New Supernova in the HST Frontier Field MACSJ0717.5+4745

ATel #5728; Gabriel Brammer (STScI), Patrick Kelly (UC Berkeley), Steve Rodney (JHU), Kasper Borello Schmidt (UC Santa Barbara), Tommaso Treu (UCSB), and the GLASS and FrontierSN Teams
on 7 Jan 2014; 03:26 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Gabriel Brammer (Brammer@stsci.edu)

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We report a supernova (SN) discovery in HST imaging of the Frontier Fields galaxy cluster MACSJ0717.5+3745 (z=0.5458) acquired as part of the Grism Lens Amplified Survey from Space (GLASS). The SN is designated HFF13cha (nicknamed "SN Chapel"), and was detected in WFC3-IR F105W (Y) and F140W (JH) images taken to calibrate and align the G102 and G141 grisms. A finder chart and the discovery images are available at http://archive.stsci.edu/pub/ffsn/macs0717/HFF13cha/snChapelHostFinder.pdf.

SN Coordinates: RA=07:17:32.781 DEC=+37:44:41.18

The SN is embedded in a host galaxy that has an F105W magnitude of 23.05 AB magnitude. The SN had ~24.4 AB mag (F105W) on Dec 24.80 and faded to ~24.8 AB mag on Dec 31.60.

The G102 grism spectrum shows a strong line consistent with H alpha emission with galaxy redshift of z=0.557. We estimate a photometric redshift z=0.55+0.021-0.115 (95%) of the host galaxy with EAZY (Brammer et al. 2008).

With the superfit (Howell et al. 2005) program, we model the observed grism spectra (8500 - 16500 A) as a linear combination of an underlying SN template and the EAZY host galaxy SED model that best reproduces the host broadband magnitudes. A fit using a Type Ia SN 1999ee spectrum near maximum light best reproduces the observed total spectrum as well as the relative SN and host galaxy fluxes, although we caution strongly that the grism spectrum has low S/N, and likely contains residual contamination from a nearby galaxy close to 8500 A and 11500 A.