Fermi-LAT detection of renewed gamma-ray activity from the FSRQs PKS 0208-512 and 4C +50.11

ATel #13558; R. Angioni (SSDC/INFN), on behalf of the Fermi Large Area Telescope Collaboration
on 16 Mar 2020; 21:59 UT
Credential Certification: Roberto Angioni (r.angioni90@gmail.com)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed renewed gamma-ray flaring activity from two sources positionally consistent with the flat-spectrum radio quasar PKS 0208-512, also known as 4FGL J0210.7-5101 (The Fermi-LAT collaboration 2020, ApJS, 247, 1), with coordinates R.A. = 32.692502 deg, Decl. = -51.017192 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.999 (Wisotzki et al. 2000, A&A, 358, 77), and with the flat-spectrum radio quasar 4C +50.11, also known as NRAO 150 and 4FGL J0359.6+5057, with coordinates R.A. = 59.873947 deg, Decl. = 50.963934 deg (J2000; Beasley et al. 2002, ApJS, 141, 13), and redshift z=1.517 (Acosta-Pulido et al. 2010, A&A, 519, 5).

Preliminary analysis indicates that PKS 0208-512 has been in an elevated gamma-ray emission state with a rising trend lasting several months (see ATel #13320), reaching a daily averaged gamma-ray flux (E>100MeV) of (2.0+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) on 15 March 2020. The latter corresponds to a flux increase of a factor of about 20 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.05+/-0.09, and is significantly smaller than the 4FGL value of 2.35+/-0.01. This hard-spectrum state coincided with the detection of two E>10 GeV photons with a probability >99% of being produced by the target source, with energies of 23 GeV and 49 GeV.

Preliminary analysis indicates that 4C +50.11 has been detected in an elevated gamma-ray emission state on 15 March 2020, with a daily averaged gamma-ray flux (E>100MeV) of (1.3+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). The latter corresponds to a flux increase of a factor of about 20 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is comparable to the highest LAT daily flux ever observed for this gamma-ray source, which was recorded in 2014 (see ATel #5838). The corresponding photon index is 2.15+/-0.15, and is significantly smaller than the 4FGL value of 2.64+/-0.03.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of these sources will continue. These sources are included in the "LAT Monitored Sources" list 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 these sources. For PKS 0208-512, the Fermi-LAT contact person is W. Collmar (wec@mpe.mpg.de). For 4C +50.11, the Fermi-LAT contact person is R. Angioni (roberto.angioni@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.