[vsnet-grb-info 26815] Fermi-LAT Gamma-ray Observations of IceCube-201114A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28918
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-201114A
DATE:    20/11/17 16:53:47 GMT
FROM:    Sara Buson at GSFC/Fermi  <sara.buson at gmail.com>

S. Garrappa (DESY-Zeuthen) and S. Buson (Univ. of Wuerzburg) on behalf of the Fermi-LAT collaboration:

We report an analysis of observations of the vicinity of the high-energy IC201114A neutrino event (GCN 28887) 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 2020-11-14 at 15:05:31.96 UT (T0) with J2000 position RA = 105.25 (+1.28, -1.12) deg, Decl. = 6.05 (+0.95, -0.95) deg (90% PSF containment). One cataloged >100 MeV gamma-ray source is located within the 90% IC201114A localization region. This is 4FGL J0658.6+0636 (4FGL, The Fermi-LAT collaboration 2020, ApJS, 247, 33), associated with the active galaxy of uncertain type NVSS J065844+063711 (Condon et al 1998, AJ, 115, 1693) at unknown redshift. Based on a preliminary analysis of the LAT data over the timescales of 1-day and 1-month prior to T0, this object is not significantly detected (> 5 sigma).

We searched for intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (> 5 sigma) new excess emission (> 100 MeV) at the IC201114A best-fit position. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC201114A best-fit position, the >100 MeV flux upper limit (95% confidence) is < 2.8e-10 ph cm^-2 s^-1 for ~12-years (2008-08-04 to 2020-11-14 UTC), and < 1.6e-8 (< 2.2e-7) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0.  

Within the 90% confidence localization of the neutrino, 1.2 deg offset from the best-fit IC201114A position, an excess of gamma rays, Fermi J0703.5+0505, was detected in an analysis of the 1-day integrated LAT data (0.1 - 800 GeV) prior to T0. This putative new transient source is detected at a statistical significance >3 sigma (calculated following the prescription adopted in the 4FGL). Assuming a power-law spectrum, the excess has best-fit localization of RA = 105.89 deg, Decl. = 5.09 deg (7 arcmin 68% containment, 14 arcmin 99% containment) with best-fit spectral parameters, flux = (3.2 +/- 2.8)e-7 ph cm^-2 s^-1, index = 2.1 +/- 0.5. In a preliminary analysis of the LAT data over one month prior to T0, Fermi J0703.5+0505 is not significantly detected in the LAT data. All values include the statistical uncertainty only. This excess of gamma rays is likely driven by two > 1 GeV photons with high probability (> 90%) to be associated with this source of 21 GeV and 1.3 GeV, respectively, observed within ~4.5 hours.

Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For these observations the Fermi-LAT contact persons are S. Garrappa (simone.garrappa at desy.de) and S. Buson (sara.buson at uni-wuerzburg.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.