Fermi-LAT detection of renewed gamma-ray activity from blazars PKS 0514-459 and TXS 1700+685

ATel #14633; Stefano Ciprini (INFN Roma Tor Vergata, & ASI Space Science Data Center, Rome, Italy), on behalf of the the Fermi Large Area Telescope Collaboration
on 16 May 2021; 17:29 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.asi.it)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar PKS 0514-459, also known as RX J0515.7-4556 and MRC 0514-459 (4FGL J0515.6-4556; Abdollahi et al. 2020, ApJS, 247, 33), with radio counterpart position R.A.: 78.938767 deg, Dec.: -45.945369 deg (J2000.0, Costa & Loyola 1996, A&AS, 115, 75) and with redshift z=0.194 (Stickel, Kuehr, & Fried 1993, A&AS, 97, 483).

Preliminary analysis indicates that on 2021 May 13, PKS 0514-459 was in an active state reaching a daily averaged gamma-ray flux (E>100 MeV) of (1.4+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 70 times greater than its ten-year average flux reported in the fourth Fermi-LAT source catalog data release 2 (4FGL-DR2; Ballet et al., arXiv:2005.11208). The corresponding daily averaged spectral photon index (E>100 MeV) of 2.1+/-0.1 (statistical uncertainty only) is smaller than the 4FGL catalog value of 2.51+/-0.06. The peak flux is detected in the 6-hour interval of May 13 between 12:00 and 18:00 UT with a 6-hour averaged gamma-ray flux (E>100 MeV) of (2.7+/-0.5) X 10^-6 photons cm^-2 s^-1, and corresponding spectral photon index (E>100 MeV) of 2.0+/-0.2.

On May 14 and 15, PKS 0514-459 continued to show a plateau with a daily averaged gamma-ray flux (E>100 MeV) of (1.4+/-0.2) X 10^-6 photons cm^-2 s^-1, on both days. GeV gamma-ray activity of PKS 0514-459 has been previously announced two times since 2016, by the Fermi LAT Collaboration (ATel#8595 and ATel#13705).

Also on May 13 the LAT has observed enhanced gamma-ray flaring activity from TXS 1700+685, also known as RX J1700.1+6830, 6C B170021.9+683437 and GB6 J1700+6830 (4FGL J1700.0+6830; Abdollahi et al. 2020, ApJS, 247, 33), with coordinates R.A. = 255.0387196 deg, Decl. = +68.5019331 deg (J2000; Petrov et al. 2008. AJ, 136, 580), and redshift z=0.301 (Henstock et al. 1997, MNRAS, 290, 380).

Preliminary analysis indicates that 2021 May 13, TXS 1700+685 was in a flaring state with a daily averaged gamma-ray flux (E>100MeV) of (1.8+/-0.2) X 10^-6 photons cm^-2 s^-1, which corresponds to a flux increase of a factor >30 relative to the ten-year average flux reported in the 4FGL-DR2 catalog. The corresponding photon index is 1.9+/-0.1, smaller than the 4FGL-DR2 value of 2.38+/-0.02. The peak flux is detected in the 6-hour interval of May 13 between 12:00 and 18:00 UT with a 6-hour averaged gamma-ray flux (E>100 MeV) of (2.1+/-0.5) X 10^-6 photons cm^-2 s^-1, and corresponding spectral photon index (E>100 MeV) of 1.7+/-0.2.

On May 14 and 15, TXS 1700+685 showed a daily averaged gamma-ray flux (E>100 MeV) of (1.0+/-0.2) X 10^-6 photons cm^-2 s^-1, on both days. GeV gamma-ray activity of TXS 1700+685 has been previously announced two times since 2009, by the Fermi LAT Collaboration (ATel#1986 and recently ATel#14463). Both sources are included in the list of publicly monitored sources, and their preliminary light curves can be found at the Fermi Science Support Center.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of these sources will continue. In consideration of the ongoing activity of this source, we encourage multiwavelength observations. For the PKS 0514-459 source the Fermi LAT contact person is S. Ciprini (stefano.ciprini at ssdc.asi.it); for the TXS 1700+685 source the Fermi LAT contact person is S. Cutini (sara.cutini at pg.infn.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.