TITLE:   GCN CIRCULAR
NUMBER:  30879
SUBJECT: GRB 210919A: Chandra rapid ToO upper limit
DATE:    21/09/25 01:27:01 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto@phys.aoyama.ac.jp>

T. Sakamoto (AGU), E. Troja (NASA/GSFC/ORAU), J. Norris (BSU),
S. D. Barthelmy (GSFC), J. L. Racusin (GSFC), N. Kawai (Tokyo Tech),
A. Fruchter (STScI), M. Im (SNU), B. Cenko (GSFC)

A Chandra ToO observation of a short GRB 200919A (Tohuvavohu et al., GCN Circ. 30846)
started on February 21 02:54 UT (~2.1 days after the GRB trigger) for a total of 19.8 ksec.

We do not detect an X-ray afterglow at the location of the enhanced XRT position
(Goad et al., GCN Circ. 30850).  The calculated 3-sigma upper limit is 3.4 x 10^-4 c/s
in the 0.3-8 keV band using aprates of the CIAO software package.  Assuming N_H of
1.5 x 10^21 cm^-2 and photon index of 2, we estimated an 3-sigma unabsorbed flux
upper limit of 6.9 x 10^-15 erg/cm2/s in the 0.3-8 keV band.

We would like to thank Patrick Slane, Harvey Tananbaum, Andrea Prestwich,
and the Chandra operation team for rapidly approving and making this observation.