[Paper Review] Gamma-Ray Bursts - The Second Revolution

Tsvi Piran|arXiv (Cornell University)|Jul 24, 1998

Gamma-ray bursts and supernovae3 citations

TL;DR

This paper reviews the second major revolution in gamma-ray burst (GRB) research, triggered by BeppoSAX's detection of X-ray afterglows, which confirmed the fireball model and revealed GRBs as the most relativistic and luminous astrophysical phenomena, involving velocities near light speed, black hole formation, and potential gravitational wave emission. The findings suggest GRBs could serve as cosmological probes for measuring cosmic parameters and studying early galaxy formation.

ABSTRACT

Gamma-ray bursts GRBs are among the most mysterious astronomical phenomenon ever discovered. Unlike most astronomical discoveries which were explained within weeks or months after their initial discovery, GRBs remain a puzzle for more than thirty years. During the last decade our understanding of GRBs has undergone two major revolutions. First, BATSE discovered that GRBs are distributed isotropically over the sky and thereby demonstrated their cosmological origin. The second revolution tool place more recently when BeppoSAX discovered GRB afterglow. This confirmed the fireball model and led to a wealth of observational data, some of which has not been fully understood yet. The emerging picture is that GRBs are the most luminous objects and the most relativistic objects ever discovered: (i) GRBs involve relativistic motion at a velocity of 0.9999c or larger. (ii) Most current GRB models involve the formation of a black hole in one way or another. (iii) If binary neutron star mergers are the sources of GRBs then GRBs are also associated with gravitational radiation signals. Finally, (iv) as cosmological power-houses that are observed to high red-shift GRBs might be used to measure cosmological parameters and to teach us about the epoch of galaxy formation.

Motivation & Objective

• To summarize the transformative impact of BeppoSAX's afterglow detections on GRB research.
• To explain how the fireball model gained credibility through observational confirmation.
• To highlight the extreme physical conditions in GRBs, including velocities near c and luminosities exceeding those of quasars.
• To explore the implications of GRBs for cosmology, including their potential use in measuring cosmological parameters.
• To discuss the connection between GRBs and gravitational wave signals, particularly in the context of binary neutron star mergers.

Proposed method

• Analyzing observational data from BeppoSAX, particularly X-ray afterglow light curves and their temporal decay indices.
• Applying the fireball model to interpret the relativistic outflows and deceleration of GRB ejecta.
• Using isotropic distribution of GRBs (from BATSE) to infer cosmological distances and redshifts.
• Modeling the energy budget and Lorentz factors of GRB outflows to estimate velocities approaching c.
• Assessing the potential for GRBs to serve as standard candles or cosmological distance indicators via high-redshift observations.
• Evaluating the role of black hole formation and binary neutron star mergers as progenitor mechanisms.

Experimental results

Research questions

• RQ1 How do the afterglow light curves observed by BeppoSAX support the fireball model of GRBs?
• RQ2 What physical conditions—such as Lorentz factors and energy budgets—are required to explain the observed GRB luminosities and relativistic motion?
• RQ3 Can GRBs be used as cosmological probes to measure parameters like the Hubble constant or dark energy density?
• RQ4 What is the connection between GRB progenitors and gravitational wave emission, particularly in binary neutron star mergers?
• RQ5 How do the extreme properties of GRBs inform our understanding of black hole formation and early galaxy evolution?

Key findings

• BeppoSAX's detection of X-ray afterglows provided strong observational confirmation of the fireball model, resolving long-standing uncertainties about GRB energetics and geometry.
• GRBs involve relativistic outflows with Lorentz factors of at least 100, corresponding to velocities of 0.9999c or higher, making them the most relativistic objects known.
• Most current GRB models involve the formation of a black hole, either directly or via neutron star collapse, suggesting a link to compact object formation.
• If binary neutron star mergers are the source of GRBs, then these events are also expected to emit gravitational waves, offering a multi-messenger opportunity.
• GRBs are so luminous that they can be observed at high redshifts, making them potential tools for probing the early universe and measuring cosmological parameters.
• The isotropic distribution of GRBs, confirmed by BATSE, established their cosmological origin and enabled distance estimates essential for cosmological applications.