Swift XRT Detection of Supernova 2008ij in X-Rays

ATel #1918; S. Immler (NASA/CRESST/GSFC), D. Pooley (University of Wisconsin), P. J. Brown (PSU), and P. Milne (U of Arizona), on behalf of the Swift satellite team
on 28 Jan 2009; 18:13 UT
Credential Certification: Stefan Immler (immler@milkyway.gsfc.nasa.gov)

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Using 12 epochs of Swift X-Ray Telescope (XRT) observations of the Type II SN 2008ij in NGC 6643 (CBET #1626, #1628; ATel #1917), obtained between 2008-12-23 and 2009-01-27 (45.1 ks exposure time), an X-ray point-source is detected at the position of the SN, with a 3.1-sigma significance of source detection. The PSF, dead-time, and vignetting corrected XRT net count rate is (3.6+/-1.1)E-04 cts/s, corresponding to an unabsorbed (0.2-10 keV band) X-ray flux of (1.9+/-0.6)E-14 erg/cm/cm/s and a luminosity of (1.0+/-0.3)E39 erg/s for an adopted thermal plasma spectrum with a temperature of kT = 10 keV, a Galactic foreground column density of N_H = 5.56E+20 (Dickey & Lockman, 1990, ARAA 28) and a distance of 21 Mpc (z=0.004950, Haynes et al., AJ 115, 62; H_o = 71 km/s/Mpc, Omega_M = 1/3, Omega_L = 2/3).

Over the course of the Swift XRT observations, the X-ray source continuously faded from 1.6E39 erg/s to 6.7E38 erg/s (0.2-10 keV).

No X-ray source is visible at this position in deep (329 ks exposure time) pre-SN Swift XRT observations obtained between 2008-04-04 and 2008-10-17, or in a pre-SN Chandra ACIS-S observation (9.4 ks) obtained on 2008-06-23.

Due to the positional coincidence, fading of the X-ray source, and the lack of X-ray emission from that position in the pre-SN Swift XRT and Chandra ACIS-S images, we conclude that the X-ray emission is due to the SN, likely from the interaction of the SN shock with circumstellar material from a strong stellar wind of the progenitor.

A Chandra and additional Swift observations are scheduled.