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ASASSN-17ai and ASASSN-17aj: Discovery of Two Probable Supernovae

ATel #9952; J. S. Brown, K. Z. Stanek, T. W.-S. Holoien, C. S. Kochanek, 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. Brimacombe (Coral Towers Observatory)
on 9 Jan 2017; 23:05 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (brown@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the quadruple 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered two new transient sources, most likely supernovae, in the galaxy KUG 1204+171 and MCG -02-30-003.

ASASSN-17ai (AT 2017hl) was discovered in images obtained on UT 2017-01-09.63 at V~17.3 mag. We also detect the object in images obtained on UT 2017-01-08.49 (V~17.4), UT 2017-01-05.49 (V~17.6), UT 2017-01-02.59 (V~17.4), and UT 2016-12-28.55 (V~17.4). We do not detect (V>17.7) the object in images taken on UT 2016-12-23.62 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-17ai is approximately 3.2" South and 3.5" East from the center of the galaxy KUG 1204+171 (z=0.023073, d=101 Mpc, via NED), giving an absolute V-band magnitude of approximately -17.8 (m-M=34.97, A_V=0.129).

ASASSN-17aj (AT 2017hm) was discovered in images obtained on UT 2017-01-09.62 at V~16.9 mag. We also detect the object in images obtained on UT 2017-01-08.48 (V~17.2) and UT 2017-01-05.34 (V~17.4). We do not detect (V>18.0) the object in images taken on UT 2017-01-03.24 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-17aj is approximately 25.5" North and 1.0" West from the center of the galaxy MCG -02-30-003 (z=0.021275, d=94.1 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.0 (m-M=34.82, A_V=0.114). 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-17ai  12:07:18.83   +16:50:26.02     2017-01-09.63      17.3          -17.8               4.74 
ASASSN-17aj  11:33:10.50   -10:13:18.40     2017-01-09.62      16.9          -18.0               25.5 

ASASSN-17ai photometry:

 
Obs. UT Date         V mag 
2016-12-23.62        >17.7 
2016-12-28.55         17.4 
2017-01-02.59         17.4 
2017-01-05.49         17.6 
2017-01-08.49         17.4 
2017-01-09.63         17.3 

ASASSN-17aj photometry:

 
Obs. UT Date         V mag 
2017-01-03.24        >18.0 
2017-01-05.34         17.4 
2017-01-08.48         17.2 
2017-01-09.62         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-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 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.