TITLE:   GCN CIRCULAR
NUMBER:  21168
SUBJECT: GRB 170524B: Swift-UVOT/XRT Confirmation of Afterglow
DATE:    17/05/30 19:07:35 GMT
FROM:    Jeffrey Gropp at PSU  <jdg44@psu.edu>

J.D. Gropp (PSU), M.H. Siegel (PSU), J.A. Kennea (PSU), A.
Cholden-Brown (PSU) reporting on behalf of the Swift team.


The Swift-UVOT and XRT began settled observations of the field of GRB
170524B 120 ks after the

BAT trigger (Barthelmy et al., GCN Circ. 21142). A fading source
consistent with the XRT position

is detected in the UVOT exposures.

Swift-XRT performed follow-up observations of the
Swift/BAT-detected burst GRB 170524B (Barthelmy et al. GCN Circ.21142),
collecting an additional 3ks (5.1 total) of Photon Counting (PC) mode data.

One uncatalogued X-ray source has been detected consistent with being
within 296 arcsec of the Swift/BAT position. There is also evidence of fading,

which is confirmed with UVOT analysis.

XRT light curve can be modeled with a power-law decay with a decay
index alpha = 1.3


The preliminary UVOT position is:
    RA  (J2000) =  06:03:28.49 =  90.86872 (deg.)
    Dec (J2000) = -17:04:58.7  = -17.08297 (deg.)
with an estimated uncertainty of 0.4 arc sec. (radius, 90% confidence).

Preliminary detections using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)                  Mag

white            120431        126833        1297          19.89+-0.08
white            274703        286595        2027          21.11+-0.23

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.19 in the direction of the burst.

The decay inferred from the UVOT white data suggests a slope of
approximately -1.3.

This circular is an official product of the Swift team.