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ASASSN-17en: Discovery of A Probable Supernova in ESO 280-G 013

ATel #10255; 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), G. Bock (Runaway Bay Observatory, Australia), I. Cruz (Cruz Observatory), J. M. Fernandez (Observatory Inmaculada del Molino), R. S. Post (Post Astronomy), G. Stone (Sierra Remote Observatories)
on 11 Apr 2017; 19:37 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 #: 10269

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014), 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 ESO 280-G 013.

ASASSN-17en (AT 2017cxy) was discovered in images obtained on UT 2017-04-08.31 at V~16.4 mag. We also detect the object in images obtained on UT 2017-04-11.24 (V~16.2), UT 2017-04-10.25 (V~16.3), UT 2017-04-09.40 (V~16.7), and UT 2017-04-04.38 (V~17.4). We do not detect (V>17.6) the object in images taken on UT 2017-03-31.32 and before. An image obtained on 2017-04-08 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-17en is approximately 0.3" North and 0.2" East from the center of the galaxy ESO 280-G 013 (z=0.020104, d=83.2 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.3 (m-M=34.56, A_V=0.186). 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-17en  18:23:17.876   -43:08:32.84     2017-04-08.31      16.4          -18.3               0.36 
Obs. UT Date         V mag 
2017-03-31.32        >17.6 
2017-04-04.38         17.4 
2017-04-08.31         16.4 
2017-04-09.40         16.7 
2017-04-10.25         16.3 
2017-04-11.24         16.2 

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 (AT 2017xyz) 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 funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, 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.