ASASSN-17cl and ASASSN-17cm: Discovery of Two Probable Supernovae in MCG -02-13-038 and 2MASX J05474279-7912525

ATel #10084; R. S. Post (Post Astronomy), R. A. Koff (Antelope Hills Observatory), S. Kiyota (Variable Star Observers League in Japan), J. Brimacombe (Coral Towers Observatory), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. S. Brown, 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), J. M. Fernandez (Observatory Inmaculada del Molino), G. Krannich (Roof Observatory Kaufering)
on 16 Feb 2017; 18:06 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), we discovered two new transient sources, most likely supernovae, in the galaxies MCG -02-13-038 and 2MASX J05474279-7912525.

ASASSN-17cl (AT 2017auf) was discovered in images obtained on UT 2017-02-14.28 at V~17.4 mag. We also detect the object in images obtained on UT 2017-02-16.27 (V~17.1) and UT 2017-02-15.22 (V~16.9). We do not detect (V>16.8) the object in images taken on UT 2017-02-10.12 and before. An image obtained on UT 2017-02-16 by R. Post confirms the discovery of the transient. This figure shows the archival Pan-STARRS (Chambers et al. 2016, arXiv:1612.05560) g-band image of the host (left) and the R. Post confirmation image (right). The red circle has a radius of 4" and is centered on the position of the transient in the R. Post image.

The position of ASASSN-17cl is approximately 0.2" South and 4.3" East from the center of the galaxy MCG -02-13-038 (z=0.013293, d=55.1 Mpc, via NED), giving an absolute V-band magnitude of approximately -16.5 (m-M=33.70, A_V=0.232).

ASASSN-17cm (AT 2017aut) was discovered in images obtained on UT 2017-02-14.03 at V~16.3 mag. We also detect the object in images obtained on UT 2017-02-16.09 (V~17.0). We do not detect (V>16.9) the object in images taken on UT 2017-02-13.11 and before. An image obtained on UT 2017-02-16 with the LCO 1-m telescope at Cerro Tololo, Chile confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the LCO r-band confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the LCO image.

The position of ASASSN-17cm is approximately 0.4" South and 0.6" East from the center of the galaxy 2MASX J05474279-7912525 (z=0.017233, d=72.5 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.3 (m-M=34.30, A_V=0.342).

Properties of the new sources and photometry are summarized below:

 
Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. V mag  Approx. Abs. Mag   Offset from Host (") 
ASASSN-17cl  05:02:19.58   -10:21:22.78      2017-02-14.28      17.4          -16.5               4.30 
ASASSN-17cm  05:47:43.06   -79:12:52.89      2017-02-14.03      16.3          -18.3               0.72 

 
Obs. UT Date         V mag 
2017-02-10.12        >16.8 
2017-02-14.28         17.4 
2017-02-15.22         16.9 
2017-02-16.27         17.1 

 
Obs. UT Date         V mag 
2017-02-13.11        >16.9 
2017-02-14.03         16.3 
2017-02-16.09         17.0 

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 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.