FACT measures new maximum flux from the HBL 1ES 1959+650 at TeV energies
ATel #9239; A. Biland (ETH Zurich) on behalf of the FACT Collaboration
on 12 Jul 2016; 09:31 UT
Credential Certification: Daniela Dorner (dorner@astro.uni-wuerzburg.de)
Subjects: Gamma Ray, TeV, VHE, AGN, Blazar
The FACT collaboration reports the measurement of an 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 in gamma rays (ATel #9010, #9139, #9148, #9168, #9203), IR (ATel #9070) and X-rays (ATel #9121, #9205). Since July 2015, several periods of enhanced activity have been observed. After the flare of MJD 57570 (ATel #9203), the flux decayed to about 0.5 Crab units within a few nights, then increased to about 1.5 Crab units (MJD 57579 and 57580).
From MJD 57581.01 till 57581.17, FACT measured a flux increasing from 2 Crab units to at least 3.5 Crab units. The source is detected with about 20 standard deviations in 3.8 hours of observation. The results of a preliminary, automatic quick look analysis are publicly available. http://fact-project.org/monitoring/index.php?y=2016&m=07&d=11&source=7&timebin=3&plot=night shows the 20-minute-binned background subtracted 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. The evolution of the nightly flux in the last month is available at http://fact-project.org/monitoring/index.php?y=2016&m=07&d=11&source=7&timebin=12&plot=month
FACT is regularly monitoring 1ES 1959+650. Currently, it is observing the source each night from 0:15 to 04:00 UTC, if weather conditions permit. The FACT contact person for this source is D. Dorner
(dorner@astro.uni-wuerzburg.de)
The First G-APD Cherenkov Telescope (FACT) is an Imaging Atmospheric 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 with an analysis threshold of 750 GeV. The Collaboration includes ETH Zurich and the Universities of Dortmund, Geneva and Wuerzburg.
