FACT measures increased gamma-ray flux from the high-energy peaked BL Lac object 1ES 1959+650 since five nights

ATel #9139; A. Biland for the FACT Collaboration
on 10 Jun 2016; 22:04 UT
Credential Certification: Adrian Biland (biland@phys.ethz.ch)

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The FACT collaboration reports the measurement of enhanced gamma ray flux at about 1 TeV from a position consistent with the HBL 1ES 1959+650 (z=0.047, Schachter et al. 1993, ApJ, 412, 541).

Recent activities from this source were reported at gamma rays (ATel #9010), IR (ATel #9070) and X-rays (ATel #9121), and the since Summer 2015 several periods of enhanced gamma-ray activity have been observed.

Since five nights, FACT measures an increased average flux corresponding to more than 0.5 Crab units with indication for intranight variability exceeding 1 Crab unit around MJD 57546.1-57546.2 and 57549.1-57549.2. For each of these five nights, the source is measured with a significance exceeding 5 standard deviations.

The results of a preliminary automatic quick look analysis are publicly available. http://fact-project.org/monitoring/index.php?y=2016&m=06&d=09&source=7&timebin=12&plot=month shows the evolution of a nightly binned background corrected light curve. These values are corrected neither for the effect of large zenith distance under which the source is observable nor for the amount of night-sky-background light, with both effects decreasing the measured gamma rate.

FACT is regularly monitoring 1ES 1959+650. Currently it is observing the source each night from 02:30 to 05:00 UTC if weather conditions permit. Contact person for this source is D. Dorner (dorner@astro.uni-wuerzburg.de)

The First G-APD Cherenkov Telescope (FACT) is an imaging air Cherenkov telescope with 9.5 sqm mirror area located in the Observatorio del Roque de los Muchachos on the Canary Island La Palma. It is pioneering the usage of silicon photosensors and monitoring bright variable sources at energies above 750 GeV. The Collaboration includes ETH Zurich and the Universities of Dortmund, Geneva and Wuerzburg.