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ASAS-SN Discovery of A Probable Supernova in 2MASX J20030163-2154516

ATel #7791; J. Brimacombe (Coral Towers Observatory), J. M. Fernandez (Observatory Inmaculada del Molino), G. Masi (Virtual Telescope Project, Ceccano, Italy), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. S. Brown, A. B. Danilet, 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), B. Nicholls (Mt. Vernon Obs., New Zealand), J. Nicolas (Groupe SNAUDE, France)
on 13 Jul 2015; 02:44 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 7802

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the quadruple 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered a new transient source, most likely a supernova, in the galaxy 2MASX J20030163-2154516.

ASASSN-15ml was discovered in images obtained on UT 2015-07-12.46 at V~16.9 mag. We do not detect (V>16.5) the object in images taken on UT 2015-06-29.43 and before. Images obtained by J. Brimacombe on UT 2015-07-12.67 with the CDK 43-cm telescope at Savannah Skies Observatory, by J. M. Fernandez on UT 2015-07-12.95 with a 20-cm Celestron C8 telescope at Observatory Inmaculada del Molina in Osuna, Spain, and by G. Masi on UT 2015-07-12.97 using the Virtual Telescope Project 17-inch Planewave telescope at Ceccano, Italy confirm the discovery of the transient. This figure shows the archival DSS image of the host (left) and the G. Masi confirmation image (right). The red circle has a radius of 3" and is centered on the position of the transient in the G. Masi image.

The position of ASASSN-15ml is approximately 3.3" North and 0.4" East from the center of the galaxy 2MASX J20030163-2154516 (z=0.018623, d=74.6 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.0 (m-M=34.36, A_V=0.495). 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-15ml  20:03:01.67   -21:54:48.25     2015-07-12.46      16.9          -18.0               3.32 
Obs. UT Date         V mag 
2015-06-29.43        >16.5 
2015-07-12.46         16.9 

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.