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ASASSN-17bs and ASASSN-17bt: Discovery of Two Probable Supernovae

ATel #10031; G. Stone (Sierra Remote Observatories), J. Brimacombe (Coral Towers Observatory), 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), G. Bock (Runaway Bay Observatory, Australia), I. Cruz (Cruz Observatory), J. M. Fernandez (Observatory Inmaculada del Molino), S. Kiyota (Variable Star Observers League in Japan), R. A. Koff (Antelope Hills Observatory), G. Krannich (Roof Observatory Kaufering), G. Masi (Virtual Telescope Project, Ceccano, Italy), B. Nicholls (Mt. Vernon Obs., New Zealand), R. S. Post (Post Astronomy)
on 31 Jan 2017; 20:13 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 galaxies IC 1269 and 2MASX J09441179+3250341.

ASASSN-17bs (AT 2017yh) was discovered in images obtained on UT 2017-01-30.66 at V~16.5 mag. We do not detect (V>18.1) the object in images taken on UT 2016-10-07.21 and before. An image obtained on 2016-01-31 by J. Brimacombe 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 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-17bs is approximately 12.9" South and 1.8" East from the center of the galaxy IC 1269 (z=0.020401, d=84.1 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.3 (m-M=34.58, A_V=0.243).

ASASSN-17bt (AT 2017yt) was discovered in images obtained on UT 2017-01-31.45 at V~17.1 mag. We do not detect (V>17.8) the object in images taken on UT 2017-01-29.510 and before. An image obtained on 2016-01-31 by G. Stone confirms the discovery of the transient. This figure shows the archival SDSS g-band image of the host (left) and the G. Stone confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the G. Stone image.

The position of ASASSN-17bt is approximately 2.6" North and 4.6" West from the center of the galaxy 2MASX J09441179+3250341 (z=0.045336, d=197 Mpc, via NED), giving an absolute V-band magnitude of approximately -19.3 (m-M=36.37, A_V=0.036). 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-17bs  17:52:06.131   +21:33:57.82     2017-01-30.66      16.5          -18.3               13.02 
ASASSN-17bt  09:44:11.460   +32:50:36.53     2017-01-31.45      17.1          -19.3               5.28 

ASASSN-17bs photometry:

 
Obs. UT Date         V mag 
2016-10-07.21        >18.1 
2017-01-30.66         16.5 

ASASSN-17bt photometry:

 
Obs. UT Date         V mag 
2017-01-29.51        >17.8 
2017-01-31.45         17.1 

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.