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ASAS-SN Discovery of A Bright Transient Near SDSS J023024.26+450717.5

ATel #8400; 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)
on 11 Dec 2015; 17:16 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 #: 8421, 8422

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 near the object SDSS J023024.26+450717.5.

ASASSN-15tx was discovered in images obtained on UT 2015-12-09.27 at V~16.5 mag. We also detect the object in images obtained on UT 2015-12-07.42 (V~16.3). We do not detect (V>17.5) the object in images taken on UT 2015-12-04.27 and before. An image obtained on UT 2015-12-11.61 with the LCOGT 1-m robotic telescope at McDonald Observatory 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-15tx is approximately 0.6" North and 1.9" East from the center of the SDSS source SDSS J023024.26+450717.5, which is labelled in the SDSS catalog as a star. Given the location of ASASSN-15tx, it is possible the transient is a supernova and SDSS J023024.26+450717.5 is its host galaxy, but the possibility that ASASSN-15tx is a new cataclysmic variable star cannot be ruled out. 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-15tx  02:30:24.44    +45:07:18.22      2015-12-09.27      16.5           N/A               1.99 
Obs. UT Date         V mag 
2015-12-04.27        >17.5 
2015-12-07.42         16.3 
2015-12-09.27         16.5 

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.