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Yet another strong GeV gamma-ray outburst of blazar CTA 102 observed by the Fermi LAT

ATel #10292; Stefano Ciprini (ASI SSDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 20 Apr 2017; 15:04 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Black Hole, Blazar, Quasar

Referred to by ATel #: 10330, 10386, 10560, 11045

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed new and strong gamma-ray activity from a source positionally consistent with the flat spectrum radio quasar CTA 102 (also known as 4C +11.69, PKS 2230+11, 3FGL J2232.5+1143) with VLBI coordinates (J2000.0), R.A.: 338.151704 deg, Dec.: 11.730807 deg (Johnston et al. 1995, AJ, 110, 880). The redshift of this blazar is z=1.037 (Schmidt 1965, ApJ, 141, 1295).

Preliminary analysis indicates that on 2017 April 19, CTA 102 was in a very high state with a daily averaged gamma-ray flux (E>100 MeV) of (13.2+/-0.6) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 80 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23), making this source the brightest in the gamma-ray sky. The corresponding daily averaged photon spectral index (E>100 MeV) of 1.9+/-0.1 (statistical uncertainty only) is smaller than the 3FGL catalog value of 2.34+/-0.03.

The peak 6-hour integrated gamma-ray flux (E>100 MeV) of (21.1+/-1.5) X 10^-6 photons cm^-2 s^-1 was reached by CTA 102 on 2017 April 19 in the interval 00:00-06:00 UT, about 130 times greater than the average flux reported in the 3FGL catalog, and about double the Vela gamma-ray flux in the same interval. A high-energy photon of 24 GeV is also positionally consistent with CTA 102.

This is renewed powerful GeV gamma-ray outburst activity, after the prolonged outburst already reported by Fermi, AGILE and DAMPE in the period between 2016 November and 2017 January (ATel#9743, ATel#9788, ATel#9840, ATel#9901, ATel#9911), and the optical flaring activity observed from the end of 2016 October through January 2017 (for example ATel#10007).

This is the seventh time that the Fermi-LAT Collaboration has announced flaring GeV gamma-ray behavior of CTA 102 after ATel#3320, ATel#4409, ATel#6631, ATel#8478, ATel#8722, ATel#9869. Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is a member of the "LAT Monitored Sources", with preliminary, uncalibrated estimation of the daily gamma-ray flux observed by Fermi LAT publicly available at http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/CTA_102 . Dedicated Fermi ToO pointed observations are under consideration based on the behavior of the source in the next hours. In consideration of the ongoing activity of this source, we encourage multiwavelength observations. The Fermi LAT contact persons for this source are S. Cutini (sara.cutini@ssdc.asi.it) and S. Buson (sara.buson@gmail.com).

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.