Duration Gamma-ray Bursts Research Articles

The X-ray afterglow of the short gamma ray burst 050724

Short duration (2 s) Gamma-ray bursts (GRBs) have been a mystery since their discovery. Until May 2005 very little was known about short GRBs, but this situation has changed rapidly in the last few months since the Swift and HETE-2 satellites have made it possible to discover X-ray and optical counterparts to these sources. Positional associations indicate that short GRBs arise in close-by galaxies (). Here we report on a detailed study of the short GRB 050724 X-ray afterglow. This burst shows strong flaring variability in the X-ray band. It clearly confirms early suggestions of X-ray activity in the 50–100 s time interval following the GRB onset seen with BATSE. Late flare activity is also observed. These observations support the idea that flares are related to the inner engine for short GRBs, as well as long GRBs.

A beta decay radiation signature from neutron-rich gamma-ray bursts?

Core collapse of massive stars and binary neutron stars or black hole–neutron star binarymergers are likely progenitors of long and short duration gamma-ray bursts respectively.Neutronized material in the former and neutron star material in the latter are ejected bythe central engine implying a neutron-rich jet outflow. A free neutron, however, beta decaysto a proton, an electron (beta) and an anti-neutrino in about fifteen minutesin its rest frame. Sudden creation of a relativistic electron is accompanied byradiation with a unique temporal and spectral signature. We calculate here thisradiation signature collectively emitted by all beta decay electrons from neutron-richoutflow. Detection of this signature may thus provide strong evidence for notonly neutron but also for proton content in the relativistic gamma-ray burst jets.

Torus formation in neutron star mergers and well-localized short gamma-ray bursts

Merging neutron stars (NSs) are hot candidates for the still enigmatic sources of short gamma-ray bursts (GRBs). If the central engines of the huge energy release are accreting relic black holes (BHs) of such mergers, it is important to understand how the properties of the BH-torus systems, in particular disc masses and mass and rotation rate of the compact remnant, are linked to the characterizing parameters of the NS binaries. For this purpose, we present relativistic smoothed particle hydrodynamic simulations with conformally flat approximation of the Einstein field equations and a physical, non-zero temperature equation of state. Thick disc formation is highlighted as a dynamical process caused by angular momentum transfer through tidal torques during the merging process of asymmetric systems or in the rapidly spinning triaxial post-merger object. Our simulations support the possibility that the first well-localized short and hard GRBs 050509b, 050709, 050724, 050813 have originated from NS merger events and are powered by neutrino-antineutrino annihilation around a relic BH-torus system. Using model parameters based on this assumption, we show that the measured GRB energies and durations lead to estimates for the accreted masses and BH mass accretion rates which are compatible with theoretical expectations. In particular, the low-energy output and short duration of GRB 050509b set a very strict upper limit of less than 100 ms for the time interval after the merging until the merger remnant has collapsed to a BH, leaving an accretion torus with a small mass of only ∼0.01 M ⊙ . This favours a (nearly) symmetric NS+NS binary with a typical mass as progenitor system.

Gamma‐Ray Burst–Selected High‐Redshift Galaxies: Comparison to Field Galaxy Populations toz∼ 3

We study the internal structural properties of 37 long duration gamma-ray burst (GRB) host galaxies imaged with the Hubble Space Telescope. Fitting exponential disk and r^1/4 models to the surface brightness profiles of eight z < 1.2 bright host galaxies, we find that the disk model is slightly preferred for most hosts, although two galaxies are fit best with an r^1/4 profile. We furthermore measure the central concentrations and asymmetries of all 37 host galaxies using the CAS system, and compare with field galaxies in the Hubble Deep Field. Our first main conclusion is that GRB hosts exhibit a surprisingly high diversity of galaxy types. A significant fraction (68%) of host galaxies are situated in a region of the concentration-asymmetry diagram occupied by spirals or peculiar/merging galaxies. Twelve hosts (32%) are situated in the region occupied by elliptical galaxies, having high concentration indices. We also find some evidence for evolution in GRB host galaxy morphology, such that hosts at z > 1 have a relatively high light concentration, indicating that these systems are perhaps progenitors of massive galaxies, or are compact blue star forming galaxies. We find that GRB hosts at z > 1 are different from the general field population at z > 1 in terms of light concentration at >99.5% confidence, yet have sizes similar to the general z > 1 population. This is the opposite of the effect at z < 1 where GRB hosts are smaller than average. We argue that GRB hosts trace the starburst population at high redshift, as similarly concentrated galaxies at z > 1 are undergoing a disproportionate amount of star formation for their luminosities. Our results show that GRBs are perhaps ideal tracers of typical galaxies undergoing star formation at any epoch.

GRBs as rare stages of stellar evolution

The association of “long” Gamma-Ray Bursts (durations &gt; 2 seconds) with peculiar Type Ic supernovae suggests strongly that this type of GRB is produced by the collapse of the rapidly rotating core of an initially very massive star to a black hole. At the time of collapse the star has lost its hydrogen-rich envelope and the GRB is thought to be produced by a collimated relativistic jet of matter ejected along the star's rotation axis. The angular momentum constraints for producing such a “collapsar” or “hypernova” suggest that the GRB-producing core collapses constitute only a small fraction of all core collapses of massive stars. As to the short-duration GRBs (&lt; 2 seconds), which make up about one third of all GRBs, the most favoured model is that of the coalescence of a double neutron star or of a neutron star-black hole binary. Also these events are expected to be very rare, having a frequency of at most one event per hundred thousand years for a galaxy like our own. Due to the collimation of the relativistically ejected matter, the observable frequency of GRB events will, like in the case of the “long” bursts, be at least a factor hundred smaller.

GRB 050509b: the elusive optical/nIR/mm afterglow of a short-duration GRB

We present multiwavelength (optical/near infrared/millimetre) observations of a short duration gamma-ray burst detected by Swift (GRB 050509b) collected between 0 seconds and ~18.8 days after the event. No optical, near infrared or millimetre emission has been detected in spite of the well localised X-ray afterglow, confirming the elusiveness of the short duration events. We also discuss the possibility of the burst being located in a cluster of galaxies at z= 0.225 or beyond. In the former case, the spectral energy distribution of the neighbouring, potential host galaxy, favours a system harbouring an evolved dominant stellar population (age ~360 Myr), unlike most long duration GRB host galaxies observed so far, i.e. thus giving support to a compact binary merger origin. Any underlying supernova that could be associated with this particular event should have been at least 3 magnitudes fainter than the type Ib/c SN 1998bw and 2.3 magnitudes fainter than a typical type Ia SN.

A possible bright blue supernova in the afterglow of GRB 020305

Astronomy & Astrophysics manuscript no. (will be inserted by hand later) arXiv:astro-ph/0504050v1 3 Apr 2005 A possible bright blue SN in the afterglow of GRB 020305 ⋆ J. Gorosabel 1,2 , J.P.U. Fynbo 3 , A. Fruchter 2 , A. Levan 4 , J. Hjorth 3 , P. Nugent 5 , A.J. Castro-Tirado 1 , J.M. Castro Cer´on 2,3 , J. Rhoads 2 , D. Bersier 2 , and I. Burud 2 Instituto de Astrof´isica de Andaluc´ia (IAA-CSIC), P.O. Box 03004, E-18080 Granada, Spain Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Kobenhavn O, Denmark Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK Lawrence Berkeley National Laboratory, MS 50-F, 1 Cyclotron Road, Berkeley, CA 94720, USA Received ; accepted Abstract. We report on ground-based and HST(+STIS) imaging of the afterglow and host galaxy of the Gamma-Ray Burst (GRB) of March 5 2002. The GRB occurred in a R = 25.17 ± 0.14 galaxy, which apparently is part of an interacting system. The lightcurve of the optical afterglow shows a rebrightening, or at least a plateau, 12–16 days after the gamma-ray event. U BV RIK ′ multi-band imaging of the afterglow ∼12 days after the GRB reveals a blue spectral energy distribution (SED). The SED is consistent with a power-law with a spectral index of β = −0.63 ± 0.16, but there is tentative evidence for deviations away from a power-law. Unfortunately, a spectroscopic redshift has not been secured for GRB 020305. From the SED we impose a redshift upper limit of z . 2.8, hence excluding the pseudo redshift of 4.6 reported for this burst. We discuss the possibilities for explaining the lightcurve, SED and host galaxy properties for GRB 020305. The most natural interpretation of the lightcurve and the SED is an associated supernova (SN). Our data can not precisely determine the redshift of the GRB. The most favoured explanation is a low redshift (z ∼ 0.2) SN, but a higher redshift (z & 0.5) SN can not be excluded. We also discuss less likely scenarios not based on SNe, like a burst occurring in a z = 2.5 galaxy with an extinction curve similar to that of the Milky Way. Key words. gamma rays: bursts – techniques: photometric 1. Introduction For long duration GRBs the relation with supernovae (SNe) became firmly established with the discovery of the type Ic su- pernova SN 2003dh associated with GRB 030329 (Stanek et al. 2003; Hjorth et al. 2003). This result lends strong support to the collapsar model (Woosley 1993), but a SN is also an ingredient in other models (e.g. Dado et al. 2003; Fryer & Heger 2004). However, the associated SNe follow a broad distribution of op- tical luminosities (Zeh et al. 2004). Furthermore the connection of GRBs with SNe of other types than Ic can not be excluded, motivated by the two possible associations of GRBs and II type SNe (SN 1997cy, Germany et al. 2000; SN 1999E, Rigon et al. 2003). Therefore, the afterglow lightcurves and SEDs around the SN peak are far from being described by an universal SN template. In this study we present ground and space-based opti- cal observations of GRB 020305 carried out from 11.5 to 321.2 days after the burst. Send offprint requests to: J. Gorosabel Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden. Correspondence to: jgu@iaa.es GRB 020305 was localised by the HETE-II satellite on March 5.4968 UT (Ricker et al. 2002). The high-energy emis- sion as seen by the Interplanetary network (IPN) consisted in two broad pulses, with a total GRB duration of ∼280s (Hurley et al. 2002), placing it in the long-soft burst category. Price et al. (2002) reported the presence of a transient optical source in the HETE-II/IPN error box in images taken ∼20 hours after the GRB. Further imaging confirmed the fading behaviour of the candidate (Lee et al. 2002; Ohyama et al. 2002). The paper is structured as follows: Sect. 2 details the ob- servations and the data reduction, Sect. 3 reports the results on the SED, lightcurve and host galaxy, Sect. 4 discusses several interpretations of the results, and finally Sect. 5 draws the con- clusions of this study. 2. Observations and data reduction 2.1. NOT observations We observed the field of GRB 020305 from the ground with the 2.56-m Nordic Optical Telescope (NOT) on 2002 March 16.95–22.18 UT, i.e. 11.45–16.68 days after the GRB. The in- strument used was the Andaluc´ia Faint Object Spectrograph (ALFOSC) equipped with a 2048 2 pixel Loral CCD having a

Effects of Screw Instability on Extracting Energy from aRotating Black Hole

Magnetic extraction of energy from a rotating black hole(BH) is discussed in the coexistence of the Blandford–Znajek (BZ)process and the magnetic coupling (MC) process by considering theeffects of the screw instability of the magnetic field. It isshown that the screw instability affects the configuration of themagnetosphere and the evolution characteristics of the BH,augmenting the energy extracted in the BZ and MC processes. Inaddition, the observed energy and duration of several gamma-raybursts can be fitted well by virtue of our model.

A Possible Origin of Bimodal Distribution of Gamma‐Ray Bursts

We study the distribution of the durations of gamma-ray bursts (GRBs) in the unified model of short and long GRBs recently proposed by Yamazaki, Ioka, and Nakamura. Monte Carlo simulations show clear bimodal distributions, with lognormal-like shapes for both short and long GRBs, in a power-law as well as a Gaussian angular distribution of the subjets. We find that the bimodality comes from the existence of the discrete emission regions (subjets or patchy shells) in the GRB jet. To explain other temporal properties of short and long GRBs, the subjet parameters should depend on the angle in the whole jet.

Gamma-ray Bursts

SummarySince their discovery in 1967 Gamma-ray bursts (GRBs) have been puzzling to astrophysicists. With the advent of a new generation of X–ray satellites in the late 90’s, it was possible to carry out deep multi-wavelength observations of the counterparts associated with the long duration GRBs class just within a few hours of occurrence, thanks to the observation of the fading X-ray emission that follows the more energetic gamma-ray photons once the GRB event has ended. The fact that this emission (the afterglow) extends at longer wavelengths, led to the discovery of optical/IR/radio counterparts in 1997-2003, greatly improving our understanding of these sources. The classical, long duration GRBs, have been observed to originate at cosmological distances in a range of redshifts with 0.1685 ≤ z ≤ 4.50 implying energy releases of ~ 1051 ergs. The recent results on GRB 021004 and GRB 030329 confirm that the central engines that power these extraordinary events are due to be collapse of massive stars rather than the merging of compact objects as previously also suggested. Short GRBs still remain a mystery as no counterparts have been detected so far.

On the Central Engine of Short Gamma-ray Bursts

SummaryWe assess the ability of neutron star binary coalescence to produce short gamma-ray bursts (GRBs). We find that the neutrino annihilation above the merged remnant will drive bipolar, relativistic jets along the initial binary rotation axis. This outflow can be collimated by the energetic, neutrino-driven baryonic wind that is blown off the remnant. Despite the narrow neutron star mass distribution the apparent luminosities will be spread over a broad range from ~ 1049 to ~ 1052erg s−1, typical jet opening half-angles are around 5 degrees. If the central core of the merger remnant does not collapse immediately convective dynamo action will set in and the available kinetic energy can be transformed into magnetic fields in excess of 1017 G. The corresponding spin-down time scale is ~ 0.2 s, just about the duration of a short GRB.

Long GRBs and Supernovae from Collapsars

SummaryLong duration gamma-ray bursts are associated with the death of massive stars as earlier observations and theoretical arguments had suggested. Supernova 2003dh observed with GRB030329 confirms this picture. Current progress in developing numerical special relativistic hydrodynamics codes with adaptive mesh refinement is allowing for high-resolution simulations of relativistic flow relevant for simulations of GRBs.

The GUSBAD Catalog of Gamma‐Ray Bursts

The GUSBAD catalog of gamma-ray bursts (GRBs) is based on archival BATSE DISCLA data covering the full 9.1 years of the Compton Gamma Ray Observatory mission. The catalog contains 2204 GRBs, including 589 bursts not listed in the Current BATSE Burst Catalog. The GUSBAD catalog is uniform in the sense that the detection criteria are the same throughout and that the properties given in the catalog are available for every burst. The detection and the derivation of the properties of the GRBs were carried out automatically. This makes the GUSBAD catalog especially suitable for statistical work and simulations, such as used in the derivation of V/Vmax. We briefly touch upon a potential problem in defining a GRB duration that is physically meaningful.

Opaque or Transparent? A Link between Neutrino Optical Depths and the Characteristic Duration of Short Gamma-Ray Bursts

Cosmological gamma-ray bursts (GRBs) are thought to occur as a result of violent hypercritical accretion onto stellar mass black holes, following either core collapse in massive stars or compact binary mergers. This dichotomy may be reflected in the two classes of bursts having different durations. Dynamical calculations of the evolution of these systems are essential if one is to establish characteristic relevant timescales. We show here for the first time the result of dynamical simulations, lasting approximately 1 s, of postmerger accretion disks around black holes, using a realistic equation of state and considering neutrino emission processes. We find that the inclusion of neutrino optical depth effects produces important qualitative temporal and spatial transitions in the evolution and structure of the disk, which may directly reflect on the duration and variability of short GRBs.

The prompt gamma-ray emissions and X-ray afterglows of gamma-ray burst jets

The distribution of the duration of gamma-ray bursts (GRBs), and the relations of the jet opening angles (theta) to prompt gamma-ray emissions and X-ray afterglow emissions have been investigated within the framework of a relativistic beaming model for a sample including 10 GRBs. The redshifts, the temporal breaks of the optical afterglow light curves and the X-ray afterglows of these GRBs have been well measured. The results show that: (i) the distribution of the intrinsic burst durations extend over only approximately one order of magnitude, suggesting that these bursts tend to have a similar burst duration; (ii) the gamma-ray fluence in the comoving frame (S(gamma)) as a function of is roughly fitted by a broken power law with indices of -0.4 and -3.79 before and after a break at theta = 0.1 rad, respectively, while the X-ray fluxes decay with following a single power law with an index of -1.8; (iii) the relation between the ratio of F(x)/S(gamma) and theta follows a turnover power law with indices of -3.2 and 2.9 before and after the break at = 0.1, respectively; and (iv) the temporal indices of X-ray afterglows are significantly anticorrelated with with a Spearman rank linear correlation coefficient of r = -0.84 and a probability of chance occurrence of p = 0.004. These results are consistent with the expectations of the beaming model. They have been interpreted using both the areas of emission regions that instruments can observe and the number of baryons contained in the jets.

The afterglow and the host galaxy of GRB 011211

We present optical, near-infrared, and X-ray observations of the optical afterglow (OA) of the X-ray rich, long- duration gamma-ray burst GRB 011211. Hubble Space Telescope (HST) data obtained 14, 26, 32, and 59 days after the burst, show the host galaxy to have a morphology that is fairly typical of blue galaxies at high redshift. We measure its magnitude to be R= 24:95 0:11. We detect a break in the OA R-band light curve which is naturally accounted for by a collimated outflow geometry. By fitting a broken power-law to the data we find a best fit with a break 1 :56 0:02 days after the burst, a pre-break slope of1 = 0:95 0:02, and a post-break slope of2 = 2:11 0:07. The UV-optical spectral energy distribution (SED) around 14 hours after the burst is best fit with a power-law with index = 0:56 0:19 reddened by an SMC-like extinction law with a modest AV= 0:08 0:08 mag. By comparison, from the XMM-Newton X-ray data at around the same time, we find a decay index ofX= 1:62 0:36 and a spectral index ofX= 1:21 +0:10 0:15 . Interpolating between the UV-optical and X-ray implies that the cooling frequency is located close to10 16 Hz in the observer frame at the time of the observations. We argue, using the various temporal and spectral indices above, that the most likely afterglow model is that of a jet expanding into an external environment that has a constant mean density rather than a wind-fed density structure. We estimate the electron energy index for this burst to be p 2:3.

High-resolution calculations of merging neutron stars - III. Gamma-ray bursts

Recent three dimensional, high-resolution simulations of neutron star coalescences are analysed to assess whether short gamma-ray bursts (GRBs) could originate from such encounters. The two most popular modes of energy extraction -- namely the annihilation of $\nu\bar{\nu}$ and magnetohydrodynamic processes- are explored in order to investigate their viability in launching GRBs. We find that $\nu\bar{\nu}$ annihilation can provide the necessary stresses to drive a highly relativistic expansion. But unless the outflow is beamed into less than one percent of the solid angle this mechanism may fail to explain the apparent isotropized energies implied for short GRBs at cosmological distances. We argue that the energetic, neutrino-driven wind that accompanies the merger event will have enough pressure to provide adequate collimation to the $\nu\bar{\nu}$-annihilation-driven jet, thereby comfortably satisfying constraints on event rate and apparent luminosity. We also assess magnetic mechanisms to transform the available energy into a GRB. If the central object does not collapse immediately into a black hole it will be convective and it is expected to act as an effective large scale dynamo amplifying the seed magnetic fields to a few times $10^{17}$ G within a small fraction of a second. The associated spindown time scale is 0.2 s, coinciding with the typical duration of a short GRB. The efficiencies of the various assessed magnetic processes are high enough to produce isotropized luminosities in excess of $10^{52}$ ergs/s even without beaming.

Production of Lithium, Beryllium, and Boron by Hypernovae and the Possible Hypernova–Gamma‐Ray Burst Connection

We investigate a possible nucleosynthetic signature of highly energetic explosions of C-O cores ("hypernovae," HNe) which might be associated with gamma-ray bursts (GRBs). We note that the direct impact of C- and O-enriched hypernova ejecta on the ambient hydrogen and helium leads to spallation reactions which can produce large amounts of the light nuclides lithium, beryllium, and boron (LiBeB). Using analytic velocity spectra of the hypernova ejecta, we calculate the LiBeB yields of different exploding C-O cores associated with observed hypernovae. The deduced yields are $\sim 10^3$ times higher than those produced by similar (direct) means in normal Type II supernovae, and are higher than the commonly used ones arising from shock wave acceleration induced by Type II supernova (SN) explosions. To avoid overproduction of these elements in our Galaxy, hypernovae should be rare events, with $\la 10^{-3}$ hypernovae per supernova, assuming a constant HN/SN ratio over time. This rate is in good agreement with that of long duration GRBs if we assume that the gamma-ray emission is focussed with a beaming factor $\Omega/4\pi \la 10^{-2}$. This encouraging result supports the possible HN-GRB association. Thus, Galactic LiBeB abundance measurements offer a promising way to probe the HN rate history and the possible HN-GRB correlation. On the other hand, if hypernovae are associated to very massive pregalactic stars (Population III) they would produce a LiBeB pre-enrichment in proto-galactic gas, which could show up as a plateau in the lowest metallicities of the Be-Fe relation in halo stars.

Evidence for a galactic origin of very short gamma ray bursts and primordial black hole sources

We systematically study the shortest time duration gamma ray bursts and find unique features that are best interpreted as sources of a galactic origin. There is a significant angular asymmetry and the V/ V max distribution provides evidence for a homogeneous sources distribution. We review the arguments that primordial black hole evaporation can give such gamma ray bursts. The rate of events is consistent with a primordial black hole origin if we assume on enhanced local density, as are the other distributions. We suggest further tests of this hypothesis.

Accretion Disks around Black Holes: Dynamical Evolution, Meridional Circulations, and Gamma‐Ray Bursts

We study the hydrodynamic evolution of massive accretion disks around black holes, formed when a neutron star is disrupted by a black hole in a binary system. The initial conditions are taken from three-dimensional calculations of coalescing binaries. By assuming azimuthal symmetry we are able to follow the time dependence of the disk structure for 0.2 s in cylindrical coordinates (r, z). We use an ideal gas equation of state and assume that all the dissipated energy is radiated away. The disks evolve because of viscous stresses, modeled with an α law. We study the disk structure and, in particular, the strong meridional circulations that are established and persist throughout our calculations. These consist of strong outflows along the equatorial plane that reverse direction close to the surface of the disk and converge on the accretor. In the context of gamma-ray bursts (GRBs), we estimate the energy released from the system in neutrinos and through magnetic-dominated mechanisms and find it can be as high as Eν ≈ 1052 ergs and EBZ ≈ 1051 ergs, respectively, during an estimated accretion timescale of 0.1-0.2 s. The ν annihilation is likely to produce bursts from only a short, impulsive energy input L ∝ t-5/2 and so would be unable to account for a large fraction of bursts that show complicated light curves. On the other hand, a gas mass ≈0.1-0.25 M☉ survives in the orbiting debris, which enables strong magnetic fields ≈1016 G to be anchored in the dense matter long enough to power short duration GRBs. We highlight the effects that the initial disk and black holes masses, viscosity, and binary mass ratio have on the evolution of the disk structure. Finally, we investigate the continuous energy injection that arises as the black hole slowly swallows the rest of the disk and discuss its consequences on the GRB afterglow emission.