GRB 080707
GCN Circular 7947
Subject
GRB 080707: Swift detection of a burst
Date
2008-07-07T08:47:33Z (17 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
P. Schady (MSSL-UCL), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), A. A. Breeveld (MSSL),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
C. Guidorzi (INAF-OAB), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (CRESST/GSFC/UMD), A. Moretti (INAF-OAB),
P. T. O'Brien (U Leicester), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
D. Perez (U Leicester), R. L. C. Starling (U Leicester) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:
At 08:27:53 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080707 (trigger=316204). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 32.632, +33.103 which is
RA(J2000) = 02h 10m 32s
Dec(J2000) = +33d 06' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a double-peaked
structure with a duration of about 40 sec. The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 08:29:02.0 UT, 68.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
32.61815, 33.10967 which is equivalent to:
RA(J2000) = 02h 10m 28.36s
Dec(J2000) = +33d 06' 34.8"
with an uncertainty of 3.1 arcseconds (radius, 90% containment). This
location is 48 arcseconds from the BAT onboard position, within the BAT
error circle.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
6.99e+20 cm^-2 (Kalberla et al. 2005).
The initial flux in the 2.5 s image was 3.59e-10 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 79 seconds 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 typical 3-sigma upper limit has been about 18.5 mag.
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.10.
Burst Advocate for this burst is P. Schady (ps 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.)
GCN Circular 7948
Subject
GRB 080707: GROND Detection of the Optical Afterglow Candidate
Date
2008-07-07T12:01:41Z (17 years ago)
From
Christian Clemens at MPE <cclemens@mpe.mpg.de>
C. Clemens, S. Loew, J. Greiner, A. Yoldas, T. Kruehler (all MPE Garching), A.
Kupcu Yoldas (ESO) and G. Szokoly (Eoetvoes Univ., Budapest) report on behalf
of the GROND team:
We observed the field of GRB 080707 (Swift trigger 316204; Schady et al., GCN
#7947) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP
120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla Observatory
(Chile).
Observations started at 10:00 UT on July 7th, 2008, 92.2 min after the GRB
trigger, and were performed at an average seeing of 2.2" and at an average
airmass of 2.6.
We found a faint source within the 2.9'' Swift-XRT error circle at
RA (J2000.0) = 02h 10m 28.40s
DEC (J2000.0) = +33d 06' 34.3''
with an uncertainty of 0.8".
The object is detected in g' band, implying a redshift smaller than 3.5.
Based on the first 4.4 min of effective exposures in g'r'i'z', we estimate
preliminary magnitudes of
g' ~ 22.1 mag,
r' ~ 21.5 mag,
i' ~ 21.4 mag and
z' ~ 21.2 mag
with typical errors of +/- 0.3. Given magnitudes are calibrated against
USNO-B1 field stars.
Please note, that no correction for the galactic foreground reddening of
E(B-V) = 0.1 mag (Schlegel et al., 1998) has been applied.
GCN Circular 7949
Subject
GRB 080707: VLT redshift
Date
2008-07-07T12:42:24Z (17 years ago)
From
Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center <malesani@astro.ku.dk>
Johan P. U. Fynbo, Daniele Malesani, & Bo Milvang-Jensen (DARK), report
on behalf of a larger collaboration:
We observed the field of GRB 080707 (Schady et al., GCN 7947) with the
ESO VLT equipped with FORS1.
Inside the XRT error circle, we detect the object first reported by
Clemens et al. (GCN 7948) in the R and I bands. The source had R ~ 19.6
on 2008 Jul 7.385 UT (47 min after the trigger), calibrated against
USNO-B1. This object is not visible in the DSS (which reaches a deeper
limit) and seems brighter than in the later observation reported by
Clemens et al. (GCN 7948). It is thus very likely the optical afterglow
of GRB 080707. A finding chart is posted at
http://www.astro.ku.dk/~malesani/GRB/080707/080707_finder.jpg
FORS1 spectra were acquired between Jul 7.397 and 7.441 UT with grism
300V. From detection of FeII and MgII absorption features, we infer a
redshift z = 1.23. A conservative upper limit z < 2.2 can be set from
the lack of Lyman alpha forest in the blue
We acknowledge excellent and enthusiastic support from the observing
staff at Paranal, in particular Chris Lidman, Lorena Faundez, Claudia
Reyes, and Dominique Naef.
[GCN OPS NOTE(07jul08): The two occurances of "GCN 7984" was changed
to "GCN 7948".]
GCN Circular 7950
Subject
GRB 080707: Enhanced Swift-XRT position
Date
2008-07-07T18:11:09Z (17 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 83 s of overlapping XRT Photon Counting mode and UVOT
data for GRB 080707, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 32.61905, +33.11020 which is equivalent
to:
RA (J2000): 02h 10m 28.57s
Dec (J2000): +33d 06' 36.7"
with an uncertainty of 2.1 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 7951
Subject
GRB 080707: Swift XRT refined analysis
Date
2008-07-07T20:35:47Z (17 years ago)
From
Rhaana Starling at U of Leicester <rlcs1@star.le.ac.uk>
R.L.C. Starling (U. Leicester) and P. Schady (MSSL-UCL) report, on behalf
of the Swift XRT team:
We have analysed the first 4 orbits of Swift XRT data (from T0+64s to
T0+17.8 ks) for GRB 080707 (trigger=316204, Schady et al., GCN Circ.
7947).
Using 1482 seconds of overlapping XRT Photon Counting (PC) mode and UVOT
data, we find an updated astrometrically corrected X-ray position (using
the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 32.61860, 33.10983 deg which is equivalent to:
RA(J2000) = 02 10 28.46
Dec(J2000)= +33 06 35.4
with an uncertainty of 1.5 arcseconds (radius, 90% confidence). This
position lies 1.35 arcseconds from the optical counterpart reported in
Clemens et al. (GCN Circ. 7948).
The light curve can be fit by an initial steep decay followed by a shallow
plateau phase. The final orbit of data so far collected may indicate a
further break to a steeper slope, but this is not required by the fit.
A singly broken power law gives alpha1=5.6+1/-0.8, Tbk=145+17/-13 and
alpha2=0.35+0.06/-0.07.
A doubly broken power law model gives the following parameters:
alpha1=5.5+0.9/-0.8, Tbk1=151+6/-15s, alpha2=0.2+0.1/-0.5,
Tbk2=5300+5400/-4200s and alpha3=0.7+0.6/-0.3.
The PC mode spectrum comprising 1.64 ks of data from the latter part of
orbit 1 and from orbit 2 (T0+96s - T0+6384s) is well fit with a power law
of photon index Gamma=2.1+0.4/-0.5 (90%) absorbed by the Galactic column
of 6.99E+20 cm^-2 (Kalberla et al. 2005) and by a column at the inferred
redshift of the host galaxy (z=1.23, Fynbo et al. GCN Circ. 7949) which
can only be constrained to be nH<1.23e22 cm^-2. The 0.3-10 keV observed
(unabsorbed) flux is 5.4e-12 (6.73-12) erg/cm^2/s, corresponding to a
count rate of 0.12 count/s, hence the observed count rate to flux
conversion is 1 count/s = 4.5e-11 erg/cm^2/s.
The predicted count rate at T0+24h is 0.011 counts/s, assuming a decay
rate of alpha=0.7 from the doubly broken power law model.
This is an official product of the Swift XRT team.
GCN Circular 7952
Subject
GRB 080707, Swift-BAT refined analysis
Date
2008-07-07T22:50:07Z (17 years ago)
From
Hans Krimm at NASA-GSFC <hans.a.krimm@nasa.gov>
G. Sato (ISAS), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
P. Schady (MSSL-UCL) M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC),
T. Ukwatta (GWU) (i.e. the Swift-BAT team):
Using the data set from T-240 to T+480 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 080707 (trigger #316204)
(Schady et al., GCN Circ. 7947). The BAT ground-calculated position is
RA, Dec = 32.627, 33.100 deg which is
RA(J2000) = 02h 10m 30.5s
Dec(J2000) = +33d 06' 01.1"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 93%.
The mask-weighted light curve consists of two main peaks of roughly
equivalent peak flux, the first a boxcar shape from T-2 to T+4 sec, and
the second a FRED beginning at T+23 sec and decaying to background by
T+32 sec. T90 (15-350 keV) is 27.1 +- 1.1 sec sec (estimated error
including systematics).
The time-averaged spectrum from T-1.8 to T+26.6 sec is best fit by a
simple power-law model. The power law index of the time-averaged
spectrum is 1.77 +- 0.19. The fluence in the 15-150 keV band is
5.2 +- 0.6 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from
T+0.22 sec in the 15-150 keV band is 1.0 +- 0.1 ph/cm2/sec. All the
quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/316204/BA/
GCN Circular 7953
Subject
UVOT observations of GRB080707
Date
2008-07-07T22:52:44Z (17 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL-UCL) and F.E. Marshall (NASA/GSFC) report on behalf of the
Swift/UVOT team:
The Swift/UVOT starting taking settled exposures of the field of GRB
080707 80 s after the BAT trigger (Schady et al., GCN Circ. 7947). A faint
source is detected in the early white and v-band observations at
RA(J2000.0) = 02:10:28.40 = 32.61833
Dec(J2000.0) = +33:06:34.2 = 33.10950
with an of 1.1 arcseconds (90% confidence), consistent with the enhanced
XRT error circle (Starling et al., GCN Circ. 7951) and the GROND position
(Clemens et al., GCN 7948).
The early-time afterglow and 3-sigma upper limits the in co-added frames
are as follows:
Filter T_start(s) T_stop(s) Exp(s) Mag/3-sigma UL
white 80 5469 294.0 21.40+/-0.31 (3.4 sigma)
white 11355 12221 844.3 > 21.93
v 186 5880 590.1 19.97+/-0.31 (3.4 sigma)
b 3971 18004 1502.6 > 21.74
u 640 17362 1040.0 > 21.18
uvw1 616 16449 1101.7 > 21.41
uvm2 591 22234 1101.7 > 21.29
uvw2 5477 5676 196.6 > 20.22
The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E(B-V) = 0.10 mag in the
direction of the burst (Schlegel et al. 1998).
GCN Circular 7954
Subject
GRB 080707: GROND Confirmation of the Optical Afterglow
Date
2008-07-08T11:34:35Z (17 years ago)
From
Christian Clemens at MPE <cclemens@mpe.mpg.de>
C. Clemens, S. Loew, J. Greiner, A. Yoldas, T. Kruehler (all MPE Garching), A.
Kupcu Yoldas (ESO) and G. Szokoly (Eoetvoes Univ., Budapest) report on behalf
of the GROND team:
We observed the field of GRB 080707 for a second time at 09:54 UT on July 8th,
2008, 25.4 hr after the GRB trigger with 25.0 min of effective exposures in
g'r'i'z'. The observations were performed at an average seeing of 1.6" and at
an average airmass of 2.4.
We still detect the faint source mentioned in GCN #7948 within the 1.1''
Swift-UVOT error circle (Schady et al., GCN #7953) with the following
preliminary magnitudes of
g' ~ 23.8 mag,
r' ~ 23.2 mag and
i' ~ 23.1 mag
and typical uncertainties of +/- 0.3 (calibrated against USNO-B1 field stars).
With a magnitude change of delta g' ~ 1.7 mag within 23.9 hr (similarily in r'
and i' band) these measurements strongly suggest that the source mentioned in
Clemens et al. (GCN #7948) is the afterglow of GRB 080707.
GCN Circular 7956
Subject
GRB 080707: possible break in the X-rays
Date
2008-07-09T15:49:07Z (17 years ago)
From
Rhaana Starling at U of Leicester <rlcs1@star.le.ac.uk>
R.L.C. Starling (U. Leicester) and P. Schady (MSSL-UCL) report on behalf
of the Swift XRT team:
We have analysed the Swift XRT X-ray light curve out to T0+162 ks for GRB
080707 (trigger=316204, Schady et al., GCN Circ. 7947). The light curve
can be fit with a multiply broken power law as described in GCN Circ.
7951, and we note a possible further break. A fit including this possible
break places it at (9 +6/-8)e4 s and the current decay rate is then
approximately alpha=2.2.
The Swift XRT light curve can be viewed in the on-line repository (Evans
et al. 2007) at http://www.swift.ac.uk/xrt_curves/00316204/
Swift XRT continues to observe this source to constrain the current decay
and confirm/reject the presence of a late-time break. Ground-based optical
observations are strongly encouraged.
This is an official product of the Swift XRT team.