VVV-WIT-03: Another transient event of unknown origin in the VVV survey

ATel #8244; J. C. Beamin (Universidad de Valparaiso, Millennium Institute of Astrophysics), D. Minniti (Universidad Andres Bello, Vatican Observatory, Millennium Institute of Astrophysics), R. K. Saito (Universidade Federal de Sergipe)
on 4 Nov 2015; 15:35 UT
Credential Certification: Roberto Saito (saito@ufs.br)

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We report the discovery of a transient event in our VVV monitoring of the Milky Way disk in the near infrared. The source position is RA(J2000)= 14:21:36.76, DEC (J2000)= -63:19:36.8. These coordinates are good to <1 arcsec. An initial very faint source is only seen in the J-band images taken on April 1 2010, but no point source is detected up to a 5 sigma limit corresponding to J=19.22. The field is typical of a random field in the Milky Way plane, showing nothing special, and the target does not appear to be very reddened (with J-Ks~0.8 in 2015).

The object is not detectable in all the Ks-band images from 2010 to 2013. Observations acquired from March 4 2010 to June 13 2013 do not show the source down to the detection limit of Ks~17.0 mag. Then during the2014 observing season the object appears badly saturated. Observations acquired between June 4 and June 16 2014 show the source was brighter than our saturation limit of Ks~10. Finally, during the observing season this year 2015, that started 325 days after our last observation in 2014, the object is marginally detected in the Ks band (Ks=16.6+/-0.15). It is also detected in the other four VVV bands around the same dates in May 2, 2015 we measured Z=18.482+/-0.060 and Y=18.110+/-0.075, and in June 7 2015, J=17.466+/-0.048, H=17.000+/-0.064.

The light curve with upper and lower limits in the Ks band and the color information in the ZYJH bands can be seen in http://figshare.com/articles/VVV_WIT_003/1593025. After the burst the source faded nearly 7 magnitudes in one year, but due to a lack of observations in this period the type of variable is unconstrained.