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Register a new userA contemporaneous infrared flash from a long gamma-ray burst: an echo from the central engine
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The explosion that results in a cosmic gamma-ray burst (GRB) is thought to produce emission from two physical processes -- the activity of the central engine gives rise to the high-energy emission of the burst through internal shocking and the subsequent interaction of the flow with the external environment produces long-wavelength afterglow. While afterglow observations continue to refine our understanding of GRB progenitors and relativistic shocks, gamma-ray observations alone have not yielded a clear picture of the origin of the prompt emission nor details of the central engine. Only one concurrent visible-light transient has been found and was associated with emission from an external shock. Here we report the discovery of infrared (IR) emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of GRB 041219a. Our robotic telescope acquired 21 images during the active phase of the burst, yielding the earliest multi-colour observations of any long-wavelength emission associated with a GRB. Analysis of an initial IR pulse suggests an origin consistent with internal shocks. This opens a new possibility to study the central engine of GRBs with ground-based observations at long wavelengths.
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The origin of gamma-ray bursts (GRBs) has been enigmatic since their discovery. The situation improved dramatically in 1997, when the rapid availability of precise coordinates for the bursts allowed the detection of faint optical and radio afterglows - optical spectra thus obtained have demonstrated conclusively that the bursts occur at cosmological distances. But, despite efforts by several groups, optical detection has not hitherto been achieved during the brief duration of a burst. Here we report the detection of bright optical emission from GRB990123 while the burst was still in progress. Our observations begin 22 seconds after the onset of the burst and show an increase in brightness by a factor of 14 during the first 25 seconds; the brightness then declines by a factor of 100, at which point (700 seconds after the burst onset) it falls below our detection threshold. The redshift of this burst, approximately 1.6, implies a peak optical luminosity of 5 times 10^{49} erg per second. Optical emission from gamma-ray bursts has been generally thought to take place at the shock fronts generated by interaction of the primary energy source with the surrounding medium, where the gamma-rays might also be produced. The lack of a significant change in the gamma-ray light curve when the optical emission develops suggests that the gamma-rays are not produced at the shock front, but closer to the site of the original explosion.
Gamma Ray Bursts (GRB) are the extremely energetic transient events, visible from the most distant parts of the Universe. They are most likely powered by accretion on the hyper-Eddington rates that proceeds onto a newly born stellar mass black hole. This central engine gives rise to the most powerful, high Lorentz factor jets that are responsible for energetic gamma ray emission. We investigate the accretion flow evolution in GRB central engine, using the 2D MHD simulations in General Relativity. We compute the structure and evolution of the extremely hot and dense torus accreting onto the fast spinning black hole, which launches the magnetized jets. We calculate the chemical structure of the disk and account for neutrino cooling. Our preliminary runs apply to the short GRB case (remnant torus accreted after NS-NS or NS-BH merger). We estimate the neutrino luminosity of such an event for chosen disk and central BH mass
Recent numerical simulations suggest that Population III (Pop III) stars were born with masses not larger than $sim 100 M_{odot}$ but typically $sim 40M_{odot}$. By self-consistently considering the jet generation and propagation in the envelope of these low mass Pop III stars, we find that a Pop III blue super giant star has the possibility to raise a gamma-ray burst (GRB) even though it keeps a massive hydrogen envelope. We evaluate observational characters of Pop III GRBs and predict that Pop III GRBs have the duration of $sim 10^5$ sec in the observer frame and the peak luminosity of $sim 5 times 10^{50} {rm erg} {rm sec}^{-1}$. Assuming that the $E_p-L_p$ (or $E_p-E_{gamma, rm iso}$) correlation holds for Pop III GRBs, we find that the spectrum peak energy falls $sim$ a few keV (or $sim 100$ keV) in the observer frame. We discuss the detectability of Pop III GRBs by future satellite missions such as EXIST and Lobster. If the $E_p-E_{gamma, rm iso}$ correlation holds, we have the possibility to detect Pop III GRBs at $z sim 9$ as long duration X-ray rich GRBs by EXIST. On the other hand, if the $E_p-L_p$ correlation holds, we have the possibility to detect Pop III GRBs up to $z sim 19$ as long duration X-ray flashes by Lobster.
Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterised by an initial phase of bright and highly variable radiation in the keV-MeV band that is likely produced within the jet and lasts from milliseconds to minutes, known as the prompt emission. Subsequently, the interaction of the jet with the external medium generates external shock waves, responsible for the afterglow emission, which lasts from days to months, and occurs over a broad energy range, from the radio to the GeV bands. The afterglow emission is generally well explained as synchrotron radiation by electrons accelerated at the external shock. Recently, an intense, long-lasting emission between 0.2 and 1 TeV was observed from the GRB 190114C. Here we present the results of our multi-frequency observational campaign of GRB~190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from $5times10^{-6}$ up to $10^{12}$,eV. We find that the broadband spectral energy distribution is double-peaked, with the TeV emission constituting a distinct spectral component that has power comparable to the synchrotron component. This component is associated with the afterglow, and is satisfactorily explained by inverse Compton upscattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed TeV component are not atypical, supporting the possibility that inverse Compton emission is commonly produced in GRBs.
The optical light that is generated simultaneously with the x-rays and gamma-rays during a gamma-ray burst (GRB) provides clues about the nature of the explosions that occur as massive stars collapse to form black holes. We report on the bright optical flash and fading afterglow from the powerful burst GRB 130427A and present a comparison with the properties of the gamma-ray emission that show correlation of the optical and >100 MeV photon flux light curves during the first 7,000 seconds. We attribute this correlation to co-generation in an external shock. The simultaneous, multi-color, optical observations are best explained at early times by reverse shock emission generated in the relativistic burst ejecta as it collides with surrounding material and at late times by a forward shock traversing the circumburst environment. The link between optical afterglow and >100 MeV emission suggests that nearby early peaked afterglows will be the best candidates for studying GRB emission at GeV/TeV energies.
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