Pre-outburst HST imaging of Gaia16cfr

ATel #9982; C. D. Kilpatrick, R. J. Foley, Y.-C. Pan (UCSC), P. J. Brown (Texas A&M University), A. V. Filippenko, D. Kasen (UC Berkeley), G. Folatelli (Universidad Nacional de La Plata), O. D. Fox (STScI), W. Hillenbrandt, S. Tauenberger (MPIA Garching), E. Hsiao (Florida State University), R. P. Kirshner, J. Parrent (Harvard), G. H. Marion, J. M. Silverman, J. C. Wheeler (UT Austin), P. Milne (University of Arizona), M. M. Phillips (Las Campanas Observatory), G. Pignata (Universidad Andres Bello), A. Riess (JHU), M. Kromer, R. Pakmor, F. Roepke (Heidelberg University and Heidelberg Institute for Theoretical Studies), I. Seitenzahl (Australian National University)
on 21 Jan 2017; 05:56 UT
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Credential Certification: Charles Kilpatrick (cdkilpat@ucsc.edu)

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We report imaging of the site of Gaia16cfr (ATel #9937, #9938) with HST/WFC3 from 2016 Jan 21 to 2016 Apr 9 as part of the HST GO program 13646 (PI=Foley). These images were taken starting 315 days before discovery by Gaia as reported by Gaia Alerts (http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia16cfr/). Images were obtained in twelve separate epochs 5-10 days apart, each consisting of 1x1260s exposure in UVIS F350LP and a single exposure in one other filter: in six epochs 1x1005.87s exposure in IR F160W, in three epochs 1x976s exposure in UVIS F555W, and in three epochs 1x976s exposure in UVIS F814W. We aligned these 24 images to stars in the field from Gaia DR1 and in all cases we detected a source within 2 pixels of the position of the source as reported by Gaia Alerts. On 2016 Jan 21, the brightness of the source was measured to be F350LP = 23.118+/-0.006 mag and F160W = 20.280+/-0.005 mag (VEGAMAG). Over the entire 79 day timescale, the source exhibited strong variability, with peak to peak brightness changes in F350LP of 1.8 mag. We transformed the HST apparent magnitudes to absolute magnitudes using the Riess et al. (2016, ApJ, 826, 56) distance m-M=31.51+/-0.05 to NGC 2442 (see also ATel #9938) and an extinction A_V=0.56 mag based on infrared dust maps from Schlegel, Finkbeiner & Davis (1998, ApJ, 500, 525) and Galactic extinction calibration from Schlafly & Finkbeiner (2011, ApJ, 737, 103). We find that the absolute magnitudes in F350LP (long pass centered near V) and F160W (H) are -8.9 and and -11.3, respectively. While these values are roughly consistent with findings in ATel #9938, the scale of variability suggests that the peak magnitude of the source associated with Gaia16cfr may be much closer to M_V=-10.3 mag reported for SN 2009ip (Foley et al. 2011, ApJ, 732, 32F).