What Are Gamma-Ray Bursts? (Princeton Frontiers in Physics, 2) 1st Edition by Joshua S. Bloom (PDF)

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A brief, cutting-edge introduction to the brightest cosmic phenomena known to scienceGamma-ray bursts are the brightest―and, until recently, among the least understood―cosmic events in the universe. Discovered by chance during the cold war, these evanescent high-energy explosions confounded astronomers for decades. But a rapid series of startling breakthroughs beginning in 1997 revealed that the majority of gamma-ray bursts are caused by the explosions of young and massive stars in the vast star-forming cauldrons of distant galaxies. New findings also point to very different origins for some events, serving to complicate but enrich our understanding of the exotic and violent universe. What Are Gamma-Ray Bursts? is a succinct introduction to this fast-growing subject, written by an astrophysicist who is at the forefront of today’s research into these incredible cosmic phenomena.Joshua Bloom gives readers a concise and accessible overview of gamma-ray bursts and the theoretical framework that physicists have developed to make sense of complex observations across the electromagnetic spectrum. He traces the history of remarkable discoveries that led to our current understanding of gamma-ray bursts, and reveals the decisive role these phenomena could play in the grand pursuits of twenty-first century astrophysics, from studying gravity waves and unveiling the growth of stars and galaxies after the big bang to surmising the ultimate fate of the universe itself.What Are Gamma-Ray Bursts? is an essential primer to this exciting frontier of scientific inquiry, and a must-read for anyone seeking to keep pace with cutting-edge developments in physics today.

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Editorial Reviews: Review “This series of books (Princeton Frontiers of Physics) is aimed at ‘students, scientists and scientifically minded general readers’. This particular book is on target, with reasonably clear explanations of most of the jargon, a useful glossary, a good index and a reference to a more advanced review for those who need it.”—D. J. Miller, Contemporary Physics Review “This is a marvelous book. It contains the new results from the fast-developing science of gamma-ray-burst astronomy along with its fascinating history. I recommend it as a good introduction for nonexperts and a fun read for researchers in the field.”―Neil Gehrels, NASA Goddard Space Flight Center”This book gives a balanced and up-to-date overview of the field of gamma-ray bursts, one that will be useful for astronomers, physicists, and other scientists. Until now, there have been no books that I know of that deal with this subject for a broader audience of scientists and educated lay people.”―Ralph A.M.J. Wijers, University of Amsterdam From the Back Cover “This is a marvelous book. It contains the new results from the fast-developing science of gamma-ray-burst astronomy along with its fascinating history. I recommend it as a good introduction for nonexperts and a fun read for researchers in the field.”–Neil Gehrels, NASA Goddard Space Flight Center”This book gives a balanced and up-to-date overview of the field of gamma-ray bursts, one that will be useful for astronomers, physicists, and other scientists. Until now, there have been no books that I know of that deal with this subject for a broader audience of scientists and educated lay people.”–Ralph A.M.J. Wijers, University of Amsterdam About the Author Joshua S. Bloom is associate professor of astronomy at the University of California, Berkeley. Excerpt. © Reprinted by permission. All rights reserved. WHAT ARE Gamma-Ray Bursts?By JOSHUA S. BLOOMPRINCETON UNIVERSITY PRESSCopyright © 2011 Princeton University PressAll right reserved.ISBN: 978-0-691-14557-0ContentsPREFACE………………………………………………….ix1 Introduction……………………………………………12 Into the Belly of the Beast………………………………403 Afterglows……………………………………………..724 The Events in Context……………………………………1135 The Progenitors of Gamma-Ray Bursts……………………….1356 Gamma-Ray Bursts as Probes of the Universe…………………169NOTES……………………………………………………203SUGGESTIONS FOR FURTHER READING…………………………….227GLOSSARY…………………………………………………231INDEX……………………………………………………249Chapter One INTRODUCTION Serendipity is jumping into a haystack to search for a needle, and coming up with the farmer’s daughter. —Julius H. Comroe Jr. 1.1 Serendipity during the Cold War Before Mythbusters and The A-Team made big explosions cool, big explosions were decidedly uncool. The threat of nuclear war between the United States and the USSR (and, perhaps, China)—made blatantly real during the Cuban Missile Crisis in October 1962—had become a fixture in everyday life. One year after the crisis, seeking to diffuse an escalating arms race and the global increase of radioactive fallout from nuclear weapons testing, Soviet Premier Nikita Khrushchev and U.S. President John F. Kennedy agreed to the Partial Test Ban Treaty. Ratifying nations agreed that all nuclear weapons testing would be conducted underground from then on: no longer would tests be conducted in oceans, in the atmosphere, or in space. The United States, led by a team at the Los Alamos National Laboratory, promptly began an ambitious space satellite program to test for “non-compliance” with the Partial Test Ban Treaty. The existence of the Vela Satellite Program was unclassified: the rationale, experimental design, and satellite instrumentation were masterfully detailed in peer-reviewed public journals while the program was on going. The concept for this space-based vigilance endeavor was informed by the physics of nuclear explosions: while the optical flash of a nuclear detonation could be shielded, the X-rays, gamma rays (sometimes written as ?-rays), and neutrons that are produced in copious numbers in the first second of an explosion are much more difficult to hide; we call the measurement of these by-products the “signature” of a nuclear detonation. Going into space for such surveillance was a must: the Earth’s atmosphere essentially blocks X-rays, gamma rays, and neutrons from space. While the signatures of nuclear detonations were well understood, the background radiation of light and particles in space was not. To avoid false alarms caused by unknown transient enhancements in the background, satellites were launched in pairs—both satellites would have to see the same very specific signatures in their respective instruments for the alarms bells to sound. Widely separated satellite pairs also had the advantage that most of the Earth could be seen at all times. While the Vela orbits provided little vantage point on the dark side of the Moon—a natural location to test out of sight—the gamma rays and neutrons from the expanding plume of nuclear-fission products would eventually come into view. In total, six pairs (Vela 1a,b through Vela 6a,b) were launched between 1964 and 1970. As evidenced by the Vela Satellite Program, the U.S. was obviously very serious about ensuring compliance. That the capabilities of the program were open was also a wonderful exercise in cold war gamesmanship—you are much less inclined to break the rules if you are convinced you will get caught. While hundreds of thousands of events were detected by the Velas—mostly from lightning on Earth and charged particles (cosmic rays) hitting the instruments—the telltale signatures of nuclear detonation were thankfully never discovered. Those events that were obviously not of pernicious or known origin were squirreled away for future scrutiny. Starting in 1969, Los Alamos employee Ray Klebesadel began the laborious task of searching, by eye, the Vela data for coincident gamma-ray detections in multiple satellites. One event, from July 2, 1967, stood out (figure 1.1). Seen in both the gamma-ray detectors of Vela 4a and Vela 4b (and weakly in the less sensitive Vela 3a and Vela 3b detectors), the event was unlike any known source. Though there was no known solar activity on that day, the event data themselves in one satellite were incapable of ruling out a Solar origin, especially if it was a new sort of phenomenon from the Sun. Over the next several years, other intriguing events similar to the July 2nd event were seen in the Vela data. By 1972, Klebesadel and his colleagues Ian Strong and Roy Olson had uncovered sixteen such events using automated computer codes to aid with the arduous searches. What were these bursts of gamma rays? To answer that question, the Los Alamos team recognized that it had better determine where on the sky the events came from. Pinpointing the direction of a light source is easy if you can focus it: this is what cameras used for photography and the human eye do well with visible light. But X-rays, and especially gamma rays, are not amenable to focusing: the energies of these photons are so high that they do not readily interact with the free electrons in metals and so cannot be reflected to large angles. The focusing of light without large-angle reflection is exceedingly difficult. The best the X-ray and gamma-ray detectors on the Velas could do was stop those photons, recording both the energy deposited in the detectors and the time that the photon arrived at the satellite. The arrival time of the photons from specific events held the key to localization. Just as a thunderclap is heard first by those closest to the lightening bolt, an impulsive source of photons would be seen first in the satellite closest to the event and then later, after the light sweeps by, with the more distant satellite. Light (and sound, in the case of thunder) has a finite travel speed. Since the Vela satellites were dispersed at large distances from each other (approximately 200,000 kilometers) the difference in the arrival times of the pulses could be used to reconstruct the origin on the sky, the location on the celestial sphere. As figure 1.2 shows, an event seen in two satellites produces an annular location on the sky, and an event seen in three satellites produces a location in two patches on the sky. This triangulation capability, albeit crude, was sufficient to convince the Los Alamos team that it had uncovered a class of events that was not coming from the Earth, Sun, Moon, or any other known Solar System object. In 1973, Klebesadel, Strong, and Olson published their findings in the Astrophysical Journal, one of the venerable peer-reviewed journals used for describing scientific results in astronomy. The paper titled “Observations of Gamma-Ray Bursts of Cosmic Origin” marked the beginning of the gamma-ray burst (GRB) enigma that to this day captivates the imagination and keeps astronomers scratching their heads. The word serendipity is overused and misused in science. Most mistake a serendipitous discovery to be synonymous with an unexpected (and unforeseen) discovery. But, as Julius Comroe’s colorful analogy in the epigraph describes, serendipity demands both an unexpected discovery and an entirely more pleasant discovery than the one being pursued. While GRBs certainly were unexpected and unforeseen, they were also much more scientifically valuable than what was being sought after: instead of the detection of a nuclear test by an enemy, a discovery that in the 1960s would have set the world down a dangerous and dark path, GRBs were a fresh light from the dark heavens. Indeed, their mysterious nature would captivate a generation of astronomers. The discovery of GRBs—not just their detection but the recognition that the events represented a new phenomenon in nature—was truly a serendipitous moment in modern science. 1.2 A New Field Begins Members of Klebesadel’s team announced the discovery of GRBs at the June 1973 meeting of the American Astronomical Society, a few days after the publication of their seminal paper. In that meeting (and in the paper) they described their observations testing the hypothesis that GRBs originated from supernovae (SNe) in other galaxies; this was the only physical model for the origin of cosmic bursts of gamma rays available at the time. By trying to correlate a GRB in time and sky position to all known SNe, the attempt to connect GRBs to the then-brightest explosions in the universe “proved uniformly fruitless.” Determining what objects and what events on those objects produced GRBs quickly became a hot topic. By the end of 1974, more than one dozen ideas for the origin of GRBs had already been published. The theories spanned an astonishing range of possibilities, from sunlight scattering off fast-moving dust grains to comets colliding with white dwarfs (WDs) to “antimatter asteroids” smashing into distant stars. All viable models necessarily accommodated the available data, but the GRB data were simply too sparse to constrain a talented and imaginative group of eager scientists. More data would be needed to narrow down the range of plausible models. By the end of 1973, the Los Alamos team had found a total of twenty-three GRBs. Teams working with other satellites equipped with gamma-ray detectors also began reporting detections of GRBs, even some of the same events seen by the Vela satellites. New programs were conceived to find more GRBs and observe them with more sensitive detectors. The supposition—if not just a hope—was that with better data some telltale signature of the origin of the events would emerge. Unbeknown to those sprinting to find the answer, for all but a few special events, those telltale signatures would take over thirty years to uncover (a veritable marathon in modern science). Light does not easily betray its origin: there is nothing in a gamma-ray photon itself that can tell us how far it traveled, nor can we learn directly just how many of those energetic photons streamed away from the event that produced the GRB. Without a measurement of the distance to a source, the pool of possible culprits is simply too broad: since we have a general sense of the types and the spatial distribution of objects in a given volume of space, if we knew that GRBs arose from distances on the size scale of the Solar System (for example), then there could be only a select set of objects responsible (comets, asteroids, planets, etc.). At a more fundamental level, without knowledge of distance, it is all but impossible to know how much energy the source put out. And without that knowledge the range of physical mechanisms that could be responsible for the sudden release of all that energy is also too broad. Case in point: a street lamp appears about as bright as the Sun, yet the scales of energy output are vastly different as are the physical origins of the light. Since light does not directly encode distance, how do astronomers determine distance to astrophysical entities? If sufficiently nearby, objects appear to be in slightly different places on the sky for observers at different places. This measurement of parallax yields a direct triangulation of distance but is exceedingly difficult to determine for most objects beyond a few hundred light years away from Earth. Beyond that, for all but a few special cases, we must infer distance by associating some source with a source whose intrinsic brightness or size we think we know (usually because we think there is an analogous system within the parallax volume). The key, then, for GRBs would be to associate the events with something else whose distance we could more readily infer. In this respect, the inability to measure a precise two-dimensional position of a GRB on the sky directly hampered the ability to measure the all-important third dimension. Getting better positions of GRBs on the sky became the driving impetus behind the next several decades of GRB observational projects. 1.3 Precise Localizations and the Search for Counterparts By the late 1970s, not only were there more satellites flying with higher-sensitivity detectors, but some of these satellites were far from Earth (in particular, near Venus and the Sun). This interplanetary network (IPN) gave a significant improvement on the timing localizations of GRBs (see figure 1.2). At a distance of up to d = 2 astronomical units (AU) (twice the distance from the Earth to the Sun), a pair of satellites with the capability to determine the time of the onset of a GRB to an accuracy of dt = 0.1 seconds would be able to produce an annular localization ring of thickness d? ≈ dt × c/d = 10-4 radian ≈ 1/3 arcminute. By 1980, there were a handful of well-localized (to tens of square arcminutes or better) GRBs, and by the end of the 1980s there were dozens of well-localized GRBs using the interplanetary timing technique. In a spatial area on the sky, while millions of times more accurate than the first GRB positions, these square-arcminute localizations proved insufficient to rule out most models. If all error boxes on the sky contained a bright star or a bright galaxy, the association with a certain physical class of objects would be secure. This was not the case. Instead, GRBs must have been associated with something faint or unseen. The enormity of the Universe and its bountiful constituents is a real shackle in this respect: in even the most empty directions looking out through our Galaxy, a single error box would contain tens of thousands of faint stars and tens of thousands of faint and distant galaxies. This amounted to a line up of culprits simply too big to get any significant traction on the question of distance and, ultimately, the origin of GRBs. Observing at gamma-ray wavelengths is just about the worst idea if the goal is to localize an event precisely. But if a counterpart at some other wavelength could be associated positively with a specific GRB, then the location of the GRB could be more precisely identified. The most credible counterpart would be an event, consistent with the GRB position, that seemed to happen at around the same time as the GRB—it is actually quite natural to expect that some energy should be pumped into channels other than gamma rays, but just how much energy and on what timescales that energy would emerge across the electromagnetic spectrum were not well known. As mentioned, no (visible-light) supernova counterparts were found by Klebesadel’s team during the early years of the field. And, despite several efforts in the 1970s and 1980s to discover a concurrent signal from radio to infrared to optical to X-ray wavelengths, no convincing counterparts were found. There was another possibility: if the “engine” (see §2.3) that produced the GRB had been active previously, then perhaps a transient counterpart could be found in the old image archives of the same place on the sky. Some tantalizing archival transients were indeed uncovered, but none proved robust under detailed scrutiny. 1.4 The March 5th Event and Soft-Gamma Ray Repeaters On March 5, 1979, an intense gamma-ray event triggered the IPN satellites distributed throughout the inner Solar System. Within the first tens of milliseconds, the event became so intensely bright that the detectors on board all nine satellites—even those pointing away from the event direction—saturated: photons arrived at such an appreciable rate that they could not be recorded fast enough. This blinding was only temporary, however, as for the next few minutes some detectors recorded a fading signal with an unusual character. Unlike all the other GRBs that had been seen to date, this decaying tail appeared to vary periodically. The fact that the initial pulse “turned on” so rapidly suggested that the size of the emitting surface was small, less than the size of the Earth. The eight-second periodicity in the signal was also an important clue for understanding the progenitor. In nature there are only a few classes of physical configurations that give rise to periodic brightness changes; of the most interest are the pulsations of an emitting surface, oscillations through an emitting object, and rotation. The natural (most physically simple) timescale for changes in pulsations and oscillations is the time t it takes for sound waves to cross the object, t ≈ l/cs (where l is the characteristic size of the object and cs is the speed of sound in the object). For rotation, that timescale is the period of the rotating object. Ordinary stars, like the Sun, have much longer sound-crossing times and rotation periods than eight seconds. On timing arguments alone, one is quickly pushed to consider a very dense (and hence large cs) and/or small object as the likely origin of such an event. (Continues…) Excerpted from WHAT ARE Gamma-Ray Bursts?by JOSHUA S. BLOOM Copyright © 2011 by Princeton University Press. Excerpted by permission of PRINCETON UNIVERSITY PRESS. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site. Read more

Reviews from Amazon users which were colected at the time this book was published on the website:

⭐Joshua S. Bloom’s What Are Gamma Ray Bursts is the second book in the Princeton University Press Frontiers in Physics Series. It shares the same concise and compact format as the earlier volume on the First Stars and Galaxies in the Universe, together with the same annoyingly small type face. It’s also very reasonably priced.Gamma Ray Bursts, first discovered as a side effect of a program to monitor the nuclear test ban treaty, are extraordinarily intense and very brief, with the duration of the gamma ray pulse being anything from less than a second to several seconds. During this time they are thousands of times brighter than a quasar and millions of times brighter than a supernova or a galaxy.Bloom traces the history of our understanding of this phenomenon, and discusses the physics believed to be involved in the phenomena. There are still many uncertainties, but it is generally believed that there at least three different types of GRBs. The so-called soft gamma ray repeaters are the least intense and most likely to be found nearby. They are believed to be neutron stars with exceptionally intense magnetic fields – magnetars – and their gamma rays are believed to be produced mostly from their rotational kinetic energy. A second type, producers of the briefest pulses, are thought to result from the mergers of two closely orbiting neutron stars. The most potent GRBs probably result from the spectacular death of a massive star, a so-called collapsar, with most of the mass of the star collapsing into a black hole while a small portion of the mass is expelled in ultra-relativistic polar jets.These last events seem to have happened mainly in the past. The most distant GRBs happened when the universe was relatively young, and the rate of occurrence seems to have declined rather steeply in the last seven billion years or so. It’s likely that there is a metallicity effect (metals being what astronomers call all the elements produced only in stars – everything except hydrogen and helium.)The book has significant technical content, but much of the discussion is at a level readily appreciated by astronomy fans with only a bit of physics training. Overall, a very good book, suitable for many readers, from amateur fan to physicists and astronomers specializing in other areas.

⭐This book is the second in Princeton’s series of monologues on exciting developments in physics. The series is aimed at the junior/senior physics undergraduate level with the exact level differing slightly from book to book. Loeb’s book is more dense and probably not suited for anyone who has not yet taken an undergraduate level course in Cosmology while Bloom’s book may be read by advanced amateur astronomers without too much trouble.I am reviewing this book as a graduate student in astrophysics studying AGN and Large-Scale Structure i.e. I don’t specialize in GRBS – the topic of the text. There is a lot of GRB phenomenology that I am completely unfamiliar with and that is where I find that the book excels – it presents to the reader an overview of the observational findings of the last 40 odd years in a concise and organized manner. I’d imagine that if I were a new graduate student looking to enter the field of GRBs, it’d be mandatory reading to bring me up to speed. So for the rest of us astronomers, it summarizes GRB phenomenology and gives a good overview of the current state-of-the-art in the theoretical understanding of GRBs in a nice small easily digested package.Hopefully, the book will get updated (rewritten?) every five-ten years as we learn more.

⭐I read the book cover to cover because of my interest in this topic. This is a hot topic and the author is an expert in the field. So, this should have been a great book. But the author’s writing style is not user friendly, at least, not for a regular physics fan (Just a fan, not a PHD).In a lot of places, I got frustrated with long, windy sentences. Most of my understanding came from the footnotes than what was written in the chapter. I suggest someone with a science journalism background edit this book for the second edition.Even the content could have been better. I did not get a good big picture of the field of GRB. For example, what is common among all GRBs? Is there anything common among all short GRBs? There are better articles available online, which provide a good overview of the state of this field.

⭐It is a nice comprehensive treatment, written at a second or third year undergraduate level, I guess. Someone with a real interest in astrophysics with less formal education could still get a lot from it, as could someone at a higher level who wanted a reasonably priced primer on the subject, in my opinion.My son is an astrophysics PhD student, studying magnetars, so I was particularly interested in those aspects of the book. But the whole thing was good – the writing was obviously by experts in the field, but still written in an engaging style.

⭐Average read.

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