MLS121106:014420+082311 is a Flare from a Late-M Dwarf
ATel #4619; E. Berger, W. Fong, N. Sanders, and R. Chornock (Harvard)
on 5 Dec 2012; 05:41 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Edo Berger (eberger@cfa.harvard.edu)
Subjects: Infra-Red, Optical, Star, Transient
Referred to by ATel #: 4632
We observed the location of the fast CRTS transient MLS121106:014420+082311 (Mahabal et al. ATel #4586, de Ugarte Postigo et al. ATEL #4589; Mahabal et al. ATEL #4605) with the FourStar near-IR imager on the Magellan/Baade 6.5-m telescope on 2012 December 4 UT in the J, H, and Ks bands, and with the IMACS optical imager in z-band on 2012 December 5 UT. The source is clearly detected in all
bands with z=22.1, J=20.3, H=19.7, and Ks=19.3 mag (with an uncertainty of about 0.1 mag in each filter; AB mag in z-band and Vega mags in JHKs-bands); the Ks-band magnitude is consistent with the value reported by Mahabal et al. ATEL #4605. The source is unresolved in our Ks-band images, with seeing of about 0.4".
A comparison to the SDSS/2MASS colors of M dwarfs (e.g. West et al. 2011, AJ, 141, 97) clearly shows that the source is an M7-M8 dwarf (expected colors of z-J=1.8, J-H=0.6 and H-K=0.4 mag). This interpretation is also consistent with the reported r~26.5+/-0.5 mag (de Ugarte Postigo et al. ATel #4589), which leads to r-J=6.2+/-0.6 mag (compared to an expected r-J=5.9 mag). The absolute magnitude for M7-M8 dwarfs of M_J=11.5 mag indicates that the source is located at a distance of ~575 pc.
We therefore conclude that the fast transient MLS121106:014420+082311 is simply an M dwarf flare (much like the previously-discovered Deep Lens Survey fast transients: Kulkarni & Rau 2006, ApJ, 644, L63) and not an extreme extragalactic transient such an orphan GRB afterglow.