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ASAS-SN Discovery of A Probable Supernova in GALEXASC J032107.24-311845.8

ATel #7912; J. Brimacombe (Coral Towers Observatory), J. S. Brown, T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, G. Simonian, U. Basu, J. F. Beacom, T. A. Thompson (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong (KIAA-PKU), E. Falco (CfA), P. R. Wozniak (LANL), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), S. Kiyota (Variable Star Observers League in Japan), G. Masi (Virtual Telescope Project, Ceccano, Italy)
on 14 Aug 2015; 20:13 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (brown@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 7932

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the double 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered a new transient source, most likely a supernova, in the galaxy GALEXASC J032107.24-311845.8.

ASASSN-15og was discovered in images obtained on UT 2015-08-13.29 at V~16.8 mag. We do not detect (V>16.4) the object in images taken on UT 2015-07-31.37 and before. An image obtained on 2015-08-14 by J. Brimacombe confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the J. Brimacombe confirmation image (right). The red circle has a radius of 3" and is centered on the position of the transient in the J. Brimacombe image.

The position of ASASSN-15og is approximately 0.98" South and 0.73" East from the center of the galaxy GALEXASC J032107.24-311845.8 (z=0.06831, d=293 Mpc, via NED), giving an absolute V-band magnitude of approximately -20.6 (m-M=37.33, A_V=0.036). Properties of the new source and photometry are summarized in the tables below:

Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. V mag  Approx. Abs. Mag   Offset from Host (") 
ASASSN-15og  03:21:07.437    -31:18:45.64      2015-08-13.29      16.8          -20.6               1.22 
Obs. UT Date         V mag 
2015-07-31.37        >16.4 
2015-08-13.29         16.8 

Follow-up observations are encouraged.

We thank LCOGT and its staff for their continued support of ASAS-SN. ASAS-SN is supported in part by Mt. Cuba Astronomical Foundation. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.