TITLE:   GCN CIRCULAR
NUMBER:  21798
SUBJECT: LIGO/Virgo G298048: Chandra X-ray Update on GW170817
DATE:    17/09/03 20:24:16 GMT
FROM:    Daryl Haggard at McGill U  <daryl.haggard@mcgill.ca>

D. Haggard, M. Nynka (McGill), V. Kalogera (Northwestern), Phil Evans (Leicester), and Brad Cenko (NASA/GSFC)

We report a new ~47 ks Chandra X-ray observation (ObsID 18988, PI Haggard) of the LVC trigger G298048, a.k.a. GW170817, beginning 2017 September 02, approximately 16 days after the trigger. These observations include the optical transient SSS17a (Coulter et al., LVC GCN 21529) and the Swift area of interest (Evans et al., LVC GCN 21612).

We detect X-ray emission from two point sources and from one extended source: (i) point-source X-ray emission at the location of the optical transient SSS17a (Coulter et al., LVC GCN 21529; Troja et al., LVC GCN 21765; Margutti LVC GCN 21786; Troja et al., LVC GCN 21787), (ii) another point source at the location of the Swift X-ray emission (Evans et al., LVC GCN 21612) also reported by Margutti et al. (LVC GCN 21786), and (iii) extended emission from the host galaxy NGC 4993 (Evans et al., LVC GCN 21612; Margutti et al., LVC GCN 21648).

We analyze these new data in combination with DDT Chandra observations acquired one day earlier (ObsID 20728, PI Troja) and report tentative evidence for decreasing fluxes from both X-ray point sources (1-sigma errors are ~1E-15 erg/s/cm2):

X-ray Counterpart to Optical Transient SSS17a (assuming PL w/ gamma=2.4):

Sep 01: 5.1E-15 erg/s/cm2 (0.3-8 keV)
Sep 02: 4.5E-15 erg/s/cm2 (0.3-8 keV)

Chandra X-ray Point Source (assuming PL w/ gamma=2.0):

Sep 01: 3.5E-15 erg/s/cm2 (0.3-8 keV)
Sep 02: 2.7E-15 erg/s/cm2 (0.3-8 keV)

We thank Belinda Wilkes and the entire Chandra team for their support of these observations.