Fermi-LAT detection of a GeV gamma-ray flare from the blazar PKS 2023-07

ATel #8932; Stefano Ciprini (ASDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration.
on 10 Apr 2016; 20:58 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 increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar PKS 2023-07 (also known as NRAO 629, TXS 2022-077, 3EG J2025-0744, 1AGLR J2027-0747 and 3FGL J2025.6-0736), with radio counterpart position R.A.: 306.419418 deg, Dec.: -7.597969 deg (J2000.0, Beasley et al. 2002, ApJS, 141, 13) and with redshift z=1.388 (Drinkwater et al. 1997, MNRAS, 284, 85).

Preliminary analysis indicates that on 2016 April 9, PKS 2023-07 was in a high state with a daily averaged gamma-ray flux (E>100 MeV) of (2.0+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 16 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23). The corresponding daily averaged spectral photon index (E>100 MeV) of 2.4+/-0.2 (statistical uncertainty only) is compatible with the 3FGL catalog value of 2.18+/-0.03.

A peak 6-hour integrated gamma-ray flux of (3.7+/-0.9) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), was reached on 2016 April 9, 06:00-12:00 UT, corresponding to about 29 times the average flux reported in the third Fermi-LAT source catalog.

Increased activity from PKS 2023-07 has been observed by LAT from July 2015. This follows about 5.5 years of a relatively quiescent state. Flaring emission was recently reported in March 2016 by AGILE (ATel#8879). This is the second announcement from the LAT collaboration of gamma-ray flaring activity from PKS 2023-07, following the ATel#2175 in August 2009.

PKS 2023-07 is one of the "LAT Monitored Sources" and consequently a preliminary estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_2023-07).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source, we encourage multiwavelength observations. For this source the Fermi LAT contact person is D. Bastieri (bastieri@pd.infn.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.