GCN Circular 16746
Subject
GRB 140824B: Swift observations
Date
2014-08-26T14:33:02Z (10 years ago)
From
Claudio Pagani at U of Leicester <cp232@star.le.ac.uk>
C. Pagani (U. Leicester), N. P. M. Kuin (UCL-MSSL) and J. R. Cummings
(GSFC/UMBC) report on behalf of the Swift team:
We report on Swift follow-up observations of the Fermi/GBM GRB 140824B
(Zhang, GCN Circ. 16743) centred at the position of the candidate
optical counterpart reported by the MASTER II robotic telescope (Tyurina
et al., GCNs 16740, 16741).
In 4.9 ks of XRT Photon Counting (PC) mode data, from 90.6 ks to 103.4
ks after the Fermi/GBM trigger, no X-ray source is detected at the
MASTER II position. The 3-sigma upper limit on the count rate is 1.8E-03
cts/s, which is 9.2E-14 erg cm^-2 s^-1 using a typical flux conversion
of 5E-11 erg cm^-2 count^-1.
The UVOT detected the reported candidate OT. The preliminary UVOT
position is:
RA (J2000) = 01:11:01.14 = 17.75473 (deg.)
Dec (J2000) = +60:33:38.6 = 60.56071 (deg.)
with an estimated uncertainty of 0.43 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 91250 91850 590 17.97 � 0.05
white 96997 97610 603 17.94 � 0.05
white 102774 103372 590 18.09 � 0.05
v 91857 92457 590 17.47 � 0.07
v 97617 98230 603 17.61 � 0.07
u 90644 91244 590 17.65 � 0.06
u 96991 96991 603 17.62 � 0.06
u 102158 102768 600 17.91 � 0.07
The magnitudes in the table are not corrected for the large, but
uncertain Galactic extinction due to the reddening of E(B-V) = 0.79 in
the direction of the burst (Schlegel et al. 1998). The UVOT magnitudes
when compared to the reported unfiltered magnitudes of 17.0 and 17.5 by
MASTER, suggest a slowly varying source.
Based on the Swift observations, the optical transient detected by
MASTER II is therefore unlikely to be the GRB afterglow.