TITLE:   GCN CIRCULAR
NUMBER:  28598
SUBJECT: GRB 201006A: Chandra upper limit on the X-ray afterglow
DATE:    20/10/11 17:30:25 GMT
FROM:    Alicia Rouco Escorial at CIERA  <alicia.rouco.escorial@northwestern.edu>

A. Rouco Escorial, W. Fong, G. Schroeder, K. Paterson, C. D. Kilpatrick, A. Nugent, J. Rastinejad, R. Margutti, K. D. Alexander (Northwestern), T. Laskar (Bath), and E. Berger (Harvard) report:

“We initiated observations with the Chandra X-ray Observatory of the short-duration GRB 201006A (Barthelmy et al., GCN 28560; Tohuvavohu, GCN 28563; Hamburg et al., GCN 28564; Lien et al., GCN 28567) starting on 2020 October 09 20:57:42 UT, with a median observation time of 3.98 days post-trigger. We obtained one ACIS-S observation under the Proposal 21400447 (ObsID 22401; PI: Fong), with an effective exposure time of 24.7 ks.

We do not detect an X-ray source within the enhanced Swift-XRT position (90% confidence; Evans et al., GCN 28562). Centered on the XRT position, we obtain a 3-sigma limit of <3.6e-4 cts/s in the 0.5-8 keV energy range (following Gehrels 1986). Applying the best-fit PC-mode XRT spectral parameters (Gamma=2.1, total NH=1.3e22 cm^-2; Evans et al., GCN 28568), we calculate a 3-sigma unabsorbed flux limit of FX<1.15e-14 erg/s/cm^2 in the 0.3-10 keV energy range.

The XRT afterglow, starting at ~153.3 s post-burst, can be modeled with a power law decline (where FX~t^alpha) with a decay index of alpha=-0.99(+0.14,-0.13) consistent with the results of Evans et al. (GCN 28568). Our Chandra upper limit is marginally consistent with the expected flux at dt~3.98 days drawn by this model.

We thank the Chandra Director, Patrick Slane, and staff for the rapid planning and scheduling of these observations.”