Fermi LAT detection of renewed GeV activity from the high redshift blazar PKS 0458-02
ATel #7952; Stefano Ciprini (ASDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration.
on 26 Aug 2015; 16:14 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar
Referred to by ATel #: 16113
The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed flaring gamma rays from a source positionally consistent with the flat spectrum radio quasar PKS 0458-02 (also known as S3 0458-02, DA 157, OA 141, and 3FGL J0501.2-0157), with radio coordinates, (J2000), R.A.: 75.303374 deg, Dec.: -1.987293 deg (Johnston et al. 1995, AJ, 110, 880). This blazar has a redshift z=2.286 (Strittmatter et al. 1974, ApJ, 190, 509).
Preliminary analysis indicates that on 24 August 2015 this distant FSRQ was in a high-flux state, with a daily gamma-ray flux (E>100MeV) of (1.6+/-0.3) X 10^-6 photons cm^-2 s^-1, and a peak 6-hour (18:00-24:00 UT) interval gamma-ray flux of (2.6+/-0.6) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 45 times greater than the average flux reported in the third Fermi-LAT source catalog, 3FGL (Acero et al. 2015, ApJS 218, 23). This flare is the brightest one seen from this source since the beginning of the Fermi mission. The corresponding spectral photon indices (E>100MeV) of respectively (2.4+/-0.2) and (2.5+/-0.3) are consistent with the average index of 2.414+/-0.036 in the 3FGL catalog.
PKS 0458-02 was at a similar flux level, (1.4+/-0.3) X 10^-6 photons cm^-2 s^-1, also on 23 and 26 August 2015. This is the third time that Fermi is announcing gamma-ray flaring activity from this FSRQ through an ATel, after those in September 2012 and March 2014 (ATel#4396 and ATel#5951).
This source is one of the "LAT Monitored Sources" and consequently a preliminary estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0458-02).
Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source, we encourage multiwavelength observations. For this source the Fermi LAT contact person is M. Orienti (orienti@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.