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ASAS-SN Discovery of A Probable Supernova in ESO 472-G018

ATel #8302; J. Brimacombe (Coral Towers Observatory), S. Kiyota (Variable Star Observers League in Japan), J. S. Brown (Ohio State), Subo Dong (KIAA-PKU), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, D. Godoy-Rivera, U. Basu (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Ping Chen (KIAA-PKU), G. Bock (Runaway Bay Observatory, Australia), B. Nicholls (Mt. Vernon Obs., New Zealand)
on 19 Nov 2015; 13:55 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 #: 8304

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the quadruple 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered a new transient source, most likely a supernova, in the galaxy ESO 472-G018.

ASASSN-15sx was discovered in images obtained on UT 2015-11-19.21 at V~16.4 mag. We also detect the object in images obtained on UT 2015-11-13.19 (V~17.2) and UT 2015-11-10.16 (V~17.4). We do not detect (V>17.4) the object in images taken on UT 2015-11-07.24 and before. An image obtained on 2015-11-19 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 5" and is centered on the position of the transient in the J. Brimacombe image.

The position of ASASSN-15sx is approximately 11.63" South and 2.01" West from the center of the galaxy ESO 472-G018 (z=0.034814, d=143 Mpc, via NED), giving an absolute V-band magnitude of approximately -19.4 (m-M=35.77, A_V=0.059). 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-15sx  00:12:14.366  -27:11:35.33      2015-11-19.21      16.4          -19.4               11.8 
Obs. UT Date         V mag 
2015-11-07.24        >17.4 
2015-11-10.16         17.4 
2015-11-13.19         17.2 
2015-11-19.21         16.4 

Follow-up observations are encouraged.

We thank LCOGT and its staff for their continued support of ASAS-SN. ASAS-SN is supported by NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the Robert Martin Ayers Sciences Fund. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.