Supernova Candidate in MACSJ1149 Galaxy Cluster Field With No Detected Host Galaxy

ATel #10005; Patrick L. Kelly (Berkeley), Jose Maria Diego (Cantabria), Mario Nonino (INAF), Adi Zitrin (Ben Gurion), Mathilde Jauzac (Durham), Alexei V. Filippenko (Berkeley)
on 25 Jan 2017; 20:10 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Patrick Kelly (pkelly@astro.berkeley.edu)

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We report discovery of a supernova (SN) candidate in the MACSJ1149 (z=0.54) galaxy-cluster field. In Hubble Space Telescope (HST) data taken on January 23, 2017 UT, we found a bright source (dubbed 'Amos') in WFC3 UVIS F606W (~23.3 mag AB) and WFC3 IR F110W (~23.7 mag) exposures. The candidate is also detected with a much fainter flux in imaging acquired on January 3, 2017, but absent from earlier data taken on December 5, 2016.

No host galaxy is detected at or near the SN coordinates in the F606W, F105W, and F160W coadditions of Hubble Frontier Field imaging of the galaxy cluster field. The candidate could be the explosion of a star in the intracluster medium (e.g., Graham et al. 2015, ApJ, 807, 13), although the MACSJ1149 intracluster light has low surface brightness near the SN location. Since the approximate limiting magnitude of the Frontier Field coadditions is M_r ~ -13 mag, the SN could instead be located in a low-luminosity cluster dwarf galaxy such as the recently discovered ultra-compact and ultra-diffuse cluster galaxies (e.g., Yagi et al. 2016, ApJS, 235, 11; Janssens et al.; arxiv:1701.00011). Alternatively, the SN host could be a faint and undetected galaxy in the cluster foreground or background.

The candidate's coordinates are RA, Dec = 177.402458, +22.388416 (J2000).

Link to finder chart

Preliminary AB photometry of the transient:

MJD FILTER MAG MAGERR
57776.681 F606W 23.33 0.05
57776.650 F110W 23.71 0.05
57756.918 F606W 26.10 0.14
57756.901 F125W 26.29 0.18
57727.037 F125W 26.63 3-sigma upper limit
57727.073 F160W 26.06 3-sigma upper limit