ATLAS17jiv: discovery of a bright supernova candidate in NGC 7187

ATel #10633; K. W. Smith, S. J. Smartt (Queen's University Belfast), D. E. Wright (University of Minnesota), J. Tonry, L. Denneau, B. Stalder, A. Heinze, H. Weiland (IfA, University of Hawaii), A. Rest (STScI)
on 11 Aug 2017; 16:44 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Ken Smith (k.w.smith@qub.ac.uk)

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ATLAS is a twin 0.5m telescope system on Haleakala and Mauna Loa. Both units are operational and are robotically surveying the sky. Two filters are used, cyan and orange (denoted c and o, all mags in AB system), more information on http://www.fallingstar.com. While carrying out the primary mission for NEOs, we search for and publicly report stationary transients (see Tonry et al. ATel #8680)

We report a new transient source, most likely a supernova in the galaxy NGC 7187. We discovered ATLAS17jiv (AT2017gah) on MJD 57975.49 == 2017-08-10.49 UTC at m_o = 15.69 +/- 0.03.

ATLAS17jiv is 43.56 arcseconds from the centre of NGC 7187 which is at z=0.008906 or d=33Mpc (from NED). Implying an absolute magnitude of M = -16.98 (assuming m-M = 32.6 and (A_r+A_i)/2 = 0.068). A summary of the transient's properties are summarised below. Follow up observations are encouraged. Forced photometry yielded a first 3.1sigma detection of o=18.47 on 57970.408, indicating the object is at least 5 days old.

 
Name      | ATLAS Name | RA (J2000)  | Dec (J2000) | Disc. MJD | Disc. Date  | Disc Mag 
AT2017gah | ATLAS17jiv | 22:02:42.43 | -32:47:33.4 | 57975.49  | 20170810.49 |  15.69 o         
 
Obs. MJD      mag  err  filter   
57970.408   18.47  0.30 o 
57970.415   18.32  0.24 o 
57975.495   15.69  0.03 o 
57975.503   15.71  0.03 o 
57975.505   15.72  0.03 o 
57975.511   15.74  0.04 o