Nature Of Gamma-ray Bursts Progenitors Research Articles

What can we learn from GRBs?

We review our recent results on the classification of long and short gamma-ray bursts (GRBs) in different subclasses. We provide observational evidences for the binary nature of GRB progenitors. For long bursts the induced gravitational collapse (IGC) paradigm proposes as progenitor a tight binary system composed of a carbon-oxygen core (COcore) and a neutron star (NS) companion; the supernova (SN) explosion of the COcore triggers a hypercritical accretion process onto the companion NS. For short bursts a NS–NS merger is traditionally adopted as the progenitor. We also indicate additional sub-classes originating from different progenitors: (COcore)–black hole (BH), BH–NS, and white dwarf–NS binaries. We also show how the outcomes of the further evolution of some of these sub-classes may become the progenitor systems of other sub-classes.

The Maximum Isotropic Energy of Gamma-Ray Bursts

Abstract The most energetic gamma-ray bursts (GRBs) are remarkable sources releasing huge amounts of energy on short timescales. Their prompt emission, which usually lasts a few seconds, is so bright that it is visible across the whole observable universe. Studying these extreme events may provide clues on the nature of GRB progenitors and on the physical processes at work in relativistic jets. In this paper, we study the bright end of the isotropic energy distribution of long GRBs. We use two samples of long GRBs with redshift detected by Fermi/GBM or Konus-Wind, two instruments that measure the spectral shape and the energetics of the prompt emission accurately. We focus on GRBs within a range of redshifts z = 1–5, a volume that contains a large number of energetic GRBs, and we propose a simple method to reconstruct the bright end of the GRB energy distribution from the observed one. We find that the GRB energy distribution cannot be described by a simple power law but requires a strong cutoff above 1 – 3 × 10 54 erg. We attribute this feature to an intrinsic limit on the energy per unit of solid angle radiated by GRBs.

Probing massive stars around gamma-ray burst progenitors

Long Gamma-Ray Bursts (GRBs) are produced by ultra-relativistic jets launched from core collapse of massive stars. Most massive stars form in binaries and/or in star clusters, which means that there may be a significant external photon field (EPF) around the GRB progenitor. We calculate the inverse-Compton scattering of EPF by the hot electrons in the GRB jet. Three possible cases of EPFs are considered: the progenitor is (I) in a massive binary system, (II) surrounded by a Wolf-Rayet-star wind, and (III) in a dense star cluster. Typical luminosities of 10^46 - 10^50 erg/s in the 1 - 100 GeV band are expected, depending on the stellar luminosity, binary separation (I), wind mass loss rate (II), stellar number density (III), etc. We calculate the lightcurve and spectrum in each case, taking fully into account the equal-arrival time surfaces and possible pair-production absorption with the prompt gamma-rays. Observations can put constraints on the existence of such EPFs (and hence on the nature of GRB progenitors) and on the radius where the jet internal dissipation process accelerates electrons.

The Mass-SFR-Metallicity Relation of Star Forming Galaxies and Its Evolution: Implications for GRB/SN Host Galaxies

Observed properties of gamma-ray burst (GRB) host galaxies are important clues to understand the nature of GRB progenitors. However, the properties of the host galaxies don’t directly tell us the nature of the GRB progenitors, and the decipherment of the clue relies on our understanding of general galaxies. The relation between stellar mass, star formation rate (SFR), and metallicity of star forming galaxies (so called the fundamental metallicity relation) has recently attracted attention regarding its possible impact upon our understanding on the properties of the long GRB host galaxies. In this study, I show the possibility of redshift evolution of the mass–SFR–metallicity relation which has been claimed to be independent of redshift, and discuss implications of the evolving relation for the properties of GRB/SN host galaxies.