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Candidate Progenitor of the Type II SN 2012A in the Near-IR

ATel #3863; J. L. Prieto (Princeton/Carnegie), D. Osip, P. Palunas (Las Campanas Observatory)
on 13 Jan 2012; 15:11 UT
Credential Certification: Jose L. Prieto (jose@obs.carnegiescience.edu)

Subjects: Infra-Red, Optical, Supernovae

Referred to by ATel #: 3956, 4066

We report a candidate progenitor detection for the nearby type II SN 2012A in NGC 3239 (CBET #2974, #2975, ATEL #3855, #3857, #3860, #3861). We retrieved pre-explosion images of NGC 3239 from the Gemini archive (PID GN-2006A-DD-2; PI P. Michaud) obtained in May 2006 with the NIRI instrument mounted on the Gemini North telescope. The set of images include dithered 20x30s exposures obtained with the NIRI f/14 camera (1024x1024 ALADDIN array; 0.05"/pixel) and the Kprime filter under excellent conditions. After standard reductions with IRAF gemini package we obtained a coadded image of 420s using the best 14 exposures and FWHM = 0.15-0.2" for point sources. In order to locate the site of the SN in the deep Gemini pre-explosion image, we observed SN 2012A in the Ks filter with the FourStar near-IR camera (4 1024x1024 HAWAII arrays; 0.16"/pixel) mounted on the Magellan I (Baade) telescope at Las Campanas Observatory on UT Jan 12.3. The FourStar images were combined in sets of ~5min coadds, also from dithered exposures, and for the analysis reported here we use only one such coadd with 0.3-0.4" seeing.

We registered the Gemini/NIRI and Magellan/FourStar images using 10 common sources and found a geometric transformation with the geomap task in IRAF. The total rms of the transformation is 0.028". We identify a point source at the SN position in the pre-explosion Gemini image within this error circle, a candidate progenitor of SN 2012A. Here we show the pre-explosion (left) and post-explosion (right) images. The red stars are the sources used for relative astrometry and the blue circle (radius = 0.55", 20x the rms of the coordinate transformation) marks the position of the candidate progenitor (left) and SN 2012A (right). We note that the progenitor is located in a fairly isolated region, in the outskirts of a large star-forming region that contains many bright stars and resolved clusters.

A preliminary photometric analysis using PSF/Daophot photometry gives K = 20.1 +/- 0.2 mag for the candidate progenitor (K=13.42 +/- 0.05 mag for SN 2012A now), calibrated using 2MASS stars in the field. This magnitude corresponds to MK = -9.4 +/- 0.5 mag using a distance modulus of 29.53 +/- 0.4 mag for the host galaxy NGC 3239 (via NED). This is consistent with the K-band absolute magnitudes of detected red-supergiant (RSG) progenitors of some nearby type IIP supernovae (e.g., Mattila et al. 2008, ApJ, 688, L91) and in the low-end of the absolute magnitude distribution of RSGs in the Magellanic Clouds (Levesque et al. 2006, ApJ, 645, 1102). We also inspected SDSS DR8 ugriz images of NGC 3239 obtained in 2005, which rule out (mag > 20-22) a bright optical detection for the progenitor. This is expected if the progenitor was a red source like a RSG, but more detailed analysis is needed to put limits on the colors of the candidate progenitor.

Candidate Progenitor of SN 2012A in K-band images