TITLE: GCN CIRCULAR NUMBER: 21938 SUBJECT: LIGO/Virgo G299232/GW170825: serendipitous XMM-Newton slew observations DATE: 17/09/27 20:43:48 GMT FROM: Eleonora Troja at GSFC/Swift A. M. Read (U. Leicester), A. Tiengo (IUSS Pavia), R. Salvaterra (INAF-IASF Milano), E. Troja (NASA/GSFC), and R. D. Saxton (ESAC) report: We analyzed the XMM-Newton slews made after the LIGO/Virgo G299232/ GW170825 event. The first two slews intercepting the GW localization map cover it for about 41.2 square degrees: Obs ID     |    date    |   T-T_GW   |coverage of localization map 9325000003 | 2017-09-07 |   12.7 d   |  8.0 deg2 9325100002 | 2017-09-09 |   14.7 d   |  33.2 deg2 For each dataset (EPIC pn data with the Medium filter) we performed the source detection following the method described in Troja et al. 2016 (ApJ, 822, L8). Typical sensitivity limits of slew observations are ~6e-13 ergs cm-2 s-1 in the 0.2-2 keV band and ~4e-12 ergs cm-2 s-1 in the 2-12 keV band. The list of the most significant 0.2-12 keV band detections (DET_ML>12) in each slew intersecting the GW170825 localization map, with no counterpart within 30 arcsec in the ROSAT All Sky Survey (Boller et al. 2016, A&A 588, A103) and with no X-ray sources with compatible position and flux detected in archival XMM-Newton observations, is reported below. The flux and counts are computed in the 0.2-12 keV energy band. Rank (1-4, 1 most likely, 4 least likely) indicates how likely the object is to be the GW counterpart. ---------- Revolution 3250, Observation ID 9325000003 RA (deg) DEC (deg) CTS DET_ML EXPOSURE(s) FLUX(ergs cm-2 s-1) Rank 269.3143 -25.1624 24.1 12.1 4.9 4.9e-11 4,extended ---------- Revolution 3251, Observation ID 9325100002 RA (deg) DEC (deg) CTS DET_ML EXPOSURE(s) FLUX(ergs cm-2 s-1) Rank 243.0149 20.2417 4.2 17.3 7.1 6.0e-12 4