NASA Detects One Of Closest And Brightest Gamma Ray Bursts
The Universe clearly works weekends; delivering one of
the brightest and closest gamma ray bursts yet on Saturday,
March 29, at 6:37 a.m. EST.
NASA's High-Energy Transient Explorer (HETE) detected the
burst, signaling the birth of a black hole, in the
constellation Leo. For more than 30 seconds, the burst out
shone the entire Universe in gamma rays, and its afterglow
was still over a trillion times brighter than the Sun two
hours later. This was the brightest burst yet detected by
HETE and is in the top one percent of all bursts in terms of
intrinsic brightness. Within seconds, HETE nailed down a
location and subsequently relayed the coordinates to the
astronomy community, allowing hundreds of scientists and
amateur astronomers to join the observation, from Australia
to Finland and across the ocean to America. Observations
poured in as scientists attempted to unravel what
caused the burst. The burst was later identified with
a new supernova in a distant galaxy.
|Artist concept of the HETE spacecraft.
"This was our biggest one ever, and it didn't get away," said
Dr. George Ricker of the Massachusetts Institute of
Technology (MIT), Cambridge, Mass., and principal
investigator for the HETE mission. "With scores of
observations now completed and more on the way, we should get
a rather clear picture of what triggered this burst."
Gamma ray bursts are the most powerful explosions in the
Universe; likely caused by the death of a massive star, in
which the core implodes to form a black hole. Bursts appear
to occur randomly, and few last more than a minute, making
them hard to study.
HETE detects the fleeting gamma ray and X-ray portions of
these bursts, and its prompt localization enables scientists
to study the burst afterglow, which can linger from days to
weeks in optical light and radio waves. Most bursts originate
in the early universe, traveling upwards of 10 billion years
at light speed to reach us.
The burst on March 29 was named GRB 030329. Both the burst
and its afterglow were brilliant. The burst poured out a
thousand trillion, trillion times the gamma rays seen in a
solar flare. When measured more than one hour after the
burst, the afterglow was still about as bright as a 12th
magnitude star. This means it was only about 10 to 100 times
dimmer than what can be seen with the naked eye, visible with
backyard telescopes. At its peak, the afterglow may have been
visible to the naked eye.
The burst originated approximately two billion light years
from Earth, which is relatively close. The GRB 030329
redshift measurement was 0.168, making this the second
closest burst with a known redshift measurement. (Redshift is
a measurement of how light from distant regions of the
Universe is "shifted" to lower energy as the Universe
expands; the greater the redshift, the greater the distance
from Earth.) "Few amateur astronomers are treated to an
event that originated billions of light years away," said
Bruce Peterson and Paul Price of the Research School of
Astronomy and Astrophysics at the Australian National
University, Canberra, first identified the burst afterglow.
An automated telescope at Japan's RIKEN science institute
quickly confirmed the location. Finnish amateur astronomers
provided even tighter constraints on the properties of the
afterglow. Multiple observations enable a thorough study of
the burst environment.
|The GRB Coordinates Network (GCN) is a system that distributes locations of GRBs detected by spacecraft and distributes follow-up observation reports submitted by the GRB community.
Gamma ray burst hunters are aided by three new developments:
fast triggers from orbiting detectors; fast relays to
observers worldwide via the Gamma ray burst Coordinates
Network (GCN); and fast responses from ground-based robotic
telescopes. HETE is the first satellite to provide and
distribute accurate burst locations within seconds.
The GCN, developed and maintained at NASA's Goddard Space
Flight Center in Greenbelt, Md., serves as a gamma ray burst
hub. HETE signals the GCN, which sends out "phone calls" and
email messages to scientists and amateurs worldwide. The GCN
Web site also posts scientific information from the
astronomers making observations.
HETE was built by MIT as a mission of opportunity under the
NASA Explorer Program, with collaboration among U.S.
universities, Los Alamos, N.M. National Laboratory,
scientists and organizations in Brazil, France, India, Italy