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Hard-spectrum gamma-ray flare from PKS 0507+17

ATel #9779; M. Kreter (University of Wurzburg) and S. Buson (NASA-GSFC) on behalf of the Fermi-LAT collaboration
on 22 Nov 2016; 04:38 UT
Credential Certification: Sara Buson (sara.buson@nasa.gov)

Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux and an unusually hard gamma-ray spectrum from a source positionally consistent with PKS 0507+17 (R.A.= 05h10m02.3691s, Dec.= +18d00m41.582s, J2000.0, Johnston et al. 1995, AJ, 110, 880). PKS 0507+17, also known as 3FGL J0510.0+1802 (Acero et al. 2015, ApJS, 218, 23), is a flat spectrum radio quasar at redshift z = 0.416 (Perlman et al. 1998, AJ, 115, 1253).

Preliminary analysis indicates that on 2016 November 20, the gamma-ray source was in a high state with a daily averaged flux (E>100 MeV) of (1.9+/-0.3) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), more than 60 times greater than the average flux reported in the third Fermi LAT source catalog. The corresponding daily averaged photon index of 1.77+/-0.08 (statistical uncertainty only) is notably smaller than the average index of 2.40+/-0.06 in the 3FGL catalog. Five photons of energies between 10 GeV and 20 GeV are positionally consistent with PKS 0507+17.

Previous hard-spectrum enhanced activity was observed by Fermi LAT on 2013 April 23 (ATel #5001). Recently, ATel #9672 reported a NIR flare from PKS 0507+17 during October 2016. PKS 0507+17 is one of the sources regularly monitored by Fermi. The light curve of the past year indicates that this source is in a state of increased emission (http://fermi.gsfc.nasa.gov/FTP/glast/data/lat/catalogs/asp/current/lightcurves/PKS0507+17_86400_1yr.png). Note the sudden outburst in the light curve.

Since Fermi operates in an all-sky scanning mode, regular monitoring of this source will continue. In consideration of the ongoing activity of this source we encourage multiwavelength observations. The Fermi LAT contact person for this source is Filippo D'Ammando (dammando@ira.inaf.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.