GCN Circular 18331

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), David Palmer (LANL), Matteo Perri
(ASDC), Judy Racusin (NASA/GSFC), Mike Siegel (PSU), Gianpiero
Tagliaferri (INAF-OAB) report on behalf of the Swift team:

Swift is observing part of the aLIGO error region for the aLIGO trigger
G184098, using the 'LIB_skymap' GW localisation map, and has so far
observed 2 fields, covering the locations of galaxies (from the GWGC
catalogue) within the aLIGO error region. The observations currently
span from 192 ks to 198 ks after the aLIGO trigger, and cover 0.3 sq
degrees on the sky (corrected for overlaps).

We have detected a 3 X-ray sources. 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 athttp://www.swift.ac.uk/ranks.php.

We have found:

  * 0 sources of rank 1
  * 0 sources of rank 2
  * 0 sources of rank 3
  * 3 sources of rank 4

We assumed a power-law spectrum with NH=3e20 cm^2, and Gamma=1.7

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 1:
  =============
    RA:          138.5272 ( = 09h 14m 6.53s)  J2000
    Dec:         -60.5355 ( = -60d 32' 07.8")  J2000
    Error:   +4.8 (radius, 90% confidence).
    Peak Rate:   4.5e-02 +/- 1.1e-02 ct/sec (0.3-10 keV)
    Peak Flux:   1.9e-12 +/- 4.5e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  XMMSL1 J091406.5-603212 in the XMM-NEWTON/XMMSLEWCLN catalogue
    Separation:  4.0" from the XRT source
    Cat Rate:    1.1e+00 +/- 3.3e-01 ct/sec (0.3-10 keV)
    Cat Flux:    1.2e-11 +/- 3.4e-12 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 galaxy.
    A SIMBAD object `HD  79905' is 2.4" away
    There are 2 2MASS objects within the source's 3-sigma error radius
    This source lies outside the UVOT field of view, but the HD 79905 star is in USNO-B1 with R=7.42, B=7.47
  Source 2:
  =============
    RA:          138.3760 ( = 09h 13m 30.24s)  J2000
    Dec:         -60.7884 ( = -60d 47' 18.2")  J2000
    Error:   +6.1 (radius, 90% confidence).
    Peak Rate:   1.2e-02 +/- 4.6e-03 ct/sec (0.3-10 keV)
    Peak Flux:   5.3e-13 +/- 2.0e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1RXS J091330.1-604707 in the ROSAT/RASSFSC catalogue
    Separation:  11.2" from the XRT source
    Cat Rate:    4.6e-02 +/- 1.1e-02 ct/sec (0.3-10 keV)
    Cat Flux:    1.3e-12 +/- 3.1e-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
    There is 1 GWGC galaxy within 200 kpc of the source.
    A SIMBAD object `ESO 126-2' is 4" away
    There are 3 2MASS objects within the source's 3-sigma error radius
    ESO 126-2, a known AGN, is clearly detected in the UVOT image at the XRT position.
  Source 3:
  =============
    RA:          124.3776 ( = 08h 17m 30.62s)  J2000
    Dec:         -67.7344 ( = -67d 44' 03.8")  J2000
    Error:   +4.7 (radius, 90% confidence).
    Peak Rate:   2.1e-02 +/- 5.5e-03 ct/sec (0.3-10 keV)
    Peak Flux:   8.8e-13 +/- 2.4e-13 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1RXS J081731.6-674414 in the ROSAT/RASSFSC catalogue
    Separation:  11.9" from the XRT source
    Cat Rate:    3.1e-02 +/- 9.6e-03 ct/sec (0.3-10 keV)
    Cat Flux:    8.6e-13 +/- 2.7e-13 erg cm^-2 s^-1 (0.3-10 keV)
       So the source  is 0.1-sigma above the catalogued flux
    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.
    UVOT detects an object consistent with this source (RA=124.37690, Dec=-69.73395),
    with a u magnitude of 17.53 with a 1-sigma statistical error of about 0.05.

This circular is an official product of the Swift team.

[GCN OPS NOTE(19sep15): This Circular was originally published on 20:47 16-Sep-2015 UT.]