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ASAS-SN Discovery of A Luminous Nuclear Transient in CGCG 042-196

ATel #6990; T. W.-S. Holoien, K. Z. Stanek (Ohio State), E. Conseil (Association Francaise des Observateurs d'Etoiles Variables), S. Kiyota (Variable Star Observers League in Japan), R. A. Koff (Antelope Hills Observatory), C. S. Kochanek, A. B. Danilet, G. Simonian, U. Basu, N. Goss, J. F. Beacom (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), J. Brimacombe (Coral Towers Observatory), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), J. M. Fernandez (Observatory Inmaculada del Molino), B. Nicholls (Mt. Vernon Obs., New Zealand)
on 25 Jan 2015; 23:44 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

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 located near the nucleus of the galaxy CGCG 042-196:

Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. V mag 
ASASSN-15cb  12:39:50.23   +03:47:49.77      2015-01-21.54    16.8 

ASASSN-15cb was discovered in images obtained on UT 2015-01-21.54 at V~16.8 mag. We also detect the object in images obtained on UT 2015-01-24.53 (V~17.1) and UT 2015-01-19.55 (V~16.9). We do not detect (V>17.2) the object in images taken on UT 2015-01-16.55 and before. Follow-up images obtained using multiple telescopes, including the LCOGT 1-m robotic telescope in Sutherland, South Africa, on UT 2015-01-25.32, confirm the discovery of the transient. This figure shows the archival SDSS g-band image of the host (left) and the LCOGT g-band confirmation image (right). The red circle has a radius of 3.0" and is centered on the position of the transient in the LCOGT image.

The position of ASASSN-15cb is approximately 0.5" North and 0.1" East from the center of the starforming galaxy CGCG 042-196 (z=0.040038, d=175 Mpc, via NED), giving an absolute V-band magnitude of approximately -19.5 (m-M=36.21, A_V=0.09) at discovery. Given the luminosity and location within the probable host, this transient is likely a supernova, but a tidal disruption event (TDE) cannot be ruled out. 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.