[vsnet-grb-info 22302] Fermi-LAT Gamma-ray Observations of IceCube-190504A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24401
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-190504A
DATE:    19/05/05 20:47:04 GMT
FROM:    Sara Buson at GSFC/Fermi  <sara.buson at gmail.com>

S. Garrappa (DESY-Zeuthen, DE), S. Buson (Univ. of Wuerzburg, DE; UMBC, USA) and S. Ciprini (INFN Roma Tor Vergata, ASI, IT) on behalf of the Fermi-LAT collaboration:


We report an analysis of observations of the vicinity of the high-energy IC190504A neutrino event (GCN 24392 and https://gcn.gsfc.nasa.gov/notices_amon/42419327_132508.amon <https://gcn.gsfc.nasa.gov/notices_amon/42419327_132508.amon>) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on  2019-05-04 18:26:49 UTC (T0) with J2000 position RA = 65.7866  deg, Decl. = -37.4431 deg (74 arcmin and 25 arcmin 90% and 50% PSF containment, respectively). 

Two cataloged >100 MeV gamma-ray source are located within the 90% IC190504A localization error. The closest one is the object 4FGL J0420.3-3745 (The Fermi-LAT Fourth Source Catalog, arXiv:1902.10045) also catalogued as 3FHL J0420.4-3744 (Ajello, M. et al. 2017, ApJS, 232, 18), at a distance of roughly 37 arcmin, and associated with the radio source NVSS J042025-374443. Based on a preliminary analysis of the LAT data over the timescale of one week before T0, this object is not significantly detected at gamma rays. The second one is 4FGL J0428.6-3756 (a.k.a. 3FHL J0428.6-3756), associated with the blazar PKS 0426-380, located at a distance of roughly 72 arcmin. This object is significantly detected at gamma rays over a timescale of one week before T0, at a flux level consistent with the 10 years average, and does not display recent remarkable activity at gamma rays.


We searched for the existence of intermediate (months to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC190504A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IceCube best-fit position, the >100 MeV flux upper limit (95% confidence) is < 1e-9 ph cm^-2 s^-1 for ~10.8-years (2008-08-04 / 2019-05-04 UTC) and < 1.1e-9ph cm^-2 s^-1 for a 8-month integration time before T0.


Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue.  For this source the Fermi-LAT contact persons are Simone Garrappa (simone.garrappa at desy.de <http://desy.de/>) and Sara Buson (sara.buson at astro.uni-wuerzburg.edu <http://astro.uni-wuerzburg.edu/>). 


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.