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Swift XRT Detection of Supernova 2008ax in X-Rays

ATel #1420; S. Immler (NASA/CRESST/GSFC), on behalf of the Swift satellite team
on 11 Mar 2008; 03:03 UT
Credential Certification: Stefan Immler (immler@milkyway.gsfc.nasa.gov)

Subjects: X-ray, Supernovae

Using three epochs of Swift X-Ray Telescope (XRT) observations of SN 2008ax (ATel #1412, #1417, CBET #1280, #1285, #1286, #1290) obtained between 2008-03-04.67 UT and 2008-03-10.56 UT (18 ks exposure time), an X-ray point-source is detected at the position of the SN, with a 3.8-sigma significance of source detection. The PSF, dead-time, and vignetting corrected XRT net count rate is (2.0+/-0.5)E-03 cts/s, corresponding to an unabsorbed (0.2-10 keV band) X-ray flux of (1.0+/-0.3)E-13 erg/cm/cm/s and a luminosity of (7.7+/-1.9)E38 erg/s for an adopted thermal plasma spectrum with a temperature of kT = 10 keV, a Galactic foreground column density of N_H = 1.78E+20 (Dickey & Lockman, 1990, ARAA 28) and a distance of 8 Mpc (z=0.001885, NED; H_o = 71 km/s/Mpc, Omega_M = 1/3, Omega_L = 2/3). The count rate, flux, and luminosity are corrected for contamination with the PSF wings of a nearby (28 arcsec) ultra-luminous X-ray source. We note that the position of the XRT X-ray source is 5.4 arcsec offset from a weak X-ray source that is visible in Chandra ACIS-S observations obtained on 2000-11-03, 2004-07-30, and 2004-11-20. Given the offset, it is unlikely that the Chandra X-ray source accounts for the X-ray flux observed by XRT or that the Chandra X-ray source represents the binary progenitor system of SN 2008ax.

Additional Swift observations are scheduled.