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ASASSN-17fd and ASASSN-17fe: Discovery of Two Probable Supernovae

ATel #10300; 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), P. Cacella (DogsHeaven Observatory), I. Cruz (Cruz Observatory), G. Masi (Virtual Telescope Project, Ceccano, Italy), B. Nicholls (Mt. Vernon Obs., New Zealand), R. S. Post (Post Astronomy), G. Stone (Sierra Remote Observatories)
on 21 Apr 2017; 17:41 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 #: 10306

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 and the 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered two new transient sources, most likely supernovae, in the galaxies ARK 481 and 2MASX J09203974-2956533.

ASASSN-17fd (AT 2017dfb) was discovered in images obtained on UT 2017-04-19.51 at V~16.5 mag. We do not detect (V>17.7) the object in images taken on UT 2017-04-15.52 and before. An image obtained on 2017-04-20 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-17fd is approximately 0.4" North and 1.9" West from the center of the galaxy ARK 481 (z=0.025955, d=111 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.9 (m-M=35.17, A_V=0.199).

ASASSN-17fe (AT 2017dfo) was discovered in images obtained on UT 2017-04-19.11 at V~17.1 mag. We do not detect (V>17.3) the object in images taken on UT 2017-04-15.15 and before. An image obtained on 2017-04-20 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-17fe is approximately 10.2" South and 22.0" West from the center of the galaxy 2MASX J09203974-2956533 (z=0.035948, d=156 Mpc, via NED), giving an absolute V-band magnitude of approximately -19.2 (m-M=35.89, A_V=0.403). 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-17fd  15:39:05.04   +05:34:16.93     2017-04-19.51      16.5          -18.9               1.94 
ASASSN-17fe  09:20:38.04   -29:57:03.53     2017-04-19.11      17.1          -19.2               24.25 

ASASSN-17fd photometry:

 
Obs. UT Date         V mag 
2017-04-15.52        >17.7 
2017-04-19.51         16.5 

ASASSN-17fe photometry:

 
Obs. UT Date         V mag 
2017-04-15.15        >17.3 
2017-04-19.11         17.1 
2017-04-20.98         17.2 

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.