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Analysis of the archival HST images of PTF11kly in M101

ATel #3582; Weidong Li (UCB), Peter Nugent (LBL/UCB), Josh Bloom (UCB), and Alex Filippenko (LBL/UCB) report on behalf of a large collaboration:
on 25 Aug 2011; 03:51 UT
Credential Certification: Weidong Li (weidong@astron.berkeley.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 3584, 3585, 3623

We have analyzed the discovery images of PTF11kly, a probable very young Type Ia supernova, reported by Nugent et al. (ATEL #3581) and performed astrometric solutions to match archival images (Program ID: 9490) taken by the Advanced Camera for Surveys (ACS) with the Hubble Space Telescope (HST) in November 2002. We were able to locate the supernova position on the ACS images to an uncertainty of 58 mas (1 sigma). A figure on the site of PTF11kly in the ACS/F435W, F555W, and F814W filters is shown at http://astro.berkeley.edu/~weidong/m101sn.gif

Each section is 5" x 5" with North is up and East to the left. The circles have a radius of 348 mas which is 6 times the 1 sigma error radius of our astrometric solution. No object is visible at the nominal position of the SN. We note, however, the presence of two sources (marked as "1" and "2") within roughly the 2 x 1 sigma uncertainty of our solution. These two sources appear rather red: they are clearly detected in the F814W image, only marginally detected in F555W, and not detected in F435W. High-resolution imaging should improve our astrometric solution, and help investigate whether these two red sources are related to PTF11kly. Further analysis of the photometry and upper limits of the images is in progress.