ASASSN-18bt: Discovery of A Probable, Bright Supernova in a Kepler Supernova Field

ATel #11253; Jon S. Brown, K. Z. Stanek, P. Vallely, C. S. Kochanek, J. Shields, T. A. Thompson (Ohio State), B. J. Shappee (IfA-Hawaii), T. W.-S. Holoien (Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong, S. Bose, Ping Chen (KIAA-PKU), M. Stritzinger, S. Holmbo (Aarhus), J. Brimacombe (Coral Towers Observatory)
on 4 Feb 2018; 17:12 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

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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 UGC 04780, which is being monitored by Kepler between Dec 7 2017 and Feb 25, 2018.

ASASSN-18bt (AT 2018oh) was discovered in images obtained on UT 2018-02-04.41 at V~15.2 mag. We also detect the object in images obtained on UT 2018-02-04.19 (g~15.2), UT 2018-02-03.94 (g~15.2), UT 2018-02-03.06 (g~15.5), and possibly in earlier epochs, subject to further analysis. We do not detect (V>17.5) the object in images taken on UT 2018-01-27.13 and before. This figure shows the archival DSS image of the host (bottom right), the ASAS-SN reference image (bottom middle), and the ASAS-SN discovery image (bottom left). Several earlier detections are shown in the top row. The red circle has a radius of 15" and is centered on the position of the transient in the discovery image.

The position of ASASSN-18bt is approximately 7.8" North and 2.0" East from the center of the galaxy UGC 04780 (z=0.010981, d=49.4 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.4 (m-M=33.44, A_V=0.124). 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-18bt  09:06:39.541   +19:20:17.77     2018-02-04.410      15.2          -18.4               8.05 

 
Obs. UT Date          mag  (V/g) 
2018-01-27.13        >17.5 (V) 
2018-02-03.06         15.5 (g) 
2018-02-03.94         15.2 (g) 
2018-02-04.19         15.2 (g) 
2018-02-04.41         15.2 (V) 

Follow-up observations are encouraged.

While we are participating in the TNS system to minimize potential confusion, ASAS-SN will continue using ASASSN-18xx 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-18xx (AT 2018xyz) 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, the Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and the Villum Fonden (Denmark). For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.