Fermi LAT observation of renewed and strong GeV gamma-ray activity from blazar CTA 102

ATel #9869; Stefano Ciprini (ASI ASDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 16 Dec 2016; 20:52 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a new phase of 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 2016 December 14, CTA 102 was in a very high state with a daily averaged gamma-ray flux (E>100 MeV) of (12.1+/-0.7) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 75 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 point source the brightest in the whole gamma-ray sky. The corresponding daily averaged photon spectral index (E>100 MeV) of 2.0+/-0.1 (statistical uncertainty only) is harder than the 3FGL catalog value of 2.34+/-0.03.

The peak 6-hour integrated gamma-ray flux (E>100 MeV) of (15.6+/-1.5) X 10^-6 photons cm^-2 s^-1 was reached by CTA 102 on 2016 December 14 in the interval 06:00-12:00 UT, equivalent to about two orders of magnitude greater than the average flux reported in the 3FGL catalog. On 2016 December 15 the daily averaged gamma-ray flux (E>100 MeV) was still very high: (10.8+/-0.5) X 10^-6 photons cm^-2 s^-1.

Increased GeV gamma-ray flux has already been reported by AGILE since 2016 November 11 in several episodes (ATel#9743, ATel#9788, ATel#9840), while a prolonged phase of outburst behavior has been observed in the optical band since the end of 2016 October (for example ATel#9676, ATel#9732, ATel#9756, ATel#9776, ATel#9801, ATel#9808, ATel#9821, ATel#9868). Enhanced activity at UV and X-ray bands was also reported by Swift (ATel#9841).

This is the sixth 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. Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. Fermi is currently in a Target of Opportunity mode with enhanced exposure to CTA 102. The TOO will continue through the next three days. 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 . In consideration of the ongoing activity of this source, we encourage multiwavelength observations. The Fermi LAT contact person for this source is S. Cutini (sara.cutini@asdc.asi.it).

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.