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ASASSN-17gl: Discovery of A Probable Supernova in MCG +04-25-014

ATel #10416; G. Stone (Sierra Remote Observatories), R. S. Post (Post Astronomy), 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), I. Cruz (Cruz Observatory), J. M. Fernandez (Observatory Inmaculada del Molino), S. Kiyota (Variable Star Observers League in Japan), G. Masi (Virtual Telescope Project, Ceccano, Italy), B. Nicholls (Mt. Vernon Obs., New Zealand)
on 23 May 2017; 03:43 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, Shappee et al. 2014), 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 MCG +04-25-014.

ASASSN-17gl (AT 2017eex) was discovered in images obtained on UT 2017-05-21.27 at V~17.4 mag. We also detect the object in images obtained on UT 2017-05-16.210 (V~17.4). We do not detect (V>17.4) the object in images taken on UT 2017-05-14.49 and before. An image obtained on 2017-05-22 by G. Stone confirms the discovery of the transient. This figure shows the archival SDSS g-band image of the host (left) and the G. Stone confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the G. Stone image.

The position of ASASSN-17gl is approximately 11.7" North and 7.7" East from the center of the galaxy MCG +04-25-014 (z=0.039660, d=173 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.8 (m-M=36.10, A_V=0.060). 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-17gl  10:23:19.355   +22:23:38.55     2017-05-21.27      17.4          -18.8               14.01 
Obs. UT Date         V mag 
2017-05-14.49        >17.4 
2017-05-16.21         17.4 
2017-05-21.27         17.4 

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 Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the Chinese Academy of Sciences South America Center for Astronomy (CASSACA). For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.