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ASAS-SN Discovery of A Probable Nearby Supernova in 2MASX J15333488-7807258

ATel #7444; B. J. Shappee (Hubble Fellow, Carnegie Observatories), Subo Dong (KIAA-PKU), K. Z. Stanek, T. W.-S. Holoien, C. S. Kochanek, A. B. Danilet, G. Simonian, U. Basu, N. Goss, J. F. Beacom, T. A. Thompson (Ohio State), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), P. R. Wozniak (LANL), E. Falco (CfA), J. Brimacombe (Coral Towers Observatory), D. Szczygiel, G. Pojmanski (Warsaw University Observatory)
on 25 Apr 2015; 06:10 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Benjamin Shappee (bshappee@obs.carnegiescience.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 7458

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the double 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered a new transient source, most likely a supernova, in the galaxy 2MASX J15333488-7807258.

ASASSN-15hs was discovered in images obtained on UT 2015-04-24.18 at V~16.6 mag. We also detect the object in images obtained on UT 2015-04-17.26 (V~17.1), 2015-04-19.22 (V~16.9), 2015-04-23.15 (V~16.8), and 2015-04-23.17 (V~16.9). We do not detect (V>16.9) the object in images taken on UT 2015-04-17.18 and before. A g-band image obtained on UT 2015-04-25.10 with the LCOGT 1-m robotic telescope in Sutherland, South Africa confirms the discovery of the transient. This figure shows the ASAS-SN reference image (bottom-left), archival DSS image of the host (bottom-right), ASAS-SN discovery difference image (top-left), and the LCOGT confirmation image (top-right). The red circle has a radius of 2" and is centered on the position of the transient in the LCOGT image.

The position of ASASSN-15hs is approximately 1.7" North and 2.2" East from the center of the galaxy 2MASX J15333488-7807258 (z=0.0.009096, d=35.1 Mpc, via NED), giving an absolute V-band magnitude of approximately -16.6 (m-M=32.94, A_V=0.297). 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-15hs  15:33:34.31   -78:07:23.46     2015-04-24.18      16.6          -16.4               2.7" 
Observation Date     V mag 
2015-04-15.25       >16.7   
2015-04-17.18       >16.9   
2015-04-17.26        17.1  0.2 
2015-04-19.22        16.9  0.1 
2015-04-23.15        16.8  0.2 
2015-04-23.17        16.9  0.1 
2015-04-24.18        16.6  0.1 

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.