Fermi LAT detection of a GeV gamma-ray flare from the distant blazar PKS 0226-559

ATel #11283; Stefano Ciprini (SSDC-ASI Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 10 Feb 2018; 00:16 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.asi.it)

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The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray emission from a source positionally consistent with the flat spectrum radio quasar PKS 0226-559 (also known as PMN J0228-5546, CGRaBS J0228-5546 and 3FGL J0228.3-5545) with radio coordinates (J2000) R.A.: 37.09004 deg, Dec.: -55.76764 deg (Fey et al. 2015, AJ, 150, 58). This blazar has a high redshift, z=2.471 (Mahony et al. 2011, MNRAS, 417, 2651).

PKS 0226-559 has brightened in GeV gamma rays since the beginning of January 2018. Preliminary analysis indicates that on February 6, 2018, PKS 0226-559 was in a flaring state with a daily averaged gamma-ray flux (E>100 MeV) of (0.8+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 35 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 photon spectral index (E>100 MeV) of 2.1+/-0.2 (statistical uncertainty only) is smaller than the 3FGL catalog value of 2.43+/-0.06.

PKS 0226-559 continued to be detected on a daily basis on February 7 and 8, 2018, with daily averaged gamma-ray fluxes (E>100 MeV) respectively of (0.3+/-0.1) X 10^-6 photons cm^-2 s^-1 and (0.4+/-0.1) X 10^-6 photons cm^-2 s^-1. The corresponding photon spectral indexes (E>100 MeV) of 1.8+/-0.2 and 1.9+/-0.2 suggest a rather hard spectral state during the current flaring state.

This is the first time that an increasing gamma-ray flux for this source has been announced by the Fermi LAT Collaboration, after almost 9.6 years of Fermi LAT all-sky survey observations. The source was also reported in a flaring state in the optical band on January 22, 2018 by MASTER Net (ATel#11225).

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 S. Ciprini (stefano.ciprini@ssdc.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.