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ASAS-SN Discovery of A Probable Supernova in 2MASX J21291986-2305268

ATel #8345; J. Brimacombe (Coral Towers Observatory), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. S. Brown, 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), I. Cruz (Cruz Observatory), S. Kiyota (Variable Star Observers League in Japan)
on 29 Nov 2015; 16:15 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 #: 8356

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 J21291986-2305268.

ASASSN-15tf was discovered in images obtained on UT 2015-11-29.04 at V~17.1 mag. We also detect the object in images obtained on UT 2015-11-27.05 (V~16.9), UT 2015-11-21.07 (V~16.9), and UT 2015-11-16.08 (V~16.6). We do not detect (V>17.6) the object in images taken on UT 2015-11-14.08 and before. An image obtained by J. Brimacombe on UT 2015-11-29.45 with the RCOS 41-cm telescope near Siding Spring Observatory 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-15tf is approximately 12.2" South and 6.2" East from the center of the galaxy 2MASX J21291986-2305268 (z=0.035288, d=145 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.8 (m-M=35.80, A_V=0.131). 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-15tf  21:29:20.31    -23:05:39.48      2015-11-29.04      17.1          -18.8               13.69 
 
Obs. UT Date         V mag 
2015-11-14.08        >17.6 
2015-11-16.08         16.6 
2015-11-21.07         16.9 
2015-11-27.05         16.9 
2015-11-29.04         17.1 

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.