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Discovery of a Supernova in HST imaging of the MACSJ0717 Frontier Field

ATel #5496; Steven A. Rodney (JHU), Jennifer Lotz (STScI), Louis-Gregory Strolger (STScI) and the Hubble Frontier Fields and FrontierSN teams
on 21 Oct 2013; 21:05 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Steven A. Rodney (rodney@jhu.edu)

Subjects: Optical, Supernovae

We report the discovery of a supernova (SN) in Hubble Space Telescope (HST) observations centered on the galaxy cluster MACSJ0717. It was discovered in the F814W (i) band of the Advanced Camera for Surveys (ACS), in observations that were collected as part of the ongoing HST Frontier Fields (HFF) program (PI:J.Lotz, HST PID 13498). The FrontierSN ID for this object is SN HFF13Zar (nicknamed "SN Zara"). Discovery images and a finder chart for spectroscopic follow-up may be downloaded from the FrontierSN public ftp site (link below).

The position of the SN in J2000 coordinates is :
07:17:24.931 +37:44:10.80
109.35388 37.736332

This locates the SN at 1.73 arcmin from the center of the cluster.

The SN is apparent in the F814W image taken on UT 2013 Oct17.9, and it is clearly absent in template images constructed from archival HST+ACS images taken in 2006 and prior. In the F814W discovery image the SN has a (Vega) magnitude of 23.53 +- 0.05.

There are three potential host galaxies within 5 arcsec of the SN. The following table gives for each host the J2000 coordinates in decimal degrees, the AB magnitudes in R and z bands, a photometric redshift from the CLASH team (A. Molino et al), projected distance from the SN position in arcsec, and the corresponding physical distance in kiloparsecs (assuming the photometric redshift is correct).

host       RA          Dec   R    z   photz   d"  d_kpc     
A   109.3537889 37.7355689  20.4 19.5  0.49  2.9  17.4 
B   109.3537579 37.7373075  18.9 18.3  0.03  3.4   2.0  
C   109.3539984 37.7367520  22.3 21.2  0.56  1.5   9.7 

Note that the redshift of the MACSJ0717 cluster is z=0.5458, so if this SN is in fact associated with host candidates A or B, then it is a foreground object. If associated with host candidate C, then it could plausibly be a SN from a galaxy in the outskirts of the cluster itself.

The next HST observations of this field will be in December, 2013, from the Grism Lens Amplified Survey from Space (GLASS), PI:Treu, HST program ID 13459.

This discovery is based on new observations for the Frontier Fields program using the NASA/ESA Hubble Space Telescope, which were made available by the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, and reduced by the STScI Frontier Fields implementation team. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

FrontierSN Discovery Images and Finder Chart