ASAS-SN Discovery of an Extreme (Delta V~9 mag) M-dwarf Flare

ATel #6771; G. Simonian, K. Z. Stanek, A. B. Davis, T. W.-S. Holoien, C. S. Kochanek, U. Basu, N. Goss, J. F. Beacom (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), J. Brimacombe (Coral Towers Observatory), D. Szczygiel, G. Pojmanski (Warsaw University Observatory)
on 30 Nov 2014; 22:24 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

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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:

 
Object       RA (J2000)   DEC (J2000)   Disc. UT Date    Disc. V mag   
ASASSN-14lc  12:02:29.55  24:12:12.6    2014-11-28.60     15.0  

ASASSN-14lc was detected in images obtained 2014 UT November 28.60 as a bright, V=15.0 new source. There was no previous activity seen at this position, including ASAS-SN data taken on 2014 November 27 and November 23. Due to built-in overlap between different ASAS-SN fields, there is also a weak limit from the edge of another CCD of V>15.5 on UT 2014-11-28.5937 (~10 minutes before the flare detection). Between our two exposures, separated by ~120 seconds. the transient faded significantly, from V=14.95 on UT 2014-11-28.60093 to V=15.75 on UT 2014-11-28.60233.

There is a very faint (g=25.3) and red (g-r=2.50) SDSS star 2.4" away from our position. There is also a 2MASS star 2.3" away with K= 15.1 and J-K=1.14. We note that at this position the line-of-sight Galactic extinction is small, A_V=0.06 (Schlafly & Finkbeiner 2011) and E(g-r)=0.02, so it is clear that the likely counterpart is not reddened, but is an intrinsically red M-dwarf. Using the 2MASS color of J-K=1.14 and H-K=0.529, we expect that this star is likely a very late type M-dwarf (West et al. 2011).

ASASSN-14lc is most likely a delta V~9 mag flare from an M-dwarf star, and given very short duration of such events possibly even stronger. Such extreme M-dwarf flares are very rarely observed, but are not unprecedented (e.g., Stanek et al. 2013: ATel #5276).

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.