- GCN Circular #12628
T. Sakamoto (GSFC/UMBC), C. Graziani (U of Chicago), J. R. Cummings (GSFC/UMBC),
S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
Automated BAT ground analysis found a burst that occurred at 08:28:11 UT
with a significance of 10.1 sigma (15-200 keV) from the failed event data
of trigger #509285. The event is temporally coincident with the Fermi GBM
345025692. The best BAT location is RA, Dec = 290.2151, +40.6686 deg, which is
RA(J2000) = 19h 20m 51.6s
Dec(J2000) = +40d 40' 07.0"
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 10%.
The mask-weighted light curve created from the failed event data
(available from 08:28:12 to 08:28:22 UT) shows a constant positive
rate from the beginning of the data and then decaying at 08:28:20 UT.
From the BAT raw light curve, the duration of the event is ~20 sec long.
The spectrum extracted using the full event data is best fit by a simple
power-law model. The power law index of the spectrum is 1.5 +- 0.3. The
fluence in 15-150 keV band measured from the 10 sec long event data is
9.8 +- 1.8 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from
08:28:19 UT is 1.3 +- 0.7 ph/cm2/sec. All the quoted errors are at the
90% confidence level.
Swift ToO observation of this burst has been scheduled.
- GCN Circular #12631
C. A. Wolf (PSU), E. A. Hoversten (PSU), and T. Sakamoto (GSFC/UMBC)
report on behalf of the Swift team:
We have analyzed 2.85 ks of XRT data for the BAT ground-detected
burst: GRB 111208A (Sakamoto et. al. GCN Circ. 12628), from 24.3 ks to
34.9 ks after the burst. The data are entirely in Photon Counting (PC)
mode. An uncataloged X-ray source is detected within the BAT error
circle and is potentially the afterglow of GRB 111208A. The refined
XRT position is RA, Dec = 290.2251, +40.6766 which is equivalent to:
RA (J2000); 19 20 54.0
Dec(J2000): +40 40 35.8
with an uncertainty of 4.1 arcsec (radius, 90% confidence). This
position is 39.7 arcsec from the BAT position, within the BAT error
circle. This position may be improved as more data are received. We
cannot determine whether the source is fading at the present time.
The Swift/UVOT began settled observations of the field of GRB 111208A
24.3 ks after the BAT trigger. No optical afterglow consistent with
the XRT position is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are:
Filter T_start(ks) T_stop(ks) Exp(s) Mag
white 24.3 34.9 2100 >22.0
The magnitude in the table is not corrected for the Galactic
extinction due to the reddening of E(B-V) = 0.12 in the direction of
the burst (Schlegel et al. 1998). We note that this is a crowded
field and that there is a source a few arcseconds outside the XRT
error circle. However, this source is clearly visible in archival
optical imaging.
- GCN Circular #12644
T. N. Ukwatta (MSU), E. Sonbas (GSFC/Adiyaman Univ.),
T. Sakamoto (GSFC/UMBC), N. Gehrels (GSFC), J. Linnemann (MSU),
K. Tollefson (MSU), and U. Abeysekara (MSU)
We observed the field of Swift GRB 111208A
(Sakamoto et al., GCN 12628) with the Lightbuckets 0.43m
rental telescope LB-0002 in South Alpen, France. Ten 60 s
observations were carried out in the R filter starting
2011-12-08 at 17:04:45 UT (~ 31 ks after the GRB trigger).
This observation is in temporal coincidence with the Swift
XRT TOO observation which spanned from 24.3 ks to 34.9 ks
(Wolf et al., GCN 12631).
In the stacked R band image, we do not detect an optical
afterglow at the XRT location. Our upper-limit based on the
observation is given below.
Time after trigger Exposure (s) Filter Magnitude
8.61 hours 600 R > 19
- GCN Circular #12658
C. A. Wolf (PSU) reports on behalf of the Swift-XRT team:
We have analysed 4.5 ks of XRT data for the Swift/BAT ground-detected
burst: GRB 111208A (Sakamoto et al. GCN Circ. 12628), from 24.3 ks to
40.8 ks after the burst. The data are entirely in Photon Counting (PC)
mode. An X-ray source is detected within the Swift/BAT error circle.
Using 4204 s of PC mode data and 6 UVOT images, we find an enhanced XRT
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 290.22434, +40.67616 which is
equivalent to:
RA (J2000): 19h 20m 53.84s
Dec(J2000): +40d 40' 34.2"
with an uncertainty of 1.6 arcsec (radius, 90% confidence). This
position is 37 arcsec from the Swift/BAT position.
The light curve can be modelled with a power-law decay with a decay
index of alpha=3.14 (+0.23, -0.90).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.14 (+0.25, -0.37). The
best-fitting absorption column is 1.7 (+1.1, -0.9) x 10^21 cm^-2,
consistent with the Galactic value of 8.4 x 10^20 cm^-2 (Kalberla et
al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 3.5 x 10^-11 (5.3 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.7 (+1.1, -0.9) x 10^21 cm^-2
Galactic foreground: 8.4 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 2.14 (+0.25, -0.37)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020190
.
This circular is an official product of the Swift-XRT team.
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