Fermi-LAT evidence for VHE emission from NVSS J065844+063711
ATel #14200; S. Buson (Univ. Wuerzburg), S. Garrappa (DESY-Zeuthen) and C. C. Cheung (Naval Research Laboratory) on behalf of the Fermi Large Area Telescope Collaboration
on 19 Nov 2020; 13:36 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)
Subjects: Gamma Ray, >GeV, VHE, Neutrinos, Request for Observations, Blazar
The Fermi-Large Area Telescope (LAT) collaboration reports possible detection of very-high-energy (VHE; E>100 GeV) gamma-ray emission from the active galaxy of uncertain type NVSS J065844+063711 with coordinates R.A. = 104.687375 deg, Decl. = 6.619861 deg (J2000; Condon et al 1998, AJ, 115, 1693). This object is associated with the Fermi-LAT catalogued source 4FGL J0658.6+0636 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), also designated 3FHL J0658.3+0636 (Ajello et al. 2017, ApJS, 232, 18).
A preliminary analysis of more than 12 years of LAT data (2008-08-04 to 2020-11-14 UTC) has identified several high-energy (HE, >10 GeV) photons positionally consistent with the source and with high probability of being associated with it (>90% probability). On average, the Fermi-LAT has detected one HE photon per year associated with this source. Among those, a 155 GeV photon (>95% probability) was detected on 2018-01-28 07:14:07.976 UTC, providing first evidence of VHE emission from this object. The detection of the VHE event was accompanied by three other HE photons within a ~1-year period.
The object NVSS J065844+063711 is listed in the third high-synchrotron peak catalog (3HSP J065845.0+063711; Chang et al. 2019 A&A 632, A77). Its broadband properties resemble those of a high-synchrotron peaked blazar, hence it is a promising VHE emitter. It is the second VHE object found within the 90% confidence region of a well-reconstructed, high-energy IceCube neutrino (i.e., IC201114A; GCN 28887, ATel #14188, GCN 28918).
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact persons are S. Buson (sara.buson@gmail.com) and S. Garrappa (simone.garrappa at desy.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.
