ASASSN-16km: Discovery of A Supernova in ESO 197-G 010

ATel #9494; J. S. Brown (Ohio State), J. L. Prieto (Diego Portales; MAS), C. Ricci (PUC), K. Oh (ETH Zurich), K. Z. Stanek, T. W.-S. Holoien, C. S. Kochanek, J. Shields (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), D. Bersier (LJMU), Subo Dong, S. Bose, Ping Chen (KIAA-PKU), J. Brimacombe (Coral Towers Observatory)
on 13 Sep 2016; 16:48 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 a Type Ia supernova in the galaxy ESO 197-G 010.

ASASSN-16km (AT 2016ggb) was discovered in images obtained on UT 2016-09-12.34 at V~16.3 mag. We also detect the object in images obtained on UT 2016-09-13.15 (V~16.2), UT 2016-09-10.15 (V~16.3), UT 2016-09-09.15 (V~16.6), UT 2016-09-05.110 (V~17.1), and UT 2016-09-02.41 (V~17.6). We do not detect (V>17.9) the object in images taken on UT 2016-08-30.18 and before. This figure shows the archival DSS image of the host (left) the ASAS-SN V-band reference image (middle), and the ASAS-SN subtraction image (right). The red circle has a radius of 10" and is centered on the position of the transient in the subtraction image.

The position of ASASSN-16km is approximately 2.2" South and 0.6" West from the center of the galaxy ESO 197-G 010 (z=0.020588, d=83.8 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.3 (m-M=34.57, A_V=0.055). An optical spectrum (range 3600-9000 Angstroms) of ASASSN-16km was obtained on UT 2016-09-13.3 with the B&C spectrograph mounted on the du Pont 2.5m telescope at Las Campanas Observatory. The spectrum is consistent with a Type Ia around peak heavily contaminated by the host galaxy light. After correcting for the redshift of the host galaxy, we measure a Si II 6355 expansion velocity of ~12000 km/s. 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-16km  01:53:12.541   -49:33:39.47     2016-09-12.34      16.3          -18.3               2.28 

 
Obs. UT Date         V mag 
2016-08-30.18        >17.9 
2016-09-02.41         17.6 
2016-09-05.11         17.1 
2016-09-09.15         16.6 
2016-09-10.15         16.3 
2016-09-12.34         16.3 
2016-09-13.15         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-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, 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.