[Paper Review] An overview of the current understanding of Gamma-ray Bursts in the Fermi era

P. N. Bhat, S. Guiriec|arXiv (Cornell University)|Nov 21, 2011

Gamma-ray bursts and supernovae14 references3 citations

TL;DR

This paper reviews gamma-ray burst (GRB) research in the Fermi era, synthesizing observational and theoretical advances from Fermi's unprecedented energy coverage (10 keV–300 GeV) and multi-wavelength data. It highlights GRB cosmological distances, prompt emission physics, afterglow behavior, and the potential for gravitational wave detection from GRB progenitors, particularly through advanced LIGO/Virgo, offering new probes of black hole properties and dark energy.

ABSTRACT

Gamma-ray bursts are the most luminous explosions in the Universe, and their origin as well as mechanism are the focus of intense research and debate. More than three decades since their serendipitous discovery, followed by several breakthroughs from space-borne and ground-based observations, they remain one of the most interesting astrophysical phenomena yet to be completely understood. Since the launch of Fermi with its unprecedented energy band width spanning seven decades, the study of gamma-ray burst research has entered a new phase. Here we review the current theoretical understanding and observational highlights of gamma-ray burst astronomy and point out some of the potential promises of multi-wavelength observations in view of the upcoming ground based observational facilities.

Motivation & Objective

• To synthesize the current understanding of gamma-ray bursts (GRBs) following the launch of the Fermi space telescope.
• To assess the implications of Fermi's wide energy coverage (10 keV–300 GeV) for GRB physics and multi-messenger astronomy.
• To evaluate the potential of gravitational wave detection from GRB progenitors, especially for probing black hole properties and dark energy.
• To highlight the role of upcoming ground-based facilities in advancing GRB and gravitational wave astronomy.

Proposed method

• Analysis of GRB data from Fermi's Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT), covering 10 keV to 300 GeV.
• Synthesis of multi-wavelength observations from Swift, BeppoSAX, HETE-2, and other missions to study prompt emission and afterglow emission.
• Theoretical modeling of GRB central engine physics, including black hole formation, magnetized neutron stars, and bar-mode instabilities.
• Evaluation of gravitational wave emission from GRB progenitors, particularly from binary black hole mergers and spinning neutron stars.
• Assessment of gravitational wave detection prospects using advanced LIGO, Virgo, and future detectors like the Einstein Telescope.
• Use of redshift measurements from Swift to constrain GRB host environments and cosmic star formation history.

Experimental results

Research questions

• RQ1 How do Fermi's observations across seven decades of energy coverage improve our understanding of GRB prompt emission and afterglow emission?
• RQ2 What are the implications of the isotropic sky distribution of long and short GRBs for their cosmological origin?
• RQ3 Can gravitational wave emission from GRB progenitors—such as merging black holes or unstable neutron stars—be detected by current and future interferometers?
• RQ4 How do X-ray afterglow plateaus and shallow decay phases relate to the formation of highly magnetized millisecond pulsars and their spin-down via gravitational wave emission?
• RQ5 What is the potential of gravitational wave 'standard sirens' from short GRB progenitors to measure the Hubble constant and probe dark energy?

Key findings

• Fermi's GBM detected 765 GRBs and LAT detected 28 within its first years, extending the energy coverage to 300 GeV and revealing high-energy emission in some bursts.
• The isotropic sky distribution of both long and short GRBs, confirmed by Fermi-GBM and earlier BATSE data, supports their cosmological origin and rules out local galactic or cluster-based sources.
• A shallow decay phase in early X-ray afterglows is observed in many GRBs and may be linked to energy injection from a highly magnetized millisecond pulsar formed in the central engine.
• Gravitational wave emission from a secular bar-mode instability in a nascent neutron star could produce a detectable signal delayed by minutes to an hour after the gamma-ray burst, offering a window for real-time detection by advanced LIGO/Virgo.
• Binary black hole mergers with masses of 10–50 solar masses are prime candidates for detectable gravitational wave signals, and such events could serve as 'standard sirens' to measure cosmic distances and the dark energy equation of state.
• Despite no confirmed gravitational wave detection coincident with GRBs to date, the commissioning of advanced LIGO and Virgo detectors by 2015 offers strong potential for future breakthroughs in multi-messenger GRB astronomy.