ASASSN-18gb: Discovery of A Probable Nova in NGC 3109

ATel #11470; J. Brimacombe (Coral Towers Observatory), P. Vallely, K. Z. Stanek, C. S. Kochanek, J. S. Brown, 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)
on 23 Mar 2018; 20:07 UT
Distributed as an Instant Email Notice Novae
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 "Payne-Gaposchkin" telescope in Sutherland, South Africa, we discovered a new transient source, most likely a nova, in the Local Group galaxy NGC 3109. To the best of our knowledge, this is the first nova candidate discovered in NGC 3109.

ASASSN-18gb (AT 2018akx) was discovered in images obtained on UT 2018-03-22.77 at V~17.5 mag. We do not detect (V>18.6) the object in images taken on UT 2018-03-20.92 and before. An image obtained on 2018-03-23 by J. Brimacombe confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the confirmation image (right). The red circle has a radius of 5" and is centered on the position of the source in the confirmation image.

The position of ASASSN-18gb is approximately 82" South and 245" East from the center of the galaxy NGC 3109 (z=0.001344, via NED), and it has an absolute g-band magnitude of approximately -8.3 (m-M=25.55, A_g=0.220). Properties of the new source and photometry are summarized in the tables below:

 
Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. g mag  Approx. Abs. Mag   Offset from Host (") 
ASASSN-18gb  10:03:23.225   -26:10:56.37     2018-03-22.77      17.5          -8.3                258.52 

 
Obs. UT Date         g mag 
2018-03-21.13        >18.2 
2018-03-22.77         17.5 

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.