ASAS-SN Discovery of A Probable Supernova in NGC 2115A

ATel #7419; B. Nicholls (Mt. Vernon Obs., New Zealand), J. Brimacombe (Coral Towers Observatory), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, 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), P. R. Wozniak (LANL), E. Falco (CfA), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), J. G. Carballo (Observatorio Cerro del Viento MPC 184), J. M. Fernandez (Observatory Inmaculada del Molino), S. Kiyota (Variable Star Observers League in Japan), R. A. Koff (Antelope Hills Observatory), G. Krannich (Roof Observatory Kaufering), L. A.G. Monard (Klein Karoo Observatory), J. Nicolas (Groupe SNAUDE, France), W. Wiethoff (University of Minnesota, Duluth)
on 20 Apr 2015; 16:03 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 NGC 2115A.

ASASSN-15hh was discovered in images obtained on UT 2015-04-20.02 at V~16.5 mag. We also detect the object in images obtained on UT 2015-04-20.02 (V~16.2), UT 2015-04-19.02 (V~16.6), UT 2015-04-18.01 (V~17.2), and UT 2015-04-18.01 (V~16.8). (The object is located in the overlapping region at the edges of two fields of view in two separate ASAS-SN cameras, and the photometry listed is approximate.) We do not detect (V>17.3) the object in images taken on UT 2015-04-12.02 and before. Images obtained by B. Nicholls on UT 2015-04-20.39 using the 30-cm telescope at Mt. Vernon Observatory and by J. Brimacombe on UT 2015-04-20.44 with the CDK 43-cm telescope at Savannah Skies Observatory confirm the discovery of the transient. This figure shows the archival DSS image of the host (left) and the B. Nicholls confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the B. Nicholls image.

The position of ASASSN-15hh is approximately 11.5" South and 10.8" West from the center of the galaxy NGC 2115A (z=0.23389, d=98.9 Mpc, via NED), part of the galaxy pair NGC 2115. This gives the transient an absolute V-band magnitude of approximately -18.6 (m-M=34.98, A_V=0.167). 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-15hh  05:51:18.69   -50:35:09.80      2015-04-20.02      16.5          -18.6               15.78 

 
Obs. UT Date         V mag 
2015-04-12.02        >17.3 
2015-04-18.01         17.2 
2015-04-18.01         16.8 
2015-04-19.02         16.6 
2015-04-20.02         16.5 
2015-04-20.02         16.2 

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.