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ASAS-SN Discovery of A Probable Supernova in DDO 151

ATel #8391; J. Brimacombe (Coral Towers Observatory), S. Kiyota (Variable Star Observers League in Japan), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. S. Brown, D. Godoy-Rivera, U. Basu (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong, Ping Chen (KIAA-PKU), G. Bock (Runaway Bay Observatory, Australia), I. Cruz (Cruz Observatory), G. Krannich (Roof Observatory Kaufering), G. Masi (Virtual Telescope Project, Ceccano, Italy), B. Nicholls (Mt. Vernon Obs., New Zealand), W. Wiethoff (University of Minnesota, Duluth)
on 9 Dec 2015; 18:41 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 8397

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 a new transient source, most likely a supernova, in the galaxy DDO 151.

ASASSN-15tw was discovered in images obtained on UT 2015-12-08.63 at V~16.4 mag. We also detect the object in images obtained on UT 2015-11-29.63 (V~16.4) and marginally detect the object in images obtained on UT 2015-11-27.64. We do not detect (V>16.5) the object in images taken on UT 2015-11-18.65 and before. Images obtained by J. Brimacombe on UT 2015-12-09.47 with the RCOS 51-cm telescope in New Mexico and by S. Kiyota on UT 2015-12-09.51 using a Planewave CDK 0.43-m telescope located near Mayhill, New Mexico confirm the discovery of the transient. This figure shows the archival DSS image of the host (left) and the J. Brimacombe confirmation image (right). The red circle has a radius of 8" and is centered on the position of the transient in the J. Brimacombe image.

The position of ASASSN-15tw is approximately 46.8" North and 20.0" West from the center of the galaxy DDO 151 (z=0.007972, d=37.6 Mpc, via NED), giving an absolute V-band magnitude of approximately -16.6 (m-M=32.88, A_V=0.123). Properties of the new source 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-15tw  12:50:28.05    -10:50:29.15      2015-12-08.63      16.4          -16.6               50.89 
Obs. UT Date         V mag 
2015-11-18.65        >16.5 
2015-11-29.63         16.4 
2015-12-08.63         16.4 

Follow-up observations are encouraged.

We thank LCOGT and its staff for their continued support of ASAS-SN. ASAS-SN is supported by NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the Robert Martin Ayers Sciences Fund. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.