[ Previous | Next | ADS ]

Further increase of gamma-ray emission from the HBL 1ES 1959+650

ATel #9148; A. Biland (ETH Zurich), D. Dorner (University of Wurzburg, FAU Erlangen), R. Mirzoyan (Max-Planck-Institute for Physics), R. Mukherjee (Barnard College, Columbia University), S. Buson (NASA-GSFC) on behalf of the FACT, MAGIC, VERITAS and Fermi-LAT collaborations and B. Kapanazde (Abastumani Astrophysical Observatory, Ilja State University)
on 13 Jun 2016; 22:14 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Adrian Biland (biland@phys.ethz.ch)

Subjects: X-ray, Gamma Ray, >GeV, TeV, VHE, AGN

Referred to by ATel #: 9168, 9203, 9239

FACT, MAGIC, VERITAS and Fermi-LAT collaborations report the measurement of a further increase of the gamma-ray flux together with bright X-ray emission seen by Swift-XRT from a position consistent with the high-energy peaked BL Lac type object 1ES 1959+650 (z=0.047, Schachter et al. 1993, ApJ, 412, 541). Enhanced TeV flux was reported by FACT between MJD 57546--57550 (ATel #9139). After a slight decrease within that period, a new maximum in the TeV flux was measured last night between MJD 57552.09 and 57552.25. Within about 2.7 hours of observations, FACT observed a a flux exceeding 2.5 Crab units, with a statistical significance of 16 standard deviations. This is twice the highest flux observed during the high states in the past week. The results of a preliminary automatic quick look analysis are publicly available, where this link: http://fact-project.org/monitoring/index.php?y=2016&m=06&d=12&source=7&timebin=12&plot=month shows the evolution of a nightly binned background subtracted light curve for the last month. 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 02:15 to 05:00 UTC if weather conditions permit. The source has also been monitored daily by the MAGIC telescopes. For the night of MJD 57552, the preliminary flux above 200GeV from automatic analysis is at the level of about 2.5 Crab units. MAGIC will continue observing the source. VERITAS observed the source for 3.5 hours under bright moonlight conditions on MJD 57552. A preliminary analysis of the data shows a strong detection of the source with a statistical significance of about 60 standard deviations, increasing in flux above 300 GeV from about 1.0e-10 cm^-2 s^-1 (80% of the Crab nebula) to a peak of over 2.6e-10 cm^-2 s^-1 (200% of the Crab nebula) at the end of the observing period. Preliminary analysis of Fermi-LAT data indicates that the object’s flux has almost doubled over the past three weeks. The observed gamma-ray flux (E>1GeV) was (1.9+/-0.5) x 10^-8 cm^-2 s^-1 during the week of 23-30 May, and (4.2+/-0.8) x 10^-8 cm^-2 s^-1 during the week of 6-13 May (statistical uncertainty only). The source detection significance (test statistic) for these weeks was 91 and 250, respectively. Monitoring with the X-ray Telescope onboard the Swift satellite (Swift-XRT) shows that the source underwent a strong X-ray flare comparable to that in 2015 November-December. The highest level during the ongoing flare is reached on June 9 with a 0.3-10 keV count rate of 20.50+/-0.15 cts/s which is only by 12% smaller than the highest historical rate recorded on 2015 December 26. Last night, where the observations was split into two orbits, the count rate was 18.55+/-0.15 cts/s, which corresponds to an unabsorbed 0.3-10 keV flux was (7.41-8.13)\times 10^{-10) erg/cm^2/s during the today's observation. Activity in gamma rays and X-rays has been reported over the past 6 months (Atel #8014, #8107, #8148, #8165, #8193, #8289, #8337, #8342, #8468) with a recent increase seen in multiple different wavebands (ATel #9010, #9070, #9121). Coordinated observations among FACT, MAGIC, VERITAS Fermi-LAT and Swift are ongoing. In consideration of the current activity of this source, we encourage multiwavelength observations. For this source, the Fermi LAT contact person is S. Buson (sara.buson@nasa.gov), for FACT is D. Dorner (dorner@astro.uni-wuerzburg.de), for MAGIC is R. Mirzoyan (Razmik.Mirzoyan@mpp.mpg.de), for VERITAS is R. Mukherjee (muk@astro.columbia.edu).