ASAS-SN Discovery of A Probable Supernova in SDSS J132112.88+401556.7

ATel #7698; J. M. Fernandez (Observatory Inmaculada del Molino), G. Masi (Virtual Telescope Project, Ceccano, Italy), J. S. Brown, T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, 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), J. Brimacombe (Coral Towers Observatory), E. Falco (CfA), P. R. Wozniak (LANL), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), E. Conseil (Association Francaise des Observateurs d'Etoiles Variables), S. Kiyota (Variable Star Observers League in Japan), J. Nicolas (Groupe SNAUDE, France)
on 23 Jun 2015; 16:56 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

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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 SDSS J132112.88+401556.7.

ASASSN-15lu was discovered in images obtained on UT 2015-06-20.32 at V~17.1 mag. We also detect the object in images obtained on UT 2015-06-22.33 (17.1) and on UT 2015-06-23.26 (17.0). We do not detect (V>17.6) the object in images taken on UT 2015-06-16.30 and before. Images obtained by J. M. Fernandez on UT 2015-06-20.93 with a 20-cm Celestron C8 telescope at Observatory Inmaculada del Molina in Osuna, Spain and by G. Masi on UT 2015-06-20.96 using the Virtual Telescope Project 17-inch Planewave telescope at Ceccano, Italy confirm the discovery of the transient. This figure shows the archival SDSS g-band image of the host (left) and the G. Masi confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the G. Masi image.

The position of ASASSN-15lu is approximately 0.3" South and 0.2" East from the center of the starbust galaxy SDSS J132112.88+401556.7 (z=0.035037, d=151 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.8 (m-M=35.89, A_V=0.044). 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-15lu  13:21:12.90    +40:15:56.44      2015-06-20.32      17.1          -18.8               0.36 

 
Obs. UT Date         V mag 
2015-06-16.30        >17.6 
2015-06-20.32         17.1 
2015-06-22.33         17.1 
2015-06-23.26         17.0 

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.