ASASSN-16om and ASASSN-16on: Discovery of Two Probable Supernovae

ATel #9827; B. Nicholls (Mt. Vernon Obs., New Zealand), J. Brimacombe (Coral Towers Observatory), J. S. Brown, K. Z. Stanek, T. W.-S. Holoien, C. S. Kochanek, J. Shields (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), S. Kiyota (Variable Star Observers League in Japan), R. S. Post (Post Astronomy), G. Stone (Sierra Remote Observatories)
on 5 Dec 2016; 21:26 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (brown@astronomy.ohio-state.edu)

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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 two new transient sources, most likely supernovae, in the galaxies AM 2329-410 and MRSS 251-044924.

ASASSN-16om (AT 2016isd) was discovered in images obtained on UT 2016-12-03.14 at V~17.6 mag. We also detect the object in images obtained on UT 2016-11-30.18 (V~17.6). We do not detect (V>17.7) the object in images taken on UT 2016-11-28.17 and before. An image obtained on 2016-12-05 by B. Nicholls confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the B. Nicholls confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the B. Nicholls image.

The position of ASASSN-16om is approximately 9.4" North and 1.8" West from the center of the galaxy AM 2329-410 (z=0.045312, d=189 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.7 (m-M=36.29, A_V=0.051).

ASASSN-16on (AT 2016isf) was discovered in images obtained on UT 2016-12-05.18 at V~16.9 mag. We do not detect (V>18.0) the object in images taken on UT 2016-12-02.110 and before. An image obtained on 2016-12-05 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-16on is approximately 0.1" North and 0.7" West from the center of the galaxy MRSS 251-044924 (no redshift information available from NED). Properties of the new sources 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-16om  23:31:54.451   -40:45:34.17     2016-12-03.14      17.6          -18.7               9.57 
ASASSN-16on  04:48:08.562   -46:28:34.49     2016-12-05.18      16.9            N/A               0.71 

ASASSN-16om photometry:

 
Obs. UT Date         V mag 
2016-11-28.17        >17.7 
2016-11-30.18         17.6 
2016-12-03.14         17.6 

ASASSN-16on photometry:

 
Obs. UT Date         V mag 
2016-12-02.11        >18.0 
2016-12-05.18         16.9 

Follow-up observations are encouraged.

While we are participating in the TNS system to minimize potential confusion, ASAS-SN will continue using ASASSN-16xx 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-16xx (AT2016xyz) to preserve, rather than anonymize, the origin of the transient.

We thank LCOGT 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.