GCN Circular 24494

N. P. M. Kuin (UCL-MSSL), M. de Pasquale (U. of Istanbul) and
M. G. Bernardini (INAF-OAB) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 190511A
131 s after the BAT trigger (Bernardini et al., GCN Circ. 24472
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 ).
A source consistent with the XRT position
(Goad et al. GCN Circ. 24481
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  08:25:46.44 = 126.44350 (deg.)
    Dec (J2000) = -20:15:33.6  = -20.25933 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).

There is a catalogued star at a distance of 1.3 arcsec. The extrapolated
brightness using the SED from the Vizier photometry tool
(
http://cdsportal.u-strasbg.fr/gadgets/ifr?url=http://cdsportal.unistra.fr/widgets/SED_plotter.xml&SED_plot_object=126.442680%2C%20-20.259685&SED_plot_radius=2
)
shows a brightness consistent with that of the white count rate seen at
several
ks after the trigger. We subtract here therefore the late time count rate
in the
following preliminary UVOT photometry of this GRB, knowing that this has to
be
refined using truely late time data. Where we did not have a late time
measurement yet available, the photometry will be reported in due time.

Preliminary detections and 3-sigma upper limits 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              131          281          147         16.0 +/- 0.1
b                 5684         5884          197         21.6 +/- 0.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.09 in the direction of the burst
(Schlegel et al. 1998).

The afterglow was also discovered by NOT (Malasani et al. GCN Circ. 24492
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 ).