ASAS-SN Discovery of A Probable Supernova in An Unknown Redshift Galaxy 2MASX J17210913+2534558

ATel #7536; J. Brimacombe (Coral Towers Observatory), K. Z. Stanek, T. W.-S. Holoien, C. S. Kochanek, J. S. Brown, A. B. Danilet, G. Simonian, U. Basu, N. Goss, 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)
on 19 May 2015; 18:31 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Krzysztof Stanek (stanek.32@osu.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 2MASX J17210913+2534558.

ASASSN-15jm was discovered in images obtained on UT 2015-05-19.41 at V=17.1, and it was also marginally detected on UT 2015-05-13.46 at V=17.6. It was not detected in images obtained on UT 2015-05-11.37 (V>17.1). An image obtained by J. Brimacombe on UT 2015-05-19T17:20 using a 33-cm telescope at Savannah Skies Observatory, Australia, confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the confirmation image (right). The red circle has a radius of 2" and is centered on the position of the transient in the J. Brimacombe image.

The position of ASASSN-15jm is approximately 1.3" from the center of the galaxy 2MASX J17210913+2534558, clearly a spiral galaxy in SDSS images, but with an unknown redshift. Properties of the new source are summarized in the table below:

 
Object       RA (J2000)     DEC (J2000)    Disc. UT Date   Disc. V mag  Approx. Abs. Mag   Offset from Host (") 
ASASSN-15jm  17:21:09.189   25:34:55.50     2015-05-19.41    17.1            ---               1.3 

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.