Pre-Explosion Chandra Observations of PTF11kly

ATel #3589; Alicia Soderberg, Jifeng Liu, Pat Slane (Harvard/CfA)
on 25 Aug 2011; 19:35 UT
Credential Certification: Alicia M. Soderberg (asoderberg@cfa.harvard.edu)

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Following the report of the probable Type Ia supernova in M101, PTF 11kly (ATEL #3581), we searched a merged dataset of archival Chandra observations for a pre-explosion X-ray source associated with the progenitor system. The merged dataset is presented in recent paper, "Chandra ACIS Survey of X-ray Point Sources in 383 Nearby Galaxies" (Liu, ApJS, 192,10, (2011)) and the associated catalog reveals no point sources coincident with the optical SN position in archival M101 data. Using this merged dataset, we find that the effective Chandra exposure time at the optical SN position is 226 ksec after correcting for vignetting. For a supersoft source with temperature 300 eV, 1 cps corresponds to 4.4e-12 erg/s/cm^2 (0.3-8 keV) assuming a foreground absorption of nH=1.2e20 cm^-2. Adopting an upper limit of 5 cnts, this non-detection corresponds to an upper limit on the X-ray luminosity of L_X < 5e35 erg/s assuming a distance of 6.4 Mpc (Shappee & Stanek 2011). Assuming a lower effective temperature of 100 eV, we derive an upper limit of L_X < 1e36 erg/s. These limits are broadly consistent with that reported in ATEL #3587 and lie within the range of values observed for typical supersoft sources, ~1e34-36 erg/s (e.g., Di Stefano 2010).