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ASASSN-17ds and ASASSN-17dt: Discovery of Two Probable Supernovae

ATel #10199; J. Brimacombe (Coral Towers Observatory), G. Masi (Virtual Telescope Project, Ceccano, Italy), J. S. Brown (Ohio State), Subo Dong (KIAA-PKU), J. L. Prieto (Diego Portales; MAS), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. Shields, T. A. Thompson (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), D. Bersier (LJMU), S. Bose, Ping Chen (KIAA-PKU), S. Kiyota (Variable Star Observers League in Japan), R. A. Koff (Antelope Hills Observatory), R. S. Post (Post Astronomy), G. Stone (Sierra Remote Observatories)
on 23 Mar 2017; 19:08 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (brown@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 10209, 10240

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 two new transient sources, most likely supernovae, in the galaxies IC 0491 and 2MFGC 08661.

ASASSN-17ds (AT 2017cfq) was discovered in images obtained on UT 2017-03-17.36 at V~17.2 mag. We do not detect (V>17.0) the object in images taken on UT 2017-03-16.14 and before. An image obtained on 2017-03-17 by J. Brimacombe confirms the discovery of the transient. This figure shows the archival SDSS g-band 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-17ds is approximately 1.5" South and 2.8" East from the center of the galaxy IC 0491 (z=0.021648, d=93.3 Mpc, via NED), giving an absolute V-band magnitude of approximately -17.7 (m-M=34.80, A_V=0.117).

ASASSN-17dt (AT 2017cig) was discovered in images obtained on UT 2017-03-19.48 at V~17.2 mag. We detect the object as early as UT 2017-03-17.49 (V~17.1). We do not detect (V>17.0) the object in images taken on UT 2017-03-16.44 and before. An image obtained on 2017-03-20 by G. Masi confirms the discovery of the transient. This figure shows the archival SDSS g-band image of the host (left) and the G. Masi confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the G. Masi image.

The position of ASASSN-17dt is approximately 10.0" North and 5.8" West from the center of the galaxy 2MFGC 08661 (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-17ds  08:03:55.206   +26:31:12.73     2017-03-17.36      17.2          -17.7                3.18 
ASASSN-17dt  11:06:47.195   +14:12:26.68     2017-03-19.48      17.2            N/A               11.56 
 

ASASSN-17ds photometry:

 
Obs. UT Date         V mag 
2017-03-16.14        >17.0 
2017-03-17.36         17.2 
2017-03-20.39         17.0 
2017-03-23.38         16.7 

ASASSN-17dt photometry:

 
Obs. UT Date         V mag 
2017-03-16.44        >17.0 
2017-03-17.49         17.1 
2017-03-19.48         17.2 
2017-03-20.38         17.5 
2017-03-23.44         17.3 

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.