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Fermi-LAT Detection of an Unusual Hard Spectrum and Enhanced Gamma-ray Emission from the FSRQ PKS 0131-522

ATel #10987; Roopesh Ojha (NASA/GSFC/UMBC), Janeth Valverde (LLR/Ecole Polytechnique), and Pfesesani van Zyl (Hartebeesthoek Radio Astronomy Observatory) on behalf of the Fermi Large Area Telescope Collaboration
on 19 Nov 2017; 15:42 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

Subjects: Gamma Ray, >GeV, TeV, AGN, Blazar, Quasar

Referred to by ATel #: 11003

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has observed increasing gamma-ray flux and an unusually hard spectrum from a source positionally consistent with the flat spectrum radio quasar PKS 0131-522 (also known as 3FGL J0133.2-5159, Acero et al. 2015, ApJS, 218, 23) with coordinates R.A.: 01h33m05.7625s Dec:-52d00m03.946s, (J2000; Johnston et al., 1995, AJ, 110, 880) and a redshift of 0.02 (Johnston et al. 1995, AJ, 110, 880).

Preliminary analysis indicates that on 16 and 17 November 2017 this source was in an extremely high-flux state, with a daily averaged gamma-ray flux (E>100MeV) of (0.8+/-0.2) X 10^-6 photons cm^-2 s^-1 and (1.6+/-0.2) X 10^-6 photons cm^-2 s^-1, respectively (statistical uncertainty only). The latter corresponds to a flux increase of a factor of about 200 relative to the average flux reported in the third Fermi LAT catalog (3FGL). The corresponding photon spectral indices of 2.0+/0.2 and 1.8+/-0.1, respectively, are significantly harder than the 3FGL value 2.6+/-0.2. The spectrum is also significantly harder than during the previous flare of this source in June 2014 (ATel#6223) when the photon spectral index was between 2.1+/-0.2 and 2.4+/-0.3. Thus, this flare is a rare example of a 'red turned blue' blazar.

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 Josefa Becerra (jbecerragonzalez@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.