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ASAS-SN Discovery of A Nuclear Transient in MRK 0887

ATel #7891; G. Masi (Virtual Telescope Project, Ceccano, Italy), J. Brimacombe (Coral Towers Observatory), T. W.-S. Holoien (Ohio State), D. Bersier (LJMU), 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), Subo Dong (KIAA-PKU), E. Falco (CfA), P. R. Wozniak (LANL), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), S. Kiyota (Variable Star Observers League in Japan), W. Wiethoff (University of Minnesota, Duluth)
on 7 Aug 2015; 18:45 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 7899

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 MRK 0887.

ASASSN-15ns was discovered in images obtained by multiple ASAS-SN cameras on UT 2015-08-06.33 at V~16.8 mag. We do not detect (V>16.9) the object in images taken on UT 2015-08-03.35 and before. Images obtained by G. Masi on UT 2015-08-06.95 using the Virtual Telescope Project 17-inch Planewave telescope at Ceccano, Italy and by J. Brimacombe on UT 2015-08-07.48 with the CDK 43-cm telescope at Savannah Skies Observatory 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 3" and is centered on the position of the transient in the G. Masi image.

The position of ASASSN-15ns is approximately 0.3" North from the center of the galaxy MRK 0887 (z=0.030671, d=129 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.8 (m-M=35.56, A_V=0.036). The archival SDSS spectrum of the host does not show signs of significant AGN activity. 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-15ns  16:40:28.02   +39:19:12.77      2015-08-06.33      16.8          -18.8               0.3 
Obs. UT Date         V mag 
2015-08-03.35        >16.9 
2015-08-06.33         16.8 

Given the proximity to the host nucleus, this could be a supernova, unusual AGN activity, or possibly even a tidal disruption event. 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.