TITLE:   GCN CIRCULAR
NUMBER:  23924
SUBJECT: IceCube-190221A: Fermi-LAT Gamma-ray observations
DATE:    19/02/22 14:16:39 GMT
FROM:    Sara Cutini at INFN  <sara.cutini@pg.infn.it>

S. Cutini (INFN Perugia), S. Buson (Univ. of Wuerzburg), S. Garrappa (DESY Zeuthen),  C. C.  Cheung (NRL) and S. Ciprini (INFN Roma2) 

on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the very high-energy IC190221A neutrino event (GCN 23918) 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 2019-02-21 08:25:40 UT (T0) with J2000 position RA = 268.81 [-1.8,+1.2] Dec: -17.04 [-0.5,+1.3]  90% PSF containment. The neutrino's position is close to the Inner Galaxy. In the preliminary 8-year Fermi-LAT source list (available here: https://fermi.gsfc.nasa.gov/ssc/data/access/lat/fl8y/ <https://fermi.gsfc.nasa.gov/ssc/data/access/lat/fl8y/>), we find two >100 MeV gamma-ray sources located within the 90% IC190221A localization error. These are  unassociated objects FL8Y J1758.6-1622 and FL8Y J1750.4-1723, at a distance of approximately 1.1 deg and 1.2 deg, respectively.

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 (0.1 - 300 GeV) within the IC190221A 90% confidence localization. Assuming a power-law spectrum (photon index = 2 fixed) for a point source at the IceCube best-fit position, the >100 MeV flux upper limits (95% confidence) are < 1.7e-9 ph cm^-2 s^-1 for ~10.5-years (2008-08-04 / 2019-01-03 UTC) integration time, < 1.2e-8   ph cm^-2 s^-1 for a 1-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 S. Cutini (sara.cutini at pg.infn.it <http://pg.infn.it/>) and S. Buson (sara.buson at gmail.com <http://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.