GRB 070724
GCN Circular 6667
Subject
Four radio sources in Swift-XRT error box of GRB 070724
Date
2007-07-25T18:21:35Z (18 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
Poonam Chandra (NRAO/UVA) and Dale A. Frail (NRAO) report on
behalf of the Caltech-NRAO-Carnegie GRB Collaboration:
"We used the Very Large Array to observe the field of view toward
GRB 070724 (GCN 6654) at a frequency of 8.46 GHz on 2007 July 25th
at 12.50 UT, 25.4 hours after the burst. Owing to VLA A-array observation,
we obtained excellent resolution of 0.33"x0.24". We find four possible
sources in the Swift-XRT error box, which are above 3-sigma. These are
Position (J2000) Flux density (Jy)
1: RA 01 51 14.105 +/- 0.002 4.3899E-04 +/- 8.40E-05
DEC -18 35 45.938 +/- 0.024
2: RA 01 51 14.125 +/- 0.002 4.0976E-04 +/- 8.51E-05
DEC -18 35 41.404 +/- 0.021
3: RA 01 51 13.824 +/- 0.003 3.1155E-04 +/- 8.48E-05
DEC -18 35 36.626 +/- 0.033
4: RA 01 51 14.104 +/- 0.003 3.1204E-04 +/- 8.47E-05
DEC -18 35 40.626 +/- 0.030
Here source 4 is closest to Josh Bloom's blue source (GCN 6658) with
offset of 1.7 arcsec. Source 2 is closest to P60 afterglow position of the
GRB (Cenko et al. GCN 6664) with offset of 1.3 arcsec.
NVSS does not show any radio source around this position.
More observations are planned to see the variability of these sources.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 6666
Subject
GRB 070724: optical observations
Date
2007-07-25T13:21:12Z (18 years ago)
From
Silvia Piranomonte at OAR <piranomonte@mporzio.astro.it>
S. Covino (INAF/OABr), S. Piranomonte (INAF/OAR), S.D. Vergani (DIAS and
DCU), P. D'Avanzo (INAF-OABr), L. Stella (INAF/OAR), report on behalf of
the MISTICI collaboration:
We observed the afterglow of GRB 070724 (Ziaeepour et al., GCN 6654)
with the ESO-VLT equipped with FORS2. Starting on 2007 Jul 25.3735 UT
(22.1 hr after the trigger), we acquired 10 minutes of imaging in the I
band. Inside the XRT error circle (Page & Ziaeepour, GCN 6659), we
detect both objects reported by Bloom (GCN 6658) and Cenko et al. (GCN
6664).
When compared with the photometry reported by Cenko et al. (GCN 6664),
none of the objects seems to have faded. The faintest object is
pointlike (seeing of 0.7").
We also took two 10-min spectra with VLT+FORS2. Based on detection of [OII] 3727
Hbeta and [OIII] 4959,5007, we confirm the redshift z=0.457 proposed by Cucchiara
et al. (GCN 6665).
We thank Brad Cenko for very useful discussion.
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GCN Circular 6665
Subject
GRB070724: Host galaxy redshift
Date
2007-07-25T10:23:16Z (18 years ago)
From
Antonino Cucchiara at PSU <cucchiara@astro.psu.edu>
A. Cucchiara, D. B. Fox (Penn State), S. B. Cenko (Caltech), E. Berger
(Carnegie),
P. A. Price (IfA) and J. Radomski (Gemini) report on behalf of a larger
collaboration:
Starting on 2007 July 25 at 06:40 UT we used GMOS on the Gemini South
telescope to obtain a set of 900 seconds spectra of the host galaxy of
GRB070724
(Ziaeepour et al., GCN 6654).
The covered wavelength range is ~5000-9000 A.
We found strong evidence of emission lines identified as [O II] 3727,
Hbeta and
[O III] 4959,5007 doublet at redshift z=0.457.
This confirms the low-redshift nature
of the host galaxy for this short burst as noted by Bloom et al. (GCN 6658).
We wish to thank and acknowledge the effort of the staff at Gemini South
in undertaking these observations.
GCN Circular 6664
Subject
GRB 070724: P60 and Gemini Observations
Date
2007-07-25T07:28:40Z (18 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
S. B. Cenko, A. Rau (Caltech), E. Berger (Carnegie/Princeton), P. A. Price
(IfA), and A. Cucchiara (Penn State) report on behalf of a larger
collaboration:
We have imaged the field of GRB070724 (Ziaeepour et al., GCN 6654) on
the night of 2007 July 24 UT with the automated Palomar 60-inch telescope
(beginning approximately 2.5 minutes after the burst) and the Gemini
Multi-Object Spectrograph (GMOS) and Near-Infrared Imager (NIRI) mounted
on the 10-m Gemini North Telescope (beginning approximately 2 hours after
the burst).
The nearby galaxy first mentioned by Bloom (GCN 6658) shows no sign of
variability, either from our P60 to our GMOS imaging (remaining at a
constant magnitude of i' ~ 20.3), or within our Gemini imaging (verified
with psf-matched digital image subtraction).
In addition the aforementioned galaxy, we find a faint source on the
outskirts of the revised XRT error circle (Page and Ziaeepour, GCN 6659)
at coordinates (J2000.0):
RA: 01:51:14.05
Dec: -18:35:42.1
with an estimated astrometric uncertainty of approximately 0.3" in each
coordinate. The object is only visible in our Gemini/GMOS i' imaging of
the field, with a magnitude of i' ~ 24.6 (using GMOS zeropoints from the
Gemini webpage). This object is not present in our earlier P60 imaging of
the field; however it is well below our detection threshold (see below).
As our only two Gemini/GMOS i' images were taken back-to-back, we have no
information on the variability of this source at the current time.
No other object is detected in the revised XRT error circle in any other
filter. Our limiting magnitudes, calculated with respect to the USNO-B
catalog (P60) or using zeropoints from the Gemini website (GMOS and NIRI),
are quoted below:
Instrument Filter UT (July 24) dt (hr) Exposure (s) Magnitude
---------------------------------------------------------------------------
P60 i' 11:13 0.32 3x60 + 3x120 > 21.5
GMOS i' 13:17 2.38 2x180 > 24.5
NIRI Ks 13:44 2.83 15x60 > 20.0
NIRI J 14:02 3.13 15x60 > 22.0
NIRI H 14:19 3.42 15x60 > 21.0
NIRI Ks 14:36 3.70 15x60 > 20.0
GCN Circular 6662
Subject
GRB 070724: IR observations
Date
2007-07-24T20:50:02Z (18 years ago)
From
Andrew Levan at U.of Leicester <anl@star.le.ac.uk>
A.J. Levan (Warwick), N.R. Tanvir (Leicester), C. Davis (JAC) report on
behalf of a large collaboration:
We observed the location of GRB 070724 in the K-band using UKIRT. Two
epochs were obtained beginning at 13:11 UT and 14:02 UT. We clearly detect
the object refered to by (Bloom GCNC 6658), and confirm that it is indeed
a galaxy.
We find no evidence of variability within the galaxy between the two
observations. No other objects are detected within the refined XRT error
circles of Page & Ziaeepour (GCNC 6659) or Bloom & Butler (GCNC 6661).
Further observations are planned.
GCN Circular 6661
Subject
GRB 070724: Closer association with DSS source
Date
2007-07-24T19:07:24Z (18 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
J. S. Bloom and N. R. Butler (UC Berkeley) remark:
"The updated XRT position of GRB 070724 from Page & Ziaeepour (GCN
#6659), puts the GRB afterglow closer to the proposed low redshift
host (Bloom GCN #6658) seen in the DSS. We emphasize that the galaxy
nature of this source has yet to be confirmed; yet, the small offset
(<~ 2") is reminiscent of the SHB 050709 (Fox et al. Nature, 437,
845, 2005) and SHB 051221 (Soderberg et al. ApJ, 650, 261, 2006)
configurations (see Bloom & Prochaska for an early SHB-host offsets
review; AIP Conf. Proc. 838, 473, 2006)." An updated finder can now
be found at:
http://lyra.berkeley.edu/~jbloom/grb070724-update1.png
We thank Massimiliano de Pasquale for helpful conversations about the
UVOT imaging.
This message could, in principle, be cited.
GCN Circular 6660
Subject
Swift/UVOT refined analysis of GRB070724
Date
2007-07-24T18:05:38Z (18 years ago)
From
Massimiliano de Pasquale at MSSL-UCL <mdp@mssl.ucl.ac.uk>
M. De Pasquale (MSSL-UCL) and H. Ziaeepour (MSSL-UCL) report on
the behalf of the Swift UVOT/team:
The Swift/UVOT observed the field of GRB070724 starting 58s after
the BAT trigger (Ziaaepour et al. GCN circ. 6654). Inside the
refined XRT error circle (Page et al., GCN circ 6659) we do not
find any new source, either in the first finding chart exposures
in the White and V filter or in the summed exposures of any of the
UVOT filters.
The 3 sigma upper limits for detecting a source inside the XRT
error circle are:
Filter T obs (s) Exp (s) Mag (3 sigma u.l.)
White 76-176 98 20.4
v 182-581 393 19.5
White 76-5531 380 21.1
v 182-5941 806 20.0
b 662-5325 216 20.3
u 636-6456 332 20.0
uvw1 612-6352 432 20.4
uvm2 587-6146 432 20.4
uvw2 692-5736 432 20.7
No correction has been done for the expected low Galactic
reddening towards the burst, E(B-V)=0.01 (Schlegel et al.
11998).
GCN Circular 6659
Subject
GRB 070724: Swift-XRT Team refined analysis
Date
2007-07-24T17:29:58Z (18 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L Page (U. Leicester) and H. Ziaeepour (UCL-MSSL) report on behalf of
the Swift-XRT team:
We have analysed the first three orbits of Swift-XRT data obtained for GRB
070724 (Ziaeepour et al., GCN Circ. 6654), which includes ~60 s of
Windowed Timing (WT) mode data and ~5.2 ks of Photon Counting (PC) data.
Using 399 s of overlapping XRT PC mode and UVOT V-band data, we find an
astrometrically corrected X-ray position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue) of RA, Dec (J2000) =
27.80815, -18.59448 which is equivalent to:
RA (J2000): 01 51 13.96
Dec (J2000): -18 35 40.1
with an uncertainty of 2.2 arcsec (radius, 90% confidence). This is 2.7
arcsec from the initial XRT position (GCN Circ. 6654) and 77.8 arcsec from
the ground-calculated BAT position (Parsons et al., GCN Circ. 6656).
The first orbit of XRT data shows flaring activity, with the underlying
power-law decay asserting itself from about 500 seconds after the trigger.
This decay slope is poorly constrained with the data currently available:
alpha ~ 0.4 +0.3/-0.2
Fitting the PC data from the second and third orbits (~4-12 ks after the
trigger) in order to avoid any spectral evolution during the flares, the
spectrum can be modelled by a power-law of Gamma = 1.3 +0.8/-0.6, absorbed
by the Galactic column in this direction of 1.43e20 cm^-2. The 0.3-10 keV
observed (unabsorbed) flux during this time is 5.18e-13 (5.27e-13) erg
cm^-2 s^-1.
If the decay continues with a slope of alpha ~ 0.4, the count rate at 24
hours is predicted to be 4e-3 count s^-1; this ranges between 2e-3 and
8e-3 count s^-1, taking into account the uncertainties on the slope. Using
the spectral fit detailed above, this corresponds to an observed flux of
(2 +7/-1)e-13 erg cm^-2 s^-1 (over 0.3-10 keV).
This circular is an official product of the XRT team.
GCN Circular 6658
Subject
GRB 070724: Pre-Imaging Shows a Source in the XRT Error Circle
Date
2007-07-24T17:03:08Z (18 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
J. S. Bloom (UC Berkeley) notes:
"The JFN color plates from the Digitized Sky Survey show a blue source in
the Northeast portion of the XRT error circle of SHB 070724 (Ziaeepour et
al. GCN 6654; Parsons et al. GCN 6656) at position RA= 01:51:14.05, DEC =
-18:35:39.1 (J2000). The source appears somewhat extended in the
north-south direction; if confirmed with new digital imaging, this would
suggest the source as a prime low redshift star-forming host galaxy
candidate."
An image may be found at:
http://lyra.berkeley.edu/~jbloom/grb070724.png
No need to cite this message.
GCN Circular 6656
Subject
GRB 070724, Swift-BAT refined analysis of a short burst
Date
2007-07-24T15:31:04Z (18 years ago)
From
Ann M. Parsons at NASA/GSFC/Swift <parsons@milkyway.gsfc.nasa.gov>
A. Parsons (GSFC), L. Barbier (GSFC), S.D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL),
N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL),
T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC),
T. Ukwatta (GWU), H. Ziaeepour (UCL-MSSL)
(i.e. the Swift-BAT team):
Using the data set from T-310 to T+ 310 sec from the recent
telemetry downlink, we report further analysis of BAT GRB 070724
(trigger #285948) (Ziaeepour, et al., GCN Circ. 6654). The BAT
ground-calculated position is RA, Dec = 27.824, -18.610 deg which is
RA(J2000) = 1h 51m 17.9s
Dec(J2000) = -18d 36' 35"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 91%.
The mask-weighted light curve for GRB 070724 consists of a single spike
peaking at T+0.2 sec. Upon inspection of the mask weighted light curve
out to T + 310 sec we find no evidence for extended emission.
T90 (15-350 keV) is 0.4 +- 0.04 sec (estimated error including
systematics).
The time-averaged spectrum from T-0.0 to T+0.4 sec is best fit by
a simple power-law model. The power law index of the time-averaged
spectrum is 1.81 +- 0.33. The fluence in the 15-150 keV band is
3.0 +- 0.7 x 10^-08 erg/cm2. The 1-sec peak photon flux measured
from T-0.30 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.
GCN Circular 6654
Subject
GRB 070724: Swift detection of a burst
Date
2007-07-24T11:22:00Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
H. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
M. De Pasquale (UCL-MSSL), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/GSFC/USRA),
H. A. Krimm (GSFC/USRA), V. Mangano (INAF-IASFPA),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
P. Romano (Univ. Bicocca & INAF-OAB), B. Sbarufatti (INAF-IASFPA),
P. Schady (MSSL-UCL), M. Stamatikos (NASA/ORAU) and
R. L. C. Starling (U Leicester) report on behalf of the Swift Team:
At 10:53:50 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070724 (trigger=285948). Swift slewed immediately to the
burst. The BAT on-board calculated location is RA, Dec 27.818,
-18.622 which is
RA(J2000) = 01h 51m 16s
Dec(J2000) = -18d 37' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a strong spike
about one second long at T+0 sec. The peak count rate was ~2700
counts/sec (15-350 keV), at ~0 sec after the trigger. This could be a
short burst although the spectrum is not hard.
The XRT began observing the field at 10:54:56 UT, 67 seconds after the
BAT trigger. Using prompt downlinked data, we find a variable,
uncatalogued X-ray source located at RA, Dec 27.8077, -18.5951 which is
RA(J2000) = 01 51 13.86
Dec(J2000) = -18 35 42.4
with an uncertainty of 4.7 arcsec (radius, 90% containment).
This location is 102 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 6.4e-10 erg/cm2/s (0.2-10 keV).
UVOT took a finding chart exposure of 100s with the White filter
starting 75s after the BAT trigger. No afterglow candidate has been
found in the initial data products. The 2.7'x2.7' sub-image covers
100% of the XRT error circle. The 3-sigma upper limit is
about 19.2 mag. No correction has been made for the expected reddening
of E(B-V) of 0.01.
Burst Advocate for this burst is H. Ziaeepour (hz AT mssl.ucl.ac.uk).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)