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GCN Circular 21937

Subject
LIGO/Virgo G298936/GW170823: serendipitous XMM-Newton slew observations
Date
2017-09-27T20:35:18Z (7 years ago)
From
Eleonora Troja at GSFC/Swift <nora.gsfc@gmail.com>
A. M. Read (U. Leicester), A. Tiengo (IUSS Pavia), R. Salvaterra
(INAF-IASF Milano), E. Troja (NASA/GSFC), and R. D. Saxton (ESAC)
report:

We analyzed the XMM-Newton slews made after the LIGO/Virgo G298936/
GW170823 event. The first three slews intercepting the GW localization
map cover it for about 23.5 square degrees:

Obs ID     |    date    |   T-T_GW   |coverage of localization map
9324900002 | 2017-09-05 |   13.1 d   |  4.2 deg2
9325000003 | 2017-09-07 |   14.7 d   |  8.7 deg2
9325100002 | 2017-09-09 |   16.7 d   |  10.6 deg2

For each dataset (EPIC pn data with the Medium filter) we performed
the source detection following the method described in Troja et al. 2016
(ApJ, 822, L8). Typical sensitivity limits of slew observations are
~6e-13 ergs cm-2 s-1 in the 0.2-2 keV band and ~4e-12 ergs cm-2 s-1
in the 2-12 keV band.
The list of the most significant 0.2-12 keV band detections (DET_ML>12)
in each slew intersecting the GW170823 localization map, with no
counterpart within 30 arcsec in the ROSAT All Sky Survey (Boller et al.
2016, A&A 588, A103) and with no X-ray sources with compatible position
and flux detected in archival XMM-Newton observations, is reported below.
The flux and counts are computed in the 0.2-12 keV energy band.Rank (1-4,
1 most likely, 4 least likely) indicates how likely the object is to be
the GW counterpart.

----------
Revolution 3250, Observation ID 9325000003
RA (deg)   DEC (deg)  CTS  DET_ML EXPOSURE(s) FLUX(ergs cm-2 s-1) Rank
259.7674   -38.478    6.0   13.3    6.2        9.7e-12              4
----------
Revolution 3251, Observation ID 9325100002
RA (deg)   DEC (deg)  CTS  DET_ML EXPOSURE(s) FLUX(ergs cm-2 s-1) Rank
267.8741  -46.1932    5.2   17.3    7.0        7.4e-12              3
264.2881  -40.5070    4.6   12.1    5.6        8.2e-12              4
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