Fermi-LAT discovery of VHE emission from blazar PKS 0903-57
ATel #13604; Sara Buson (Univ. Wuerzburg) on behalf of the Fermi Large Area Telescope Collaboration
on 1 Apr 2020; 18:09 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)
Subjects: >GeV, VHE, Request for Observations, Blazar
The Fermi-Large Area Telescope (LAT) collaboration reports the discovery of very-high energy (VHE; E>100 GeV) gamma-ray emission from the blazar PKS 0903-57, also known as 4FGL J0904.9-5734 (The Fermi-LAT collaboration 2020, ApJS, 247, 1), with coordinates R.A. = 136.2215792 deg, Decl. = -57.5849397 deg (J2000; Fey et al. 2004, AJ, 128, 2593). A tentative redshift of z=0.695 has been reported in the literature (Thompson et al. 1990, PASP, 102, 1235). If this redshift is accurate, this object would be among the most distant VHE blazars.
A preliminary analysis of the LAT data of March 31, 2020 has identified several high-energy (>10 GeV) photons positionally consistent with the source and with high probability of being associated with it. Among those, a 106 GeV photon was detected at 2020-03-31 13:56:27.000 UTC, providing the first evidence of VHE emission from this blazar. On March 31, 2020, the LAT recorded a daily averaged gamma-ray flux (E>100MeV) of (8.2 +/- 0.5) X 10^-6 photons cm^-2 s^-1 and a corresponding photon index of 1.80 +/- 0.04 (statistical uncertainty only). PKS 0903-57 is currently experiencing a bright flare in the gamma-ray band as reported by the LAT (ATel #13599, GCN #1585406753, GCN #1585493148, GCN #1585579548, GCN #1585752493) and confirmed by AGILE (ATel #13602).
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is included in the "LAT Monitored Sources" list and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/). We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Isabella Mereu (mereuisabella@gmail.com).
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.
