ASAS-SN Discovery of A Probable Supernova in Robert's Quartet

ATel #8479; S. Kiyota (Variable Star Observers League in Japan), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. S. Brown, D. Godoy-Rivera, U. Basu (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong, Ping Chen (KIAA-PKU), J. Brimacombe (Coral Towers Observatory), I. Cruz (Cruz Observatory), G. Krannich (Roof Observatory Kaufering), G. Masi (Virtual Telescope Project, Ceccano, Italy), L. A.G. Monard (Klein Karoo Observatory)
on 30 Dec 2015; 19:25 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 quadruple 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered a new transient source, most likely a supernova, in the galaxy group Robert's Quartet.

ASASSN-15ut was discovered in images obtained on UT 2015-12-30.12 at V~16.8 mag. We do not detect (V>17.0) the object in images taken on UT 2015-12-28.13 and before. An image obtained by S. Kiyota on UT 2015-12-30.43 using a 0.5-m CDK + FLI PL-9000 at the ITelescope.NET site at Siding Springs Observatory confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the S. Kiyota confirmation image (right). The red circle has a radius of 4" and is centered on the position of the transient in the S. Kiyota image.

The position of ASASSN-15ut is approximately 5.7" South and 10.2" West from the center of the galaxy NGC 88 (z=0.011471, d=44.8 Mpc, via NED), the central galaxy of Robert's Quartet, giving an absolute V-band magnitude of approximately -16.5 (m-M=33.26, A_V=0.053). 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-15ut  00:21:21.09    -48:38:30.34      2015-12-30.12      16.8          -16.5               11.68 

 
Obs. UT Date         V mag 
2015-12-28.13        >17.0 
2015-12-30.12         16.8 

Follow-up observations are encouraged.

We thank LCOGT and its staff for their continued support of ASAS-SN. ASAS-SN is supported by NSF grant AST-1515927, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Mt. Cuba Astronomical Foundation, George Skestos, and the Robert Martin Ayers Sciences Fund. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.