GRB 050925
GCN Circular 4034
Subject
GRB050925: Swift-BAT detection of a short burst
Date
2005-09-25T10:05:01Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
S.T. Holland (GSFC/USRA), S. Barthelmy (GSFC), A. Beardmore (U. Leicester),
N. Gehrels (GSFC), J. Kennea (PSU), K. Page (U. Leicester),
D. Palmer (LANL), S. Rosen (MSSL)
on behalf of the Swift team:
At 09:04:33 UT, Swift-BAT triggered and located GRB050925 (trigger=156838).
The BAT on-board calculated location is RA,Dec 303.445d,+34.334d
{20h 13m 47s,+34d 20' 04"} (J2000), with an uncertainty of 3 arcmin
(radius, 90% containment, stat+sys). We note that the galactic latitude
is -0.1. The BAT light curve shows a single-peak structure with a total
duration of less than 128 msec. The peak count rate was ~8000 counts/sec
(15-350 keV), for the 128-msec binning at 0.00 seconds after the trigger.
The spacecraft slewed immediately and the XRT began observing the GRB at
09:06:05 UT, 92 sec after the BAT trigger. The on-board detection algorithm
failed to centroid on a source, so no prompt X-ray position is available.
The XRT prompt spectra and lightcurve show no signficant X-ray emission
in the field, suggesting that any X-ray counterpart to this burst is faint.
The UVOT began observing this field 91 sec after the BAT trigger.
The small UVOT TDRSS image covers 25% of the BAT error circle. However,
the full-field UVOT source list contains only catalogued sources,
and in particular no uncatalogued source is found inside the BAT error circle.
At the present time it is not possible to determine a limiting magnitude
for this field. The V-band extinction in this direction is A_V = 7.05 mag.
We note that this burst has soft emission in BAT which may not be consistent
with it being in the short-hard class of GRB. At low galactic latitude
it is possible that it is a new SGR. At this point we can not be sure
of its classification.
GCN Circular 4035
Subject
GRB050925: Faulkes Telescope North R-band limit
Date
2005-09-25T12:02:02Z (20 years ago)
From
Carole Mundell at ARI, JMU,Liverpool <cgm@astro.livjm.ac.uk>
C. Guidorzi, C.G. Mundell, A. Gomboc, I. A. Steele, C.J. Mottram,
A. Monfardini, R.J. Smith, D. Carter, M.F. Bode (Liverpool JMU),
E. Rol, P. O'Brien, N. Bannister (Leicester) report:
"The 2-m Faulkes North Telescope robotically followed up Swift burst
GRB050925 3.3 min after the GRB trigger time. The automatic "detection
mode" procedure did not detect any obvious candidate brighter than about
R=19 mag from 3x10-s images (mean epoch of 3.7 min after the GRB), with
FOV of 4.6'x4.6' centred on the BAT in-flight location. The field is
crowded and the extinction in V is about 6.3 mag (Schlegel et al. maps).
Visual inspection of the images confirms the reported non-detection.
The limiting magnitude is automatically calculated with respect to the
USNOB1.0 'R2' values of the field objects."
GCN Circular 4036
Subject
GRB 050925 : I-band observation at Xinglong observatory
Date
2005-09-25T15:16:35Z (20 years ago)
From
Yuji Urata at RIKEN <urata@crab.riken.go.jp>
Y. Qiu, C.L. Lu (BAO), Y.Q. Lou (THCA), Y. Urata (RIKEN), K.Y. Huang
(NCU) on behalf of EAFON report
" We have imaged the entire error region of GRB 050925 (Holland et
al. GCN 4034) using 0.8-m telescope at XingLong Observatory, China.
The I-band observations were performed form 11.27 UT to 11.78 UT (~
2.19 to 2.70 hours after the burst). Compare with DSS-II images, no
new source was found in our co-add image (300s x 6). The limiting
magnitude is I~ 20.6, in comparison with USNO-B1.0 stars(S/N=3). The
extinction in I is about 4.1 mag (Schlegel et al. 1998).
This message may be cited."
GCN Circular 4038
Subject
GRB050925: Swift UVOT upper limits
Date
2005-09-26T17:04:31Z (20 years ago)
From
Simon Rosen at MSSL-UCL <srr@mssl.ucl.ac.uk>
S. Rosen (MSSL), S. T. Holland (GSFC/USRA), F. Marshall(GSFC),
P. Boyd (GSFC-UMBC), N. Gehrels (GSFC) on behalf of the Swift/UVOT team.
The Swift/UVOT began observing the field of the short-soft burst, GRB050925,
at 09:06:03 UT, 90s seconds after the BAT trigger (Holland et al., GCN 4034).
There has been no reported XRT detection of a fading afterglow and no
counterpart found in ground-based observations (GCN 4035 and 4036) so
no positional information other than the BAT location (revised position
from Markwardt et al., GCN 4037) is currently available.
Within the 1.5 arcmin BAT error circle (GCN 4037), no new optical/UV source
is detected and we derive the following 3 sigma upper limit magnitudes
on any optical/UV counterpart in the summed images in each UVOT filter
(from 6" radius apertures centred on the BAT location which is
representative of the local background).
Filter T_range(sec) Exp(sec) 3sig UL
V 90-50567 3885 20.2
B 3787-57196 4600 21.8
U 3682-56297 4654 21.2
UVW1 3578-52239 4080 21.4
UVM2 3473-51474 4541 21.8
UVW2 3892-62080 4356 21.8
Where T_range is the time post-trigger over which
the summed images were accumulated and Exp is the
total exposure time. The magnitudes upper limits
are not corrected for extinction which is high since
the BAT position is in the galactic plane.
GCN Circular 4039
Subject
GRB 050925: WSRT Radio Observations
Date
2005-09-26T17:15:40Z (20 years ago)
From
Alexander van der Horst at U of Amsterdam <avdhorst@science.uva.nl>
A.J. van der Horst (University of Amsterdam) reports on behalf of a larger
collaboration:
"We observed the position of the short burst GRB 050925 at 4.9 GHz with
the Westerbork Synthesis Radio Telescope at Sep 25 13.48 UT to Sep 26 1.47
UT, i.e. 0.18 - 0.68 days after the burst (GCN 4034).
No radio sources are seen in the refined Swift-BAT error circle (GCN 4037)
above a 3-sigma level of 72 microJy. We measure a formal flux of 44 +/- 24
microJy at the center of the error circle (GCN 4037).
We note there is a bright radio source, with a flux of 878 +/- 31 microJy,
just outside this error circle at RA 20h13m47.8s, Dec +34d18'38" (J2000)."
This message may be cited.
GCN Circular 4043
Subject
GRB050925: Swift/XRT limits
Date
2005-09-27T06:48:40Z (20 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
A.P. Beardmore (U. Leicester), K.L. Page (U. Leicester), N. Gehrels (GSFC),
J. Greiner (MPE), J. Kennea (PSU), J. Nousek (PSU), J.P. Osborne (U.
Leicester) and G. Tagliaferri (INAF-OAB) report on behalf of the Swift/XRT
team:
We have analysed 27.8 ks of XRT data for the BAT soft short burst (trigger
156838; GCN 4034, Holland et al.), starting 99.5 s after the BAT trigger.
No fading X-ray source is found within the refined BAT error circle (GCN
4037, Markwardt et al.). However, there exists a source with a constant
count rate of 0.0015+/-0.0004 counts s^-1 at RA(2000) = 20 13 48.0,
Dec(J2000) = +34 19 53.7 (6.4 arcsec radius uncertainty at 90%
containment) within the BAT error circle, coincident with a B=13.0, R=11.6
magnitude USNO object (GSC0267902398 in the Guide Star Catalogue).
The spectrum of this source is best modelled by either a blackbody (with a
temperature of 0.19 +0.10/-0.05 keV, column density < 0.3E22 cm^-2 and an
unabsorbed 0.2-10.0 keV flux of 7.0E-14 ergs cm^-2 s^-1) or a thermal
plasma Mekal model (with a temperature of 0.87 +0.41/-0.44 keV, column
density < 0.2E22 cm^-2, an abundance consistent with solar and an
unabsorbed 0.2-10.0 keV flux of 4.6E-14 ergs cm^-2 s^-1). We note the
observed column density upper limit to this source is significantly less
than the Galactic value of 1.1E22 cm^-22 (Dickey & Lockman, 1990),
suggesting it is nearby and unlikely to be a GRB.
Except for the XRT source coincident with the USNO object, there are
no sources detected within the BAT error circle. The 3 sigma upper
limit on the count-rate is 0.0006 counts s^-1, corresponding to an
unabsorbed 0.2-10 keV flux of 3.0E-14 ergs cm^-2 s^-1 assuming a
Crab-like spectrum.
GCN Circular 4057
Subject
GRB 050925: Second Epoch WSRT Radio Observations
Date
2005-10-02T13:52:58Z (20 years ago)
From
Alexander van der Horst at U of Amsterdam <avdhorst@science.uva.nl>
A.J. van der Horst (University of Amsterdam) reports on behalf of a larger
collaboration:
"We reobserved the position of the short burst GRB 050925 at 4.9 GHz with
the Westerbork Synthesis Radio Telescope at Oct 1 14.66 UT to Oct 2 1.08
UT, i.e. 6.23 - 6.67 days after the burst (GCN 4034). No radio sources are
seen in the refined Swift-BAT error circle (GCN 4037) above a 3-sigma
level of 66 microJy. We measure a formal flux of 10 +/- 22 microJy at the
center of the error circle (GCN 4037). The bright radio source we reported
in GCN 4039, just outside this error circle, has a flux of 881 +/- 32
microJy; so this source did not vary significantly between ~0.43 and ~6.45
days."
This message may be cited.
GCN Circular 4274
Subject
GRB050925: analysis of the XMM-Newton observation
Date
2005-11-15T18:44:45Z (20 years ago)
From
Andrea De Luca at IASF-CNR,Milano <deluca@iasf-milano.inaf.it>
A.De Luca, P.Caraveo, P.Esposito, S.Mereghetti, A.Tiengo (INAF/IASF Mi),
report:
we have analyzed the data from the XMM-Newton observation of
the soft short burst GRB050925, observed by Swift to have
characteristics similar to that of Soft Gamma Repeaters (SGRs)
(Holland et al., GCN4034). An independent analysis of the XMM
data was reported by Rea et al.(GCN4264).
We give here the detailed results of a source detection on the
EPIC dataset. Such results will become an important reference
in case the putative SGR will enter a phase of enhanced activity.
We used independently the pn camera data and the combined
MOS1+MOS2 data. We selected the energy ranges 0.3-2 keV,
2-8 keV and 0.3-8 keV. The MOS and pn positions are found to
be consistent within ~1.5 arcsec, in agreement with the known
astrometric accuracy of the EPIC cameras. Thus, we assume 1.5
arcsec as the 1sigma uncertainty on the X-ray sources' positions.
In the source list below we quote the J2000 coordinates
as derived from the pn camera (unless otherwise specified).
Since the field of GRB050925 is very crowded we focus on the
region closer to the 1.5 arcmin BAT error circle (Markwardt
et al., GCN4037). 6 X-ray sources (named XMM1...XMM6) are
detected within 2 arcmin of the BAT coordinates.
Finding charts from pn and MOS data may be found at
http://www.iasf-milano.inaf.it/~deluca/grb050925
Please note that the circles around XMM sources are meant
to help locate them. In the scale used for the figures the
XMM error boxes are smaller than 1 pixel.
Sources inside the BAT circle:
XMM1 - RA 20:13:47.81, Dec +34:19:51.9 - it is the brightest
source located within the BAT error circle. It is the
steady source discovered in Swift/XRT data by Beardmore
et al. (GCN4043) and interpreted as a field star.
Its coordinates, within errors, are consistent with a bright
optical source (B~12.4, R~11.9, source id.1243-0400741 in
USNO-B1). Its spectrum is well described by a mekal plasma
model with NH<5x10^20 cm^-2, kT~0.6 keV, abundance ~0.3 solar
values and observed flux of 2.7x10^-14 erg cm^-2 s^-1
in 0.3-8 keV. The resulting Fx/Fopt is of ~3x10^-4.
Thus, in agreement with Beardmore et al.(GCN4043), we
conclude that source XMM1 is most likely a nearby star.
Rea et al.(GCN4264), assuming a smaller X-ray error circle,
questioned the association with the bright optical source
XMM2 - RA 20:13:57.85, Dec +34:19:56.5 - detected with S/N~3,
in the 0.3-2 keV range only.
Assuming a Crab spectrum with Galactic absorption
(1.1x10^22 cm^-2 according to Dickey & Lockman, 1990), its
observed flux is (2-3)x10^-15 erg cm^-2 s^-1 (0.3-2 keV).
No obvious optical counterparts are found in the DSS plates.
Sources outside the BAT circle:
XMM3 - RA 20:13:54.97, Dec +34:18:22.4 - located at 1.55 arcmin
from the BAT position, it is detected with S/N~3
in MOS data only (in the pn detector it lies on a bad column),
with a flux similar to source XMM2.
An optical source with R~17 is found within 3 arcsec.
XMM4 - RA 20:13:56.06, Dec +34:21:28.9 - located at 1.61 arcmin
from the BAT position, it is detected with S/N~3
in MOS data only (in the pn detector it lies on a bad column),
with a flux similar to source XMM2.
An optical source with R~16.5 is found within 2.2 arcsec.
XMM5 - RA 20:14:01.59, Dec +34:21:03.1 - located at 1.89 arcmin
from the BAT position, it lies within 1.5 arcsec of a
bright optical source (B~13.1, R~11.4, source id.1243-0401091
in USNO-B1 catalog), its spectrum is consistent with a mekal
plasma model with absorption smaller than the Galactic value,
kT~0.67 keV and abundance ~0.4 solar values; the observed flux
is ~1x10^-14 erg cm^-2 s^-1 (0.2-5 keV). Fx/Fopt is ~10^-4.
It is most likely a star.
XMM6 - RA 20:13:45.17, Dec +34:20:23.8 - located at 1.93 arcmin
from the BAT position, its spectrum is consistent
with a power law (photon index ~1.8) absorbed by the Galactic
column. Its observed flux is ~2x10^-14 erg cm^-2 s^-1
(0.2-8 keV). No obvious optical counterparts.
No other sources within 2 arcmin of the BAT position are seen.
Using the present XMM observation we can estimate the upper limit
flux as follows: assuming a Crab-like spectrum with Galactic
absorption, a S/N=3 detection corresponds to a flux of ~3x10^-15 erg
cm^-2 s^-1 in the 0.3-2 keV band and ~8x10^-15 erg cm^-2 s^-1 in
the 0.3-8 keV band.
We thank the XMM Project Scientist, N.Schartel, for approval of
this TOO, and the XMM people at Vilspa for performing it.