MLS121106:014420+082311 is a Flare from a Late-M Dwarf

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....