GRB 050724
GCN Circular 3665
Subject
GRB050724: a short-burst detected by Swift
Date
2005-07-24T13:34:04Z (20 years ago)
From
Stefano Covino at Brera Astronomical Observatory <covino@merate.mi.astro.it>
S. Covino (INAF/OAB), L.A. Antonelli (INAF/OAR), P. Romano (INAF/OAB),
D. Palmer (LANL), C. Markwardt(GSFC, UMd), D. Burrows (PSU), N. Gehrels
(GSFC), S. Barthelmy (GSFC), M. Chester (PSU), S. Hunsberger (PSU), J.
Cummings (GSFC/NRC) on behalf of the Swift team
At 12:34:09 UT, Swift-BAT triggered and located GRB050724
(trigger=147478). The spacecraft slewed immediately. The BAT on-board
calculated location is RA,Dec 246.214, -27.524 {+16h 24m 51s, -27d 31'
25"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment,
stat+sys). The light curve appears to be short, with full-width half
maximum of less than 0.25 sec, and a peak rate of 10,000 ct/s in that
interval.
The XRT started the observation at 12:35:22.9 UT with XRT in automatic
state, 74 sec after the BAT Trigger. A rapidly fading, uncatalogued, X-
ray source was detected at the following position RA, Dec 16h 24m 44.9s,
-27d 32' 34.0" with an uncertainty of about 6 arcsec (90% containment).
This is 1.78 arcmin from the BAT position reported above.
This message can be cited.
GCN Circular 3666
Subject
GRB 050724: possible host galaxy in DSS
Date
2005-07-24T14:25:16Z (20 years ago)
From
Angelo Antonelli at Obs. Astro. di Roma <a.antonelli@mporzio.astro.it>
L.A. Antonelli (INAF/OAR), S. Covino (INAF/OAB), D. Malesani (SISSA),
P. Romano, A. Moretti (INAF/OAB) on behalf of the MISTICI collaboration
report:
We looked at the DSS image of the field of the short GRB 050724 (Covino
et al., GCN 3665). We note the presence of a faint object located at
RA: 16h 24m 44.9s DEC -27d 32' 33.3" (J2000) and centered on XRT
position (Covino et al., GCN 3665) which is under the threshold of both
USNO and 2MASS catalogues. We estimated a R mag for this object of 19.1
calibrating with the nearby USNO star (U600_20428424 RA: 16:24:47.92,
DEC: -27:32:21.05 R=16.5 mag).
This message can be cited
GCN Circular 3667
Subject
GRB050724: Refined analysis of the Swift-BAT possible short burst
Date
2005-07-24T16:27:35Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hinshaw (GSFC-SPSYS), D. Hullinger (GSFC/UMD), C. Markwardt (GSFC/UMD),
K. McLean (LANL) D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
J. Tueller (GSFC)
on behalf of the Swift-BAT team:
Using the full data set from the recent telemetry downlink, we report
further analysis of Swift-BAT Trigger #147478 (Covino, et al., GCN 3665).
The ground-analysis position is RA,Dec 246.177,-27.525 (J2000) with an
uncertainty of 3 arcmin (radius, 90%, stat+sys). T90 is 3 +- 1 sec.
The lightcurve has an initial hard FRED peak at T+0.00 sec (FWHM of 0.256 sec)
and there is a smaller much softer peak at T+1.00 sec. Fitting a simple
power law over the full interval from T-1.0 to T+3.0 seconds, the photon index
is 1.71 +/- 0.16 with a fluence of 6.3 +/- 1.0 X 10^-7 erg/cm^2.
The peak flux in a 1-sec wide window starting at T+0.04 seconds
is 3.9 +/- 0.3 ph/cm^2/sec. All values are in the 15-350 keV band
at the 90% confidence level.
Given the second emission peak at T+1, the T90 of 3 sec, and
the power law index value of 1.71, we can not confirm, nor rule out,
that this burst falls into the short-burst category. However, in the
energy range above 25 keV, the second, softer peak and subsequent emission
is much less prominent, and so it is likely that BATSE would have
classified this as a short GRB.
GCN Circular 3668
Subject
GRB 050724 : Lulin early R-band monitoring observations
Date
2005-07-24T16:48:46Z (20 years ago)
From
Yuji Urata at RIKEN <urata@crab.riken.go.jp>
I.C. Yen (NTNU), H.C. Lin, K.Y. Huang, W.H. Ip (NCU),
Y. Urata (RIKEN), Y. Qiu (BAO), Y.Q. Lou (THCA)
on behalf of EAFON report:
" We started to image the GRB 050724 error region (Covino et al GCN
3665) at 14.26 UT (~1.69 hours after the burst) using 1.0-m telescope
at Lulin Observatory, Taiwan. The source reported by Antonelli et
al. (GCN 3666) was detected in a series of R-band 300 sec
exposure. Our preliminary analysis shows the brightness of the source
do not have significant variability during our monitoring observations
(1.69-3.59 hours after the burst).
This message may be cited."
GCN Circular 3669
Subject
GRB 050724: early Swift XRT analysis results
Date
2005-07-24T18:30:47Z (20 years ago)
From
Pat Romano at OAB-Swift <romano@merate.mi.astro.it>
P. Romano, A. Moretti, S. Covino (INAF-OAB), L.A. Antonelli(IANF-OAR),
D.N. Burrows, D. Grupe (PSU), M. Chester (PSU), G. Chincarini, G.
Tagliaferri (INAF-OAB), P. Boyd (GSFC-UMBC) on behalf of the Swift-XRT
Team report.
We have analyzed the Swift XRT data from the first orbit observation of
GRB 050724 (Covino et al., GCN 3665). The new refined coordinates are:
RA(J2000) = 16h 24m 45s Dec(J2000) = -27 32 25.2. This position is 65
arcseconds from the refined BAT position given in GCN 3667 (H. Krimm et
al), and 9 arcseconds from the XRT position given in GCN 3665. We
estimate an uncertainty of 6.3 arcseconds radius (90% containment).
However, we note that there is accumulating evidence of a time-dependent
systematic shift in XRT positions derived from ground-processed data
towards lower declinations than the optical counterparts. This effect is
being investigated but is not yet understood. Extrapolation of earlier
positional errors suggests that the correct position could be
approximately 7 arcseconds north of the position given above, which
would be close to the on-board position given in GCN 3665.
A preliminary spectral fit (simple absorbed power-law) to the WT data
yields a photon index of 1.93-/+0.05 in the [0.5-10] keV band. The
derived NH is (5.7)E21 cm^-2, which is higher than the Galactic value
(1.46E+21 cm-2; Dickey & Lockman 1990). The average (79-342 seconds from
trigger) estimated unabsorbed 0.5-10 keV flux is 5.3E-9 ergs/s/cm2.
The light curves in Windowed Timing (WT) and Photon Counting (PC) mode
start 79 and 343 seconds from the BAT trigger (T0), and they show a
fading afterglow which can be fitted with a broken power law of slopes
-3.2+/-0.1 and -0.8+/-0.2. The unabsorbed 0.5-10.0 keV flux at 24 hours
after the burst is then estimated to 9E-14 ergs/s/cm2.
GCN Circular 3670
Subject
GRB 050724: Swift/UVOT Upper Limit
Date
2005-07-24T21:10:45Z (20 years ago)
From
Margaret Chester at PSU <chester@astro.psu.edu>
M. Chester (PSU), S. Covino (OAB), P. Schady (MSSL), P. Roming (PSU) N.
Gehrels (GSFC), on behalf of the Swift UVOT team.
Using summed images from Swift/UVOT of the field of GRB 050724 (Covino
et al., GCN 3665), accumulated during the first forty minutes after the
BAT trigger, no new source is detected within the XRT error circle in
the V filter down to a 3-sigma limit of V=18.84.
The magnitudes are based on preliminary zero-points, measured in orbit,
and will require refinement with further calibration.
GCN Circular 3671
Subject
GRB 050724: RTT150 optical observations
Date
2005-07-24T22:40:13Z (20 years ago)
From
Rodion Burenin at IKI, Moscow <rodion@hea.iki.rssi.ru>
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), A. Alpar (SabUni),
I. Bikmaev, N. Sakhibullin (KSU/AST)
report:
We observed the error box of GRB 050724 (Covino et al., GCN 3665) with
Russian-Turkish 1.5-m telescope (RTT150, Bakyrlytepe, TUBITAK National
Observatory, Turkey). We made a set of 600s exposures in R, starting at
18:11 UT, July 24, i.e. approximately 5.6 hours after the burst.
Observations were made at very high zenith distance (65-75 degrees) and
in poor seeing conditions (~2 arcsec).
We found no variable sources brighter than our limiting magnitude, which
is only slightly deeper than DSS.
This message may be cited.
GCN Circular 3672
Subject
GRB 050724: Optical imaging/astrometry
Date
2005-07-25T01:09:43Z (20 years ago)
From
Josh Bloom at Harvard/CFA <jbloom@cfa.harvard.edu>
J. S. Bloom (UC Berkeley), A. Dupree (Smithsonian Astrophysical
Observatory), H-W. Chen (MIT), & J. X. Prochaska (UC Santa Cruz) report:
"Comparison of the 2MASS catalog with a short exposure with the
unfiltered MIKE (Magellan II/Clay) guider CCD camera beginning on
2005-07-24 23:25:25 UTC shows faint sources near the XRT localizations
(GCNs #3665 & #3669). We find the following positions (systematic
error relative to the ICRS is 0.2" in both RA and DEC):
A 16:24:44.964 -27:32:23.21 J2000 Source 1 in #3669 error circle
B 16:24:44.912 -27:32:32.73 J2000 Source 1 in #3665 error circle,
noted by Antonelli et al. #3666
C 16:24:45.303 -27:32:34.67 J2000 Source 2 in #3665 error circle
D 16:24:44.398 -27:32:26.85 J2000 Bright galaxy to the West of
XRT error circles
Source D appears to be an extended galaxy and, while formally excluded
by the 90% confidence regions of the various positions reported for
the X-ray afterglow, is of interest nonetheless (especially given what
appears to be an emerging trend of low-redshift galaxies associated
with short bursts)."
A finding chart may be found at:
http://astro.berkeley.edu/~jbloom/grb050724.png
Please email JSB if you would like to make use of the guider FITS image.
This message may be cited.
[GCN OPS NOTE 924jul05): Per author's request, hanged "astronomy" to
"astrometry" in the Subject.]
GCN Circular 3673
Subject
GRB 050724: optical and near-IR observations
Date
2005-07-25T02:38:16Z (20 years ago)
From
Javier Gorosabel at LAEFF-INTA, Madrid <jgu@laeff.esa.es>
A.J. Castro-Tirado, J. Gorosabel, A. de Ugarte Postigo,
S. Guziy and M. Jel�nek (IAA-CSIC), M. Karrer (Obs.
de Geneve), H.-J. Roeser (MPI Heidelberg), N. El�as-Rosa
(Obs. Astr. di Padova), O. Bogdanov (Nikolaev State Univ.)
and A. Aguirre (CAHA Almer�a)
report:
"We have imaged a 6' x 6' region centred on the SWIFT/BAT
error box for the short/hard GRB 050724 (Covino et al.
GCNC 3665) with the 1.2-m Mercator telescope (+ Merope) at
the Observatorio del Roque de los Muchachos on La Palma
starting on July 24.890 UT (i.e. 8.8 hours after the
GRB) under good meteorological conditions. Within
the refined SWIFT/XRT position (Romano et al. GCNC 3669),
the co-added R-band image (5400 s exposure time) shows a
source close to the center of the 6.3 arcsec radius error
box, labelled as A by Bloom et al. (GCN Circ. 3672).
Coordinates yield: RA(2000) = 16 24 44.96, Dec(2000)
= -27 32 23.6 (+/- 0.5"). We measure R = 22.40 +/- 0.13
using the USNO-A2.0 star at RA(2000) = 16 24 44.55, Dec(2000)
= -27 32 59.9. This source is blue, since it is barely
detected in contemporaneous J- and K-band images obtained
at the 3.5-m telescope (+ Omega2000) at the German-Spanish
Calar Alto Observatory and in H-band frames obtained at the
3.5-m Telescope Nazionale Galileo (+ NICS) on La Palma. The
colours of objects B and C are also consistent with being
blue, in contrast to the redder galaxy labelled D. Further
observations are needed to confirm whether any of these
objects has any relationship to GRB 050724."
This message can be quoted.
GCN Circular 3674
Subject
GRB 050724: Optical limit
Date
2005-07-25T03:56:34Z (20 years ago)
From
Ken ichi Torii at RIKEN <torii@crab.riken.go.jp>
K. Torii (Osaka U.) reports on behalf of the ART collaboration:
The error region of the possible short GRB 050724 (Covino et
al. 3665, Krimm et al. GCN 3667) was observed by the 14 inch Automated
Response Telescope in Osaka. The imaging started at 2005 July 24
12:40:35 UT (75 s after the alert reception; 386 s after the
trigger) and RcIcBV frames of 60s integration were obtained.
We find no optical counterpart for the X-ray afterglow (GCN 3665,
Romano et al. GCN 3669) and derive its 3-sigma upper limit
relative to USNO-B1.0 magnitude as follows.
================================
Start(UT) Filter Mag Exposure
--------------------------------
12:41:43 Ic >14.5 60s
--------------------------------
GCN Circular 3675
Subject
GRB 050724: spectroscopy of object in the XRT error circle
Date
2005-07-25T18:05:48Z (20 years ago)
From
Silvia Piranomonte at OAR <piranomonte@mporzio.astro.it>
S. Piranomonte (INAF/OAR), D. Fugazza (INAF/OABr), F. Fiore (INAF/OAR), S. Covino (INAF/OABr),
P. D'Avanzo (INAF/OABr), D. Malesani (SISSA), G. Tagliaferri (INAF/OABr), G. Chincarini (Univ.
Milano-Bicocca) and L. Stella (INAF/OAR), on behalf of the MISTICI collaboration, report:
Using the FORS1 instrument at the ESO VLT, we obtained a spectrum of the
object indicated by Antonelli et al. (GCN 3666), also named as object B
by Bloom et al. (GCN 3672). This object is liying close to the XRT
errorbox center (Covino et al., GCN 3665; Romano et al., GCN 3669).
Observations were obtained on 2005, July 24, starting at 23:16:00
UT, under good seeing conditions. We used the grism 300V with a slit of
1.0 arcsec. The integration time was 900 s.
The object is identified with a star trough Ca, CN, G-band, Hbeta, Na
and Halpha faint absorption lines. It has therefore no likely
association with GRB 050724.
We thank the excellent work by the ESO staff in performing these
observations.
This message may be cited.
[GCN OPS NOTE(28jul05): Per author's request, in the Subject-line
the "GRB 050624" was changed to "GRB 050724".]
GCN Circular 3676
Subject
GRB050724: Radio Observation
Date
2005-07-25T21:19:00Z (20 years ago)
From
Patrick B. Cameron at Caltech <pbc@astro.caltech.edu>
P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf
of the Caltech-NRAO-Carnegie collaboration:
"We observed the field of GRB050724 (GCN 3665) with the Very Large
Array at 8.5 GHz on July 25.09. We identify one radio source that is
~9" west from the center of the XRT error circle (GCN#3669). Its
position is (J2000): RA= 16:24:44.35, Dec= -27:32:26.9.
We note that, within our current astrometric errors this source is
positionally coincident with with the bright galaxy identified as
Source D by Bloom et al. (GCN#3672). Based on background source
counts, we expect 0.02 sources per square arcminute above this
brightness (~170 uJy). Further observations are planned to determine
the nature of this radio source.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 3677
Subject
RXTE ASM Detection of GRB050724
Date
2005-07-25T22:55:57Z (20 years ago)
From
Ron Remilard at MIT <rr@space.mit.edu>
Ron Remillard (MIT), Jean Swank (GSFC), and Alan Levine (MIT)
report for the RXTE/ASM team at MIT and NASA/GSFC
The RXTE All-Sky Monitor detected GRB050724 in a single camera (SSC 2)
with a significance of 9.5 sigma. The event duration is 2.0 (0.5) s,
and the burst (integrated) is detected in each of the 3
standard ASM energy bands: 1.5-3, 3-5, and 5-12 keV. When plotted at
32 ms time resolution, the instantaneous maximum is 10.8 (3.0) Crab.
Despite weak statistics, the burst profile appears to show
two peaks, as reported in GCN Circular 3667, and both peaks are
stronger at 5-12 keV, compared to 2-5 keV
(see http://xte.mit.edu/~rr/grb050724_32ms.ps).
GCN Circular 3678
Subject
GRB 050724: SWIFT XRT refined position
Date
2005-07-25T23:46:41Z (20 years ago)
From
Angelo Antonelli at Obs. Astro. di Roma <a.antonelli@mporzio.astro.it>
L.A. Antonelli (INAF/OAR), P. Romano, A. Moretti, S. Covino (INAF/OAB),
D. Burrows (PSU) on behalf of the SWIFT XRT Team report:
We have analyzed the first 20 ksec of the Swift XRT observation of GRB
050724 (GCN 3665, Covino et al.). We derived a refined position of the
X-ray afterglow
by performing a boresight correction based on the USNO catalog. The new
coordinates of the X-ray afterglow are: RA(J2000) = 16h 24m 44.8s,
Dec (J2000) = -27d 32' 31.8" with an uncertainty of 5.4 arcseconds
radius (3 sigma). This position is 69 arcseconds from the refined BAT
position given in GCN 3667 (H. Krimm et al), 2.6 arcseconds from the
XRT position given in GCN 3665 and 7.1 arcseconds from the XRT position
given in GCN 3669 (Romano et al.).
This message can be cited.
GCN Circular 3679
Subject
GRB 050724: GMOS Imaging and Spectroscopy
Date
2005-07-26T00:44:54Z (20 years ago)
From
Jason Prochaska at UCO/Lick Obs <xavier@ucolick.org>
J.X. Prochaska (UCO/Lick), H.-W. Chen (MIT), J.S. Bloom (UCB),
and A. Stephens (Gemini) report on behalf of the GRAASP
collaboration:
We have obtained GMOS/R400 spectroscopy (2400s) of the Sources
identified as A, B and D in GCN #3672. We confirm
the identification of Source B as a Galactic star
(GCN #3675). We tentatively identify Source A as a
Galactic star based on its PSF and featureless spectrum.
Our acquisition image of the field clearly demonstrates
that Source D is extended and therefore a galaxy. Our
spectrum of the galaxy is nearly featureless
(lambda=5000-9000A), indicating the galaxy is an early
type consistent with its red color (GCN #3673).
We assign a possible redshift of z=0.257 based on
absorption features at ~6510A and ~7415A which we
associate with MgI and NaI. The galaxy is located
7.2" from the refined XRT position (GCN #3678) which
would correspond to 27kpc at z=0.257.
Further observations are encouraged.
We thank the Gemini staff for their help in acquiring
this dataset.
Plots of the data can be found here:
http://www.graasp.org/Data/050724
----------------------------------------------
Jason X. Prochaska
UCO/Lick Observatory
UC Santa Cruz
Santa Cruz, CA 95064
xavier@ucolick.org
http://www.ucolick.org/~xavier/
831-459-2135 (Direct)
831-459-2991 (UCO/Lick Main)
831-459-5244 (Fax)
GCN Circular 3680
Subject
GRB 050724: J-band observations
Date
2005-07-26T01:21:06Z (20 years ago)
From
Javier Gorosabel at LAEFF-INTA, Madrid <jgu@laeff.esa.es>
A. de Ugarte Postigo, J. Gorosabel, A.J. Castro-Tirado,
M. Jelinek, S. Guziy (IAA-CSIC), H.-J. Roeser (MPI Heidelberg),
A. Aguirre, S. Pedraz (CAHA), O. Bogdanov (Nikolaev State Univ.),
report:
"We have observed the field of GRB 050724 (GCN Circ. 3665) in the
J-band with the 3.5m Calar Alto telescope (mean observing epoch July
25.86 UT, Texp=45 min). A comparison with the images taken yesterday
with the same telescope (mean observing epoch July 24.87 UT, Texp=15
min) did not reveal any variable source in the reported XRT error
boxes (GCN Circ. 3678, 3665, 3669) down to J~20. At first epoch we
note the presence of a possible object on our detection limit (J~20.5)
located at RA(J2000)=16:24:45.02, DEC(J2000)=-27:32:29.1. However, the
worse seeing on July 25.86 UT prevented us from confirming its
potential variability."
This message can be cited.
GCN Circular 3681
Subject
GRB 050724: Optical Variability in Nearby Galaxy
Date
2005-07-26T07:50:06Z (20 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
A. Gal-Yam, S. B. Cenko (Caltech), E. Berger (Carnegie), W. Krzeminski
(LCO) and B. Lee (Toronto) report on behalf of the Caltech-NRAO-Carnegie
collaboration:
We have obtained three epochs of optical imaging of the field of GRB
050724 (Covino et al., GCN 3665) with the RetroCam CCD Camera on the
1.0-m Swope telescope at Las Campanas Observatory. Each epoch consisted
of 2 x 15 min exposures in I-band, with the last epoch also containing one
additional ten minute exposure.
We subtracted the coadded sum image obtained during the second night of
observations (epoch 3; July 26.05 UT) from the coadded sum images taken
during the first night (epoch 1, July 25.02 UT; epoch 2, July 25.11 UT ) using
the CPM (Gal-Yam et al. 2004) and ISIS (Alard et al. 1999) codes. We
clearly detect a variable point source superposed on galaxy "D" of
Bloom et al. (GCN 3672).
The variable source is offset from the galaxy core (see figure at
http://www.its.caltech.edu/~cenko/grb050724/grb050724.jpg; the green
circle is centered on the galaxy core from epoch 3, the red is centered
on the OT). Furthermore, the light distribution in epoch 1 is markedly
different from that in epoch 3, due to the effect of the OT light,
disfavoring the possibility that the optical variability results from
Galaxy D being an AGN.
Calibrating the OT magnitudes against "I2" magnitudes of four nearby stars
from the USNO B1 catalog, we find that the OT brightened by 0.6
magnitudes between epochs 1 and 2 (I=21.25 at epoch 1, 12 hours after
the burst; I=20.65 at epoch 2, 14.3 hours after the GRB). We note that
such behavior is rare among optical afterglows.
GCN Circular 3684
Subject
GRB050724: Further Radio Observations
Date
2005-07-26T20:48:52Z (20 years ago)
From
Alicia Soderberg at Caltech <ams@astro.caltech.edu>
A. M. Soderberg, P. B. Cameron (Caltech) and D. A. Frail
(NRAO) report on behalf of the Caltech-NRAO-Carnegie collaboration:
"We have undertaken additional VLA observations of GRB050724 (GCN 3665) on
2005 July 26.21 UT. The flux density of the radio source, identified in
GCN 3676, has varied significantly between these two epochs.
This radio variability, together with the close proximity of the radio
source with the XRT position (GCN 3676; chance coincidence<0.15%), and
the optical variations noted in GCN 3681, argue that this is the afterglow
of GRB050724. Further observations are planned.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 3685
Subject
GRB 050724: dust-scattered X-ray halo detected in SWIFT/XRT observation
Date
2005-07-26T22:11:58Z (20 years ago)
From
Pat Romano at OAB-Swift <romano@merate.mi.astro.it>
P. Romano, A. Moretti (OAB), S. Vaughan (U. Leicester), L. A. Antonelli (OAR), S. Campana,
G. Chincarini, S. Covino,D. Malesani, G. Tagliaferri (OAB), J. Osborne, R. Willingale,
P.T. O'Brien, A. Levan, K. L. Page, M. R. Goad (U. Leicester), D. N. Burrows (PSU), report:
Analysis of the SWIFT XRT observation of GRB050724 in Photon Counting (PC) mode has revealed
in the first orbit a diffuse X-ray halo centered around the afterglow location. The halo has
the form of complete ring which increases in radius through the observation and reached
the distance of ~100 arcsec during the first ~2000 sec after the trigger (T0). We can exclude
it is due to instrumental effects. During the observation, which started ~343 seconds after
the burst trigger time (PC mode), the observed halo follows the expected behaviour of a "light-echo"
as X-rays are scattered by dust in our Galaxy. From the radial expansion of the halo we estimate
a distance of 175 -/+ 50 pc to the dust (from the observer, 90% confidence interval).
GRB 050724 is in the direction (Galactic) l = 350.37, b = 15.10 degrees, in which the density
of interstellar medium is quite high as testified by both the neutral Hydrogen column density
nH=1.5E21 cm-2 and the optical extiction E(B-V)=0.61 (A_V=2.029, A_K=0.225). This line of sight
includes the Scorpius Centaurus OB association at ~150-200 pc, consistent with the derived distance
to the scattering medium.
The X-ray WT spectrum of GRB050724 is represented by a powerlaw with Photon index 1.93-/+0.05
in the [0.5-10] keV band (as reported in GCN 3669; Romano et al.). The scattered X-ray light has,
as expected, a softer spectrum with Photon index 3.2-0.8+1.0 (first orbit).
More information is posted at: http://www.merate.mi.astro.it/~romano/grb050724/index.html
GCN Circular 3690
Subject
GRB050724: VLT observations of the variable source
Date
2005-07-27T09:01:59Z (20 years ago)
From
Paolo D'Avanzo at INAF-OAB <davanzo@merate.mi.astro.it>
P. D'Avanzo, S. Covino (INAF/OABr), L.A. Antonelli, A. Melandri
(INAF/OAR), D. Malesani (SISSA), A. Moretti, P. Romano, G. Tagliaferri
(INAF/OAB), S. Piranomonte (INAF/OAR), G. Chincarini (Univ. Milano-
Bicocca), and L. Stella (INAF/OAR) report on behalf of the MISTICI
collaboration
We observed the afterglow of GRB050724 (Covino et al., GCN 3665) with
the ESO-VLT equipped with the FORS1 camera, starting on 2005 Jul 25.01
and Jul 25.98 (12 and 35 hours after the burst respectively). The seeing
was 1.0" and 0.8" in the two epochs respectively. Observations were
carried out in the R and I filters.
We clearly detect all the sources listed by Bloom et al. (GCN 3672) and
Castro-Tirado et al. (GCN 3673).
PSF-matched image subtraction was performed with the ISIS package (Alard
& Lupton, 1998). A highly significant variable source is detected
superimposed to the galaxy named as source "D" in GCN 3672 (for a figure
see http://www.merate.mi.astro.it/~covino/GRB050724). The source is
slightly offset with respect to the galaxy center. We give below the
0.2" uncertainty position of the galaxy and the OT:
Galaxy centroid: 16:24:44.405 -27:32:26.95
OT centroid: 16:24:44.400 -27:32:27.90
Assuming the object has completely disappeared in our second epoch, the
magnitude of the variable source was I = 20.85 +/- 0.05 at our first
epoch. This value was derived by adding artificial stars of known
brightness to the reference frame, calibrated with Landolt standard
stars. This source faded between the two epochs in both the R and I
bands.
Therefore, we confirm the variability reported by Gal-Yam et al. (GCN
3681). However, our source appears (in both the R and I bands) 1" South
with respect to the core of the host galaxy. This is at variance with
the picture posted by Gal-Yam et al. (GCN 3681), where the variable
object appears North of the host galaxy centroid. After the
rebrightening episode reported by them, the source has therefore clearly
faded.
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GCN Circular 3694
Subject
GRB 050724, SMARTS optical/IR afterglow observations
Date
2005-07-28T18:24:13Z (20 years ago)
From
Bethany Cobb at Yale U <cobb@astro.yale.edu>
B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 050724
(GCN 3665, Covino et al.) at two separate epochs.
The two epochs had mid-exposure times of 2005-07-25 01:58 UT
(13.4 hours post-burst) and 2005-07-27 03:21 UT (62.8 hours
post-burst). Total summed exposure times at each epoch
amounted to 36 minutes in I and 30 minutes in J, resulting in
approximate limiting magnitudes of I>22 and J>20.
In order to search for variability in the host galaxy of GRB 050724
("source D" from Bloom et al. GCN 3672), the ISIS image subtraction
routine was used (Alard et al. 1999). When the second epoch
images are subtracted from the first epoch images, the residual light
of the afterglow is clearly detected in both the I and J
subtracted frames (in agreement with both GCN 3681, Gal-Yam
et al. GCN 3690, D'Avanzo et al.). The centroid of this residual is ~0.2"
west and ~0.5" south of the centroid of the host galaxy.
Preliminary differential photometry of the host galaxy yields a decay
of 0.19 +/- 0.03 magnitudes in I and 0.17 +/- 0.05 magnitudes in J
between the two imaging epochs.
Assuming the afterglow no longer contributes significantly to the
brightness of the host galaxy at the second epoch, then the magnitude
of the host galaxy is I = 18.78 +/- 0.27 and J = 16.94 +/- 0.09.
Unfortunately, imaging was done under non-photometric conditions so
no Landolt or Persson standard stars are available with which
to determine the offset between instrumental and apparent
magnitude. Therefore, the above values are determined using "on-chip"
standards (USNO-B1 stars in the optical and 2MASS stars in the IR) and the
error is strongly dominated by the uncertainty in the offset derived from
these stars.
Given the above values for the magnitude of the host and its
dimming, the afterglow of GRB 050724 is determined to have a magnitude of
I = 20.58 +/- 0.32 and J = 18.87 +/- 0.32 at 13.4 hours post-burst.
GCN Circular 3696
Subject
GRB050724: Refined Radio Position
Date
2005-07-28T20:07:36Z (20 years ago)
From
Alicia Soderberg at Caltech <ams@astro.caltech.edu>
A. M. Soderberg (Caltech) reports on behalf of the
Caltech-NRAO-Carnegie collaboration:
"Further observations of the radio afterglow (GCN 3676, 3684)
of GRB050724 (GCN 3665) have allowed for a position to be derived
with increased astrometric accuracy:
RA (J2000) 16 24 44.369 � 0.007s
DEC (J2000) -27 32 27.5 � 0.2"
which is consistent with the position of the optical transient
(GCN 3681, 3690)."
GCN Circular 3697
Subject
GRB 050724: Chandra Observations of the X-ray Afterglow
Date
2005-07-28T21:14:02Z (20 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
D. N. Burrows, D. Grupe (PSU), C. Kouveliotou, S. Patel (MSFC), P. Meszaros
(PSU), B. Zhang (UNLV), and R. A. M. J. Wijers (U. Amsterdam) report:
We observed the X-ray afterglow of the short GRB 050724 (Covino et al., GCN
3665) with the Chandra X-ray observatory from 20:09 UT on 26 July 2005 to
10:45 UT on 27 July 2005. The total exposure time was 50 ks. We find an
uncataloged X-ray source coincident with the VLT source reported by
D'Avanzo et al. (GCN 3690) and the VLA source reported by Cameron and Frail
(GRB 3676) as updated by Soderberg (GCN 3696). The Chandra position is:
RA (J2000) = 16 24 44.36
Dec (J2000) = -27 32 27.5.
The astrometry has been verified by comparisons with one 2MASS star with an
X-ray counterpart on the ACIS S-3 chip. We estimate an uncertainty of 0.2
arcseconds radius.
The X-ray source flux appears to decrease during the Chandra observation,
although with marginal statistical significance.
GCN Circular 3699
Subject
GRB 050724: WHT optical observations
Date
2005-07-29T17:58:10Z (20 years ago)
From
Klaas Wiersema at GRACE/U of Amsterdam <kwrsema@science.uva.nl>
K. Wiersema (U. of Amsterdam), E. Rol (U. of Leicester),
R. Starling (U. of Amsterdam), N. Tanvir (U. of Hertfordshire),
D. S. Bloomfield, H. Thompson (Queen's University Belfast)
report:
We have observed the position of the short burst
GRB 050724 (Covino et al. GCN 3665) with the William Herschel
Telescope at the Observatorio del Roque de los Muchachos on
La Palma, using the Aux port Imager.
We observed two epochs, with midpoints 0.424 days and 3.405
after burst. The epoch 1 observations consisted of
4 x 15 + 5 minutes exposure time in R band. Epoch 2
consisted of 4 x 15 minutes in R band.
At the first epoch the weather conditions were good with an
average seeing of 0.8 arcsec. During the second epoch the seeing
was considerably worse, with an average seeing ~1.3 arcsec.
PSF-matched image subtraction of the two epochs using the
ISIS code (Alard et al. 1999) reveals a clearly fading source.
This behaviour is confirmed in a subtraction of the first and
last image from the first epoch. The position of the fading
source matches that described in e.g. GCNs 3690 and 3694,
as well as the radio (GCN 3684) and X-ray afterglow position
(GCN 3683, 3697).
We performed aperture photometry of the host galaxy plus the OT
with respect to two unsaturated USNO stars: 0624-0502999 and
0624-0503050, whose values we take from the USNO-B catalogue.
We find a magnitude difference of approximately 0.2 magnitudes
between the two epochs.
Assuming the contribution of the afterglow to the total flux
at the second epoch to be negligible, we estimate the afterglow to
be approximately R ~22.1 at our first epoch.
A jpg image showing the position of the afterglow and the host
can be found on:
http://remote.science.uva.nl/~kwrsema/grb050724/
We thank the staff of the WHT for outstanding support for these
observations.
GCN Circular 3700
Subject
GRB 050724: Secure Host Redshift from Keck
Date
2005-07-29T18:13:53Z (20 years ago)
From
Jason Prochaska at UCO/Lick Obs <xavier@ucolick.org>
J. X. Prochaska (UCO/Lick), J. S. Bloom (UCB), H.-W. Chen (MIT),
B. Hansen (UCLA), J. Kalirai (UCSC), M. Rich (UCLA) and H. Richer (UBC)
report on behalf of the GRAASP collaboration:
"We have obtained LRISb spectroscopy (900s; 2005-07-29 06:31 UT)
of the putative host galaxy of GRB 050724 (Object D in GCN #3672).
We confirm our previously reported redshift (GCN #3679)
based on the identification of Ca H+K, G-band absorption features,
and the 4000Ang break. We report a redshift z=0.258 +/- 0.002.
The velocity dispersion based on CaK appears to exceed 200km/s.
The galaxy shows no [OII] emission in our spectrum suggesting minimal
current star formation.
PAIRITEL imaging of the galaxy from July 29 UT yields a K-band magnitude
of 15.3 +/- 0.2 in a 3" radius aperture. At this redshift,
and including the effects of Galactic extinction, the galaxy
is 1.7 L* based off the 2MASS luminosity function.
The properties of this galaxy -- a massive early-type at
moderate redshift -- are strikingly similar to the probable host
galaxy of GRB 050509b (GCN #3399).
Based on this redshift and the reported fluence in GCN #3667,
the isotropic -equivalent energy release is
E_gamma(iso) = 9.9e49 erg [19-440 keV, comoving], more than 1
order of magnitude brighter than 050509b
(Bloom et al. astro-ph/0505480)."
Figures and imaging can be found at this following site:
http://www.graasp.org/Data/050724
GCN Circular 3892
Subject
Subaru Observations of GRB050724
Date
2005-08-27T14:49:11Z (20 years ago)
From
Elena Pian at ITESRE-CNR,Bologna <pian@ts.astro.it>
A. Pastorello (MPA), K. Kawabata (Hiroshima Univ.), E. Pian, (INAF-OATs),
K. Nomoto (Tokyo Univ.), P. Mazzali (INAF,MPA,Tokyo), T. Hattori, M. Iye,
T. Sasaki (Subaru,NAOJ), on behalf of a larger collaboration, report:
On August 10, 2005, at 07.7 UT we observed the field of GRB050724 with
Subaru+FOCAS and I filter. The exposure time was 2 minutes. The seeing
was 0.4". No object is detected at the position of the optical transient
reported by Berger et al. (submitted to Nature, astro-ph/0508115). The
3-sigma upper limit is I = 23 (this is not corrected for the Galactic
reddening).
This message may be cited.