The End of Days

Alerted by a supernova patrol, scientists have used NASA's Chandra X-ray Observatory to capture a rare glimpse of X-radiation from the early phases of a supernova.

From NASA/Marshall Media Relations.

Dec. 15, 1999: Through a combination of serendipity and skill, scientists have used NASA's Chandra X-ray Observatory to capture a rare glimpse of X-radiation from the early phases of a supernova, one of the most violent events in nature. Although more than a thousand supernovae have been observed by optical astronomers, the early X-ray glow from the explosions has been detected in less than a dozen cases.

Right: Supernova 1999em (the letters designate its sequence in the discoveries this year) appears just off the spiral arm of galaxy NGC 1637. Because the galaxy is not very bright in X-rays, the contours of the X-ray observation are superimposed on a negative image of the galaxy. Links to 2250x2045-pixel, 195KB JPG. Credit: NASA and Chandra Science Center.

The Chandra observations were made under the direction of a team of scientists from the Massachusetts Institute of Technology (MIT) in Cambridge, led by Walter Lewin and his graduate student, Derek Fox. When combined with simultaneous observations by radio and optical telescopes, the X-ray observations tell about the thickness of the shell that was blown off, its density, its speed, and how much material was shed by the star before it exploded.

Chandra observed an X-ray glow from SN1999em with the total power of 50,000 suns. Ten days later it observed the supernova for another nine hours, and found that the X-rays had faded to half their previous intensity. The optical luminosity, which had the brightness of 200 million suns, had faded somewhat less. No radio emission was detected at any time.

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With this information, the MIT group and their colleagues are already piecing together a picture of the catastrophic explosion. Observations by optical astronomers showed that SN1999em was a Type II supernova produced by the collapse of the core of a star ten or more times as massive as the sun.

Left: A close-up of the X-ray contours of SN 1999em. At 25 million light years, the supernova is still too small to appear as anything but a bright point even to Chandra. Credit: NASA and Chandra Science Center.

The intense heat generated in the collapse produces a cataclysmic rebound that sends high-speed debris flying outward at speeds in excess of 20 million miles per hour. The debris crashes into matter shed by the former star before the explosion. This awesome collision generates shock waves that heat expanding debris to three million degrees. The X-ray glow from this hot gas was detected by Chandra and gives astrophysicists a better understanding of the dynamics of the explosion, as well as the behavior of the doomed star in the years before the explosion.

"The combination of X-ray detection and radio non-detection is unusual, but may have less to do with the supernova and more to do with the great sensitivity of Chandra," said Roger Chevalier of University of Virginia, Charlottesville. Chevalier explained that the combined observations indicate that SN1999em shed a relatively small amount of matter before it exploded, compared to other supernovae observed in X-rays. The Chandra observation is important because it may represent a more common type of supernova.

The Chandra observation also provides an inside look at the hectic, exciting world of the international "quick response" network that scientists have set up to track and investigate supernovae.

On Friday, October 29, Alex Fillipenko of the University of California, Berkeley, notified Bob Kirshner at Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., that his automated supernova search project had a good candidate in a relatively nearby spiral galaxy, NGC 1637. Nearby in this case means about 25 million light years from Earth. Wei Dong Li, who is visiting Fillipenko's group from the Beijing Astronomical Observatory in China, called his colleagues in Beijing, who confirmed the supernova when the Earth rotated into a position to make viewing from China possible.

Left: A visible-light view of SN 1999em as seen by the 0.8-m Katzman Automatic Imaging Telescope of the Lick Observatory Supernova Search. Credit: Lick Observatory.

The astronomers also notified the International Astronomical Union's central bureau for astronomical telegrams in Cambridge, Mass., from which the discovery was broadcast worldwide. Radio astronomers Christina Lacey and Kurt Weiler at the Naval Research Laboratory in Washington, D.C., Schuyler van Dyk at the California Institute of Technology, Pasadena and Richard Sramek at the National Radio Astronomy Observatory's Very Large Array, Socorro, N.M., were alerted.

Kirshner then got in touch via e-mail with Harvey Tananbaum, director of the Chandra X-ray Center at Harvard-Smithsonian a little before 11 p.m. on Saturday night. The Chandra operations team replanned the telescope's observation activities and by Monday morning, and by Monday morning, Chandra was pointed at the supernova and observed it for about nine hours.

Lewin, who had been awarded the rights to Chandra's first observation of a nearby supernova, was ecstatic. "This is a unique chance that we have been hoping for!!!!" he wrote in an e-mail to Tananbaum.

The birth announcement. This IAU Circular notified the astrophysics community of 1999em.

SUPERNOVA 1999em IN NGC 1637
W. D. Li, University of California at Berkeley, on behalf of the Lick Observatory Supernova
Search, report the discovery, on an unfiltered CCD frame taken on Oct. 29.44 UT with the
0.8-m Katzman Automatic Imaging Telescope, of a supernova (mag about 13.5) located at
R.A. = 4h41m27s.04, Decl. = -2 51'45".2 (equinox 2000.0), which is 15".2 west and
25".1 north of the nucleus of NGC 1637. SN 1999em was confirmed at the Beijing Astronomical
Observatory on Oct. 29.7.  A KAIT image of the same field on Oct. 20.45 showed nothing
at the position of SN 1999em (limiting mag about 19.0).

"I was impressed by how rapid the Chandra response was, " said Kirshner.

"Supernovae expand quickly and cool quickly, so each day we delay observing the supernova it has changed irretrievably," Filippenko said. "We caught this really early, only a day or two after the explosion. We were lucky."

The Chandra observation was taken with the Advanced CCD Imaging Spectrometer (ACIS) on November 1 and 2, and 11 and 12, 1999 in two separate observations that lasted approximately nine hours each. ACIS was built by Pennsylvania State University, University Park, and MIT.

To follow Chandra's progress, visit the Chandra sites at: http://chandra.harvard.edu and http://chandra.nasa.gov.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program. TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.

High resolution digital versions of the X-ray image (JPG, 300 dpi TIFF) and other information associated with this release are available on the Internet at:

http://chandra.harvard.edu/photo/sn1999em/ or via links in http://chandra.harvard.edu

The Katzman Automatic Imaging Telescope at the Lick Observatory discovered SN 1999em.
Xrayastronomy.com, science news from the Chandra X-Ray Observatory
Chandra X-ray Observatory Center home page, with links to education, news, and technical pages.
Chandra news from Marshall Space Flight Center
Chandra Project Science is managed at NASA/Marshall, has links to individual instruments and the prime contractor.
X-ray astrophysics branch at NASA/Marshall conducts a broad range of research and technology work, as well as supporting the Chandra X-ray Observatory.

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