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ASAS-SN Discovery of A Probable Supernova in GALEXASC J002041.66+251341.1

ATel #8347; S. Kiyota (Variable Star Observers League in Japan), J. S. Brown, T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, 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)
on 1 Dec 2015; 00:11 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (brown@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 8350, 8354

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 GALEXASC J002041.66+251341.1.

ASASSN-15tg was discovered in images obtained on UT 2015-11-30.21 at V~16.9 mag. We do not detect (V>16.7) the object in images taken on UT 2015-11-28.35 and before. An image obtained on 2015-11-30 with the LCOGT 1-m robotic telescope at Siding Spring confirms the discovery of the transient. This figure shows the archival SDSS g-band image of the host (left) and the LCOGT V-band confirmation image (right). The red circle has a radius of 2" and is centered on the position of the transient in the LCOGT image.

The position of ASASSN-15tg is approximately 4.6" North and 7.3" West from the center of the galaxy GALEXASC J002041.66+251341.1 (z=0.03561, d=145 Mpc, via NED), giving an absolute V-band magnitude of approximately -19.0 (m-M=35.81, A_V=0.079). 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-15tg  00:20:41.06   +25:13:44.61      2015-11-30.21      16.9          -19.0               8.63 
Obs. UT Date         V mag 
2015-11-28.35        >16.7 
2015-11-30.21         16.9 

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.