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ASAS-SN Discovery of A Probable Supernova in 6dF J1403085-382831

ATel #6864; Subo Dong (KIAA-PKU), A. B. Davis, T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, G. Simonian, U. Basu, N. Goss, J. F. Beacom (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), P. R. Wozniak (LANL), J. Brimacombe (Coral Towers Observatory), D. Szczygiel, G. Pojmanski (Warsaw University Observatory)
on 2 Jan 2015; 17:04 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 6882

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the double 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered a new transient source, most likely a supernova, in the galaxy 6dF J1403085-382831:

Object       RA (J2000)     DEC (J2000)    Disc. UT Date   Disc. V mag 
ASASSN-15ab  14:03:06.24   -38:28:29.9       2015-01-02.33   16.4 
ASASSN-15ab was discovered in images obtained on UT 2015-01-02.33 and 2015-01-02.36 at V~16.4 mag, taken by both Cassius telescopes. We do not detect (V>16.7) the object in images taken on UT 2014-12-31.33 and before. See the ASAS-SN discovery image: the top left panel shows the reference image, the top right panel shows the DSS image on the same angular scale, the lower left panels shows one of the 90 second V-band images from 2015-01-02, and the lower right panel shows the image subtraction residuals on 2015-01-02. The 5" radius circle has the same position in all panels.

The position of ASASSN-15ab is approximately 1.3" North and 27" West from the center of the galaxy 6dF J1403085-382831 (z=0.0178, d=77 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.3 (m-M=34.4, A_V=0.3). The position of the SN candidate is very close to what appears to be a star-forming region. Follow-up observations 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.