Gamma-ray Burst Sources Research Articles

Megaelectronvolt astronomy with HERMES: spectroscopy, polarimetry, and synergies with fast Cherenkov arrays

Sensitive observations of energetic space phenomena in the 0.3 – 10 MeV range are needed to investigate a number of hot issues of modern astrophysics and cosmology. With the advanced technology of thick double sided silicon strip detectors (Si-DSSDs) it is possible to construct a space-borne gamma-ray telescope with sensitivity 30-100 times better than that of CGRO/COMPTEL. Synergies of MeV range observations from space with GeV-TeV range spectra to be obtained with future fast and sensitive imaging atmospheric Cherenkov arrays (CTA, TAIGA-IACT, ALEGRO) would allow one to reveal complex mechanisms of energy conversion in transient gamma-ray objects, in particular, sources of gamma-ray bursts. In this short note we briefly outline most demanding objectives of 0.3 – 10 MeV range astronomy and present a schematic view of HERMES gamma-ray spectrometer being developed at the Ioffe Institute.

A new delay time distribution for merging neutron stars tested against Galactic and cosmic data

The merging of two neutron stars (MNS) is thought to be the source of short gamma-ray bursts (SGRB) and gravitational wave transients, as well as the main production site of r-process elements like Eu. We have derived a new delay time distribution (DTD) for MNS systems from theoretical considerations and we have tested it against (i) the SGRB redshift distribution and (ii) the Galactic evolution of Eu and Fe, in particular the [Eu/Fe] vs [Fe/H] relation. For comparison, we also tested other DTDs, as proposed in the literature. To address the first item, we have convolved the DTD with the cosmic star formation rate, while for the second we have employed a detailed chemical evolution model of the Milky Way. We have also varied the DTD of Type Ia SNe (the main Fe producers), the contribution to Eu production from core-collapse SNe, as well as explored the effect of a dependence on the metallicity of the occurrence probability of MNS. Our main results can be summarized as follows: (i) the SGRB redshift distribution can be fitted using DTDs for MNS that produce average timescales of 300-500 Myr; (ii) if the MNS are the sole producers of the Galactic Eu and the occurrence probability of MNS is constant the Eu production timescale must be on the order of <30 Myr; (iii) allowing for the Eu production in core-collapse SNe, or adopting a metallicity-dependent occurrence probability, allow us to reproduce both observational constraints, but many uncertainties are still present in both assumptions.

Galactic foreground of gamma-ray bursts from AKARI Far-Infrared Surveyor

Abstract We demonstrate the use of the AKARI FIS All-Sky Survey maps in the study of extragalactic objects. A quick but reliable estimate of the Galactic foreground is essential for extragalactic research in general. We explored the galactic foreground and calculated hydrogen column densities using AKARI FIS and other recent all-sky survey data, and compared our results to former estimates. Our AKARI-FIS-based foreground values were then used toward gamma-ray burst (GRB) sources as input for X-ray afterglow spectrum fitting. From those fits the intrinsic column densities at the GRB sources were derived. The high-angular-resolution AKARI-FIS-based Galactic foreground hydrogen column densities are statistically very similar, but for most of the tested directions somewhat lower than previous estimates based on low-resolution data. This is due to the low filling factor of high-density enhancements in all galactic latitudes. Accordingly, our AKARI-FIS-based new intrinsic hydrogen column densities are usually higher or similar compared to the values calculated based, e.g., on the low-resolution Leiden/Argentine/Bonn survey data and listed in the Leicester database. The variation, however, is typically smaller than the error of the estimate from the fits of the X-ray afterglow spectra. There are a number of directions where the improvement of the foreground estimates resulted in an overestimate of magnitude or higher increment of the derived intrinsic hydrogen column densities. We concluded that most of the GRBs with formerly extremely low intrinsic hydrogen column densities are in fact normal, but we confirmed that GRB050233 is indeed a non-enveloped long GRB.

How to understand high-energy gamma-ray bursts?

Gamma-ray bursts (GRBs) are short-duration flashes of gamma rays occurring at cosmological distances and the most violent explosive phenomena since the cosmic big bang. GRBs were accidentally discovered by Vela military satellites of United States in 1967. The BATSE instrument onboard the Compton Space Gamma-Ray Observatory found two types of GRBs, long-duration ($T_{90}>$ 2s) and short-duration ($T_{90} Science as one of the top ten scientific breakthroughs of the year. In 1999, long GRBs were found to be associated with the birth of stellar mass black holes. In 2003, the HETE-II satellite discovered the first direct association of a long GRB with a type Ic supernova, confirming that long GRBs are linked to the core collapse of massive stars. Science ranked these two major advances as one of the worlds top ten scientific breakthroughs of the year in 1999 and 2003, respectively. In 2005, the Swift satellite made the first accurate localization of short GRBs, leading to the discoveries of afterglows, host galaxies and redshifts of short GRBs. These observations provide indirect evidence that short GRBs originate from mergers of binary systems of compact objects (at least including one neutron star) at cosmological distances. In particular, on 2017 August 17, the LIGO/Virgo gravitational wave (GW) detectors, for the first time, discovered a GW event from a binary neutron star (BNS) merger, GW170817. About 1.74 s after the merger, Fermi/GBM detected a short gamma-ray burst (named GRB170817A). Subsequently, many ground-based and space-based telescopes detected X-ray, ultraviolet, optical, nearly infrared, and radio counterparts to GW170817, especially including a multi-wavelength kilonova (named AT2017gfo). These discoveries mark the beginning of a new era of multi-messenger astronomy. To summarize, all the observations have shown that long bursts originate from the core collapse of massive stars and short bursts originate from the mergers of binary compact objects (at least including one neutron star); besides prompt gamma-ray emission, the sources of GRBs produce X-ray, optical and radio afterglows in timescales of weeks, months and years after the burst trigger, respectively. Theoretically, prompt gamma-ray emissions of GRBs are thought to arise from some energy dissipation processes in the interiors of relativistic jets and multi-wavelength afterglows arise from forward shocks due to collisions between the jets and their ambient media. Therefore, GRBs are not only astronomical laboratories of studying extremely physical phenomena (e.g., newborn compact objects including stellar-mass black holes and neutron stars, gravitational waves, ultra-high-energy cosmic rays, and high-energy neutrinos) and of testing the basic physical principles with high accuracy, but also become an important probe of the star formation and evolution in the early universe, high-redshift galaxies, and cosmology. GRBs now are a multidisciplinary field (including astronomy, cosmology, and physics) and thus one of the most competitive fundamental research fields. In this paper, we review recent researches of GRBs and electromagnetic counterparts to gravitational waves, by focusing on the relevant key scientific issues, and discuss how to seize the opportunity to plan the interdisciplinary strategy based on the development trend and the research foundation in China, to maximize domestic scientific equipment achievements, and to enhance Chinese international influence in this field.

Observation of Cosmic Gamma Ray Bursts in the Experiments Onboard Lomonosov and Vernov Satellites

The study of cosmic gamma ray bursts (GRBs) is one of the main goals of the Lomonosov space mission. The main advantage of this mission is simultaneous multiwavelength observations of GRBs covering the optical, X-ray and gamma-ray ranges. The mission payload includes the GRB monitor BDRG, wide-field optical cameras SHOK, and the UFFO instrument. Data are recorded mainly by the event trigger provided by the BDRG instrument, which measures the spectral and temporal properties of the burst in the energy range 10–3000 keV. The BDRG instrument also provides estimation of the source coordinates by comparing the readings of three differently directed detectors with an accuracy of several degrees. Wide-field SHOK optical cameras have a field of view of ~20° × 40°. They fix a set of images with a frequency of about five frames per second prior to the trigger and another set immediately after the trigger. The UFFO instrument includes the UBAT telescope with a coded mask for measurements in hard X-ray and soft gamma-ray ranges and an optical telescope with a slewing mirror (SMT) that can be directed on the GRB source for a time ~1 s for measuring GRB prompt emission in the early stages. In response to an BDRG trigger signal, the real-time data on a detected GRB are transmitted to the Earth via Globalstar network to the Gamma-ray Coordinates Network (GCN) and ground-based observatories. During observations on the Lomonosov satellite, 20 gamma-ray bursts were detected and catalogued. Several gamma-ray bursts were also detected in the Vernov satellite experiment. An example of such an event is given.

Prompt and Follow-up Multi-wavelength Observations of the GRB 161017A

Abstract This paper presents data on the simultaneous and complementary observations of the gamma-ray burst (GRB) GRB 161017A for optical, X-ray, and gamma wavelengths obtained by the Russian multi-messenger Lomonosov space observatory and supplemented by additional data from the Swift satellite as well as the ground-based MASTER Global Robotic Net and the 10 m Gran Telescopio Canarias. Multifrequency spectra of this very powerful explosion indicate that it originated at a distance of 10 billion light years from Earth. Here, we present the results of the prompt, early, and afterglow optical observations. The light curves and spectra suggest that the prompt optical and high-energy emissions occur in the same region near the GRB source.

Evidence for a maximum mass cut-off in the neutron star mass distribution and constraints on the equation of state

We infer the mass distribution of neutron stars in binary systems using a flexible Gaussian mixture model and use Bayesian model selection to explore evidence for multi-modality and a sharp cut-off in the mass distribution. We find overwhelming evidence for a bimodal distribution, in agreement with previous literature, and report for the first time positive evidence for a sharp cut-off at a maximum neutron star mass. We measure the maximum mass to be $2.0M_\odot < m_\mathrm{max} < 2.2M_\odot$ (68\%), $2.0M_\odot < m_\mathrm{max}< 2.6M_\odot$ (90\%), and evidence for a cut-off is robust against the choice of model for the mass distribution and to removing the most extreme (highest mass) neutron stars from the dataset. If this sharp cut-off is interpreted as the maximum stable neutron star mass allowed by the equation of state of dense matter, our measurement puts constraints on the equation of state. For a set of realistic equations of state that support $>2M_\odot$ neutron stars, our inference of $m_\mathrm{max}$ is able to distinguish between models at odds ratios of up to $12:1$, whilst under a flexible piecewise polytropic equation of state model our maximum mass measurement improves constraints on the pressure at $3-7\times$ the nuclear saturation density by $\sim 30-50\%$ compared to simply requiring $m_\mathrm{max}> 2M_\odot$. We obtain a lower bound on the maximum sound speed attained inside the neutron star of $c_s^\mathrm{max} > 0.63c$ (99.8\%), ruling out $c_s^\mathrm{max} < c/\sqrt{3}$ at high significance. Our constraints on the maximum neutron star mass strengthen the case for neutron star-neutron star mergers as the primary source of short gamma-ray bursts.

Complete set of detectors for studying cosmic gamma-ray bursts onboard the Lomonosov satellite

The scientific instruments onboard the Lomonosov satellite include a complete set of detectors designed to study the gamma and optical emission of cosmic gamma-ray bursts (GRBs). The BDRG gamma spectrometer ensures producing a trigger of a GRB and studying GRB properties in the energy range of 10–3000 keV as well as determining the GRB source coordinates by comparing readings of three differently directed detectors. The SHOK optical cameras (with a field of view of ~20 × 40 degrees) fix a set of images by the GRB trigger preceding the trigger and a post-trigger set at a frequency of about five frames per second. The UFFO instrument incorporates the UBAT telescope with a coding mask for measurements within a range of hard X rays and soft gamma rays and the SMT optical slewing mirror telescope, which can be directed at the GRB source in about 1 s to measure the GRB optical emission at early stages.

Gravitational wave and E&amp;M wave astronomy event data provide strong evidence for Binary Neutron Star kilonovae, nucleosysnthesis, and one source of Gamma Ray Bursts

<i>Gravitational wave and E&amp;M wave astronomy event data provide strong evidence for Binary Neutron Star kilonovae, nucleosysnthesis, and one source of Gamma Ray Bursts</i>

Spatial Distribution of Gamma-Ray Burst Sources

The spatial distribution of sources of gamma-ray bursts (GRB) with known red shifts is analyzed by the conditional density and pairwise distance methods. The sample of GRB is based on data from the Swift mission and contains fluxes, coordinates, and red shifts for 384 GRB sources. Selection effects that distort the true source distribution are taken into account by comparing the observed distribution with fractal and uniform model catalogs. The Malmqvist effect is modeled using an approximation for the visible luminosity function of the GRB. The case of absorption in the galactic plane is also examined.This approach makes it possible to study the spatial structure of the entire sample at one time without artificial truncations. The estimated fractal dimensionality is $D=2.55\pm0.06$ on scales of $2\div6$ Gpc.

Data analysis of massive gravitational waves from gamma ray bursts

We investigate the detectability of massive mode of polarization of Gravitational Waves (GWs) in [Formula: see text] theory of gravity associated with Gamma Ray Bursts (GRBs) sources. We obtain the beam pattern function of Laser Interferometric Gravitational wave Observatory (LIGO) corresponding to the massive polarization of GWs and perform Bayesian analysis to study this polarization. It is found that the massive polarization component with a mass of [Formula: see text][Formula: see text]eV/c2 is too weak to be detected at LIGO with its current configuration.

Magnetorotational collapse of supermassive stars: Black hole formation, gravitational waves, and jets.

We perform magnetohydrodynamic simulations in full general relativity of uniformly rotating stars that are marginally unstable to collapse. These simulations model the direct collapse of supermassive stars (SMSs) to seed black holes that can grow to become the supermassive black holes at the centers of quasars and active galactic nuclei. They also crudely model the collapse of massive Population III stars to black holes, which could power a fraction of distant, long gamma-ray bursts. The initial stellar models we adopt are Γ = 4/3 polytropes initially with a dynamically unimportant dipole magnetic field. We treat initial magnetic-field configurations either confined to the stellar interior or extending out from the stellar interior into the exterior. We find that the black hole formed following collapse has mass MBH ≃ 0.9M (where M is the mass of the initial star) and dimensionless spin parameter aBH/MBH ≃ 0.7. A massive, hot, magnetized torus surrounds the remnant black hole. At Δt ~ 400-550M ≈ 2000 - 2700(M/106M⊙)s following the gravitational wave peak amplitude, an incipient jet is launched. The disk lifetime is Δt ~ 105(M/106M⊙)s, and the outgoing Poynting luminosity is LEM ~ 1051-52 ergs/s. If of this power is converted into gamma rays, Swift and Fermi could potentially detect these events out to large redshifts z ~ 20. Thus, SMSs could be sources of ultra-long gamma-ray bursts (ULGRBs), and massive Population III stars could be the progenitors that power a fraction of the long GRBs observed at redshift z ~ 5-8. Gravitational waves are copiously emitted during the collapse and peak at ~15(106M⊙/M) mHz [~0.15(104 M⊙/M) Hz], i.e., in the LISA (DECIGO/BBO) band; optimally oriented SMSs could be detectable by LISA (DECIGO/BBO) at .Hence, 104M⊙ SMSs collapsing at z ~ 10 are promising multimessenger sources of coincident gravitational and electromagnetic waves.

MODELING THE SWIFT BAT TRIGGER ALGORITHM WITH MACHINE LEARNING*

ABSTRACT To draw inferences about gamma-ray burst (GRB) source populations based on Swift observations, it is essential to understand the detection efficiency of the Swift burst alert telescope (BAT). This study considers the problem of modeling the Swift/BAT triggering algorithm for long GRBs, a computationally expensive procedure, and models it using machine learning algorithms. A large sample of simulated GRBs from Lien et al. is used to train various models: random forests, boosted decision trees (with AdaBoost), support vector machines, and artificial neural networks. The best models have accuracies of ≳97% (≲3% error), which is a significant improvement on a cut in GRB flux, which has an accuracy of 89.6% (10.4% error). These models are then used to measure the detection efficiency of Swift as a function of redshift z, which is used to perform Bayesian parameter estimation on the GRB rate distribution. We find a local GRB rate density of n 0 &sim; 0.48 &minus; 0.23 &plus; 0.41 Gpc &minus; 3 yr &minus; 1 ?> with power-law indices of n 1 &sim; 1.7 &minus; 0.5 &plus; 0.6 ?> and n 2 &sim; &minus; 5.9 &minus; 0.1 &plus; 5.7 ?> for GRBs above and below a break point of z 1 &sim; 6.8 &minus; 3.2 &plus; 2.8 ?> . This methodology is able to improve upon earlier studies by more accurately modeling Swift detection and using this for fully Bayesian model fitting.

MIRAX sensitivity for Gamma Ray Bursts

In this work we present the detection capability of the MIRAX (Monitor e Imageador de RAios-X) experiment for Gamma-Ray Bursts (GRBs). MIRAX is an X-ray astronomy mission designed to perform a wide band hard X-ray (10–200 keV) survey of the sky, especially in the Galactic plane. With a total detection area of 169 cm2, large field of view (FoV, 20°×20°), angular resolution of 1°45′ and good spectral and time resolution (∼8% at 60 keV, 10 μs), MIRAX will be optimized for the detection and study of transient sources, such as accreting neutron stars (NS), black holes (BH), Active Galactic Nuclei (AGNs), and both short and long GRBs. This is especially important because MIRAX is expected to operate in an epoch when probably no other hard X-ray wide-field imager will be active. We have performed detailed simulations of MIRAX GRB observations using the GEANT4 package, including the background spectrum and images of GRB sources in order to provide accurate predictions of the sensitivity for the expected GRB rate to be observed. MIRAX will be capable of detecting ∼44 GRBs per year up to redshifts of ∼4.5. The MIRAX mission will be able to contribute significantly to GRB science by detecting a large number of GRBs per year with wide band spectral response. The observations will contribute mainly to the part of GRB spectra where a thermal emission is predicted by the Fireball model. We also discuss the possibility of detecting GRB afterglows in the X-ray band with MIRAX.

Magnetar-driven explosions as power source of Gamma-ray Bursts and Supernovae

AbstractWe present photometry and spectroscopy of SN 2011kl associated to GRB 111209A. Peculiarities arise from both the ultra-long GRB and the very luminous SN, brighter than any other GRB-associated SN observed to date. We present unequivocal evidence in favor of a scenario where a newly-formed magnetar powers both the GRB and the SN.

Study of the Large-Scale Distribution of Gamma-Ray Burst Sources by the Method of Pairwise Distances

The method of pairwise distances developed earlier by the authors is used to study the spatial distribution of 352 sources of gamma-ray bursts with measured redshifts. Three cosmological models are considered: a model with a Euclidean metric, the “tired light” model, and the standard ΛCDM model. It is found that this set has fractal features and may be multifractal. The fractal dimensionalities are estimated.

MAXI observations of gamma-ray bursts

Abstract The Monitor of All-sky X-ray Image (MAXI) Gas Slit Camera (GSC) detects gamma-ray bursts (GRBs), including bursts with soft spectra, such as X-ray flashes (XRFs). MAXI/GSC is sensitive to the energy range from 2 to 30 keV. This energy range is lower than other currently operating instruments which are capable of detecting GRBs. Since the beginning of the MAXI operation on 2009 August 15, GSC observed 35 GRBs up to the middle of 2013. One third of them were also observed by other satellites. The rest of them show a trend to have soft spectra and low fluxes. Because of the contribution of those XRFs, the MAXI GRB rate is about three times higher than those expected from the BATSE log N–log P distribution. When we compare it to the observational results of the Wide-field X-ray Monitor on the High Energy Transient Explorer 2, which covers the the same energy range as that of MAXI/GSC, we find the possibility that many of the MAXI bursts are XRFs with Epeak lower than 20 keV. We discuss the source of soft GRBs observed only by MAXI. The MAXI log N–log S distribution suggests that the MAXI XRFs are distributed over a closer distance than hard GRBs. Since the distributions of the hardness of galactic stellar flares and X-ray bursts overlap with those of MAXI GRBs, we discuss the possibility of confusion of such galactic transients with the MAXI GRB samples.

Nearby stars as sources of gamma-ray bursts

Observations of ground-based telescopes and the Hubble space telescope made it possible to identify a part of gamma-ray bursts with far objects (redshift parameter Z ≥ 1).However, it remains unclear what are other bursts and what are their sources. The possibility of identifying other bursts with close sources known as small-mass flare stars is considered. The coordinates of space gamma-ray bursts (GRBs) for 2008–2013 and close stars (within the radius r < 25 pc) were compared by the correlation analysis method. Six coincidences were found with an accuracy of ∼0.1°. The probability of accidental coincidence of GRBs with stars is 4 · 10−8, which undoubtedly proves their stellar origin.

Spreading of ultrarelativistically expanding shell: An application to GRBs

Optically thick energy dominated plasma created in the source of Gamma-Ray Bursts (GRBs) expands radially with acceleration and forms a shell with constant width measured in the laboratory frame. When strong Lorentz factor gradients are present within the shell it is supposed to spread at sufficiently large radii. There are two possible mechanisms of spreading: hydrodynamical and thermal ones. We consider both mechanisms evaluating the amount of spreading that occurs during expansion up to the moment when the expanding shell becomes transparent for photons. We compute the hydrodynamical spreading of an ultrarelativistically expanding shell. In the case of thermal spreading we compute the velocity spread as a function of two parameters: comoving temperature and bulk Lorentz factor of relativistic Maxwellian distribution. Based on this result we determine the value of thermal spreading of relativistically expanding shell. We found that thermal spreading is negligible for typical GRB parameters. Instead hydrodynamical spreading appears to be significant, with the shell width reaching ∼1010cm for total energy E=1054erg and baryonic loading B=10-2. Within the fireshell model such spreading will result in the duration of Proper Gamma-Ray Bursts up to several seconds.

Whistler instability in a semi-relativistic bi-Maxwellian plasma

Employing linearized Vlasov-Maxwell system, the Weibel instability embedded in an ambient magnetic field is discussed for a semi-relativistic bi-Maxwellian distribution hoping such a scenario occurs in some relativistic environments e.g., gamma-ray burst sources and relativistic jet sources, supernovae, and galactic cosmic rays where the perpendicular temperature is much dominated over the parallel . The dispersion relations are analyzed analytically along with the graphical representation and the estimates of the growth rate are presented along with the instability threshold condition in the limiting cases i.e., xi<=1 (resonant case) and xi>>1 (non-resonant case). It is observed that the relativistic effect suppresses the instability and also lowers the threshold for the instability to set in. The ambient magnetic field contribution to instability appears only in non-resonant case resulting in reduction of growth rate. However, the effect of the ambient magnetic field is diminished as we go from the weak relativistic regime to the highly relativistic one. We also note that the ambient magnetic field generates real oscillations and the reletivistic effect reduces these oscillations. Further for field free case i.e., B0=0, the growth rates for Weibel instabilities are also presented in a semi-relativistic bi- Maxwellian plasma for both the limiting cases.