Fermi-LAT detection of hard spectrum gamma-ray activity from the FSRQ PKS 1532+01
ATel #7175; S. Ciprini (ASI Science Data Center Rome & INFN Perugia, Italy), C. C. Cheung (Naval Research Laboratory, USA) on behalf of the Fermi Large Area Telescope Collaboration
on 4 Mar 2015; 18:31 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux and an unusually hard gamma-ray spectrum from a source positionally consistent with the flat spectrum radio quasar (FSRQ) PKS 1532+01 (also known as 3FGL J1534.5+0128, Acero et al. 2015, arXiv:1501.02003) with radio counterpart coordinates (J2000.0), R.A. = 233.71856 deg, Dec. = 1.51784 deg (Johnston et al. 1995, AJ, 110, 880). This FSRQ has redshift z=1.425 (White et al. 1988, ApJ, 327, 561).
Preliminary analysis indicates that on February 27, 2015, the gamma-ray source was in a high state with a daily averaged flux (E>100 MeV) of (0.3+/-0.1) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), more than 10 times greater than the average flux reported in the third Fermi LAT source catalog (3FGL). The corresponding daily-averaged photon index (E>100 MeV) of 1.7+/-0.2 (statistical uncertainty only) is notably smaller than the average index of 2.779+/-0.114 in the 3FGL catalog. The weekly averaged flux (E>100 MeV) from February 23 - March 1, 2015 is (0.2+/-0.1) x 10^-6 photons cm^-2 s^-1, with a corresponding photon index of 2.0 +/- 0.2.
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 S. Ciprini (stefano.ciprini@asdc.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.
