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Evidence for X-ray emission from the type Ia SN PTF11kly

ATel #3592; Derek B. Fox (Penn State)
on 26 Aug 2011; 00:18 UT
Credential Certification: Derek B. Fox (dfox@astro.psu.edu)

Subjects: Radio, Optical, Ultra-Violet, X-ray, Supernovae, Transient

Referred to by ATel #: 3593

I have analyzed the first 4.5 ksec of Swift XRT observations of PTF11kly (ATEL #3581), also reported by Margutti & Soderberg (ATEL #3584). I correct the Swift native astrometry using the Chandra point source catalog of Liu (2011, ApJS, 192, 10), using seven detected XRT sources, and finding a correction of (dRA, dDec) = (-0.1", -3.6") to the Swift native coordinates. Within a 5" aperture centered on the location of PTF11kly I find a single detected X-ray photon, where 0.11 +/- 0.02 photons would be expected on the basis of background estimates. Given the absence of any source at this position in deep Chandra preimaging (Liu 2011; see also ATELs #3587, #3589), this detection provides 90%-confidence level evidence of X-ray emission from PTF11kly.

The inferred count rate of ~2.2 cts ksec^-1 falls below the quoted upper limit of 4 cts ksec^-1 from ATEL #3584 and is not in conflict with that report. Assuming a photon index alpha=2 spectrum, the source X-ray flux would be ~7.6e-14 erg cm-2 s-1 (0.3-10 keV), and the X-ray luminosity at M101 would be ~3.8e+38 erg s-1 (0.3-10 keV). This luminosity may be compared to that of the only type Ia SN previously thought to be detected in X-rays, SN 2005ke, which had a >3-sigma detection and estimated L_X = (2 +/- 1)e+38 erg s^-1 in Swift observations over 1 to 54 days after explosion (Immler et al. 2006, ApJL, 648, L119).

If this X-ray excess represents X-ray emission from PTF11kly, a point source should be detectable with several days' continued monitoring with Swift.