GCN Circular 20495

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), N. Gehrels (NASA/GSFC), P. Giommi (ASI), C. Gronwall
(PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien
(GSFC/UMBC), D. Malesani (DARK/NBI), F.E. Marshall (NASA/GSFC), A.
Melandri (INAF-OAB), B. Mingo (U. Leicester),  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 has performed a series of 134 observations of galaxies (from the
GWGC catalogue) within the LVC error region for the GW trigger G270580,
using the 'LIB_skymap' GW localisation map. The observations currently
span from 19 ks to 40 ks after the LVC trigger, and cover 15.8 sq
degrees on the sky (corrected for overlaps). This covers 0.011 of the
probability in the LVC skymap, and 0.14 of the probability in the LVC
map after weighting by galaxies in the GWGC catalogue.

Unfortunately these observations result in significant heating of the
XRT detector, which produced an artificially elevated, inhomogeneous
background, which produced a number of spurious source detections which
were circulated as 'counterpart' notices, however only 2 of these
sources are deemed to be real upon manual inspection (we remind readers
that the counterpart notices are the result of a purely automated
process, human vetting is performed before these circulars are
produced).

We have detected 2 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 at http://www.swift.ac.uk/ranks.php.

We have found:

  * 0 sources of rank 1
  * 0 sources of rank 2
  * 0 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 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: 	 280.1625 ( = 18h 40m 39.00s) J2000
    Dec:	 -77.1591 ( = -77d 09' 32.8") J2000
    Error:	 +5.1 (arcsec, radius, 90% confidence).
    Peak Rate:	 2.1e-01 +/- 6.0e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 8.9e-12 +/- 2.6e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1SXPS J184038.0-770928 in the 1SXPS catalogue
    Separation:  5.3" from the XRT source
    Cat Rate:	 2.5e-01 +/- 5.6e-03 ct/sec 
    Cat Flux:	 1.1e-11 +/- 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.
    There are 10 GWGC or 2MPZ galaxies within 200 kpc of the source.
    A SIMBAD object `ATPMN J184038.5-770929' is 3.9" away.
    There is 1 2MASS object within the source's 3-sigma error radius.
  
  Source 4:
  =============
    RA: 	 110.1196 ( = 07h 20m 28.70s) J2000
    Dec:	 +71.5431 ( = +71d 32' 35.2") J2000
    Error:	 +5.7 (arcsec, radius, 90% confidence).
    Peak Rate:	 1.8e-01 +/- 7.3e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 7.9e-12 +/- 3.1e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1AXG J072025+7132 in the ASCA/ASCAGIS catalogue
    Separation:  17.4" from the XRT source
    Cat Rate:	 2.4e-03 +/- 0.0e+00 ct/sec 
    Cat Flux:	 0.0e+00 +/- 0.0e+00 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 are 2 GWGC or 2MPZ galaxies within 200 kpc of the source.

This circular is an official product of the Swift team.