OGLE-IV Light Curve of the Swift J1745-26 Transient
ATel #4921; A. Udalski (Warsaw University Observatory) on behalf of the OGLE-IV Team
on 27 Mar 2013; 18:18 UT
Credential Certification: Andrzej Udalski (udalski@astrouw.edu.pl)
Subjects: Optical, Black Hole, Transient, Variables
Referred to by ATel #: 5084
Optical counterpart of the Swift J1745-26 transient, a new black hole candidate, is located in the Galactic bulge fields regularly monitored by the OGLE-IV Survey (http://ogle.astrouw.edu.pl). Although the field belongs to lower cadence OGLE fields and the September 2012 outburst of J1745-26 occurred at the end of the Galactic bulge observing season - the OGLE Survey secured several images of the field that constrain the parameters of the outburst.
First, the first optical detection of the Swift transient (I~18.9 mag) occurred on the image taken on HJD'=6183.623 (HJD'=HJD-2450000). This is more than three days before the Swift BAT detection! The optical counterpart was not seen on the previous image taken on HJD'=6179.576 constraining the beginning of the outburst. The transient was also not detected on any image from the beginning of the OGLE-IV observations up to the outburst (>April 2010; 98 epochs; limit I>~21.0 mag).
Secondly, the optical counterpart of the Swift J1745-26 transient is still clearly seen on the OGLE-IV images - after ~190 days after the eruption. During the past 30 days its light curve reveals a broad plateau at I~19 mag. Thus, it is still within the reach of larger telescopes and follow up observations.
OGLE-IV Light Curve of the Swift J1745-26 Transient
