ASAS-SN Discovery of A Probable Supernova in APMUKS(BJ) B215839.70-615403.9

ATel #7642; B. Nicholls (Mt. Vernon Obs., New Zealand), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. S. Brown, 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), G. Masi (Virtual Telescope Project, Ceccano, Italy)
on 16 Jun 2015; 15:48 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 double 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered a new transient source, most likely a supernova, in the galaxy APMUKS(BJ) B215839.70-615403.9.

ASASSN-15lh was discovered in images obtained on UT 2015-06-14.25 at V~17.0 mag. It was also marginally detected on a number of epochs, with first detection on UT 2015-05-18.32 (V~17.3). We do not detect (V>17.3) the object in images obtained on UT 2015-05-15.33 and before. Images obtained by B. Nicholls on UT 2015-06-16.38 with the 30cm telescope at Mt. Vernon Observatory and on UT 2015-06-16.45 with the LCOGT 1-m robotic telescope in Cerro Tololo, Chile confirm the discovery of the transient. This figure shows the archival DSS image of the host (left) and the LCOGT V-band confirmation image (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-15lh is approximately 0.04" South and 0.41" East from the center of the galaxy APMUKS(BJ) B215839.70-615403.9, which has no redshift available in NED. 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-15lh  22:02:15.45   -61:39:34.64      2015-06-14.25      17.0          N/A                    0.41 

 
Obs. UT Date         V mag 
2015-05-15.33        >17.3 
2015-05-18.32         17.3 
2015-05-22.32         17.2 
2015-05-26.31         17.0 
2015-05-27.34         16.9 
2015-06-08.36         16.9 
2015-06-09.25         16.8 
2015-06-11.40         17.1 
2015-06-12.22         17.1 
2015-06-13.23         16.9 
2015-06-14.25         17.0 

Follow-up observations, particularly spectroscopy, 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.