[vsnet-grb-info 26913] IceCube-201209A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29016
SUBJECT: IceCube-201209A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation
DATE:    20/12/09 17:31:14 GMT
FROM:    Volodymyr Savchenko at ISDC,U of Geneve  <savchenk at in2p3.fr>

V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
A. Coleiro (APC, France)
S. Mereghetti (INAF IASF-Milano, Italy)

on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration

Using combination of INTEGRAL all-sky detectors (following [1]):
SPI/ACS, IBIS/Veto, and IBIS  we have performed a search for a prompt
gamma-ray counterpart of IceCube-201209A (GCN 29012).

At the time of the event (2020-12-09 10:15:44 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 79 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(17% of optimal) response of ISGRI, strongly suppressed (36% of
optimal) response of IBIS/Veto, and near-optimal (89% of optimal)
response of SPI-ACS.

The background within +/-300 seconds around the event was very stable
(excess variance 1.2).

We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in [2]), IBIS, and IBIS/Veto data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 2e-07 erg/cm^2 (within the
50% probability containment region of the source localization) for a
burst lasting less than 1 s with a characteristic short GRB spectrum
(an exponentially cut off power law with alpha=-0.5 and Ep=600 keV)
occurring at any time in the interval within 300 s around T0. For a
typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and
Ep=300 keV), the derived peak flux upper limit is ~1.7e-07 (5.9e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

We report for completeness and in order of FAP, all excesses
identified in the search region. We find: 1 possibly associated
excess:

T-T0     | scale   | S/N | flux ( x 1e-06 erg/cm2/s)      | FAP    
-0.0869  | 0.05    | 3.4 |     1.01 +/- 0.281  +/- 0.257  | 0.0103 

5 likely background excesses:

T-T0     | scale   | S/N | flux ( x 1e-06 erg/cm2/s)      | FAP    
199      | 6.5     | 3.5 |    0.885 +/- 0.241  +/- 0.225  | 0.223 
296      | 1.4     | 4.8 |     2.53 +/- 0.521  +/- 0.641  | 0.372 
160      | 1.5     | 3.7 |     1.94 +/- 0.503  +/- 0.492  | 0.554
-3.94    | 0.05    | 3.3 |    0.979 +/- 0.28   +/- 0.249  | 0.627
39.1     | 0.55    | 3.4 |     2.93 +/- 0.833  +/- 0.744  | 0.63

Note that FAP estimates (especially at timescales above 2s) may be
possibly further affected by enhanced non-stationary local background
noise. This list excludes any excesses for which FAP is close to
unity.



All results quoted are preliminary.

This circular is an official product of the INTEGRAL Multi-Messenger
team.

[1] Savchenko et al. 2017, A&A 603, A46 
[2] Savchenko et al. 2012, A&A 541A, 122S
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