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ASASSN-17ac: Discovery of A Probable Supernova in 2MASX J14342552-3828081

ATel #9939; J. Brimacombe (Coral Towers Observatory), J. S. Brown, K. Z. Stanek, T. W.-S. Holoien, C. S. Kochanek, J. Shields, T. A. Thompson (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong, S. Bose, Ping Chen (KIAA-PKU), J. M. Fernandez (Observatory Inmaculada del Molino), S. Kiyota (Variable Star Observers League in Japan), G. Masi (Virtual Telescope Project, Ceccano, Italy), R. S. Post (Post Astronomy)
on 4 Jan 2017; 22:13 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (brown@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

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 2MASX J14342552-3828081.

ASASSN-17ac (AT 2017ad) was discovered in images obtained on UT 2017-01-04.36 at V~16.6 mag. We also detect the object in images obtained on UT 2017-01-02.36 (V~17.3). We do not detect (V>16.2) the object in images taken on UT 2016-12-27.36 and before. An image obtained on 2017-01-04 by J. Brimacombe confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the J. Brimacombe confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the J. Brimacombe image.

The position of ASASSN-17ac is approximately 1.5" South and 5.9" East from the center of the galaxy 2MASX J14342552-3828081 (z=0.033320, d=143 Mpc, via NED), giving an absolute V-band magnitude of approximately -19.4 (m-M=35.71, A_V=0.280). 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-17ac  14:34:26.012   -38:28:09.71     2017-01-04.36      16.6          -19.4               6.09 
Obs. UT Date         V mag 
2016-12-27.36        >16.2 
2017-01-02.36         17.3 
2017-01-04.36         16.6 

Follow-up observations are encouraged.

While we are participating in the TNS system to minimize potential confusion, ASAS-SN will continue using ASASSN-17xx transient names as our primary nomenclature (including supernovae, but also other classes of transients), and we encourage others to do the same. We prefer merging the names as ASASSN-17xx (AT2017xyz) to preserve, rather than anonymize, the origin of the transient.

We thank Las Cumbres Observatory 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 Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and the 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.