[vsnet-grb-info 25424] LIGO/Virgo S200224ca: Swift XRT observations, 8 X-ray sources

Fri Apr 10 22:14:56 JST 2020

TITLE:   GCN CIRCULAR
NUMBER:  27524
SUBJECT: LIGO/Virgo S200224ca: Swift XRT observations, 8 X-ray sources
DATE:    20/04/10 13:13:23 GMT
FROM:    Kim Page at U.of Leicester  <klp5 at leicester.ac.uk>

P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U.
Toronto), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester),
M.G. Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL), P. Brown (TAMU),
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), D. Hartmann (U. Clemson), H.A. Krimm (CRESST/GSFC/USRA), N.J.
Klingler (PSU), 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. Birmingham), P.T. O'Brien (U. Leicester), J.P. Osborne (U.
Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), M.J.Page
(UCL-MSSL), 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 carried out 675 observations of the LVC error region for the
GW trigger S200224ca convolved with the 2MPZ catalogue (Bilicki et al.
2014, ApJS, 210, 9), using the 'bayestar' (version 1) GW localisation
map. As this is a 3D skymap, galaxy distances were taken into account
in selecting which ones to observe. The observations currently span
from 21 ks to 1542 ks after the LVC trigger, and the XRT has covered
64.5 deg^2 on the sky (corrected for overlaps). This covers 81% of the
probability in the 'LALInference' (version 1) skymap, and 79% after
convolving with the 2MPZ galaxy catalogue, as described by Evans et al.
(2016, MNRAS,  462, 1591). These pointings and associated metadata have
been reported to the Treasure Map (Wyatt et al., arXiv 2001.00588;
http://treasuremap.space/alerts?graceids=S200224ca).

We have detected 8 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 https://www.swift.ac.uk/ranks.php.

We have found:

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

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 ID	 | RA		  | Dec 	   | Err90   |
|  S200224ca_X5  | 11h 35m 31.08s | -12d 42' 10.0" |	6.3" |
|  S200224ca_X9  | 11h 37m 19.09s | -04d 43' 59.6" |	6.2" |

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 ID	 | RA		  | Dec 	   | Err90   |
|  S200224ca_X1  | 11h 42m 19.04s | -14d 22' 38.7" |	5.2" |
|  S200224ca_X3  | 11h 35m 55.12s | -11d 42' 24.8" |	5.9" |
|  S200224ca_X4  |  10h 50m 7.75s | +11d 32' 31.0" |	4.5" |
|  S200224ca_X7  | 11h 41m 41.71s | -14d 07' 50.2" |	5.2" |
|  S200224ca_X8  | 11h 25m 51.91s | -07d 42' 25.5" |	5.1" |
| S200224ca_X10  |  11h 52m 3.55s | -11d 22' 21.8" |	4.7" |

The Swift-XRT observations also covered the locations of 13 sources
reported by other observers, thus:

* AT2020dlp (GCN27227)		F < 4.1x10^-12 erg cm^-2 s^-1.
* AT2020dlt (GCN27227)		F < 4.2x10^-12 erg cm^-2 s^-1.
* AT2020dlu (GCN27227)		F < 4.4x10^-12 erg cm^-2 s^-1.
* AT2020dlv (GCN27227)		F < 2.9x10^-12 erg cm^-2 s^-1.
* AT2020dlw (GCN27227)		F < 2.5x10^-12 erg cm^-2 s^-1.
* AT2020dmb (GCN27227)		F < 4.1x10^-12 erg cm^-2 s^-1.
* AT2020dmc (GCN27227)		F < 4.1x10^-12 erg cm^-2 s^-1.
* AT2020dme (GCN27227)		F < 2.4x10^-12 erg cm^-2 s^-1.
* AT2020dmg (GCN27227)		F < 3.9x10^-12 erg cm^-2 s^-1.
* AT2020dmh (GCN27227)		F < 4.6x10^-12 erg cm^-2 s^-1.
* AT2020dmi (GCN27227)		F < 2.0x10^-13 erg cm^-2 s^-1.
* AT2020dmj (GCN27227)		F < 3.4x10^-12 erg cm^-2 s^-1.
* AT2020dmk (GCN27227)		F < 2.8x10^-12 erg cm^-2 s^-1.

Flux limits are 3-sigma upper limits on the 0.3-10 keV observed flux.

For all flux conversions and comparisons with catalogues and upper
limits from other missions, we assumed a power-law spectrum with
NH=3x10^20 cm^-2, and photon index (Gamma)=1.7

The results of the XRT automated analysis, including details of the
sources listed above, are online at
https://www.swift.ac.uk/LVC/S200224ca

This circular is an official product of the Swift XRT team.