[vsnet-grb-info 25779] Fermi-LAT Gamma-ray Observations of IceCube-200530A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27879
SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-200530A
DATE:    20/06/01 12:22:11 GMT
FROM:    Simone Garrappa at DESY  <simone.garrappa at desy.de>

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

We report an analysis of observations of the vicinity of the high-energy 
IC200530A neutrino event (GCN 27865) 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 2020-05-30 07:54:29.43 UT 
(T0) with J2000 position RA = 255.37 (+2.48, -2.56) deg, Decl. = 26.61 
(+2.33, -3.28) deg 90% PSF containment. Two cataloged >100 MeV gamma-ray 
sources are located within the 90% IC200530A localization error. These 
are 4FGL J1702.2+2642 (associated with the BL Lac object MG2 
J170210+2643) and 4FGL J1659.0+2627 (associated with the FSRQ 4C 
+26.51). Based on a preliminary analysis of LAT data at timescales of 
1-month and 1-day prior to T0, these objects are not significantly 
detected (>5sigma).

We searched for the existence of intermediate (days to years) timescale 
emission from a new gamma-ray transient source. Preliminary analysis 
indicates no significant (>5sigma) new excess emission (>100 MeV) at 
the IC200530A best-fit position. 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 < 2.4e-10 ph cm^-2 
s^-1 for ~11-years (2008-08-04 / 2020-05-30 UTC), < 1e-8 (< 1.7e-7) ph 
cm^-2 s^-1 for a 1-month (1-day) integration time before T0.

In the analysis of the ~11-years integrated LAT data (0.1 - 800 GeV), a 
4.0 sigma new excess of gamma rays, Fermi J1707.0+2528 , was detected 
1.7 deg offset from the best-fit IC200530A position and within the 90% 
confidence localization of the direction of the neutrino. Assuming a 
power-law spectrum, the best-fit localization is (J2000) RA: 256.77, 
Dec: 25.48 (12 arcmin 95% containment, 7 arcmin 68% containment). The 
gamma-ray best-fit spectral parameters are flux = (1.2+/-0.4)e-9 ph 
cm^-2 s^-1 and index = 2.2+/-0.2. In a preliminary analysis of the LAT 
data over 1-day and 1-month prior T0, Fermi J1707.0+2528 is not 
significantly detected in the LAT data.

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. Buson (sara.buson at uni-wuerzburg.de 
<http://uni-wuerzburg.de/>) and S. Garrappa (simone.garrappa at desy.de 
<http://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.