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GCN Circular 26708

Subject
Fermi-LAT ANTARES coincidence: No significant detection in HAWC
Date
2020-01-11T17:52:51Z (4 years ago)
From
Hugo Ayala at Pennsylvania State University <hgayala@psu.edu>
On 2020-01-08 at 09:30:14 UTC, the AMON Fermi-LAT+ANTARES stream
detected a coincident event with a false alarm rate of 2.39 per year.
Location of the coincidence is at
RA: 43.48 J2000
Dec: -18.06 J2000
with an uncertainty of  0.832 deg (90% containment)
https://gcn.gsfc.nasa.gov/gcn3/26674.gcn3
(GCN circular 26674).

We performed two types of analyses for the follow-up. The first is for
a steady source in archival data and the second is a search for a
transient source. We assume a power-law spectrum with an index of -2.3
for both analyses.

Search for a steady source in archival data:
The archival data spans from November 2014 to November 2019.
We searched inside the reported error region from the circular.
The highest significance, 1.76 sigma (0.17 post-trials),
is at RA 44.52 deg, Dec -18.52 deg (+-1.8 deg 68% containment) J2000.
We set a time-integrated 95% CL  upper limit on gamma rays at the
maximum position of:
E^2 dN/dE = 9.24e-13 (E/TeV)^-0.3 TeV cm^-2 s^-1

Search for a transient source.
Since the coincident alert fall outside the HAWC field of view,
we report on the result for the transit before and after the event.
Data acquisition started on Data Start: 2020/01/07 03:54:26 UTC and ended
2020/01/09 04:01:36 UTC.
The most significant location, with 1.60 sigma (-0.26 post-trials),
is at RA 44.03 deg, Dec -18.41 deg (+- 1.80 deg 68% containment) J2000.
We set a time-integrated 95% CL upper limit at the position of
maximum significance of:
E^2 dN/dE = 2.38e-11 (E/1TeV)^-0.3 TeV cm^-2 s^-1

HAWC is a very-high-energy gamma-ray observatory operating in Central
Mexico at latitude 19 deg. north. Operating day and night with over
95% duty cycle, HAWC has an instantaneous field of view of 2 sr and
surveys 2/3 of the sky every day. It is sensitive to gamma rays from
300 GeV to 100 TeV.
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