nature of the SN1987A twin rings is due to the high eccentricity of the binary NSJ. The GRBs from the nearby Andromeda halo might be detected as soon as the instrumental sensitivity is increased. 相似文献
10.
Relativistic shocks provide an efficient method for high-energy particle acceleration in many astrophysical sources. Multiple
shock systems are even more effective and of importance, for example, in the internal shock model of gamma-ray bursts. We
investigate the reacceleration of pre-existing energetic particles at such relativistic internal shocks by the first order
Fermi process of pitch angle scattering. We use a well established eigenfunction method to calculate the resulting spectra
for infinitely thin shocks. Implications for GRBs and relativistic jets are discussed.
Paul Dempsey would like to thank IRCSET for their financial support. 相似文献
11.
Martin G. Haehnelt Guinevere Kauffmann 《Monthly notices of the Royal Astronomical Society》2000,318(3):L35-L38
Popular models for the origin of gamma-ray bursts (GRBs) include short-lived massive stars as the progenitors of the fireballs. Hence the redshift distribution of GRBs should track the cosmic star formation rate of massive stars accurately. A significant proportion of high-mass star formation activity appears to occur in regions that are obscured from view in the optical waveband by interstellar dust. The amount of dust-enshrouded star formation activity taking place has been estimated by observing the thermal radiation from the dust that has been heated by young stars in the far-infrared and submillimetre wavebands. Here we discuss an alternative probe – the redshift distribution of GRBs. GRBs are detectable at the highest redshifts, and because gamma-rays are not absorbed by dust, the redshift distribution of GRBs should therefore be unaffected by dust extinction. At present the redshifts of GRBs can only be determined from the associated optical transient emission; however, useful information about the prevalence of dust-obscured star formation can also be obtained from the ratio of GRBs with and without an associated optical transient. Eight GRBs currently have spectroscopic redshifts. Once about a hundred redshifts are known, the population of GRBs will provide an important test of different models of the star formation history of the Universe. 相似文献
12.
Edo Berger 《New Astronomy Reviews》2011,55(1-2):1-22
The study of short-duration gamma-ray bursts (GRBs) experienced a complete revolution in recent years thanks to the discovery of the first afterglows and host galaxies starting in May 2005. These observations demonstrated that short GRBs are cosmological in origin, reside in both star forming and elliptical galaxies, are not associated with supernovae, and span a wide isotropic-equivalent energy range of ～1048–1052 erg. However, a fundamental question remains unanswered: What are the progenitors of short GRBs? The most popular theoretical model invokes the coalescence of compact object binaries with neutron star and/or black hole constituents. However, additional possibilities exist, including magnetars formed through prompt channels (massive star core-collapse) and delayed channels (binary white dwarf mergers, white dwarf accretion-induced collapse), or accretion-induced collapse of neutron stars. In this review I summarize our current knowledge of the galactic and sub-galactic environments of short GRBs, and use these observations to draw inferences about the progenitor population. The most crucial results are: (i) some short GRBs explode in dead elliptical galaxies; (ii) the majority of short GRBs occur in star forming galaxies; (iii) the star forming hosts of short GRBs are distinct from those of long GRBs, and instead appear to be drawn from the general field galaxy population; (iv) the physical offsets of short GRBs relative to their host galaxy centers are significantly larger than for long GRBs; (v) there is tentative evidence for large offsets from short GRBs with optical afterglows and no coincident hosts; (vi) the observed offset distribution is in good agreement with predictions for NS–NS binary mergers; and (vii) short GRBs trace under-luminous locations within their hosts, but appear to be more closely correlated with the rest-frame optical light (old stars) than the UV light (young massive stars). Taken together, these observations suggest that short GRB progenitors belong to an old stellar population with a wide age distribution, and generally track stellar mass. These results are fully consistent with NS–NS binary mergers and rule out a dominant population of prompt magnetars. However, a partial contribution from delayed magnetar formation or accretion-induced collapse is also consistent with the data. 相似文献
13.
The short duration (T
90 < 2 s) gamma-ray bursts (GRBs) detected in the SPI-ACS experiment onboard the INTEGRAL observatory are investigated. Averaged
light curves have been constructed for various groups of events, including short GRBs and unidentified short events. Extended
emission has been found in the averaged light curves of both short GRBs and unidentified short events. It is shown that the
fraction of the short GRBs in the total number of SPI-ACS GRBs can range from 30 to 45%, which is considerably larger than
has been thought previously. 相似文献
14.
Igor G. Mitrofanov 《Astrophysics and Space Science》1995,231(1-2):103-110
New statistical results for cosmic gamma-ray bursts are presented, based on aligned average time profiles. General signatures are discussed of averaged flux/spectrum evolution of the full set of the Second BATSE Catalog GRBs (Fishmanet al., 1995), as well as of the bright and dim subsets. The contradictory conclusions made by Norriset al., (1994) and Mitrofanovet al., (1995a) about the presence or the absence of the time-dilation of dim GRBs are discussed. The well-established effect of hardness/brightness correlation of GRBs is presented. The consequences of these statistical studies are discussed for the cosmological and galactic paradigms of GRBs sources. 相似文献
15.
Li-Xin Li 《Monthly notices of the Royal Astronomical Society》2008,388(4):1487-1500
The current Swift sample of gamma-ray bursts (GRBs) with measured redshifts allows us to test the assumption that GRBs trace star formation in the Universe. Some authors have claimed that the rate of GRBs increases with cosmic redshift faster than the star formation rate, whose cause is not yet known. In this paper, I investigate the possibility of interpreting the observed discrepancy between the GRB rate history and the star formation rate history using cosmic metallicity evolution. I am motivated by the observation that cosmic metallicity evolves with redshift and GRBs tend to occur in low-metallicity galaxies. First, I derive a star formation history up to redshift z = 7.4 from an updated sample of star formation rate densities. This is obtained by adding the new ultraviolet measurements of Bouwens et al. and the new ultraviolet and infrared measurements of Reddy et al. to the existing sample compiled by Hopkins & Beacom. Then, adopting a simple model for the relation between GRB production and the cosmic metallicity history as proposed by Langer & Norman, I show that the observed redshift distribution of the Swift GRBs can be reproduced with good accuracy. Although the results are limited by the small size of the GRB sample and the poorly understood selection biases in detection and localization of GRBs and in redshift determination, they suggest that GRBs trace both star formation and metallicity evolution. If the star formation history can be accurately measured with other approaches, which is presumably achievable in the near future, it will be possible to determine the cosmic metallicity evolution using the study of the redshift distribution of GRBs. 相似文献
16.
The variability of a gamma-ray burst (GRB) is thought to be correlated with its absolute peak luminosity, and this relation had been used to derive an estimate of the redshifts of GRBs. Recently, Amati et al. presented the results of spectral and energetic properties of several GRBs with known redshifts. Here, we analyse the properties of two groups of GRBs: one group with known redshift from afterglow observation and another group with redshift derived from the luminosity–variability relation. We study the redshift dependence of various GRBs features in their cosmological rest frames, including the burst duration, the isotropic luminosity and radiated energy, and the peak energy Ep of ν F ν spectra. We find that, for these two groups of GRBs, their properties are all redshift-dependent, i.e. their intrinsic duration, luminosity, radiated energy and peak energy Ep are all correlated with the redshift, which means that there are cosmological evolution effects on gamma-ray burst features, and this can provide an interesting clue to the nature of GRBs. If this is true, then the results also imply that the redshift derived from the luminosity–variability relation may be reliable. 相似文献
17.
We review models of cosmological gamma-ray bursts (GRBs). The statistical and -ray transparency issues are summarized. Neutron-star and black-hole merger scenarios are described and estimates of merger rates are summarized. We review the simple fireball models for GRBs and the recent work on non-simple fireballs. Alternative cosmological models, including models where GRBs are analogs of active galactic nuclei and where they are produced by high-field, short period pulsars, are also mentioned. The value of neutrino astronomy to solve the GRB puzzle is briefly reviewed. 相似文献
18.
Recent localizations of cosmic gamma-ray bursts (GBRs) are studied taking into account the estimations of their intensities. The increase of the avergage intensity of GRBs along galactic longitudesl=220–260° andl=40–80° is found. It may be associated with the Orion spiral arm and the central region of the Galaxy. Corresponding enhancement of the number of intense GRBs for directions along the Orion arm is also found. Astrophysical conclusions from this possible galaxy-scale distribution of GRBs are discussed. 相似文献
19.
GRBs are the most energetic combination of jets and disks in the Universe. Observations made using Swift reveal a complex temporal and spectral behaviour. We propose that this behaviour can be used to refine the GRB classification scheme and align it better with progenitor types. The early (prompt) X-ray light curve can be well described by an exponential which relaxes into a power law. The transition time between the exponential and the power law gives a well-defined timescale, T p , for the burst duration which we use with the spectral index of the prompt emission, β p , and the prompt power law decay index, α p to define four classes of burst: short, slow, fast and soft. Short bursts tend to decline more gradually than long bursts. Most GRBs display a second “afterglow” component which can be fitted in a similar way to the early emission. During the decay of this second component, few GRBs show jet breaks in accord with pre-Swift predictions. However, the start time of the final afterglow decay, T a , correlates with the peak of the prompt γ-ray emission spectrum, E peak, in an analogous way to the Ghirlanda relation found between optical “jet-break” times, t j , and E peak. These data are inconsistent with simple achromatic jet-break models casting doubt on the reliability of using late temporal breaks to determine the jet collimation. 相似文献
20.
R. Salvaterra S. Campana G. Chincarini S. Covino G. Tagliaferri 《Monthly notices of the Royal Astronomical Society》2008,385(1):189-194
Long gamma-ray bursts (GRBs) are important for the study of the Universe near and beyond the epoch of reionization. In this paper, we describe the characteristics of an 'ideal' instrument that can be used to search for GRBs at z ≥ 6–10. We find that the detection of these objects requires soft-band detectors with high sensitivity and a moderately large field of view. In light of these results, we compare available and planned GRB missions, deriving conservative predictions of the number of high-redshift GRBs detectable by these instruments along with the maximum accessible redshift. We show that the Swift satellite will be able to detect various GRBs at z ≥ 6, and likely at z ≥ 10 if the trigger threshold is decreased by a factor of ∼2. Furthermore, we find that INTEGRAL and GLAST are not the best tools to detect bursts at z ≥ 6, the former being limited by the small field of view, and the latter by its hard energy band and relatively low sensitivity. Finally, future missions ( SVOM , EDGE and, in particular, EXIST ) will provide a good sample of GRBs at z ≥ 6 within a few years of operation. 相似文献