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ASAS-SN Discovery of A Probable Supernova in 2MASX J05395948-8022191

ATel #8469; J. S. Brown, K. Z. Stanek, T. W.-S. Holoien, 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), Subo Dong, Ping Chen (KIAA-PKU), J. Brimacombe (Coral Towers Observatory)
on 28 Dec 2015; 18:32 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (brown@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

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 2MASX J05395948-8022191.

ASASSN-15um was discovered in images obtained on UT 2015-12-28.19 at V~16.0 mag. We also detect the object in images taken on 2015-12-25.06 (V~16.2), 2015-12-23.20 (V~16.6), and 2015-12-20.11 (V~16.86). We do not detect (V>17.5) the object in images taken on UT 2015-12-15.23 and before. This figure shows the archival DSS image of the host (left), the ASAS-SN V-band reference image (middle), and the ASAS-SN subtraction image (right). The red circle has a radius of 5" and is centered on the position of the transient in the subtraction image.

The position of ASASSN-15um is approximately 3" South and 15" East from the center of the galaxy 2MASX J05395948-8022191 (no redshift information available from NED). 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-15um  05:40:05.191  -80:22:22.63      2015-12-28.19      16.0         N/A              15.3 
Obs. UT Date         V mag 
2015-12-15.23        >17.57 
2015-12-20.11         16.86 
2015-12-23.20         16.61 
2015-12-25.06         16.22 
2015-12-28.19         16.03 

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.