GCN Circular 18733

P.A. Evans (U. Leicester), J.A. Kennea (PSU), Scott Barthelmy
(NASA/GSFC), Dave Burrows (PSU), Sergio Campana (INAF-OAB), Brad Cenko
(NASA/GSFC), Neil Gehrels (NASA/GSFC), Paolo Giommi (ASI), Frank
Marshall (NASA/GSFC), John Nousek (PSU), Paul O'Brien (U. Leicester),
Julian Osborne (U. Leicester), Kim Page (U. Leicester), David Palmer
(LANL), Matteo Perri (ASDC), Judy Racusin (NASA/GSFC), Mike Siegel
(PSU), Gianpiero
Tagliaferri (INAF-OAB) report on behalf of the Swift team:

Further Swift observations have been downlinked. The observations
currently span from 140 ks to 164 ks after the aLIGO trigger, and cover

2.8 sq degrees on the sky (corrected for overlaps), and are ongoing.

Since the last Swift GCN, we have detected 3 extra X-ray sources, these
are. Each source is assigned 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
* 3 sources of rank 3
* 0 sources of rank 4

We assumed a power-law spectrum with NH=3e20 cm^2, and 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 3:
=============
RA: 202.5552 ( = 13h 30m 13.25s) J2000
Dec: -20.9046 ( = -20d 54' 16.6") J2000
Error: +5.3 (radius, 90% confidence).
Peak Rate: 9.6e-03 +/- 5.2e-03 ct/sec (0.3-10 keV)
Peak Flux: 4.1e-13 +/- 2.2e-13 erg cm^-2 s^-1 (0.3-10 keV)
1SXPS UL: 1.2e-03 ct/sec, (0.3-10 keV)
So the source is not significantly above the 1SXPS 3-sigma limit
RASS UL: 5.1e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)
So the source is not significantly above the RASS 3-sigma limit
There is no evidence for fading
NOTE: this source is not within 200 kpc of a GWGC galaxy.
There is 1 2MASS object within the source's 3-sigma error radius

Source 4:
=============
RA: 202.5674 ( = 13h 30m 16.18s) J2000
Dec: -20.9240 ( = -20d 55' 26.4") J2000
Error: +5.5 (radius, 90% confidence).
Peak Rate: 1.5e-02 +/- 6.5e-03 ct/sec (0.3-10 keV)
Peak Flux: 6.6e-13 +/- 2.8e-13 erg cm^-2 s^-1 (0.3-10 keV)
1SXPS UL: 1.2e-03 ct/sec, (0.3-10 keV)
So the source is not significantly above the 1SXPS 3-sigma limit
RASS UL: 5.2e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)
So the source is not significantly above the RASS 3-sigma limit
There is no evidence for fading
NOTE: this source is not within 200 kpc of a GWGC galaxy.
There is 1 2MASS object within the source's 3-sigma error radius

Source 5:
=============
RA: 202.3542 ( = 13h 29m 25.01s) J2000
Dec: -21.2270 ( = -21d 13' 37.2") J2000
Error: +5.7 (radius, 90% confidence).
Peak Rate: 2.7e-02 +/- 8.4e-03 ct/sec (0.3-10 keV)
Peak Flux: 1.1e-12 +/- 3.6e-13 erg cm^-2 s^-1 (0.3-10 keV)
RASS UL: 2.5e-02 ct/sec, 3-sigma, converted to XRT (0.3-10 keV)
So the source is not significantly above the RASS 3-sigma limit
There is no evidence for fading
NOTE: this source is not within 200 kpc of a GWGC galaxy.

This circular is an official product of the Swift team.