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ASAS-SN Discovery of A Probable Supernova in NGC 4108

ATel #7634; G. Masi (Virtual Telescope Project, Ceccano, Italy), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. S. Brown, A. B. Danilet, G. Simonian, U. Basu, J. F. Beacom, T. A. Thompson (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong (KIAA-PKU), J. Brimacombe (Coral Towers Observatory), E. Falco (CfA), P. R. Wozniak (LANL), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), E. Conseil (Association Francaise des Observateurs d'Etoiles Variables), S. Kiyota (Variable Star Observers League in Japan), G. Krannich (Roof Observatory Kaufering)
on 15 Jun 2015; 20:41 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Thomas Holoien (tholoien@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 a new transient source, most likely a supernova, in the galaxy NGC 4108.

ASASSN-15lf was discovered in images obtained on UT 2015-06-15.34 at V~16.2 mag. We do not detect (V>17.3) the object in images taken on UT 2015-06-10.34 and before. An image obtained by G. Masi on UT 2015-06-15.82 using the Virtual Telescope Project 17-inch Planewave telescope at Ceccano, Italy confirms the discovery of the transient. This figure shows the archival DSS image of the host (left) and the G. Masi confirmation image (right). The red circle has a radius of 3" and is centered on the position of the transient in the G. Masi image.

The position of ASASSN-15lf is approximately 23.2" South and 5.9" East from the center of the galaxy NGC 4108 (z=0.008382, d=36 Mpc, via NED), giving an absolute V-band magnitude of approximately -16.6 (m-M=32.78, A_V=0.049). At the redshift of the host, the offset of the transient from the host nucleus corresponds to a distance of 4.2 kpc. 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-15lf  12:06:45.56   +67:09:24.00      2015-06-15.34      16.2          -16.6               23.94 
Obs. UT Date         V mag 
2015-06-10.34        >17.3 
2015-06-15.34         16.2 

Follow-up observations are encouraged.

We thank LCOGT and its staff for their continued support of ASAS-SN. ASAS-SN is supported in part by 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.