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AUTHOR COMMENTARIES - From Special Topics

Gamma-ray Bursts - June 2009
Interview Date: July 2009
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Dale Frail
Dale Frail
From the Special Topic of Gamma-ray Bursts

According to our Special Topics analysis of gamma-ray burst (GRB) research over the past decade, the scientist whose work ranks at #3 by total cites is Dr. Dale Frail, with 92 papers cited a total of 4,745 times. In Essential Science IndicatorsSM from Thomson Reuters, his record includes 115 papers, the majority of which are classified in Space Science, cited a total of 5,507 times between January 1, 1999 and February 28, 2009.


Dr. Frail is an Astronomer and Assistant Director for Scientific and Academic Affairs at the National Radio Astronomy Observatory in Socorro, New Mexico.

In the interview below, he talks with ScienceWatch.com about his highly cited work related to GRBs.

 Would you tell us a bit about your educational background and research experiences?

I received my Ph.D. from the University of Toronto in 1989. I came from a physics background but I specialized in radio astronomy for my Ph.D.

I've always been interested in high-energy astrophysics. Many high-energy astrophysical phenomena (pulsars, active galactic nuclei, supernovae, etc.) emit at radio wavelengths. High-energy electrons radiate at these wavelengths as they interact with magnetic fields.

 What first interested you in GRBs?

"...GRB energetics remain one of our best tools to understanding the central engine properties."

In 1993 the GRB mystery was more than 20 years old—it has an interesting history tied into the Cold War and nuclear test-ban treaties. I read a paper by Bohdan Paczyn'ski and James E. Rhoads that predicted the existence of faint "afterglows" visible at radio wavelengths because of the energetic electrons accelerated in the shock generated by the gamma-ray burst.

Given our background in radio astronomy, my colleague, Shri Kulkarni, and I immediately knew this paper was onto the right idea. We began an observational program in 1993 that finally bore fruit in 1997 after the launch of the Italian-Dutch satellite BeppoSAX. Our group is credited with discovering the first radio "afterglow" as well as establishing that GRBs are at cosmological distances.

 One of your most-cited papers in our analysis is the 2001 Astrophysical Journal paper, "Beaming in gamma-ray bursts: Evidence for a standard energy reservoir" (Frail DA, et al., 562[1]: L55-8, Part 2, 20 November 2001). Would you tell us about this paper, and why you think it's so highly cited?

Measuring the energy release of GRBs is one of the key pieces to understanding what the "central engine" is that gives rise to these short-lived, relativistic explosions. If the explosion was isotropic, the implied energy released from some of these events was 1054 ergs.

This is comparable to converting the rest mass energy of our Sun into gamma-rays and doing it on a timescale of 10 s. Such energies were hard to contemplate and to build realistic theoretical models.

In 2001, we published this paper, which pulled together all the available afterglow data at the time and showed that gamma-ray burst outflows were not isotropic but rather beamed into narrow opening angles. This lowered the energies substantially to the point where most events had an energy release of order 1051 ergs. This is comparable to the energy release in a supernova explosion—large but not out of the realm of theory.

It's hard to say why a paper gets cited more often than others. The paper was a synthesis of what we knew in 2001 and it reached some conclusions about GRB energetics that are still not fully resolved even today. It comes back to the fact that GRB energetics remain one of our best tools to understanding the central engine properties.

 Late last year, you were part of the team on the Astrophysical Journal paper, "New imaging and spectroscopy of the locations of several short-hard gamma-ray bursts" (Gal-Yam A, et al., 686[1]: 408-16, 10 October 2008). Could you tell our readers something about this paper?

There are two classes of GRBs: long-duration bursts, which we started studying the afterglows from in 1997, and short-hard bursts (SHB). The SHBs were difficult to observe until the launch of NASA's Swift satellite in 2004.

"...because of their extreme brightnesses, GRBs and their afterglows can be detected from the earliest stages of our universe, a time when the first stars and black holes were beginning to form."

This paper does a synthesis of all the data we have on SHBs and starts to draw some conclusions about the progenitor population from which they originate. While not definitive, the evidence is growing that SHBs originate from the gravitational merger of two compact objects (black hole or neutron star). The interest in this paper and others like it is tied to the major efforts that are underway to detect gravitational waves (e.g. LIGO). This paper provides some estimates of the event rate of such compact coalescence events.

 How has our knowledge of GRBs changed over the past decade?

At the start of 1997 our ignorance was almost total. We really didn't know whether GRBs were in our Galaxy or whether they were a cosmological population. If we fast forward 12 years we recognize a diverse range of cosmological explosions, we understand what the progenitor populations are for many of them, and we are starting to use them as probes of the early Universe.

 Where would you like to take your research on GRBs in the next decade?

In short—the highest energies and the highest redshifts. Energetics are still a key part to understanding where and how these explosions originate. NASA's Fermi mission is capable of detecting GeV photons from gamma-ray bursts. Such events may represent some of nature's most extreme explosions in terms of total energy and therefore put our theories to the most stringent tests.

Second, because of their extreme brightnesses, GRBs and their afterglows can be detected from the earliest stages of our universe, a time when the first stars and black holes were beginning to form. Last month we detected a GRB at a redshift of z=8.2, a time when the universe was only 630 million years old. If stellar collapse gave rise to gamma-ray bursts there is nothing in principle stopping us from observing GRBs at even earlier epochs in the age of the universe.

 What would you say the "take-home message" about your work should be?

"Don't be afraid to kiss some frogs." When we started looking for afterglows in 1993 we didn't really know if our radio telescopes were sensitive enough. We took a risk and we persisted. For that we were among the first to work in this new field of afterglows.

Any success we have had has come from being early to this field and by trying to ask the big, overarching questions. You cannot build an entire research career on tackling high-risk projects, but it is difficult to make a significant impact without taking some risks.

Dale A. Frail
Office of Science and Academic Affairs
National Radio Astronomy Observatory
Socorro, NM, USA

Dale Frail's current most-cited paper in Essential Science Indicators, with 438 cites:
Gehrels N, et al., "The Swift gamma-ray burst mission," Astrophys. J 611(2): 1005-20, Part 1, 20 August 2004. Source: Essential Science Indicators from Thomson Reuters.
Additional Information:
  Dale Frail is featured in ISIHighlyCited.com

KEYWORDS: GAMMA-RAY BURSTS, SWIFT GAMMA-RAY BURST MISSION, RADIO ASTRONOMY, AFTERGLOW, COSMOLOGICAL DISTANCES, ENERGY RELEASE, BEPPOSAX, GRB ENERGENETICS, LONG-DURATION BURSTS, SHORT-HARD BURSTS, PROGENITORS, GRAVIATIONAL WAVES, REDSHIFTS.

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Special Topics : Gamma-ray Bursts : Dale Frail Interview - Special Topic of Gamma-ray Bursts
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