GCN Circular 21233
Subject
LIGO/Virgo G288732: Swift-XRT follow up of the putative LAT counterpart
Date
2017-06-09T14:10:32Z (7 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), J.A. Kennea (PSU), S.D. Barthelmy
(NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld (UCL-MSSL),
D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC), G.
Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB),
V.D'Elia(ASDC), S.W.K. Emery (UCL-MSSL), P. Giommi (ASI), C. Gronwall
(PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien
(GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A.
Nousek (PSU), S.R. Oates (U. Warwick), P.T. O'Brien (U. Leicester),
J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page
(U.Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin
(NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M.H. Siegel (PSU), G.
Tagliaferri (INAF-OAB), E. Troja (NASA/GSFC/UMCP) report on behalf of
the Swift team:
Swift performed a four-pointing follow up of the possible LAT source in
the error region of GW trigger G288732 (Omodei et al., LVC Circ.
21227). The observations currently span from 63 ks to 91 ks after the
LVC Trigger, and we obtained 1.4-3.9 ks per field.
We have detected 7 X-ray sources. Sources 4&5 are known X-ray emitters
(1RXS J083249.9+432322 and 1RXS J083409.3+431912 respectively). The
remaining sources are uncatalogued and have fluxes consistent with
catalogue upper limits, and show no evidence for fading. We therefore
cannot reliably associate any of these with either the possible LAT
detection or the GW event. Unfortunately, this region of the sky is now
in Swift's Sun observing constraint until September, so no further
follow up will be conducted before that time.
The automated analysis assigns each source is a rank of 1-4 which
describes how likely it is to be related to the GW trigger, with 1
being the most likely and 4 being the least likely. The ranks are
described at http://www.swift.ac.uk/ranks.php.
We have found:
* 0 sources of rank 1
* 0 sources of rank 2
* 4 sources of rank 3
* 2 sources of rank 4
For all flux conversions and comparisons with catalogues and upper
limits from other missions, we assumed a power-law spectrum with
NH=3e20 cm^2, and photon index (Gamma)=1.7
RANK 3 sources
==============
These are uncatalogued X-ray sources, however they are not brighter
than previous upper limits, so do not stand out as likely counterparts
to the GW trigger.
Source 1:
=============
RA: 128.2633 ( = 08h 33m 3.19s) J2000
Dec: +43.2130 ( = +43d 12' 46.8") J2000
Error: +8.6 (arcsec, radius, 90% confidence).
Peak Rate: 1.4e-02 +/- 1.1e-02 ct/sec (0.3-10 keV)
Peak Flux: 6.1e-13 +/- 4.6e-13 erg cm^-2 s^-1 (0.3-10 keV)
RASS UL: 1.4e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)
so the source is not above the RASS 3-sigma upper limit.
The source may be fading, at the 0.6-sigma level.
There is 1 GWGC or 2MPZ galaxy within 200 kpc of the source
and consistent (within 3-sigma) with the distance to the GW object.
A SIMBAD object `LEDA 2215540' is 6.4" away.
There is 1 2MASS object within the source's 3-sigma error radius.
Source 2:
=============
RA: 128.0321 ( = 08h 32m 7.70s) J2000
Dec: +43.4975 ( = +43d 29' 51.0") J2000
Error: +5.7 (arcsec, radius, 90% confidence).
Peak Rate: 3.9e-03 +/- 2.4e-03 ct/sec (0.3-10 keV)
Peak Flux: 1.7e-13 +/- 1.0e-13 erg cm^-2 s^-1 (0.3-10 keV)
RASS UL: 1.6e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)
so the source is not above the RASS 3-sigma upper limit.
There is no evidence for fading.
NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
which is consistent (within 3-sigma) with the distance to the GW
object.
Source 3:
=============
RA: 127.8821 ( = 08h 31m 31.70s) J2000
Dec: +43.4300 ( = +43d 25' 48.0") J2000
Error: +6.3 (arcsec, radius, 90% confidence).
Peak Rate: 1.3e-02 +/- 9.7e-03 ct/sec (0.3-10 keV)
Peak Flux: 5.4e-13 +/- 4.2e-13 erg cm^-2 s^-1 (0.3-10 keV)
RASS UL: 4.2e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)
so the source is not above the RASS 3-sigma upper limit.
The source may be fading, at the 0.4-sigma level.
NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
which is consistent (within 3-sigma) with the distance to the GW
object.
Source 6:
=============
RA: 128.4283 ( = 08h 33m 42.79s) J2000
Dec: +43.2892 ( = +43d 17' 21.1") J2000
Error: +5.0 (arcsec, radius, 90% confidence).
Peak Rate: 5.1e-03 +/- 2.0e-03 ct/sec (0.3-10 keV)
Peak Flux: 2.2e-13 +/- 8.6e-14 erg cm^-2 s^-1 (0.3-10 keV)
RASS UL: 2.1e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)
so the source is not above the RASS 3-sigma upper limit.
There is no evidence for fading.
NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
which is consistent (within 3-sigma) with the distance to the GW
object.
There is 1 2MASS object within the source's 3-sigma error radius.
Source 7:
=============
RA: 127.8022 ( = 08h 31m 12.53s) J2000
Dec: +43.4288 ( = +43d 25' 43.7") J2000
Error: +7.6 (arcsec, radius, 90% confidence).
Peak Rate: 1.2e-02 +/- 7.4e-03 ct/sec (0.3-10 keV)
Peak Flux: 5.1e-13 +/- 3.2e-13 erg cm^-2 s^-1 (0.3-10 keV)
RASS UL: 3.2e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)
so the source is not above the RASS 3-sigma upper limit.
There is no evidence for fading.
NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
which is consistent (within 3-sigma) with the distance to the GW
object.
There is 1 2MASS object within the source's 3-sigma error radius.
RANK 4 sources
==============
These are catalogued X-ray sources, showing no signs of outburst
compared to previous observations, so they are not likely to be related
to the GW trigger.
Source 4:
=============
RA: 128.2174 ( = 08h 32m 52.18s) J2000
Dec: +43.3858 ( = +43d 23' 08.9") J2000
Error: +6.0 (arcsec, radius, 90% confidence).
Peak Rate: 8.7e-03 +/- 5.4e-03 ct/sec (0.3-10 keV)
Peak Flux: 3.7e-13 +/- 2.3e-13 erg cm^-2 s^-1 (0.3-10 keV)
Cat Source: 1RXS J083249.9+432322 in the ROSAT/RASSFSC catalogue
Separation: 28.2" from the XRT source
Cat Rate: 1.7e-02 +/- 8.5e-03 ct/sec
Cat Flux: 4.9e-13 +/- 2.4e-13 erg cm^-2 s^-1 (0.3-10 keV)
so the source is not above the catalogued flux.
There is no evidence for fading.
NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
which is consistent (within 3-sigma) with the distance to the GW
object.
Source 5:
=============
RA: 128.5303 ( = 08h 34m 7.27s) J2000
Dec: +43.3192 ( = +43d 19' 09.1") J2000
Error: +7.2 (arcsec, radius, 90% confidence).
Peak Rate: 9.4e-03 +/- 5.8e-03 ct/sec (0.3-10 keV)
Peak Flux: 4.0e-13 +/- 2.5e-13 erg cm^-2 s^-1 (0.3-10 keV)
Cat Source: 1RXS J083409.3+431912 in the ROSAT/RASSFSC catalogue
Separation: 22.5" from the XRT source
Cat Rate: 2.3e-02 +/- 1.1e-02 ct/sec
Cat Flux: 6.5e-13 +/- 3.1e-13 erg cm^-2 s^-1 (0.3-10 keV)
so the source is not above the catalogued flux.
The source may be fading, at the 0.3-sigma level.
NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
which is consistent (within 3-sigma) with the distance to the GW
object.
This circular is an official product of the Swift team.