PG 1553+113 detected in bright optical state with ATOM
ATel #12631; Felix Jankowsky, Stefan Wagner (Landessternwarte Heidelberg)
on 5 Apr 2019; 16:16 UT
Credential Certification: Felix Jankowsky (f.jankowsky@lsw.uni-heidelberg.de)
Subjects: Optical, AGN, Blazar, Transient
Optical observations of the BL Lac object PG 1553+113 with the Automatic Telescope for Optical Monitoring (ATOM) in Namibia show this blazar in an emerging flare which appears to exceed any previously seen levels. Preliminary analysis of measurements performed in the night of 4 to 5 April 2019 (MJD 58578.108) result in an R flux of 12.7 optical magnitudes. Simultaneous B observations yield 13.5 optical magnitudes. This represents the momentary culmination of a continuous rise starting in the night of 5 to 6 February 2019 (MJD 58520.157) with 13.0 in R- and 13.8 in B-band.
PG 1553+113 has shown indications of periodic variations in the gamma-ray band (Ackermann 2015, ApJ, 813, 41). The flux cycle lasting around 800 days and the current optical brightening is in phase with an anticipated new maximum.
ATOM is a 75 cm telescope located at the H.E.S.S. site in the Khomas Highlands of Namibia. It monitors galactic and extragalactic gamma-ray emitters. PG 1553+113 forms part of this programme since 2007. ATOM will continue its coverage of PG 1553+113 in order to further characterise the flux variability of PG 1553+113.
