Fermi LAT detection of a GeV flare from the radio-loud narrow-line Seyfert 1 Galaxy PKS 2004-447

ATel #13229; Andrea Gokus (University of Wuerzburg, Remeis Observatory Bamberg & ECAP) on behalf of the Fermi Large Area Telescope Collaboration
on 26 Oct 2019; 21:01 UT
Credential Certification: David J. Thompson (David.J.Thompson@nasa.gov)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray flux from a source positionally consistent with PKS 2004-447, also known as 4FGL J2007.9-4432 (The Fermi-LAT collaboration 2019, arXiv:1902.10045), with coordinates R.A.= 301.979929 deg, Decl.= -44.578967 deg (J2000; Gaia Collaboration, 2018, A&A, 616, A1), a radio-loud narrow-line Seyfert 1 galaxy at z=0.24 (Drinkwater et al., 1997, MNRAS, 284, 85). Although PKS 2004-447 is included in all Fermi-LAT gamma-ray source catalogs, it has so far not been reported in outburst. Radio- and gamma-bright narrow-line Seyfert 1 galaxies are a rare class of objects seen by Fermi-LAT, and flares in these sources are even rarer events.

Preliminary analysis indicates that the source was in a high state on October 25, with a gamma-ray flux (E>100MeV) of (1.1+/-0.2) x 10^-6 photon cm^-2 s^-1 (statistical uncertainty only), which represents an increase of a factor of 55 with respect to the average source 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 2.4+/-0.2, slightly smaller than the 4FGL value of 2.60+/-0.05. Its flux has steadily increased since October 23.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is being added to the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available at http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/. Given that the source's flux has been increasing over the past three days, and this source shows the first outburst since Fermi-LAT observations started, we strongly encourage further multifrequency observations of this source. For this source, the Fermi-LAT contact person is Andrea Gokus (andrea.gokus@astro.uni-wuerzburg.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.