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Gamma-ray Bursts (gamma-ray + burst)
Selected AbstractsShort Gamma-ray bursts: a bimodal origin?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008R. Salvaterra ABSTRACT Short-hard Gamma-Ray Bursts (SGRBs) are currently thought to arise from gravitational wave driven coalescences of double neutron star systems forming either in the field or dynamically in globular clusters. For both channels, we fit the peak flux distribution of BATSE SGRBs to derive the local burst formation rate and luminosity function. We then compare the resulting redshift distribution with Swift 2-yr data, showing that both formation channels are needed in order to reproduce the observations. Double neutron stars forming in globular clusters are found to dominate the distribution at z, 0.3, whereas the field population from primordial binaries can account for the high- z SGRBs. This result is not in contradiction with the observed host galaxy type of SGRBs. [source] The GRB early optical flashes from internal shocks: application to GRB 990123, GRB 041219a and GRB 060111bMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007D. M. Wei ABSTRACT With the successful launch of the Swift Gamma-ray Burst Explorer, it is widely expected that the prompt optical flashes like GRB 990123 would be easily detected. However, the observations show that for a number of Gamma-ray bursts (GRBs) no early optical flash has been detected, which indicates that the reverse shock emission must be suppressed. Here we explore the possibility that the optical flash may arise from the internal shock emission. For GRB 990123 and GRB 060111b, although their optical emission are not correlated with the gamma-ray emission, we propose here that their optical and gamma-ray emission may arise from different internal shocks (which can be formed by collision of different shells), and find that, under certain circumstances, the optical flashes of GRB 990123 and GRB 060111b can well be explained by the internal shock model. For GRB 041219a, the prompt optical emission was correlated with the gamma-ray emission, which can also be explained by the internal shock model if we assume the optical emission was the low-energy extension of the gamma-ray emission, and we find its redshift is about z, 0.2. As for GRB 050904, we have shown in previous paper that the optical flash was produced by synchrotron radiation and the X-ray flare was produced by the synchrotron,self-Compton (SSC) mechanism. Therefore we conclude that the early optical flashes of GRBs can usually arise from the internal shock emission. Meanwhile in our model since the shells producing the optical flashes would be easily disrupted by other shells, so we suggest that the bright optical flash should not be common in GRBs. In addition, we also discussed the SSC emission in the internal shock model, and find that for different values of parameters, there would be several kinds of high-energy emission (at ,100 keV, ,10 MeV or GeV) accompanying the optical flash. For a burst like GRB 990123, a GeV flare with fluence about 10,8 erg cm,2 s,1 is expected, which might be detected by the GLAST satellite. [source] Short Gamma-ray bursts: a bimodal origin?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2008R. Salvaterra ABSTRACT Short-hard Gamma-Ray Bursts (SGRBs) are currently thought to arise from gravitational wave driven coalescences of double neutron star systems forming either in the field or dynamically in globular clusters. For both channels, we fit the peak flux distribution of BATSE SGRBs to derive the local burst formation rate and luminosity function. We then compare the resulting redshift distribution with Swift 2-yr data, showing that both formation channels are needed in order to reproduce the observations. Double neutron stars forming in globular clusters are found to dominate the distribution at z, 0.3, whereas the field population from primordial binaries can account for the high- z SGRBs. This result is not in contradiction with the observed host galaxy type of SGRBs. [source] Measuring ,M and ,, with long-duration gamma-ray burstsASTRONOMISCHE NACHRICHTEN, Issue 8 2010A. Balastegui Abstract Gamma-ray bursts (GRBs) are one of the most luminous events in the Universe. In addition, the Universe itself is almost transparent to , -rays, making GRBs detectable up to very high redshifts. As a result, GRBs are very suitable to probe the cosmological parameters. This work shows the potential of long-duration GRBs for measuring the cosmological parameters ,M and ,, by comparing the observed log N -log P distribution with the theoretical one. Provided that the GRBs rate and luminosity function are well determined, the best values and 1, confidence intervals obtained are ,M = 0.22+0.05,0.03 and ,, = 1.06+0.05,0.10. Finally, a set of simulations show the ability of the method to measure ,M and ,, (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hard electron energy distribution in the relativistic shocks of gamma-ray burst afterglowsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008L. Resmi ABSTRACT Particle acceleration in relativistic shocks is not a very well understood subject. Owing to that difficulty, radiation spectra from relativistic shocks, such as those in gamma-ray burst (GRB) afterglows, have been often modelled by making assumptions about the underlying electron distribution. One such assumption is a relatively soft distribution of the particle energy, which need not be true always, as is obvious from observations of several GRB afterglows. In this paper, we describe modifications to the afterglow standard model to accommodate energy spectra which are ,hard'. We calculate the overall evolution of the synchrotron and Compton flux arising from such a distribution. We also model two afterglows, GRB010222 and GRB020813, under this assumption and estimate the physical parameters. [source] Peak energy of the prompt emission of long gamma-ray bursts versus their fluence and peak fluxMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008L. Nava ABSTRACT The spectral-energy (and luminosity) correlations in long gamma-ray bursts are being hotly debated to establish, first of all, their reality against possible selection effects. These are best studied in the observer planes, namely the peak energy Eobspeak versus the fluence F or the peak flux P. In a recent paper, we have started to investigate this problem considering all bursts with known redshift and spectral properties. Here, we consider instead all bursts with known Eobspeak, irrespective of redshift, adding to those a sample of 100 faint BATSE bursts representative of a larger population of 1000 objects. This allows us to construct a complete, fluence-limited, sample, tailored to study the selection/instrumental effects we consider. We found that the fainter BATSE bursts have smaller Eobspeak than those of bright events. As a consequence, the Eobspeak of these bursts is correlated with the fluence, though with a slope flatter than that defined by bursts with z. Selection effects, which are present, are shown not to be responsible for the existence of such a correlation. About six per cent of these bursts are surely outliers of the Epeak,Eiso correlation (updated in this paper to include 83 bursts), since they are inconsistent with it for any redshift. Eobspeak also correlates with the peak flux, with a slope similar to the Epeak,Liso correlation. In this case, there is only one sure outlier. The scatter of the Eobspeak,P correlation defined by the BATSE bursts of our sample is significantly smaller than the Eobspeak,F correlation of the same bursts, while for the bursts with known redshift the Epeak,Eiso correlation is tighter than the Epeak,Liso one. Once a very large number of bursts with Eobspeak and redshift will be available, we thus expect that the Epeak,Liso correlation will be similar to that currently found, whereas it is very likely that the Epeak,Eiso correlation will become flatter and with a larger scatter. [source] A case of mistaken identity?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007GRB 060912A, short GRB divide, the nature of the long ABSTRACT We investigate the origin of the GRB 060912A, which has observational properties that make its classification as either a long or short burst ambiguous. Short-duration gamma-ray bursts (SGRBs) are thought to have typically lower energies than long-duration bursts, can be found in galaxies with populations of all ages and are likely to originate from different progenitors to the long-duration bursts. However, it has become clear that duration alone is insufficient to make a distinction between the two populations in many cases, leading to a desire to find additional discriminators of burst type. GRB 060912A had a duration of 6 s and occurred only ,10 arcsec from a bright, low-redshift (z= 0.0936) elliptical galaxy, suggesting that this may have been the host, which would favour it being a short burst. However, our deep optical imaging and spectroscopy of the location of GRB 060912A using the Very Large Telescope (VLT) shows that GRB 060912A more likely originates in a distant star-forming galaxy at z= 0.937, and is most likely a long burst. This demonstrates the risk in identifying bright, nearby galaxies as the hosts of given gamma-ray bursts (GRBs) without further supporting evidence. Further, it implies that, in the absence of secure identifications, ,host' type, or more broadly discriminators that rely on galaxy redshifts, may not be good indicators of the true nature of any given GRB. [source] GRB 060418 and 060607A: the medium surrounding the progenitor and the weak reverse shock emissionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007Z. P. Jin ABSTRACT We constrain the circumburst medium profile with the rise behaviour of the very early afterglow light curves of gamma-ray bursts (GRBs). Using this method, we find a constant and low-density medium profile for GRB 060418 and GRB 060607A, which is consistent with the inference from the late afterglow data. In addition, we show that the absence of the infrared flashes in these two afterglows is consistent with the standard hydrodynamical external reverse shock model. Although a highly magnetized model can explain the data, it is no longer demanded. A weak reverse shock in the standard hydrodynamical model is achievable if the typical synchrotron frequency is already below the band at the shock-crossing time. [source] Baryon loading and the Weibel instability in gamma-ray burstsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006M. Fiore ABSTRACT The dynamics of two counter-streaming electron,positron,ion unmagnetized plasma shells with zero net charge is analysed in the context of magnetic field generation in gamma-ray burst internal shocks due to the Weibel instability. The effects of large thermal motion of plasma particles, arbitrary mixture of plasma species and space charge effects are taken into account. We show that, although thermal effects slow down the instability, baryon loading leads to a non-negligible growth rate even for large temperatures and different shell velocities, thus guaranteeing the robustness and the occurrence of the Weibel instability for a wide range of scenarios. [source] Magnetic jets from swirling discsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006D. Lynden-Bell ABSTRACT A broad swathe of astrophysical phenomena, ranging from tubular planetary nebulae through Herbig,Haro objects, radio galaxy and quasar emissions to gamma-ray bursts and perhaps high-energy cosmic rays, may be driven by magnetically dominated jets emanating from accretion discs. We give a self-contained account of the analytic theory of non-relativistic magnetically dominated jets wound up by a swirling disc and making a magnetic cavity in a background medium of any prescribed pressure, p(z). We solve the time-dependent problem for any specified distribution of magnetic flux P(R, 0) emerging from the disc at z= 0, with any specified disc angular velocity ,d(R). The physics required to do this involves only the freezing of the lines of force to the conducting medium and the principle of minimum energy. In a constant pressure environment, the magnetically dominated cavity is highly collimated and advances along the axis at a constant speed closely related to the maximum circular velocity of the accretion disc. Even within the cavity the field is strongly concentrated towards the axis. The twist in the jet field ,B,,/,|Bz|, is close to and the width of the jet decreases upwards. By contrast, when the background pressure falls off with height with powers approaching z,4, the head of the jet accelerates strongly and the twist of the jet is much smaller. The width increases to give an almost conical magnetic cavity with apex at the source. Such a regime may be responsible for some of the longest strongly collimated jets. When the background pressure falls off faster than z,4, there are no quasi-static configurations of well-twisted fields and the pressure confinement is replaced by a dynamic effective pressure or a relativistic expansion. In the regimes with rapid acceleration, the outgoing and incoming fields linking the twist back to the source are almost anti-parallel so there is a possibility that magnetic reconnections may break up the jet into a series of magnetic ,smoke-rings' travelling out along the axis. [source] Millimetric properties of gamma-ray burst host galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006R. S. Priddey ABSTRACT We present millimetre (mm) and submillimetre (submm) photometry of a sample of five host galaxies of gamma-ray bursts (GRBs), obtained using the Max Planck Millimetre Bolometer (MAMBO2) array and Submillimetre Common-User Bolometer Array (SCUBA). These observations were obtained as part of an ongoing project to investigate the status of GRBs as indicators of star formation. Our targets include two of the most unusual GRB host galaxies, selected as likely candidate submm galaxies: the extremely red (R,K, 5) host of GRB 030115, and the extremely faint (R > 29.5) host of GRB 020124. Neither of these galaxies is detected, but the deep upper limits for GRB 030115 impose constraints on its spectral energy distribution, requiring a warmer dust temperature than is commonly adopted for submillimetre galaxies (SMGs). As a framework for interpreting these data, and for predicting the results of forthcoming submm surveys of Swift -derived host samples, we model the expected flux and redshift distributions based on luminosity functions of both submm galaxies and GRBs, assuming a direct proportionality between the GRB rate density and the global star formation rate density. We derive the effects of possible sources of uncertainty in these assumptions, including (1) introducing an anticorrelation between GRB rate and the global average metallicity, and (2) varying the dust temperature. [source] New soft gamma-ray bursts in the BATSE records and spectral properties of X-ray rich burstsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Yana Tikhomirova ABSTRACT A population of X-ray dominated gamma-ray bursts (GRBs) observed by Ginga, BeppoSAX and the High Energy Transient Explorer (HETE-2) should be represented in the Burst and Transient Source Experiment (BATSE) data as presumably soft bursts. We have performed a search for soft GRBs in the BATSE records in the 25,100 keV energy band. The softness of a burst spectrum could explain why it has been missed by the on-board procedure and by the previous searches for untriggered GRBs tuned to the 50,300 keV range. We have found a surprisingly small number (, 20 yr,1 with fluxes down to 0.1 photon cm,2 s,1) of soft GRBs where the count rate is dominated by the 25,50 keV energy channel. This fact, as well as the analysis of HETE-2 and common BeppoSAX/BATSE GRBs, indicates that the majority of GRBs with a low Epeak have a relatively hard tail with a high-energy power-law photon index , > ,3. An exponential cutoff in GRB spectra below 10,15 keV may be a distinguishing feature of non-GRB events. [source] Probing the dark ages with redshift distribution of gamma-ray burstsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002T. Roy Choudhury Abstract In this article, we explore the possibility of using the properties of gamma-ray bursts (GRBs) to probe the physical conditions in the epochs prior to reionization. The redshift distribution of GRBs is modelled using the Press,Schechter formalism with an assumption that they follow the cosmic star formation history. We reproduce the observed star formation rate obtained from galaxies in the redshift range 0 < z < 5, as well as the redshift distribution of the GRBs inferred from the luminosity,variability correlation of the burst light curve. We show that the fraction of GRBs at high redshifts, the afterglows of which cannot be observed in the R and I bands owing to H i Gunn,Peterson optical depth can, at the most, account for one third of the dark GRBs. The observed redshift distribution of GRBs, with much less scatter than the one available today, can put stringent constraints on the epoch of reionization and the nature of gas cooling in the epochs prior to reionization. [source] Quiescent times in gamma-ray bursts , I. An observed correlation between the durations of subsequent emission episodesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2001Enrico Ramirez-Ruiz Although more than 2000 astronomical gamma-ray bursts (GRBs) have been detected, the precise progenitor responsible for these events is unknown. The temporal phenomenology observed in GRBs can significantly constrain the different models. Here we analyse the time histories of a sample of bright, long GRBs, searching for the ones exhibiting relatively long (more than 5 per cent of the total burst duration) ,quiescent times', defined as the intervals between adjacent episodes of emission during which the gamma-ray count rate drops to the background level. We find a quantitative relation between the duration of an emission episode and the quiescent time elapsed since the previous episode. We suggest here that the mechanism responsible for the extraction and the dissipation of energy has to take place in a metastable configuration, such that the longer the accumulation period, the higher the stored energy available for the next emission episode. [source] The late time evolution of gamma-ray bursts: ending hyperaccretion and producing flaresMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006Daniel Proga ABSTRACT We consider the properties of a hyperaccretion model for gamma-ray bursts (GRBs) at late times when the mass supply rate is expected to decrease with time. We point out that the region in the vicinity of the accretor and the accretor itself can play an important role in determining the rate of accretion, and its time behaviour, and ultimately the energy output. Motivated by numerical simulations and theoretical results, we conjecture that the energy release can be repeatedly stopped and then restarted by the magnetic flux accumulated around the accretor. We propose that the episode or episodes when the accretion resumes correspond to X-ray flares discovered recently in a number of GRBs. [source] Soft gamma-ray repeater giant flares in the BATSE short gamma-ray burst catalogue: constraints from spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2005Davide Lazzati ABSTRACT The giant flare observed on 2004 December 27 from SGR 1806,20 has revived the idea that a fraction of short (<2 s) gamma-ray bursts (GRBs) are due to giant flares from soft gamma-ray repeaters (SGRs) located in nearby galaxies. One of the distinguishing characteristics of these events is the thermal (blackbody) spectrum with temperatures ranging from ,50 to ,180 keV, with the highest temperature observed for the initial 0.2-s spike of the 2004 December 27 event. We have analysed the spectra of a complete sample of short GRBs with peak fluxes greater than 4 photon s,1 cm,2 detected by BATSE. Of the 115 short GRBs so selected, only 76 had sufficient signal-to-noise ratio to allow the spectral analysis. We find only three short GRBs with a spectrum well fitted by a blackbody, with 60 ,kT, 90 keV, albeit with a considerably longer duration (i.e. ,1 s) and a more complex light curve than the 2004 December 27 event. This implies a stringent limit on the rate of extragalactic SGR giant flares with spectral properties analogous to the December 27 flare. We conclude that up to 4 per cent of the short GRBs could be associated with giant flares (2, confidence). This implies that either the distance to SGR 1806,20 is smaller than 15 kpc or the rate of Galactic giant flares is lower than the estimated 0.033 yr,1. [source] Probing the existence of the Epeak,Eiso correlation in long gamma ray burstsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2005Giancarlo Ghirlanda ABSTRACT We probe the existence of the Epeak,Eiso correlation in long gamma-ray bursts (GRBs) using a sample of 442 BATSE bursts with known Epeak and with redshift estimated through the lag,luminosity correlation. This sample confirms that the rest-frame peak energy is correlated with the isotropic equivalent energy. The distribution of the scatter of the points around the best-fitting line is similar to that obtained with the 27 bursts with spectroscopic redshifts. We interpret the scatter in the Epeak,Eiso plane as due to the opening angle distribution of GRB jets. By assuming that the collimation corrected energy correlates with Epeak we can derive the observed distribution of the jet opening angles, which turns out to be lognormal with a peak value of . [source] Measuring ,M and ,, with long-duration gamma-ray burstsASTRONOMISCHE NACHRICHTEN, Issue 8 2010A. Balastegui Abstract Gamma-ray bursts (GRBs) are one of the most luminous events in the Universe. In addition, the Universe itself is almost transparent to , -rays, making GRBs detectable up to very high redshifts. As a result, GRBs are very suitable to probe the cosmological parameters. This work shows the potential of long-duration GRBs for measuring the cosmological parameters ,M and ,, by comparing the observed log N -log P distribution with the theoretical one. Provided that the GRBs rate and luminosity function are well determined, the best values and 1, confidence intervals obtained are ,M = 0.22+0.05,0.03 and ,, = 1.06+0.05,0.10. Finally, a set of simulations show the ability of the method to measure ,M and ,, (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the detection of high-frequency oscillations in short gamma-ray burstsASTRONOMISCHE NACHRICHTEN, Issue 4 2009B.E. Zhilyaev Abstract In this work we present the results of an investigation aimed at a search for an oscillatory phenomenon during short gamma-ray bursts. The wavelet technique, used for this analysis, is applied to the data from the BATSE 3B catalogue. We have detected oscillations, which periods are found to be in the milliseconds range and their amplitudes up to dozens of percents. A possible scenario for such a phenomenon is the coalescence of stellar-mass black holes and neutron stars. During the coalescence process the matter orbiting the black hole produces rapid, periodic phenomena. Such system will also emit gravitational waves which cause the orbital radius to decrease and leads to the emission of a chirp of radiation. Estimates lead to a timescale of milliseconds for the coalescence process and oscillation frequencies of hundreds of Hz. The gamma-ray bursts considered in this paper, show both frequencies and survival times of oscillations close to the mentioned values. A chirp phenomenon is also present. We therefore argue in favor of the black hole , neutron star coalescence as a scenario for the production of short gamma-ray bursts (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] TAROT: Robotic observatories for gamma-ray bursts and other sources,ASTRONOMISCHE NACHRICHTEN, Issue 3 2008A. Klotz Abstract TAROT (Télescopes ŕ Action Rapide pour les Objets Transitoires) are two robotic observatories designed to observe the early optical counterpart of gamma-ray bursts (GRBs) sources. As GRBs do not occur often, we use TAROT to observe other celestial targets: variable stars, minor-planets, supernovae, etc. In this paper we present the software tools presently used to manage the observations and to process and archive the data. We present also CADOR (Coordination et Analyse des Données des Observatoires Robotiques) which will centralize virtual observatory services associated to both TAROT telescopes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Simulations of magnetic fields in the cosmosASTRONOMISCHE NACHRICHTEN, Issue 5-6 2006M. Brüggen Abstract The origin of large-scale magnetic fields in clusters of galaxies remains controversial. The intergalactic magnetic field within filaments should be less polluted by magnetised outflows from active galaxies than magnetic fields in clusters. Therefore, filaments may be a better laboratory to study magnetic field amplification by structure formation than galaxy clusters, which typically host many more active galaxies. We present highly resolved cosmological adaptive mesh refinement simulations of magnetic fields in the cosmos and make predictions about the evolution and structure of magnetic fields in filaments. Comparing our results to observational evidence of magnetic fields in filaments suggests that amplification of seed fields by gravitational collapse is not sufficient to produce intergalactic medium fields. Finally, implications for cosmic ray transport and the impact of magnetic fields on delayed photons from gamma-ray bursts are discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Super-LOTIS (Livermore Optical Transient Imaging System)ASTRONOMISCHE NACHRICHTEN, Issue 6-8 2004D. Pérez-Ramírez Abstract The 0.6-m Super-LOTIS telescope is a fully robotic system dedicated to the search for prompt optical emission from gamma-ray bursts (GRBs). The telescope began routine operations from its Steward Observatory site atop Kitt Peak (KPNO) in April 2000. This system is capable of responding to the Gamma-ray burst Coordinate Network (GCN) triggers within seconds. Together with LOTIS, these systems have been monitoring the GCN real-time data for automatic HETE2 GRB triggers. We will summarize the current capabilities of the system and present recent scientific results. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||