ASAS-SN Discovery of a Bright, Unusual Outburst from 1RXS J204455.9-115151

ATel #6306; T. W.-S. Holoien, K. Z. Stanek, B. J. Shappee, A. B. Davis, C. S. Kochanek, J. Jencson, U. Basu, J. F. Beacom (Ohio State), J. L. Prieto (Universidad Diego Portales), D. Bersier (LJMU), J. Brimacombe (Coral Towers Observatory), D. Szczygiel, G. Pojmanski (Warsaw University Observatory)
on 10 Jul 2014; 16:40 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Thomas Holoien (tholoien@astronomy.ohio-state.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from both the quadruple 14-cm "Brutus" telescope in Haleakala, Hawaii and the recently commissioned double 14-cm "Cassius" telescope in Cerro Tololo, Chile, we discovered a bright and unusual outburst from the star 1RXS J204455.9-115151:

 
Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. V mag 
ASASSN-14ds  20:44:55.90   -11:51:51.5       2014-07-08.22       15.7 

ASASSN-14ds was discovered in images obtained 2014 UT July 08.22 at V~15.7 mag. We also detect the outburst in images obtained 2014 UT July 08.42 (V~14.1), 2014 UT July 09.44 (V~13.2), 2014 UT July 10.12 (V~13.7), and 2014 UT July 10.51 (V~14.0), but we do not detect the outburst (V>16.2) in images obtained on 2014 UT July 07.23 and before. This figure shows the ASAS-SN light curve beginning on 2014 UT July 06.1 and spanning 6 days.

A cross-check of the transient's ASAS-SN position in Vizier reveals that the source of the outburst is the star 1RXS J204455.9-115151. The light curve of this source in the Catalina Sky Survey (shown here) shows no bright outbursts for 9 years, but indicates that the source is highly variable in quiescence (V~16.2-17.2). Palomar-NEAT data obtained between July 1998 and Sep. 2005 indicate that the object underwent a similar delta_V~2.5 mag outburst in Aug. 2002 that lasted roughly 10 days, a timescale and magnitude that are both similar to those measured in the current outburst.

Please see the vsnet-alert for more information. Follow-up observations are encouraged.

We thank LCOGT and its staff for their continued support of ASAS-SN. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.