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ASAS-SN Discovery and Spectroscopic Confirmation of A Supernova in 2MFGC 04848

ATel #8217; S. Kiyota (Variable Star Observers League in Japan), J. Brimacombe (Coral Towers Observatory), R. A. Koff (Antelope Hills Observatory), J. S. Brown (Ohio State), D. Bersier (LJMU), 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), Subo Dong, Ping Chen (KIAA-PKU), G. Bock (Runaway Bay Observatory, Australia), E. Conseil (Association Francaise des Observateurs d'Etoiles Variables), W. Wiethoff (University of Minnesota, Duluth)
on 26 Oct 2015; 18:40 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 2MFGC 04848.

ASASSN-15sb was discovered in images obtained on UT 2015-10-23.34 at V~16.7 mag. We also detect the object in images obtained on UT 2015-10-10.32 (V~16.9), and UT 2015-10-24.31 (V~16.4). We do not detect (V>16.1) the object in images taken on UT 2015-10-09.26 and before. An image obtained on 2015-10-24 by S. Kiyota confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the S. Kiyota confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the S. Kiyota image.

The position of ASASSN-15sb is consistent with the center of the galaxy 2MFGC 04848 (z=0.022712, d=96.2 Mpc, via NED), giving an absolute V-band magnitude of approximately -19.4 (m-M=34.92, A_V=1.167). We obtained a follow-up optical spectrum (400-800 nm) of the transient on 2015-10-25 with the 2.0-m Liverpool Telescope (+ SPRAT) at the Roque de los Muchachos Observatory. According to the "SuperNova Identification" code (SNID; Blondin and Tonry 2007, ApJ 666, 1024), the spectrum is a good match to a normal Type Ia. 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-15sb  06:00:48.095   -15:23:57.26      2015-10-23.34      16.7          -19.4               N/A 
Obs. UT Date         V mag 
2015-10-09.26        >16.1 
2015-10-10.32         16.9 
2015-10-23.34         16.7 
2015-10-24.31         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.