Fermi LAT detection of renewed and strong GeV gamma-ray flares from blazars PKS 0903-57 and PKS 0346-27
ATel #11644; Stefano Ciprini (SSDC-ASI Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 15 May 2018; 18:11 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.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 high-level gamma-ray activity from sources positionally consistent with the active galaxy PKS 0903-57 (also known as MRC 0903-573 and 3FGL J0904.8-5734, Acero et al. 2015, ApJS, 218, 23) and with the flat spectrum radio quasar PKS 0346-27 (also known as OE -278, TXS 0346-279, MRC 0346-279 and 3FGL J0348.6-2748).
PKS 0903-57 with VLBI radio coordinates (J2000.0) R.A.: 136.221579 deg, Dec.: -57.58494 deg (Fey et al. 2004, AJ, 128, 2593) and redshift z=0.695 (Thompson et al. 1990, PASP, 102, 1235), and is considered a blazar candidate of unknown type in the third Fermi-LAT source catalog (3FGL).
Preliminary analysis indicates that on 2018 May 14, PKS 0903-57 was in a high state with a daily averaged gamma-ray flux (E>100 MeV) of (2.2+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 55 times greater than its four-year average flux reported in the 3FGL catalog. This is the highest flux level observed since the start of the Fermi LAT survey.
The corresponding photon spectral index (E>100 MeV) of 2.0+/-0.1 (statistical uncertainty only) is harder than the 3FGL catalog value of 2.25+/-0.05. The peak 6-hour integrated gamma-ray flux (E>100 MeV) of (2.8+/-0.5) X 10^-6 photons cm^-2 s^-1 was reached by PKS 0903-57 in the interval 12:00-18:00 UT, with corresponding photon spectral index of 1.8+/-0.1. This is the second time that the Fermi-LAT Collaboration has announced flaring GeV gamma-ray behavior from PKS 0903-57 (see ATel#7704).
PKS 0346-27 with VLBI radio coordinates (J2000.0) R.A.: 57.158935 deg, Dec.: -27.820434 deg (Beasley et al. 2002, ApJS, 141, 13) is a flat spectrum radio quasar with redshift z=0.991 (White et al. 1988 ApJ, 327, 561). Preliminary analysis indicates that on 2018 May 13, PKS 0346-27 was in a high state with a daily averaged gamma-ray flux (E>100 MeV) of (1.4+/-0.2) X 10^-6 photons cm^-2 s^-1, about 150 times greater than its four-year average flux reported in the 3FGL catalog. This is the highest flux level observed since the start of the Fermi LAT survey. The corresponding photon spectral index (E>100 MeV) of 1.9+/-0.1 is significantly harder than the 3FGL catalog value of 2.38+/-0.12. On May 14, 2018 the daily averaged flux is (0.7+/-0.1)e-6 with corresponding photon spectral index of 1.8+/-0.1. At least one photon of 30.3 GeV energy is detected in this day to be preliminary consistent with this source. This is the second time that the Fermi-LAT Collaboration has announced flaring GeV gamma-ray behavior from PKS 0346-27 (see ATel#11251).
These two sources are members of the "LAT Monitored Sources", with preliminary, uncalibrated estimations of the daily gamma-ray flux observed by Fermi LAT publicly available respectively at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0903-57 and at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0346-27 .
In consideration of the ongoing gamma-ray activity of this source, we encourage multiwavelength observations. The Fermi LAT contact person for PKS 0903-57 is B. Carpenter (carpbr01@gmail.com). The Fermi LAT contact person for PKS 0346-27 is R. Angioni (angioni@mpifr-bonn.mpg.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.