[AAVSO-HEN] GRB 090621B: Swift-XRT refined analysis

[grb at aavso.org]

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TITLE:   GCN CIRCULAR
NUMBER:  9550
SUBJECT: GRB 090621B: Swift-XRT refined analysis
DATE:    09/06/22 10:16:55 GMT
FROM:    Andy Beardmore at U Leicester  <apb at star.le.ac.uk>

A.P. Beardmore, K.L. Page (U. Leicester) and P.A. Curran (UCL-MSSL)
report on behalf of the Swift-XRT team:

We have analysed five orbits of Swift-XRT photon counting (PC) mode data 
from GRB 090621B (Curran et al., GCN Circ. 9545), spanning the interval 
T+80 s to T+19.5 ks after the trigger.  In 10.0 ks we find a refined XRT 
position of RA, Dec = 313.47049, 69.02845, which is equivalent to

RA (J2000) =  20:53:52.92
Dec(J2000) = +69:01:42.4

with an uncertainty of 4.0 arcsec (90% containment). This position
is 1.2 arcsec from the XRT position quoted in GCN Circ. 9545.

The X-ray light-curve shows a faint, fading source with a decay index
of 0.61  +/- 0.19. If the source continues to decay at the same rate 
we predict an XRT count rate of 8.6e-4 count s^-1 at T+24 hours.

The PC mode spectrum from T+80 s to T+17.1 ks can be fit by an absorbed 
powerlaw with a photon index of 1.47+/-0.66, assuming a Galactic column 
density of 1.9e21cm^-2 in the direction of the burst.  The observed 
(unabsorbed) 0.3-10keV flux for this model is 3.8e-13 (4.5e-13)
erg cm^-2 s^-1.

This circular is an official product of the Swift-XRT team.