First Fermi LAT detection of a strong GeV gamma-ray flare from blazar PKS 0403-13

ATel #9242; Stefano Ciprini (ASI ASDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 12 Jul 2016; 21:02 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 0403-13 (also known as TXS 0403-132, OF -105, RX J0405.5-1308, and 3FGL J0405.5-1307), with radio counterpart position R.A.: 61.391680 deg, Dec.: -13.137136 deg (J2000.0, Fey et al. 2004, AJ, 127, 3587) and with redshift z=0.5706+/-0.0001 (Marziani et al. 1996, ApJS, 104, 37).

Preliminary analysis indicates that on 2016 July 11, PKS 0403-13 was in a high state with a daily averaged gamma-ray flux (E>100 MeV) of (1.6+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 140 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 2.3+/-0.2 (statistical uncertainty only) is compatible with the 3FGL catalog value of 2.35+/-0.11.

Peak 6-hour integrated gamma-ray fluxes of (2.3+/-1.0) X 10^-6 photons cm^-2 s^-1 and (2.0+/-0.6) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), were reached by PKS 0403-13 on 2016 July 11, respectively in the intervals 06:00-12:00 UT and 12:00-18:00 UT, corresponding to about 180 times the average flux reported in the 3FGL catalog.

This is the first time that the Fermi-LAT Collaboration is announcing this level of gamma-ray flux on daily timescale from PKS 0403-13. Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is being added to 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/. In consideration of the ongoing activity of this source, we encourage multiwavelength observations. For this source the Fermi LAT contact person is S. Ciprini (stefano.ciprini@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.