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ASAS-SN Discovery of A Probable Supernova in 2MASX J23273537+2924275

ATel #8365; G. Masi (Virtual Telescope Project, Ceccano, Italy), 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), S. Kiyota (Variable Star Observers League in Japan)
on 4 Dec 2015; 20:41 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 8393

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, most likely a supernova, in the galaxy 2MASX J23273537+2924275.

ASASSN-15tm was discovered in images obtained on UT 2015-12-04.25 at V~17.2 mag. We also detect the object in images obtained on UT 2015-12-02.25 (V~17.5). We do not detect (V>17.5) the object in images taken on UT 2015-11-29.21 and before. An image obtained by G. Masi on UT 2015-12-04.69 using the Virtual Telescope Project 17-inch Planewave telescope at Ceccano, Italy confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the G. Masi confirmation image (right). The red circle has a radius of 4" and is centered on the position of the transient in the G. Masi image.

The position of ASASSN-15tm is approximately 3.4" North and 2.9" East from the center of the galaxy 2MASX J23273537+2924275, which has no redshift available in NED. NED also reports a nearby radio source, AGC 333540, with a redshift of 0.016722, though the reported position of this source is offset from ASASSN-15tm by 20.2". 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-15tm  23:27:35.60    +29:24:31.17      2015-12-04.25      17.2          N/A               4.47 
Obs. UT Date         V mag 
2015-11-29.21        >17.5 
2015-12-02.25         17.5 
2015-12-04.25         17.2 

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 Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, 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.