Nearby Gamma-ray Bursts Research Articles

Searching for narrow absorption and emission lines inXMM-Newtonspectra of gamma-ray bursts

We present the results of a spectroscopic search for narrow emission and absorption features in the X-ray spectra of long gamma-ray burst (GRB) afterglows. Using XMM-Newton data, both EPIC and RGS spectra, of six bright (fluence >10^{-7} erg cm^{-2}) and relatively nearby (z=0.54-1.41) GRBs, we performed a blind search for emission or absorption lines that could be related to a high cloud density or metal-rich gas in the environ close to the GRBs. We detected five emission features in four of the six GRBs with an overall statistical significance, assessed through Monte Carlo simulations, of <3.0 sigma. Most of the lines are detected around the observed energy of the oxygen edge at ~0.5 keV, suggesting that they are not related to the GRB environment but are most likely of Galactic origin. No significant absorption features were detected. A spectral fitting with a free Galactic column density (N_H) testing different models for the Galactic absorption confirms this origin because we found an indication of an excess of Galactic N_H in these four GRBs with respect to the tabulated values.

GRBs not fatal for life in early universe

Astronomy![Figure][1] Artist's conception of a gamma-ray burst PHOTO: ESO/A. ROQUETTE A nearby gamma-ray burst (GRB) could hugely damage Earth's atmosphere, triggering a mass extinction. GRBs were more common in the early universe, so they might have prevented the early emergence of complex

CAN LIFE SURVIVE GAMMA-RAY BURSTS IN THE HIGH-REDSHIFT UNIVERSE?

Nearby Gamma-Ray Bursts (GRBs) have been proposed as a possible cause of mass extinctions on Earth. Due to the higher event rate of GRBs at higher redshifts, it has been speculated that life as we know it may not survive above a certain redshift (e.g. $z>0.5$). We examine the duty cycle of lethal (life-threatening) GRBs in the solar neighborhood, in the Sloan Digital Sky Survey (SDSS) galaxies and GRB host galaxies, with the dependence of the long GRB rate on star formation and metallicity properly taken into account. We find that the number of lethal GRBs attacking Earth within the past 500 Myr ($\sim$ epoch of the Ordovician mass extinction) is $0.93$. The number of lethal GRBs hitting a certain planet increases with redshift, thanks to the increasing star formation rate and decreasing metallicity in high-$z$ galaxies. Taking 1 per 500 Myr as a conservative duty cycle for life to survive, as evidenced by our existence, we find that there are still a good fraction of SDSS galaxies beyond $z=0.5$ where the GRB rate at half-mass radius is lower than this value. We derive the fraction of such benign galaxies as a function of redshift through Monte Carlo simulations, and find that the fraction is $\sim 50\%$ at $z\sim 1.5$ and $\sim 10\%$ even at $z \sim 3$. The mass distribution of benign galaxies is dominated by Milky-Way-like ones, thanks to their commonness, relatively large mass, and low star formation rate. GRB host galaxies are among the most dangerous ones.

On the origin of short GRBs with extended emission and long GRBs without associated SN

Abstract The Burst and Transient Source Experiment classifies cosmological gamma-ray bursts (GRBs) into short (less than 2 s) and long (over 2 s) events, commonly attributed to mergers of compact objects and, respectively, peculiar core-collapse supernovae. This standard classification has recently been challenged by the Swift discovery of short GRBs showing extended emission (SGRBEE) and nearby long GRBs without an accompanying supernovae (LGRBN). Both show an initial hard pulse, characteristic of SGRBs, followed by a long duration soft tail. We here consider the spectral peak energy (Ep, i)–radiated energy (Eiso) correlation and the redshift distributions to probe the astronomical and physical origin of these different classes of GRBs. We consider Swift events of 15 SGRBs, 7 SGRBEEs, 3 LGRBNs and 230 LGRBs detected by Swift. The spectral-energy properties of the initial pulse of both SGRBEE and LGRBNs are found to coincide with those of SGRBs. A Monte Carlo simulation shows that the redshift distributions of SGRBs, SGRBEE and LGRBNs fall outside the distribution of LGRBs at 4.75σ, 4.67σ and 4.31σ, respectively. A distinct origin of SGRBEEs with respect to LGRBs is also supported by the elliptical host galaxies of the SGRBEE events 050509B and 050724. This combined evidence supports the hypothesis that SGRBEE and LGRBNs originate in mergers as SGRBs. Moreover, long/soft tail of SGRB and LGRBNs satisfy the same Ep, i-Eiso Amati correlation holding for normal LGRBs. This fact points to rapidly rotating black holes as a common long-lived inner engine produced by different astronomical progenitors (mergers and supernovae).

An Exceptionally Bright Gamma-Ray Burst

A detailed observation of a nearby gamma-ray burst should provide a clearer understanding in the process of the death of massive stars.

THE VERY BRIGHT AND NEARBY GRB130427A: THE EXTRA HARD SPECTRAL COMPONENT AND IMPLICATIONS FOR VERY HIGH-ENERGY GAMMA-RAY OBSERVATIONS OF GAMMA-RAY BURSTS

The extended high-energy gamma-ray (&gt;100 MeV) emission occurring after the prompt gamma-ray bursts (GRBs) is usually characterized by a single power-law spectrum, which has been explained as the afterglow synchrotron radiation. We report on the Fermi Large Area Telescope (LAT) observations of the &gt;100 MeV emission from the very bright and nearby GRB 130427A, up to ~100 GeV. By performing time-resolved spectral fits of GRB 130427A, we found a strong evidence of an extra hard spectral component above a few GeV that exists in the extended high-energy emission of this GRB. This extra spectral component may represent the first clear evidence of the long sought-after afterglow inverse Compton emission. Prospects for observations at the very high-energy gamma-rays, i.e., above 100 GeV, are described.

HIGH-ENERGY EMISSION OF GRB 130427A: EVIDENCE FOR INVERSE COMPTON RADIATION

A nearby superluminous burst GRB 130427A was simultaneously detected by six γ-ray space telescopes (Swift, the Fermi GLAST Burst Monitor (GBM)/Large Area Telescope, Konus-Wind, SPI-ACS/INTEGRAL, AGILE, and RHESSI) and by three RAPTOR full-sky persistent monitors. The isotropic γ-ray energy release is ∼1054 erg, rendering it the most powerful explosion among gamma-ray bursts (GRBs) with a redshift z ⩽ 0.5. The emission above 100 MeV lasted about one day, and four photons are at energies greater than 40 GeV. We show that the count rate of 100 MeV–100 GeV emission may be mainly accounted for by the forward shock synchrotron radiation and the inverse Compton radiation likely dominates at GeV–TeV energies. In particular, an inverse Compton radiation origin is favored for the ∼(95.3, 47.3, 41.4, 38.5, 32) GeV photons arriving at t ∼ (243, 256.3, 610.6, 3409.8, 34366.2) s after the trigger of Fermi-GBM. Interestingly, the external inverse Compton scattering of the prompt emission (the second episode, i.e., t ∼ 120–260 s) by the forward-shock-accelerated electrons is expected to produce a few γ-rays at energies above 10 GeV, while five were detected in the same time interval. A possible unified model for the prompt soft γ-ray, optical, and GeV emission of GRB 130427A, GRB 080319B, and GRB 090902B is outlined. Implications of the null detection of >1 TeV neutrinos from GRB 130427A by IceCube are discussed.

Neutrinos from collapsars

Long gamma-ray bursts (GRBs) are associated with the gravitational collapse of very massive stars. The central engine of a GRB can collimate relativistic jets that propagate inside the stellar envelope. The shock waves produced when the jet disrupts the stellar surface are capable of accelerating particles up to very high energies. If the jet has hadronic content, neutrinos will be produced via charged pion decays. The main goal of this work is to estimate the neutrino emission produced in the region close to the surface of the star, taking pion and muon cooling into account, along with subtle effects arising from neutrino production in a highly magnetized medium. We estimate the maximum energies of the different kinds of particles and solve the coupled transport equations for each species. Once the particle distributions are known, we calculate the intensity of neutrinos. We study the different effects on the neutrinos that can change the relative weight of different flavors. In particular, we consider the effects of neutrino oscillations, and of neutrino spin precession caused by strong magnetic fields. The expected neutrino signals from the shocks in the uncorking regions of Population III events is very weak, but the neutrino signal produced by Wolf-Rayet GRBs with $z<0.5$ is not far from the level of the atmospheric background. The IceCube experiment does not have the sensitivity to detect neutrinos from the implosion of the earliest stars, but a number of high-energy neutrinos may be detected from nearby long GRBs. The cumulative signal should be detectable over several years ($\sim 10$ yr) of integration with the full 86-string configuration.

DISCOVERY OF AN EXTRA HARD SPECTRAL COMPONENT IN THE HIGH-ENERGY AFTERGLOW EMISSION OF GRB 130427A

The extended high-energy gamma-ray (>100 MeV) emission occurred after the prompt gamma-ray bursts (GRBs) is usually characterized by a single power-law spectrum, which has been explained as the afterglow synchrotron radiation. The afterglow inverse-Compton emission has long been predicted to be able to produce a high-energy component as well, but previous observations have not revealed such a signature clearly, probably due to the small number of >10 GeV photons even for the brightest GRBs known so far. In this Letter, we report on the Fermi Large Area Telescope (LAT) observations of the >100 MeV emission from the very bright and nearby GRB 130427A. We characterize the time-resolved spectra of the GeV emission from the GRB onset to the afterglow phase. By performing time-resolved spectral fits of GRB 130427A, we found a strong evidence of an extra hard spectral component that exists in the extended high-energy emission of this GRB. We argue that this hard component may arise from the afterglow inverse Compton emission.

A history of the gamma-ray burst flux at the Earth from Galactic globular clusters

Nearby gamma-ray bursts (GRBs) are likely to have represented a significant threat to life on the Earth. Recent observations suggest that a significant source of such bursts is compact binary mergers in globular clusters. This link between globular clusters and GRBs offers the possibility to find time intervals in the past with higher probabilities of a nearby burst, by tracing globular cluster orbits back in time. Here we show that the expected flux from such bursts is not flat over the past 550 Myr but rather exhibits three broad peaks, at 70, 180 and 340 Myr ago. The main source for nearby GRBs for all three time intervals is the globular cluster 47 Tuc, a consequence of its large mass and high stellar encounter rate, as well as the fact that it is one of the globular clusters which comes quite close to the Sun. Mass extinction events indeed coincide with all three time intervals found in this study, although a chance coincidence is quite likely. Nevertheless, the identified time intervals can be used as a guide to search for specific signatures of GRBs in the geological record around these times.

FermiGBM Capabilities for Multi-Messenger Time-Domain Astronomy

Owing to its wide sky coverage and broad energy range, the Fermi Gamma-ray Burst Monitor (GBM) is an excellent observer of the transient hard X-ray sky. GBM detects about 240 triggered Gamma-Ray Bursts (GRBs) per year, including over 30 which also trigger the Swift Burst Alert Telescope (BAT). The number of GRBs seen in common with Swift is smaller than expected from the overlap in sky coverage because GBM is not as sensitive as the BAT and the GBM GRB population is thus skewed to the brighter, closer bursts. This population includes about 45 short GRBs per year, giving GBM an excellent opportunity to observe the electromagnetic counterpart to any gravitational wave candidate resulting from the merger of compact binary members. The same characteristics make GBM an ideal partner for neutrino searches from nearby GRBs, and for the elusive Very-High Energy (VHE) counterparts to GRBs. With the deployment of the next-generation gravitational-wave detectors (Advanced LIGO/VIRGO) and VHE experiments (CTA and HAWC) potentially within the lifetime of the Fermi Gamma-ray Space Telescope, the prospects for breakthrough observations are good.

A redshift–observation time relation for gamma-ray bursts: evidence of a distinct subluminous population

We show that the redshift and peak flux distributions of gamma-ray bursts (GRBs) have an observation time dependence that can be used to discriminate between different burst populations. We demonstrate how observation time relations can be derived from the standard integral distributions and that they can differentiate between GRB populations detected by both the Burst and Transient Source Experiment (BATSE) and Swift satellites. Using Swift data, we show that a redshift–observation time relation (log Z–log T) is consistent with both a peak flux–observation time relation (log P–log T) and a standard log N–log P brightness distribution. As the method depends only on rarer small-z events, it is invariant to high-z selection effects. We use the log Z–log T relation to show that subluminous GRBs are a distinct population occurring at a higher rate of the order of 150+ 180− 90 Gpc− 3 yr− 1. Our analysis suggests that GRB 060505 – a relatively nearby GRB observed without any associated supernova – is consistent with a subluminous population of bursts. Finally, we show that our relations can be used as a consistency test for some of the proposed GRB spectral energy correlations.

GRB 120422A: A LOW-LUMINOSITY GAMMA-RAY BURST DRIVEN BY A CENTRAL ENGINE

GRB 120422A is a low-luminosity Gamma-ray burst (GRB) associated with a bright supernova, which distinguishes itself by its relatively short T90 ~ 5 s and an energetic X-ray tail. We analyze the Swift BAT and XRT data and discuss the physical implications. We show that the early steep decline in the X-ray light curve can be interpreted as the curvature tail of a late emission episode around 58-86 s, with a curved instantaneous spectrum at the end of the emission episode. Together with the main activity in the first ~ 20 s and the weak emission from 40 s to 60 s, the prompt emission is variable, which points towards a central engine origin, in contrast to the shock breakout origin as invoked to interpret some other nearby low-luminosity supernova GRBs. The curvature effect interpretation and interpreting the early shallow decay as the coasting external forward shock emission in a wind medium both give a constraint on the bulk Lorentz factor \Gamma to be around several. Comparing the properties of GRB 120422A and other supernova GRBs, we found that the main criterion to distinguish engine-driven GRBs from the shock breakout GRBs is the time-averaged luminosity, with a separation line of about ~ 10^48 erg s^-1.

Ultra-high-energy cosmic ray acceleration in engine-driven relativistic supernovae

The origin of ultra-high-energy cosmic rays (UHECRs) remains an enigma. They offer a window to new physics, including tests of physical laws at energies unattainable by terrestrial accelerators. They must be accelerated locally, otherwise, background radiations would severely suppress the flux of protons and nuclei, at energies above the Greisen-Zatsepin-Kuzmin (GZK) limit. Nearby, gamma ray bursts (GRBs), hypernovae, active galactic nuclei and their flares have all been suggested and debated as possible sources. A local sub-population of type Ibc supernovae (SNe) with mildly relativistic outflows have been detected as sub-energetic GRBs, X-ray flashes and recently as radio afterglows without detected GRB counterparts. Here, we measure the size-magnetic field evolution, baryon loading and energetics, using the observed radio spectra of SN 2009bb. We place such engine-driven SNe above the Hillas line and establish that they can readily explain the post-GZK UHECRs.

Z= 1 multifractality of Swift short GRBs?

Aims. We analyze and characterize the angular distribution of selected samples of gamma ray bursts (GRBs) from BATSE and Swift data to confirm that the division into two classes of short- and long-duration GRBs also correspond to two distinct spatial populations. Methods. The angular distribution is analyzed using multifractal analysis and characterized by a multifractal spectrum of dimensions. Different spectra of dimensions relate to different angular distributions. Results. The spectra of dimensions of short and long bursts indicate that the two populations indeed have two different angular distributions. Both Swift and BATSE long bursts appear to be homogeneously distributed across the sky with a monofractal distribution. In contrast, short GRBs follow a multifractal distribution for both the two samples. Even if BATSE data do not enable a unique interpretation of their angular distribution to be made because of the instrumental selection effects that mainly favor the detection of nearby GRBs, the results from Swift short GRBs confirm this behavior, also when including GRBs corrected by the redshift factor. The distributions traced by short GRBs, up to z = 1, depict a universe with a structure similar to that of a disordered porous material with uniformly distributed heterogeneous irregular structures, appearing more clustered than expected.

A Gamma-Ray Burst/Pulsar for Cosmic Ray Positrons with a Dark Matter-Like Spectrum

We propose that a nearby gamma-ray burst (GRB) or GRB-like (old, single, and short-lived) pulsar, supernova remnant, or microquasar about 105–6 years ago may be responsible for the excesses of cosmic ray positrons and electrons recently observed in the PAMELA, ATIC/PPB-BETS, Fermi, and HESS experiments. We can reproduce the smooth Fermi/HESS spectra as well as the spiky ATIC/PPB-BETS spectra. The spectra have a sharp cutoff that is similar to the dark matter predictions, sometimes together with a line (not similar), since high-energy cosmic rays cool fast where the cutoff/line energy marks the source age. A GRB-like astrophysical source is expected to have a small but finite spread in the cutoff/line as well as anisotropy in the cosmic ray and diffuse gamma-ray flux, providing a method for the Fermi and future CALET experiments to discriminate between dark matter and astrophysical origins.

The late jet in gamma-ray bursts and its interactions with a supernova ejecta and a cocoon

Late X-ray flares observed in X-ray afterglows of gamma-ray bursts (GRBs) suggest late central engine activities at a few minuets to hours after the burst. A few unambiguously confirmed cases of supernova associations with nearby long GRBs imply that an accompanying supernova-like component might be a common feature in all long GRB events. These motivate us to study the interactions of a late jet, responsible for a x-ray flare, with various components in a stellar explosion, responsible for a GRB. These components include a supernova shell-like ejecta, and a cocoon that was produced when the main jet producing the GRB itself was propagating through the progenitor star. We find that the interaction between the late jet and the supernova ejecta may produce a luminous (up to 10^49 erg s^-1) thermal X-ray transient lasting for ~ 10 s. The interaction between the late jet and the cocoon produces synchrotron self-absorbed non-thermal emission, with the observed peak X-ray flux density from 0.001 micro Jy to 1 mJy at 1 keV and a peak optical flux density from 0.01 micro Jy to 0.1 Jy (for a redshift z= 2). The light curve due to the late jet - cocoon interaction has very small pulse-width-to-time ratio, \Delta t / t \approx 0.01 - 0.5, where t is the pulse peak time since the burst trigger. Identifying these features in current and future observations would open a new frontier in the study of GRB progenitor stars.

High-energy emission as a test of the prior emission model for gamma-ray burst afterglows

Abstract We study high-energy gamma-ray afterglow emission from gamma-ray bursts (GRBs) in the prior emission model, which is proposed to explain the plateau phase of the X-ray afterglow. This model predicts the high-energy gamma-ray emission when the prompt GRB photons from the main flow are up-scattered by relativistic electrons accelerated at the external shock due to the prior flow. The expected spectrum has the peak of ∼10–100 GeV at around the end time of the plateau phase for typical GRBs, and high-energy gamma-rays from nearby and/or energetic GRBs can be detected by the current and future Cherenkov telescopes such as MAGIC, VERITAS, CTA and possibly Fermi. Multiwavelength observations by ground-based optical telescopes as well as Fermi and/or Swift satellites are important to constrain the model. Such external inverse-Compton emission may even lead to GeV–TeV gamma-ray signals with the delay time of ∼10–100 s, only if the plateau phase is short lived.

A search for pulsations from the compact object of GRB 060218

A fraction of massive stars are expected to collapse into compact objects (accreting black holes or rapidly rotating neutron stars) that successfully produce gamma-ray bursts (GRBs). We examine the possibility of directly observing these gamma-ray burst compact objects (GCOs) using post-explosion observations of past and future GRB sites. In particular, we present a search for early pulsations from the nearby (z=0.0335) gamma-ray burst GRB 060218, which exhibited features possibly consistent with a rapidly spinning neutron star as its underlying GCO. We also consider alternative techniques that could potentially achieve a detection of GCOs either in the Local Volume or near the plane of our own Galaxy.

A relativistic type Ibc supernova without a detected γ-ray burst

Long duration gamma-ray bursts (GRBs) mark the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. They are distinguished by the production of an energetic and collimated relativistic outflow powered by a central engine (an accreting black hole or neutron star). Observationally, this outflow is manifested in the pulse of gamma-rays and a long-lived radio afterglow. Until now, central-engine-driven supernovae have been discovered exclusively through their gamma-ray emission, yet it is expected that a larger population goes undetected because of limited satellite sensitivity or beaming of the collimated emission away from our line of sight. In this framework, the recovery of undetected GRBs may be possible through radio searches for type Ibc supernovae with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. A comparison with our radio survey of type Ibc supernovae reveals that the fraction harbouring central engines is low, about one per cent, measured independently from, but consistent with, the inferred rate of nearby GRBs. Independently, a second mildly relativistic supernova has been reported.