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Supernova data rewards years of work

Years of hard work by MIT scientists at the Center for Space Research (CSR) paid off last week when orbiting astronomical observatories began to glean important information from a supernova discovered March 28 by an amateur optical astronomer in Spain.

The scientists, who are involved separately in international NASA collaborations with Germany and Japan, are:

  • Professor Walter H. G. Lewin of the Department of Physics, who with a colleague, Dr. Uli Zimmermann at the Max Planck Institute in Garching, Germany, is leading a team using the German/NASA Roentgen Satellite (ROSAT).
  • Dr. George R. Ricker, senior research scientist at the CSR, who is the US principal investigator for the X-ray CCD camera aboard the Japan/NASA Advanced Satellite for Cosmology and Astrophysics (ASCA).

ROSAT, on April 3, was the first satellite to observe X-ray emissions from the supernova.

Professor Lewin was delighted with the data. "This is going to give us a new page in the history of red supergiants," he said.

On April 5, the MIT-designed X-ray cameras aboard ASCA captured spectral data that will permit scientists to make the first accurate chemical analyses of heavy elements from the early days of a supernova explosion.

"Over the coming weeks to months, as the shocked material we are seeing begins to cool, it is very possible that the ASCA SIS (Solid State Imaging Spectrometer) may see the characteristic lines of the newly synthesized elements produced by the supernova explosion'turn on'-a very exciting prospect never before observed in the X-ray band," Dr. Ricker said.

The X-ray observations suggest that they are arising from extremely hot gas, with a temperature hotter than 100-million degrees. Scientists believe that the hot gas is created by the collision that occurs when the blast wave from the supernova explosion-hurtling outward at 13,000 km per second-overtakes the stellar wind that has emanated from the red supergiant for thousands of years at a more liesurely 10 km per second. Professor Lewin was in Washington Monday evening where he had been invited to give a talk at a meeting of the American Physical Society on the ROSAT observations.

Dr. Ricker's group was in contact throughout the holiday weekend with colleagues in Japan as ASCA continued its observations. Involved besides Dr. Ricker were Marshall W. Bautz, Geoffrey B. Crew and Steve E. Kissel, all of the CSR, and postdoctoral student Dr. Andrew Rasmussen, graduate student Keith Gendreau and undergraduate Lucas Maccri. They began the laborious process of precisely measuring the X-ray spectrum, as well as separating the X-rays from a previously known source in the M81 spiral galaxy where the supernova is located, about 10 million light years away from the Milky Way, just around the corner as space scientists figure distances.

Professor Lewin told MIT Tech Talk that as soon as he heard about the sighting of the supernova on March 30 he sent faxes to his colleagues in both Germany and Japan urging that ROSAT and ASCA begin observing the star.

Colleagues in Germany at first wanted to wait until April 12 to start observing with the preprogrammed ROSAT because no one expected to see X-rays immediately. But at Professor Lewin's insistance they finally decided to start as early as April 3. The news of the completely unexpected strong X-ray signal from supernova SN1993J reached Professor Lewin on April 4 at 3am. He was in his office where he was spending the night to await the news.

Before the latest supernova flare was discovered, members of the ASCA team were in the initial phases of putting their unique X-ray cameras into operation.

ASCA scientists had been looking at a 100,000-year-old supernova remnant in the Southern Hemisphere called Puppis A. Dr. Ricker said the detectors aboard the satellite use a powerful new photon counting and imaging X-ray spectrometer which not only can record X-ray images, but can at the same time measure the energy of individual X-ray photons.

A 10-minute trial observation of the remnant produced "a real-time spectrum of a quality never before seen" using only half the raw data the system detected, he said.

A version of this article appeared in the April 14, 1993 issue of MIT Tech Talk (Volume 37, Number 29).

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