FIRST-EVER INFRARED FLASH CHALLENGES OLD NOTION OF NATURE’S BIGGEST BANG

MAUNA KEA, Hawaii (May 11th, 2005) The W. M. Keck Observatory has helped confirm a big discovery by an unassumingly small robotic telescope in Arizona. The first infrared flash found during a gamma-ray burst, one of nature’s brightest explosions, looked much like a low energy version of the burst itself suggesting a common origin between the flash and the high-energy burst. This result challenges notions that only high energy gamma-rays could be produced during such an event. The results are discussed in the May 12 issue of Nature.

“This possibility of an infrared flash wasn’t discussed much in gamma-ray burst theory,” said Joshua Bloom, senior author of the paper announcing the results and astronomy professor at the University of California at Berkeley. “It’s like having a new look at an old friend. This flash in the infrared was very unexpected.”

Infrared light has been seen before in the hours to days following a gamma-ray burst, but that emission is thought to come from interactions with the material around the explosion site. But the quick work of a robotic telescope on the ground named the Peters Automated Infrared Imaging Telescope (PAIRITEL) helped astronomers “see” the infrared light concurrent with the gamma-ray bursting. Follow-up observations from the W. M. Keck Observatory measured the emission as it faded by an order of magnitude in the days following the blast.

“Results from the Keck telescopes are often added to data from other telescopes to form a more complete picture of an event,” said Dr. Frederic Chaffee, director of the W. M. Keck Observatory in Hawaii. “Just like a symphony orchestra, when all instruments play together, when data from multiple telescopes, each with its own capabilities, are combined, the result is greater than the sum of its parts.”

In just a few seconds, a gamma-ray explosion can liberate more energy than hundreds of billions of stars combined. An afterglow is created when the shock of the initial explosion impacts or heats up the surrounding material. Seeing afterglow effects from Earth requires astronomers to point their telescopes on the burst location in the hours to days after the burst occurs. Large infrared telescopes like those at the W. M. Keck Observatory are ideal for the study of gamma ray bursts and their environments because they can keep measuring the burst’s afterglow weeks to months after the afterglow fades to undetectable levels for other telescopes.

Cullen Blake, first year graduate student at Harvard University and first author on the paper, said “It’s very rewarding, to have worked so hard to get PAIRITEL ready for Swift, to catch a gamma-ray burst on the fly, and to have found such a remarkably bright flash.”

Robotic telescopes, such as the Peters Automated Infrared Imaging Telescope in Arizona are essential for studying gamma-ray bursts from the ground. PAIRITEL detected the gamma-ray burst just six minutes after the initial detection was made by the space satellite INTEGRAL on December 19, 2004. The burst was only the third gamma ray source bursts localized on board by the Burst Alert Telescope (BAT) on the NASA SWIFT space satellite, which was still in its commissioning phase on December 19th.

PAIRITEL was able to follow the source for three nights after the gamma-ray burst until it faded to undetectable levels. The Keck telescopes picked up where PAIRITEL left off: Two nights of Keck observations combined with the PAIRITEL exposures provide a complete time history of the afterglow. The results show a burst that brightens, and then very rapidly fades after just nine minutes. Eleven minutes later, the burst re-brightens, and gradually fades away again over the following days.

Matching the light curve to well-understood physical processes, the team suggests that the burst had both a forward and reverse shock at later times, which left the origin of the initial flash a mystery. The authors concluded that the initial flash must have been due to the internal shock, the process that creates the burst itself.

Writing up the results of the infrared flash during the December holidays, Bloom was determined to get the results out quickly. The only catch: he was on a family cruise in the Atlantic Ocean during the critical first week after the burst. “It was bizarre—writing a paper, paying $50 per hour for Internet connectivity while being blasted by Jingle Bell Rock from the Lido Lounge.” Bloom then mused, “I’d do it all over again.”

The team responsible for the observations include Bloom and Kevin Hurley of the University of California, Berkeley, Cullen Blake of Harvard College Observatory, Emilio Falco and Andrew Szentgyorgyi of the Smithsonian Astrophysical Observatory, Mike Skrutskie of the University of Virginia, Ed Fenimore and Kass McClean of Los Alamos National Labs, Gaspard Duchene of Laboratoire d’Astrophysique de Grenoble, France, Andrea Ghez, Seth Hornstein and Quinn Konopacky of the University of California, Los Angeles, Jason Prochaska of the University of California, Santa Cruz; Caer McCabe and Karl Stapelfeldt of the Jet Propulsion Laboratory; Randy Campbell, Marc Kassis and Fred Chaffee of the W. M. Keck Observatory, Dan Starr of Gemini North Observatory, Neil Gehrels, Scott Barthelmy, Jay R. Cummings, Derek Hullinger, Hans Krimm, Craig Markwardt, Ann Parsons and Jack Tueller of NASA.

Funding for the project was provided by the Harvard Milton Fund and the Smithsonian Institution. The W. M. Keck Observatory was made possible through a generous grant from the W. M. Keck Foundation and is operated by the California Association for Research in Astronomy, a non-profit scientific partnership of the California Institute of Technology, the University of California, and NASA. On the Web at www.keckobservatory.org.