GRB 080913
GCN Circular 8217
Subject
GRB 080913: Swift detection of a burst
Date
2008-09-13T07:03:29Z (17 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
P. Schady (MSSL-UCL), A. P. Beardmore (U Leicester),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
O. Godet (U Leicester), C. Gronwall (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC), D. Perez (U Leicester),
R. L. C. Starling (U Leicester) and E. Troja (INAF-IASFPA) report on
behalf of the Swift Team:
At 06:46:54 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080913 (trigger=324561). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 65.725, -25.110 which is
RA(J2000) = 04h 22m 54s
Dec(J2000) = -25d 06' 36"
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 10 sec. The peak count rate
was ~800 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 06:48:33.6 UT, 99.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 65.72800,
-25.12945 which is equivalent to:
RA(J2000) = 04h 22m 54.72s
Dec(J2000) = -25d 07' 46.0"
with an uncertainty of 2.4 arcseconds (radius, 90% containment). This
location is 70 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
3.17e+20 cm^-2 (Kalberla et al. 2005).
UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 105 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
2.7'x2.7' sub-image covers 25% of the BAT error circle and 100% of
the XRT error circle. The 3-sigma upper limit at the XRT position is
20.7 mag. The 8'x8' region for the list of sources generated
on-board covers 100% of the BAT 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 0.04.
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 8218
Subject
GRB 080913: GROND observation of a high-z optical/NIR afterglow candidate
Date
2008-09-13T09:07:05Z (17 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
A. Rossi (Tautenburg Obs.), J. Greiner, T. Kruehler, A. Yoldas (all MPE),
S. Klose (Tautenburg Obs.), A. Kuepcue Yoldas (ESO)
report on behalf of the GROND team:
We observed the field of GRB 080913 (Swift trigger 324561; Schady et
al., GCN #8217), simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2m ESO/MPI telescope at La Silla
Observatory (Chile). Observations started at 06:50 UT on September 13, 2008,
3 min after the GRB trigger. We detect a faint optical object inside
the 2.4 arcsec Swift/XRT error box (Schady et al., GCN #8217).
We detect the object only in the z'-band and NIR, but not in i'-band
or bluer. Preliminary photometry yields the following magnitudes calibrated
against USNO-B1 and 2MASS field stars in stacked images:
r' > 23.2 mag,
i' > 23.0 mag,
z' = 22.4 mag,
not corrected for the expected Galactic foreground reddening of E(B-V) =
0.05 mag (Schlegel et al., 1998).
The non-detection in i' and bluer may indicate a redshift of about 6.
We caution however, that the drop-out is only 0.6 mag in depth between
our i' and z' bands, and our lack of better sensitivity could make this
a wrong interpretation. We encourage deeper observations.
GCN Circular 8219
Subject
GRB 080913: Enhanced Swift-XRT position
Date
2008-09-13T09:10:38Z (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 2223 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 080913, 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 = 65.72775, -25.12950 which is equivalent
to:
RA (J2000): 04h 22m 54.66s
Dec (J2000): -25d 07' 46.2"
with an uncertainty of 1.9 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 8220
Subject
GRB 080913: REM NIR early observations
Date
2008-09-13T09:58:37Z (17 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
P. D'Avanzo, S. Covino, L.A. Antonelli, D. Malesani, D. Fugazza, L.
Calzoletti, S. Campana, G. Chincarini, M.L. Conciatore, S. Cutini, V.
D'Elia, F. D'Alessio, F. Fiore, P. Goldoni, D. Guetta, C. Guidorzi,
G.L. Israel, E. Maiorano, N. Masetti, A. Melandri, E. Meurs, L.
Nicastro, E. Palazzi, E. Pian, S. Piranomonte, L. Stella, G. Stratta,
G. Tagliaferri, G. Tosti, V.Testa, S.D. Vergani, F. Vitali report on
behalf of the REM team:
The robotic 60-cm REM telescope located at La Silla (Chile) observed
automatically the field of the GRB 080913 (Schady et al. GCN 8217) on
Sep 13 starting about 6 min after the burst. Observations were carried
out at high airmass. Coadding a series of 10s, 30s and 60s exposures, at
a mean t-t0 ~ 40 min we do not see the object reported by Rossi et al.
(GCN 8218) or any other afterglow candidate inside the refined XRT error
box (Beardmore et al.; GCN 8219) down to J > 17.1, H > 17.2 and K > 15.8
(3sigma c.l.).
GCN Circular 8221
Subject
GRB 080913: VLT/FORS2 observations
Date
2008-09-13T10:58:48Z (17 years ago)
From
Paul Vreeswijk at Dark Cosmology Centre,U.of Copenhagen <pmv@dark-cosmology.dk>
P.M. Vreeswijk, J.P.U. Fynbo, D. Malesani (DARK/NBI) report on behalf
of a larger collaboration:
The field of GRB 080913 (Swift trigger 324561; Schady et al., GCN
#8217) was observed in target-of-opportunity mode with VLT+FORS2 using
the imaging sequence RzIVBR, starting at 7:31 UT on September 13, 2008,
i.e. 45 minutes after the GRB.
In the z-band image a faint source is detected within the Swift/XRT
error circle, with magnitude z(AB) = 23.1 (based on a very preliminary
calibration), while this object is not detected in any of the other
optical filters. Comparison with the z-band magnitude reported by Rossi
et al. (GCN #8218) suggests that the object has faded between 3 and 45
minutes after the burst, and therefore is likely the afterglow of GRB
080913.
We are very grateful for the excellent support by the Paranal
observatory staff, in particular Rachel Gilmour and Heidi Korhonen.
[GCN OPS NOTE(06nov08): Per author's request, "Heidi Schmidt" was
changed to "Hiedi Korhonen".]
GCN Circular 8222
Subject
GRB 080913, Swift-BAT refined analysis
Date
2008-09-13T16:07:01Z (17 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <jayc@milkyway.gsfc.nasa.gov>
M. Stamatikos (GSFC/ORAU), 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), G. Sato
(ISAS),
P. Schady (MSSL-UCL), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 080913 (trigger #324561) (Schady,
et al.,
GCN Circ. 8217). The BAT ground-calculated position is
RA, Dec = 65.741, -25.127 deg which is
RA(J2000) = 04h 22m 57.9s
Dec(J2000) = -25d 07' 38.6"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 39%.
The mask-weighted light curve shows multiple overlapping peaks, somewhat
smooth in character. T90 (15-350 keV) is 8 +- 1 sec (estimated error
including systematics).
The time-averaged spectrum from T-3.8 to T+5.2 sec is best fit by a
power law
with an exponential cutoff. This fit gives a photon index 0.46 +- 0.70,
and Epeak of 93.1 +- 56.1 keV (chi squared 38.53 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 5.6 +- 0.6 x 10-07
erg/cm2
and the 1-sec peak flux measured from T+0.11 sec in the 15-150 keV band is
1.4 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index
of 1.36 +- 0.15 (chi squared 44.56 for 57 d.o.f.). 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/324561/BA/
GCN Circular 8223
Subject
GRB 080913: GROND photo-z
Date
2008-09-13T16:39:12Z (17 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
J. Greiner, T. Kruehler (both MPE), A. Rossi (Tautenburg Obs.)
report on behalf of the GROND team:
We have analyzed more data of our GROND observing run (Rossi et al. 2008,
GCN #8218) of GRB 080913 (Schady et al. 2008, GCN #8217; Stamatikos et al.
2008, GCN #8222). The object reported previously is clearly detected in
several epochs. The position is
RA (2000.0) = 04:22:54.74
Decl. (2000.) = -25:07:46.2
with an uncertainty of 0.5 arcsec. This position is consistent with the
astrometrically corrected Swift X-ray position (Beardmore et al. 2008,
GCN #8219).
z'-band data spanning the time period from 3 min to 3 hrs after the burst
clearly show a fading source and are well fit with a power law
of decay slope 0.6 +- 0.3. This confirms the fading seen with the VLT
(Vreeswijk et al. 2008, GCN #8221). If this fading continues, we predict
z(AB) ~ 25 mag at 24 hrs after the GRB.
The afterglow is detected in z'JHK, but not in g'r'i-bands. After
correction for foreground extinction of A_V=0.129, we obtain (AB system)
g > 23.3 +- 0.1
r > 23.3 +- 0.1
i > 23.0 +- 0.1
z = 22.52 +- 0.15
J = 20.90 +- 0.06
H = 20.67 +- 0.09
K = 20.54 +- 0.21
at 07:13 UT (mid-time of 12 min exposure), 26 min after the GRB.
A fit to this simultaneously obtained 7-filter spectral energy distribution,
using Hyper-z (Bolzonella et al. 2000) results in a photometric redshift of
z = 6.44 +- 0.3. The SED-fit is shown on http://www.mpe.mpg.de/~jcg/grb080913.html
GCN Circular 8224
Subject
GRB080913: Swift/UVOT Upper Limits
Date
2008-09-13T16:40:12Z (17 years ago)
From
Samantha Oates at MSSL <sro@mssl.ucl.ac.uk>
S. R. Oates and P. Schady report on behalf of the Swift/UVOT team.
The Swift/UVOT began settled observations of the field of GRB 080913
starting
105s after the BAT trigger (Schady et al., GCN 8217). We do not detect an
afterglow in any of the UVOT filters inside the UVOT-enhanced XRT
error circle (Beardmore et al., GCN 8219).
The 3 sigma upper limits for the finding charts (fc) and summed images
are given below:
Filter T_start(s) T_stop(s) Expo(s) Magnitude (3 sigma UL)
-----------------------------------------------------------------
White (fc) 105 205 98 >20.92
White 105 1964 238 >21.26
v (fc) 211 611 393 >20.08
v 211 1858 865 >20.39
b 691 1957 97 >19.62
u 666 1932 117 >19.36
w1 641 1907 117 >19.48
m2 616 1882 78 >18.84
w2 721 1833 58 >18.99
----------------------------------------------------------------
The above magnitudes are not corrected for the Galactic extinction
corresponding to a
reddening of E_{B-V} = 0.04 mag (Schlegel et al., 1998, ApJS, 500, 525).
The photometry
is on the UVOT flight system described in Poole et al.
(2008,MNRAS,383,627).
GCN Circular 8225
Subject
GRB 080913: VLT/FORS spectrum
Date
2008-09-13T17:28:26Z (17 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
J.P.U. Fynbo (DARK/NBI), J. Greiner, T. Kruehler (both MPE),
A. Rossi (Tautenburg Obs), P. Vreeswijk, D. Malesani (both DARK/NBI)
report on behalf of a larger collaboration
Based on the rapid determination of an i'-band drop out we triggered
VLT/ToO observations (program-ID 081.A-0135; PI Greiner) and obtained
spectroscopy with FORS2+Gris600z of the afterglow of GRB080913
(Schady et al. 2008, GCN #8217; Stamatikos et al. 2008, GCN #8222).
Observations started at 8:30, about 100 min after the GRB, and continued
until morning twilight. We detect a red continuum that disappears
bluewards of a break around 9400 AA. Interpreting this break
as the onset of the Lyman-alpha forest we infer a redshift
of about z=6.7 consistent with the photometric redshift determined
by GROND (Greiner et al., GCN #8223).
We are very grateful for the excellent support by the Paranal
observatory staff, in particular Rachel Gilmour and Heidi Korhonen.
[GCN OPS NOTE(06nov08): Per author's request, "Heidi Schmidt" was
changed to "Hiedi Korhonen".]
GCN Circular 8226
Subject
GRB 080913: Swift-XRT refined analysis
Date
2008-09-13T17:30:12Z (17 years ago)
From
Andy Beardmore at U Leicester <apb@star.le.ac.uk>
A.P. Beardmore (U. Leicester) and P. Schady (MSSL-UCL) report on behalf
of the Swift-XRT team :
The Swift-XRT started observing the field of GRB 080913 (trigger number
324561, Schady et al., GCN Circ. 8217) at 2008-09-13 06:48:30 UT, 94 s
after the trigger. The best XRT position is the UVOT-enhanced position
reported by Beardmore et al. (GCN Circ. 8219).
The X-ray light curve presently spans 5 orbits of photon counting mode
data from T+108 s to T+23 ks. The light curve shows a number of small
flares in the first orbit, with the largest giving a factor of ~7
increase in count rate at T+1.8 ks, on top of a power-law decay of
index 1.20 +0.16 -0.13.
A 2.7 ks exposure X-ray spectrum from T+108 s to T+7.6 ks can be well
fit by an absorbed power-law with a photon index of 1.69 +0.46 -0.41
and a column density consistent with the Galactic value of 3.2 x 10^20 cm^-2
in the direction of the burst. The observed 0.3-10.0 keV flux is
(3.2 +0.9 -1.6) x 10^-12 erg cm^-2 s^-1 which corresponds to an unabsorbed
flux of (3.7 +1.6 -1.7) x 10^-12 erg cm^-2 s^-1. The count to flux
conversion factor is 4.6 x 10^-11 erg cm^-2 count^-1.
Providing the source continues to decay at the same rate, we predict a
count rate of 2.8 x 10^-4 count s^-1 at T+1 day.
This circular is an official product of the Swift-XRT team.
GCN Circular 8256
Subject
GRB 080913: Konus-Wind and Swift/BAT joint spectral analysis
Date
2008-09-17T09:41:53Z (17 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
V. Pal'shin, S. Golenetskii, R.Aptekar, E. Mazets, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team,
T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
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), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), and T. Ukwatta (GWU)
on behalf of the Swift-BAT team,
report:
We performed the Konus-Wind and the Swift/BAT joint spectral analysis
of GRB 080913 (Swift/BAT trigger #324561: Schady et al., GCN Circ. 8217,
Stamatikos et al. GCN Circ. 8222).
Since the Konus-Wind observed this GRB in the waiting mode, we only
have 3 channel spectral data for the Konus-Wind which cover the energy
range from 20 keV to 1.3 MeV. Therefore, the joint spectral analysis of
the Konus-Wind and the Swift/BAT data enables to derive the broad-band
spectral parameters of this burst.
The time interval of the spectral data for each instrument is chosen
from T0(BAT)-4.1 to T0(BAT)+4.7 sec where T0(BAT) is the trigger time
of BAT at 06:46:54.1 UTC. The energy ranges which we used in the joint
spectral analysis are 20-1300 keV and 14-150 keV for the Konus-Wind and
the Swift/BAT respectively. The spectral data of two instruments are
fit with the spectral model multiplied by the constant factor to take
into account the systematic effective area uncertainties in the response
matrices of each instrument.
The spectrum is well fit with a power-law with exponential cutoff model:
dN/dE ~ E^{alpha}*exp(-(2+alpha)*E/Epeak). The constant factors of each
instrument agree within 5%. No systematic residual from the best fit
model is seen in the spectral data of each instrument. The best fit
spectral parameters are: alpha = -0.89(-0.46, +0.65) and Epeak = 131
(-48/+225) keV (chi2/dof = 43.7/58). The best fit spectral parameters
for the Band function fixing beta=-2.5 are: alpha = -0.82(-0.53, +0.75)
and Epeak = 121 (-39/+232) keV (chi2/dof = 43.9/58). The energy fluence
in the 15-1000 keV band calculated by a power-law with exponential
cutoff model for this 8.8 sec interval is 8.5(-2.2, +6.0)x10^-7 erg/cm2
All the quoted errors are at the 90% confidence level.
Assuming z = 6.7 (Fynbo et al., GCN Circ. 8225) and a standard cosmology
model with H_0 = 71 km/s/Mpc, Omega_M = 0.27, Omega_Lambda = 0.73, the
isotropic energy release is E_iso ~7x10^52 erg in 1 keV to 10 MeV at
the GRB rest frame extrapolating the best Band function fit fixing
beta=-2.5.
Looking only at the parameters of the prompt emission, namely T90~1 sec
and Ep ~900 keV in the GRB rest frame, this burst could be classified as
a short burst.
GCN Circular 8267
Subject
GRB080913: Swift-BAT spectral lag
Date
2008-09-18T14:15:23Z (17 years ago)
From
Dong Xu at DARK,NBI <dong@astro.ku.dk>
Dong Xu (DARK/NBI) reports
The Swift/BAT data were reduced in a standard way. Making use of the
Cross Correlation Function (CCF) for different energy bands over 15-150
keV, we found negligible spectral time lags, being consistent with the
values/range of previous Swift short-duration GRBs. Also we note the
rest-frame energy band which BAT corresponds to for this burst (z~6.7,
Fynbo et al. GCN 8225) is higher than that for previous GRBs.
DX is grateful to R. L. C. Starling, P. T. O'Brien, and K. Page through
the SPARTAN program on Swift data reduction.
GCN Circular 9321
Subject
GRB 080913: 250 GHz upper limit for a z=6.7 GRB with MAMBO-2 at the IRAM 30m
Date
2009-05-04T18:16:48Z (16 years ago)
From
Dominik A. Riechers at Caltech <dr@caltech.edu>
D. A. Riechers (Caltech), F. Walter (MPIA Heidelberg), F. Bertoldi
(AIfA Bonn), C. L. Carilli (NRAO), P. Cox (IRAM) report:
"We used the Max-Planck-Millimeter Bolometer (MAMBO-2) array at the
IRAM 30-m telescope to observe the field of view toward the host
galaxy of GRB 080913 (GCN 8217) at redshift z=6.7 (GCN 8225), RA
04:22:54.74, Dec -25:07:46.2 (J2000) at 250 GHz. Observations were
carried out for 3.7 hr between 2008 November 13 and 15. We obtained a
non-detection of
S_nu(250 GHz,1.20 mm) = 0.34 +/- 0.45 mJy
(1 sigma error), i.e. a 3 sigma upper flux density limit of 1.35 mJy
on the dust continuum in the GRB host galaxy at 1.2 mm (rest-frame 156
um). The 117-element MAMBO-2 bolometer detectors cover 210-290 GHz
(half power). The bolometers have a FWHM beam size of 10.7 arcsec, at
a pixel spacing of 20 arcsec. Observations were carried out in ON-OFF
observing mode under good weather conditions. Calibrations were
performed on J0348-278 and J0609-157.
We acknowledge the excellent support of the staff at IRAM. IRAM is
supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). This
message may be cited."