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Discovery and Classification of HFF15Cru, a Type Ia Supernova in Abell 370

ATel #8545; M. L. Graham, I. Shivvers, A. V. Filippenko, P. Kelly (UC Berkeley); S. Rodney (U. of South Carolina); L. Strolger, G. Brammer, D. Coe (STScI); A. Molino (IAG-USP); O. Graur (NYU / AMNH); R. Foley (Illinois); M. Bradac (UC Davis); T. Matheson (NOAO); J. Hjorth, J. Selsing, L. Christensen (DARK); S. W. Jha (Rutgers); A. Zitrin (CalTech); B. Weiner (Arizona); K. Sharon (U. Michigan); C. McCully (LCOGT); K. Schmidt (AIP); X. Wang (UCLA); T. Treu (UCLA)
on 15 Jan 2016; 02:31 UT
Credential Certification: Melissa Lynn Graham (melissalynngraham@gmail.com)

Subjects: Optical, Supernovae

We report the discovery of a supernova (SN) in Hubble Space Telescope (HST) observations collected on 26 Dec. 2015 UT as part of the Frontier Fields survey. This SN is located at RA,Dec (J2000) = 02:39:52.55,-01:35:53.3, approximately 1.3' south of the center of galaxy cluster Abell 370 (z=0.375), and offset ~1" from its likely host galaxy, which has a photo-z consistent with the redshift of the cluster. The ID for this object is HFF15Cru (nicknamed "SN Crusher"). HFF15Cru is visible in optical F435W and F814W images from HST's Advanced Camera for Surveys (ACS) obtained on and after 24 Dec. 2015 UT, and reached a peak magnitude of 21.9 in F814W on 9 Jan. 2016 UT. We obtained a CCD spectrum (range 500-950 nm) of HFF15Cru and its host galaxy on 7 Jan. 2016 UT with DEIMOS on the 10-m Keck II telescope in good conditions (seeing ~0.6"). We extracted two apertures, one of the SN and one of its host galaxy, the latter appearing consistent with an early-type galaxy at the redshift of Abell 370. For the SN spectrum, we performed classification with Superfit (Howell et al, 2005, ApJ, 634, 119), and find a best fit to a normal Type Ia supernova near maximum light at the redshift of Abell 370. The light-curve shape and peak magnitude of HFF15Cru are consistent with its spectroscopic classification as a SN Ia in the cluster Abell 370. This discovery is based on new observations for the Hubble Frontier Fields program (HST PID: GO-13790) using the NASA/ESA Hubble Space Telescope, which were made available by the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.