HAWC-190806A

V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N.
Burrows (PSU), J. D. Gropp (PSU), A.P. Beardmore (U. Leicester), J.P.
Osborne (U. Leicester), A. Melandri (INAF-OAB) and P.A. Evans (U.
Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the HAWC-detected
candidate GRB 19086A (GCN Circ. 25284
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 ) in a series of observations
tiled on the sky. The total exposure time is 3.8 ks, distributed over 4
tiles; the maximum exposure at a single sky location was 2.6 ks. The
data were collected between T0+25.6 ks and T0+32.8 ks, and are entirely
in Photon Counting (PC) mode.

Five uncatalogued X-ray sources have been detected, however none of
them is above the RASS limit or shows definitive signs of fading.
Therefore, at the present time we cannot identify which, if any, is the
afterglow. Further observations are planned.

Details of these sources are given below:

Source 1:
   RA (J2000.0):  77.7590  =  05:11:2.16
   Dec (J2000.0): +6.6677  =  +06:40:03.6
   Error: 8.5 arcsec (radius, 90% conf.)
   Count-rate: (9.6 [+5.2, -3.9])e-3 ct s^-1
   Distance: 1339 arcsec from HAWC position.

Source 2:
   RA (J2000.0):  78.0710  =  05:12:17.03
   Dec (J2000.0): +6.4737  =  +06:28:25.2
   Error: 5.6 arcsec (radius, 90% conf.)
   Count-rate: 0.0102 [+0.0033, -0.0028] ct s^-1
   Distance: 457 arcsec from HAWC position.
   Flux: (2.31 [+0.75, -0.62])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

Source 3:
   RA (J2000.0):  78.0613  =  05:12:14.72
   Dec (J2000.0): +6.2531  =  +06:15:11.3
   Error: 10.6 arcsec (radius, 90% conf.)
   Count-rate: (6.6 [+4.1, -2.9])e-3 ct s^-1
   Distance: 1230 arcsec from HAWC position.

Source 4:
   RA (J2000.0):  78.0233  =  05:12:5.59
   Dec (J2000.0): +6.7577  =  +06:45:27.9
   Error: 12.7 arcsec (radius, 90% conf.)
   Count-rate: (3.9 [+2.2, -1.6])e-3 ct s^-1
   Distance: 708 arcsec from HAWC position.

Source 5:
   RA (J2000.0):  77.8911  =  05:11:33.86
   Dec (J2000.0): +6.7469  =  +06:44:48.9
   Error: 6.1 arcsec (radius, 90% conf. [Enhanced position])
   Count-rate: 0.0102 [+0.0049, -0.0038] ct s^-1
   Distance: 1011 arcsec from HAWC position.
   Flux: (3.7 [+1.8, -1.4])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)

The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00084.

This circular is an official product of the Swift-XRT team.

J. Wood (NASA/MSFC) and S. Poolakkil (UAH) report on behalf of the Fermi GBM Team:

For HAWC-190806A, Fermi-GBM was observing the full localization region at event time.

There was no Fermi-GBM onboard trigger around the event time of HAWC-190806A (GCN 25284
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 ). An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/-30 s around trigger time, and also identified no counterpart candidates.

We therefore set upper limits on impulsive gamma-ray emission. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395
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 , we set the following 3 sigma flux upper limits over 10-1000 keV (in units of 10^-7 erg/s/cm^2):

Timescale  Soft     Normal   Hard
------------------------------------
0.128 s:   2.4      4.8      14.
1.024 s:   0.9      1.5      4.6
8.192 s:   0.4      0.7      1.7

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 INTEGRAL/SPI-ACS realtime data, and following [1], we have performed
a search for prompt gamma-ray counterparts of HAWC-190806A (GCN 25284
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 ).

At the time of the event (2019-08-06 13:20:48 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The event localization was at an
angle of 33 deg with respect to thespacecraft pointing axis.
This orientation implies a strongly suppressed(17% of optimal)
response of ISGRI, a strongly suppressed (31% ofoptimal) response of
IBIS/Veto, and a near-optimal (75% of optimal)response of SPI-ACS.
This orientation implies a favorableresponse of IBIS/PICsIT.

Thebackground within +/-300 seconds around�� the event was ratherstable
(excess variance 1.3, slightly higher than usual).

We have performed a search for any impulsive events in INTEGRAL SPI-ACS
(as described in [2]) data. We detect a marginal event (S/N 3.3) at a 3.5s
time scale atT0-1.8s. The peak count rate of the signal in SPI-ACS is
713 cts/s,
which corresponds to a flux between 1.2e-07 and 1.7e-07 erg/cm2/s,
depending on thelocation within the source localization region, and
assuming a typical short GRB spectrum (an exponentially cut offpower law
with
alpha=-0.5 and Ep=600 keV). This estimate does not take into account
the uncertaintyrelated to the unknown event spectrum, the 20% systematic
uncertainty on theresponse, or any dead-time correction. We derive
preliminary
estimate of the association FAP at the level of 0.011 (2.3 sigma).
This tentatively indicates a random association.

Further analysis, taking into account accurate FAR measured on
the basis of the study ofthe background during days surrounding
the event might be reported in aforthcoming circulars.

In the IBIS/PICsIT analysis, we do not detect any relevant signal,
despite an
orientation favorable for this instrument. This disfavours a cosmic origin
of the observed SPI-ACS excess.

Otherwise, we estimate a 3-sigma upper limit on the 75-2000 keV
fluence of 2e-07 erg/cm^2 for a burst lasting less than 1 s
with a characteristic short GRB spectrum�� 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 (6.9e-08) erg/cm^2/s at 1 s (8 s) time
scale in 75-2000 keV energy range.

In addition, we identify the following low-S/N excesses,
which likely belong to thebackground:

scale | T�������� | S/N | flux ( x 1e-7 erg/cm2/s) | FAP
2.9���� | -135�� | 3.8 | 1.9 �� 0.5 �� 0.8������������������ | 0.2
2.7���� | -238�� | 4.2 | 2.1 �� 0.5 �� 0.8������������������ | 0.231
0.1���� | -9.26 | 4.2 | 10.6 �� 2.7 �� 4.4���������������� | 0.248
0.8���� | 92.7�� | 4.1 | 3.6 �� 0.9 �� 1.5������������������ | 0.341
0.5���� | -113�� | 3.9 | 4.5 �� 1.2 �� 1.8 �� �� �� ���� | 0.786
1.1���� | -275�� | 3.9 | 3.0 �� 0.8 �� 1.2������������������ | 0.896

Note that FAP estimates (especially at timescales above 2s) may be
further affected by possibly 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

Y. G. Zheng, C. Cai, Q. Luo, S. Xiao, Q. B. Yi, 
Y. Huang, C. K. Li, G. Li, X. B. Li, J. Y. Liao, S. L. Xiong,
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, 
Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, 
Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team:

Insight-HXMT was taking data normally around the trigger time
(T0=2019-08-06T13:20:48.00 UTC) of HAWC-190806A event 
(GCN #25284
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 ), which was monitored without any occultation by 
the Earth. 

Within T0 +/- 100 s, no significant excess events (SNR > 3 sigma) are 
found in a search of the Insight-HXMT/HE raw light curves.

Assuming the counterpart GRB with three typical GRB Band spectral 
models, two typical duration timescales (1 s, 10 s) from the center 
of the position of the alert is (RA=78.125 deg, DEC=6.589 deg), 
the 5-sigma upper-limits fluence (0.2 - 5 MeV, incident energy) are 
reported below:

Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV):
1 s:   1.8e-08 erg cm^-2
10 s:  1.8e-07 erg cm^-2

Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):
1 s:   3.6e-08 erg cm^-2
10 s:  3.3e-07 erg cm^-2

Band model 3 (alpha=-0.0, beta=-1.5, Ep=1000 keV):
1 s:   1.8e-07 erg cm^-2
10 s:  1.2e-06 erg cm^-2

All measurements above are made with the CsI detectors operating in the
regular mode with the energy range of about 80-800 keV (deposited energy).
Only gamma-rays with energy greater than about 200 keV can penetrate
the spacecraft and leave signals in the CsI detectors installed inside
of the spacecraft.