Chandra Links Pulsar to Historic Supernova
New evidence from NASA's Chandra X-ray Observatory suggests that a
known pulsar is the present-day counterpart to a supernova that exploded in
386 AD, a stellar explosion witnessed by Chinese astronomers. If
confirmed, this will be only the second known pulsar to be clearly
associated with a historic event.
In roughly the past 2,000 years, less than 10 reports of probable
supernovae have been archived, mostly by Asian astronomers. Until now,
the Crab Nebula has been the only pulsar whose birth is associated with a
historic event, the supernova of 1054 AD, making it the only neutron star
with a firm age.
"Determining the true ages of astronomical objects is notoriously
difficult," said Victoria Kaspi of the McGill University, Montreal,
Canada, "and for this reason, historical records of supernova are of great
These results were presented on January 10, 2001 by Kaspi and Mallory
Roberts, also of McGill University, at the American Astronomical Society
meeting in San Diego, California. Also participating in the research were
Gautum Vasisht from NASA's Jet Propulsion Laboratory, Pasadena, California;
Eric Gotthelf from Columbia University, New York City; Michael Pivovaroff
from Thermawave, Inc., Fremont, California; and Nobuyuki Kawai from the
Institute of Physical and Chemical Research, Japan.
Scientists used Chandra to locate the pulsar exactly at the geometric
center of the supernova remnant known as G11.2-0.3. This location
provides very strong evidence that the pulsar, a neutron star spinning 14
times per second, was formed in the supernova of 386 AD, making it 1,615
Since pulsars move rapidly once they are formed, Chandra's ability to
pinpoint the pulsar at the remnant's center implies the system must be
very young. "We believe that the pulsar and the supernova remnant
G11.2-0.3 are both likely to be left over from the explosion seen by the
Chinese observers over 1,600 years ago," said Roberts. "While this is
exciting by itself, it also raises new questions about what we know about
pulsars, especially during their infancies."
These questions arose when the team of the Japanese Advanced Satellite
for Cosmology and Astrophysics (ASCA) applied the present spin rate to
current models to determine the pulsar's estimated lifetime and compared it
to the age of G11.2-0.3. The result was an age of roughly 24,000 years -
far predating the birth year of 386 AD. To explain this contradiction,
the Chandra team argues that this pulsar may have had approximately the
same spin rate today as it did at its birth. If true, this could have
important implications for conventional wisdom regarding pulsars, which
may be spinning more slowly than previously thought.
Between mid-April and mid-May in the year 386 AD, the sudden appearance
of a new star, presumably a supernova, was recorded by Chinese observers
in the direction of the sky now known as the constellation Sagittarius. In
the 1970s, radio astronomers discovered an expanding nebula of gas and
high-energy particles, called G11.2-0.3, believed to be the remnant of
that explosion. In 1997, a team of X-ray astronomers used ASCA to
discover a pulsar in the same area of the sky.
Chandra observed G11.2-0.3 with the Advanced CCD Imaging Spectrometer
at two points in time: August 6, 2000, and October 15, 2000, for
approximately 20,000 and 15,000 seconds respectively.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the
Chandra program. The Smithsonian's Chandra X-ray Center controls science
and flight operations from Cambridge, Massachusetts. In addition to
their appointments at McGill, Kaspi is also affiliated with the
Massachusetts Institute of Technology, Cambridge, and Roberts is a Quebec
Merit Postdoctoral Fellow. The National Science Foundation and NSERC
(Canada) also provided funding for this work.
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