* Astronomy

DISCOVERY OF X-RAY EMISSION FROM SUPERNOVA 1970G WITH Chandra:
FILLING THE VOID BETWEEN SUPERNOVAE AND SUPERNOVA REMNANTS

Chandra observations of the oldest supernova, (SN 1970G), discovered using X-ray technologies, lead astronomers to think that we might be watching a star in the transition phase between its old life as a giant blue star that went supernova, and its new life as a type II supernova remnant.


Position(2000): RA 14 : 03.2, Dec +54 : 21

In paper entitled "Discovery of X-Ray Emission from Supernova 1970G with Chandra" Stefan Immler of NASA's Goddard Space Flight Centre and K.D. Kuntz of John Hopkins University report that, "As the oldest SN detected in X-rays, SN 1970G allows, for the first time, direct observation of the transition from a SN to its supernova remnant (SNR) phase"

ABSTRACT:
We report on the discovery of X-ray emission from SN 1970G in M101, 35 years after its outburst, using deep X-ray imaging with the Chandra X-ray observatory. The Chandra ACIS spectrum shows that the emission is soft ((_ 2 keV) and characteristic for the reverse shock region. The X-ray luminosity, L0.3.2 = (1.1 ± 0.2) × 1037 ergs s.1, is likely caused by the interaction of the supernova (SN) shock with dense circumstellar matter. If the material was deposited by the stellar wind from the progenitor, a mass-loss rate of ÿ M = (2.6 ± 0.4) × 10.5 M⊙ yr.1 (vw/10 km s.1) is inferred.
Utilizing the high-resolution Chandra ACIS data of SN 1970G and its environment, we reconstruct the X-ray lightcurve from previous ROSAT HRI, PSPC, and XMM-Newton EPIC observations, and find a best-fit linear rate of decline of L / t.s with index s = 1.7 ± 0.6 over a period of 12–35 years after the outburst. As the oldest SN detected in X-rays, SN 1970G allows, for the first time, direct observation of the transition from a SN to its supernova remnant (SNR) phase.

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"The measured mass-loss rate for SN 1970G is similar to those inferred for other Type II SNe, which typically range from 10-5 to 10-4 solar masses per year. This is indicative that the X-ray emission arises from shock-heated CSM deposited by the progenitor rather than shock-heated ISM, even at this late epoch after the outburst."

"Supernovae usually fade away quickly in the near aftermath of their explosion as the shock wave reaches the outer boundaries of the stellar wind, which becomes thinner and thinner. A few hundred years later, however, the shock runs into the interstellar medium, and produces copious X-ray emission due to the high densities of the ISM. Measurements of the densities at the shock front of 1970G showed that they are characteristic of stellar winds, which are more than an order of magnitude smaller than the densities of the ISM." - Stefan Immler.

SN1970G was observed with the Chandra observatory as part of the 1 Ms observation of the host galaxy M101 (also known as the Pinwheel Galaxy) from July 5–11, 2004. It lies 22 million light-years away in the constellation Ursa Major.
http://www.nhn.ou.edu/~cowan/research/


Three supernovae have been discovered in M101: The first one, SN 1909A, appeared on Jan 26, 1909 and was discovered by Max Wolf; it was of peculiar type and reached mag 12.1 (Glyn Jones reports that the discovery took place in February, and the SN reached only mag 13.5).
The second supernova 1951H was of type II, occurred in September 1951 and reached mag 17.5, while the third, SN 1970G, also type II, occurred on Jul 30, 1970 and reached mag 11.5.


-- Edited by Blobrana at 12:44, 2005-06-10