Continued Chandra monitoring of GW170817 at 4.8 yr post-merger
Abstract
The Chandra X-ray Observatory (CXO) carried out observations of GW170817 starting at 1671 d post-merger (ObsIDs: 25733, 25734; PI: Troja) for 59.4 ks, an additional epoch was performed starting at 1734 d (ObsID: 25527) for 36.6 ks. The data were re-processed and the astrometry corrected following Troja et al. 2020, MNRAS, 4, 5643. In the 0.5-8 keV energy range we measure 2 counts within a 1" aperture centered on the X-ray position. A background contribution of about 0.85 counts was estimated from adjacent source-free regions. Following Kraft, Burrows, and Nousek (1991), we derive a 95% upper limit of <5.5 source counts, yielding a rate of <6E-5 cts/s in the combined 95.8 ks. This corresponds to a 0.3-10 keV flux limit of 1.3E-15 erg/cm2/s for a power-law with photon index of 1.585. This limit is comparable to the value measured at 1234 d (1.6E-15 erg/cm2/s; Troja et al. 2022, MNRAS, 510, 1902), and does not show evidence for a rebrightening of the X-ray emission. By combining this new epoch with the CXO observations acquired in December 2021 at 1575 d (Hajela et al. 2021, GCN 31231), we obtain a weak (3-sigma) detection with an average count-rate of 3E-05 cts/s, and a 0.3-10 keV flux of ~0.6E-15 erg/cm2/s. An updated light curve can be found at this link: https://nora.users.roma2.infn.it/GW170817_May2022.jpg We thank the Chandra staff for scheduling these observations.
- Publication:
-
GRB Coordinates Network
- Pub Date:
- May 2022
- Bibcode:
- 2022GCN.32065....1O