Fermi-LAT detection of renewed gamma-ray activity from the blazars PKS 0346-27 and PKS 2246+208

ATel #12693; A. Gokus (University of Wuerzburg, Remeis Observatory Bamberg & ECAP), R. Angioni (MPIfR-Bonn) on behalf of the Fermi Large Area Telescope Collaboration
on 26 Apr 2019; 08:22 UT
Credential Certification: Roberto Angioni (angioni@mpifr-bonn.mpg.de)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed the highest historically recorded gamma-ray flaring activity from sources positionally consistent with the flat-spectrum radio quasar PKS 0346-27 (4FGL J0348.5-2749; RA = 57.1589354 deg, DEC = -27.8204344 deg, J2000; Beasley et al. 2002 ApJS, 141, 13), at redshift 0.991 (White et al. 1988 ApJ, 327, 561) and with the flat-spectrum radio quasar PKS 2246+208 (4FGL J2248.9+2106; RA = 342.252361 deg, DEC = 21.11745 deg, J2000; Beasley et al. 2002, ApJS, 141, 13) at redshift 1.274 (Sowards-Emmerd et al. 2005, ApJ, 626, 95).

PKS 0346-27 has been flaring in gamma-rays since the beginning of 2018, as reported in ATel #11251 and ATel #11644. Preliminary analysis indicates that this source reached its historical maximum gamma-ray flux on 24 April 2019, with a daily averaged gamma-ray flux (E>100MeV) of (3.2+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). The latter corresponds to a flux increase of a factor of ~180 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL; The Fermi-LAT collaboration 2019, arXiv:1902.10045). The corresponding photon index is 2.1 +/- 0.1, and is significantly harder than the 4FGL value of 2.5 +/- 0.1.

The source coincident with PKS 2246+208 has been identified as a new X-ray/Gamma-ray blazar in January 2019 in ATel#12403 by the Fermi-LAT Collaboration. Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 24 April, with a daily averaged gamma-ray flux (E>100MeV) of (1.1+/- 0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), a factor ~200 greater than reported in the 4FGL. This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 1.8 +/- 0.2, and is consistent with the values reported in ATel#12403. It is significantly harder than the 4FGL value of 2.3+/-0.1.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of both sources will continue. Both sources are included in the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/). We encourage multifrequency observations of both PKS 0346-27 and PKS 2246+208. For PKS 0346-27, the Fermi-LAT contact person is Roberto Angioni (angioni@mpifr-bonn.mpg.de). For PKS 2246+208, the contact persons are Stefano Ciprini (stefano.ciprini@ssdc.asi.it) and Roberto Angioni (angioni@mpifr-bonn.mpg.de).

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.