ASASSN-16cx: Discovery of an Extreme (Delta V ~ 8 mag) M-dwarf flare

ATel #8803; G. Simonian, K. Z. Stanek (OSU), S. Schmidt (Leibniz Institute for Astrophysics - Potsdam), C. S. Kochanek, J. S. Brown, T. W.-S. Holoien, 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), J. Brimacombe (Coral Towers Observatory)
on 11 Mar 2016; 19:05 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-16cx   16:11:58.48   +54:56:42.9     2016-03-10.48   15.0 

ASASSN-16cx was discovered at V=15.0 in "Brutus" images taken on 2016 UT March 10.48 as a new source. There was no previous activity seen at this position in the 400+ images taken at this location since March 2012. This includes data taken on 2016 March 6. Between our three exposures, separated by ~ 100 seconds, the transient faded, from V = 15.01 on UT 2016-03-10.47712 to V = 15.15 on UT 2016-03-10.47838 to V = 15.25 on UT 2016-03-10.47964.

A counterpart has been identified in SDSS data: a faint (r = 21.97 +/- 0.13), extremely red (r-z ~ 4.41) source ~1" away from the ASAS-SN detection. The i-z, i-J, i-K, z-J, J-H, J-K, and H-K colors were all consistent with those of M9 dwarfs from Schmidt et al. (2015, AJ, 149, 158). Applying the distance relation of Dupuy et al. (2012, ApJs, 201, 19) with WISE W2 gives a distance of 77 pc.

ASASSN-16cx is most likely a delta V~8 mag flare from an M-dwarf star, and given the very short duration of such events possibly even stronger. Similarly strong or even stronger flares have been observed from other late-M dwarfs (e.g. Stanek et al. 2013, ATel #5276; Schmidt et al. 2015, ApJ, 781, 24; Simonian et al 2014, ATel #6771) and recently an L dwarf (Shappee et al 2016, ATel #8553).

We thank LCOGT and its staff for their continued support of ASAS-SN. ASAS-SN is supported by NSF grant AST-1515927, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Mt. Cuba Astronomical Foundation, George Skestos, 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.