GRB 080928
GCN Circular 8316
Subject
GRB 080928: Fermi GBM detection
Date
2008-10-03T16:17:37Z (17 years ago)
From
Bill Paciesas at UAH <bill.paciesas@nasa.gov>
Bill Paciesas, Michael Briggs and Rob Preece
(UAH), report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 15:04:56 UT on 28 September 2008, the Fermi Gamma-Ray Burst Monitor
(GBM) triggered and located GRB 080928 (trigger 244307097 / 080928.628),
which had triggered the Swift BAT ~204 s earlier (Sakamoto et al. GCN 8292).
The on-ground calculated location, using the GBM trigger data, is RA = 93.9,
Dec = -53.1 (+/- 4.9)(J2000 degrees), with an uncertainty of 4.9 degrees
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which is currently estimated to be 2 to 3 degrees),
consistent with the Swift location (Sakamoto et al. GCN 8292; Osborne et al.
8295).
The emission detected by GBM lasted about 87 s with the strongest emission
in the first 20 s, and is approximately coincident with the main emission
detected by Swift (Cummings et al. GCN 8294). The time-averaged spectrum
from T-5 to T+24 s can be fit by a power-law with an index of -1.80 +/-
0.08. The fluence between 50 and 300 keV over these 87 seconds is (1.5 +/-
.1) x 10^-6 erg/cm^2.
The spectral analysis results presented above are preliminary; the final
results will be published in the GBM GRB Catalog."
GCN Circular 8304
Subject
GRB080928: redshift retraction
Date
2008-10-01T15:53:55Z (17 years ago)
From
Antonino Cucchiara at PSU <cucchiara@astro.psu.edu>
A. Cucchiara and D. B. Fox (Penn State) report on behalf of a larger
collaboration:
We re-processed the data acquired on GRB080928 in order to reconcile our
results
with the redshift identification reported by Vreesvijk et al. (GCN 8301).
Upon comparison of our two individual exposures, we cannot confirm the
presence
of the metal absorption features reported in GCN 8300. We therefore
conclude that
the redshift z=2.49 for GRB 080928 reported by us previously is not
correct. Line
misidentifications are probably the result of inaccurate sky-line and
sky-fringe
modeling in extraction of the 1D spectrum. We retract also the claim of
a DLA
system at z~2.5.
We confirm the detection of strong MgII doublet and associated MgI
absorption from
a system at z=1.69, which - as reported by Vreeswijk et al. - represents
the lower
limit and most likely redshift for GRB 080928.
We apologize for any confusion.
GCN Circular 8303
Subject
GRB 080928: Watcher observations
Date
2008-10-01T14:22:05Z (17 years ago)
From
Alejandro Ferrero at U College,Dublin <alejandro.ferrero@ucd.ie>
Alejandro Ferrero (UCD School of Physics), John French (UCD School of
Physics/ DARK/NBI), and Gary Melady (UCD School of Physics) report on
behalf of a larger collaboration:
We observed the field of GRB 080928� (Sakamoto et al. GCN 8292) with
the Watcher robotic telescope at Boyden Observatory, South Africa. The
afterglow previously reported (Sakamoto et al. GCN 8292, Rykoff et al.
GCN 8293, Rossi et al. GCN 8296, Kuin et al. GCN 8298) is detected in
a stacked sequence of 10 unfiltered 120s exposures with an exposure
midtime of 10.56 hrs from the Swift triggger. Comparison with USNO-B1
R-band magnitudes gives a magnitude of 19.37 +/- 0.11 for the optical
afterglow at this time. Comparison with later GROND observations
(Rossi et al. GCN 8296) indicates a steep decay slope of approx. -3
+/- 0.4 from 10.56 hours to 18.27 hours from the trigger.
GCN Circular 8301
Subject
GRB 080928: VLT redshift
Date
2008-09-29T16:26:29Z (17 years ago)
From
Paul Vreeswijk at Dark Cosmology Centre,U.of Copenhagen <pmv@dark-cosmology.dk>
Paul Vreeswijk, Daniele Malesani, Johan Fynbo (DARK/NBI), Pall
Jakobsson (U. of Iceland), Christina Thoene, Jesper Sollerman, Darach
Watson, Bo Milvang-Jensen (DARK/NBI) report on behalf of a larger
collaboration:
The afterglow of GRB 080928 detected by Swift (Sakamoto et al., GCN
8292, see also Rykoff et al., GCN 8293) was observed with FORS2
mounted on the Antu telescope of ESO's VLT on Cerro Paranal, Chile.
Following an acquisition image, which was started at 6:31 UT on
September 29, 2008 (15.5 hr after the GRB trigger), a single 1800 s
spectrum was secured. It was taken with a 1" slit and the 300V grism,
resulting in an approximate resolution of 11 A, and a useful
wavelength coverage of 3800-9300 A. From the 60 s acquisition image,
we measure an afterglow magnitude of R = 20.4 based on USNO-B1
magnitudes.
The extracted spectrum shows a multitude of significant absorption
lines, which we identify with common resonance lines of mainly MgII
and FeII, originating in at least two absorption systems at z=0.735
and z=1.692. The latter redshift presumably corresponds to that of the
GRB host galaxy. We do not find evidence for a spectral break due to
the Lyman alpha forest down to 3800 A, setting a firm upper limit on
the GRB redshift of z < 2.1. These results are consistent with the
redshift limits set by GROND (Rossi et al., GCN 8296) and UVOT (Kuin
et al., GCN 8298), but not with the value of z=2.49 reported by
Cucchiara et al. (GCN 8300).
The equivalent width of the MgII 2796 line of the z=0.735 system
(EW_rest ~ 4.3 A) is much larger than that of the z=1.692 system. We
note the presence of an R ~ 22 object, not covered by the slit, at
2.6" NNE of the afterglow position, which could possibly be a bright
host galaxy, or the counterpart of the z=0.735 absorber. The slit
serendipitously covers a galaxy 30" away from the afterglow (at
R.A. 06:20:13.35, decl. -55:11:55.0), which shows an apparent emission
line at 6470 A; this can be identified as [OII] 3727 at a redshift of
z=0.736. At this redshift, 2.6 and 30" correspond to projected
distances of 19 and 219 kpc, respectively.
We are grateful for the excellent support from the Paranal observing
staff, in particular Stephane Brillant, Michelle Doherty and Patricia
Guajardo.
GCN Circular 8300
Subject
GRB080928: Gemini-South Absorption Redshift
Date
2008-09-29T15:31:33Z (17 years ago)
From
Antonino Cucchiara at PSU <cucchiara@astro.psu.edu>
A. Cucchiara, D. B. Fox (Penn State), S. B. Cenko (Berkeley) and E. Berger
(Harvard) report on behalf of a larger collaboration:
Starting at 06:54 UT on 2008 September 29 (T0+16h) we observed the optical
counterpart of GRB 080928 (Sakamoto et al., GCN 8292, Rykoff et al.,
GCN 8293)
using Gemini-South with the GMOS-South spectrograph (R~1200).
We acquired 2x900s spectra which covered the wavelength range 4000A-8000A.
Our spectrum shows a flux cut-off blueward of 4500A indicating a likely DLA
associated with the GRB host galaxy, consistent with a redshift of z ~ 2.6.
We also identify multiple metal absorption features including FeII(2249),
FeII(2260), SiIV(1393), SiIV(1402), CIV(1548), CIV(1550), NiII(1741) and
NiII(1751) at a common redshift of z = 2.49.
Therefore we conclude that GRB080928 occurred in a possible DLA galaxy
at z = 2.49.
We thank the Gemini staff for conducting these observations.
[GCN OPS NOTE(29sep08): Per author's request, the affiliation for EB
was corrected to Harvard.]
GCN Circular 8299
Subject
GRB 080928: Swift-XRT refined analysis
Date
2008-09-29T12:56:41Z (17 years ago)
From
Cristiano Guidorzi at INAF-OAB <cristiano.guidorzi@brera.inaf.it>
C. Guidorzi, R. Margutti, J. Mao (INAF-OAB) and T. Sakamoto (GSFC/UMBC)
report on behalf of the Swift-XRT team:
We have analysed the first 7 orbits of Swift-XRT data obtained for
GRB 080928 (Sakamoto et al., GCN Circ. 8292), covering 325 s of Windowed
Timing (WT) mode data and 15.3 ks of Photon Counting (PC) mode data.
The UVOT-enhanced XRT position was given by Osborne et al. in GCN Circ.
8295.
The light-curve can be modelled by a broken power-law, with a couple
of bright flares peaking at 210 and 360 s with a FWHM duration of 55
and 35 s and a peak count rate of 420 +/- 10 and 75 +- 3 count s^-1,
respectively. The power-law decay index changes from an initial value
of 1.20 +- 0.03 to 1.7 +- 0.2 after a break time of (11 +- 2) ks
(uncertainties at 1 sigma). The first flare coincides with the main
emission seen by BAT (Fenimore et al. GCN Circ. 8297).
A spectrum extracted from WT data around the first flare, from 176 to 250 s,
can be modelled with an absorbed power-law, with Gamma = 1.45 +- 0.06 and
NH = (1.7 +- 0.2)x1e21 cm^-2, in excess of the Galactic column in this
direction of 5.6e20 cm^-2. Another spectrum extracted around the second
flare, from 300 to 470 s, can be fit with the same model, with
Gamma = 1.85 +- 0.06 and NH = (1.1 +- 0.2)x1e21 cm^-2.
A later spectrum extracted from PC data, from 5 to 47 ks, can be fit with
an absorbed power law with Gamma = 2.2 +- 0.2 and NH = (1.2 +- 0.4)x1e21
cm^-2. The observed (unabsorbed) flux over this time interval is 8.4x10^-12
(1.2x10^-11) erg cm^-2 s^-1.
If the light-curve continues to decay with the current rate, the count
rate 24 hours after the burst is estimated to be 5.6e-3 count s^-1, which
corresponds to an observed flux of 2.5x10^-13 erg cm^-2 s^-1.
This is an official product of the Swift-XRT team.
GCN Circular 8298
Subject
GRB 080928: Swift/UVOT observations
Date
2008-09-29T12:54:16Z (17 years ago)
From
Paul Kuin at MSSL <npkuin@googlemail.com>
N. P. M. Kuin (MSSL/UCL), T. Sakamoto (NASA/UMBC),and Stephen
Holland (GSFC) report on behalf of the Swift UVOT team
The Swift UltraViolet/Optical Telescope (UVOT) began observations of
GRB080928 (Swift BAT trigger number 326115, Sakamoto et al., GCN Circ.
8292), on September 28, 2008, at 15:04:15 UT, 161 seconds after the
trigger with a setling exposure in the UVOT v filter.
We detect a new source at position :
RA=06:20:16.836 Dec=-55:11:58.95 (95.07015, -55.199708 deg (J2000)),
with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence).
The initial magnitude observed for GRB080928 is given below for the
first observation in the UVOT v filters:
Filter Tstart(s) Tstop(s) Exp(s) Magnitude
wh(fc) 179 279 99.8 19.09 +/- 0.14 7.3-sigma
v (fc) 285 479 193.7 19.07 +/- 0.43 2.5-sigma
uvm2 4227 4427 196.6 >19.47 3-sigma upper limit (weak signal)
uvw1 4432 4632 196.6 18.64 +/- 0.19 5.6-sigma
u 4638 4838 199.8 17.96 +/- 0.09 12.1-sigma
b 4843 5043 199.8 18.40 +/- 0.09 11.9-sigma
uvw2 5255 5455 196.6 >19.89 3-sigma upper limit
v 5460 5660 199.8 18.03 +/- 0.15 7.3-sigma
The upper limits in the UV filters uvw2 and uvm2 indicate an
upper limit to the redshift of z < 1.8. An initial rise is seen
up to about 200s in the white filter event data.
The values quoted above are on the UVOT Photometric System
(Poole et al, 2008, MNRAS 383,627). They are not corrected for the
expected galactic reddening of E(B-V) = 0.067 in the direction of
the burst (Schlegel et al. 1998).
GCN Circular 8297
Subject
GRB 080928, Swift-BAT final refined analysis
Date
2008-09-29T12:41:32Z (17 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
E. Fenimore (LANL), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+494 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080928 (trigger #326115)
(Sakamoto, et al., GCN Circ. 8292). The BAT ground-calculated position is
RA, Dec = 95.061, -55.176 deg, which is
RA(J2000) = 06h 20m 14.6s
Dec(J2000) = -55d 10' 34.8"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 84%.
With all the data downlinked, the mask-weighted light curve shows
that BAT triggered on a weak blip that occurred long before the
main emission of this burst. The initial peak started at ~T-10 sec,
peaked at ~T_zero, and returned to baseline around T+30 sec.
Then a second, slightly larger peak, started at ~T+50 and ended at ~T+130 sec.
Then the main emission started at ~T+170, with a pair of peaks at ~T+205 and
~T+215 sec. The emaission tails down to almost background at T+400 sec
at which time Swift started to enter the SAA and the errors on the flux
become large. T90 (15-350 keV) is 280 +- 30 sec (estimated error
including systematics).
The time-averaged spectrum from T+51.1 to T+381.5 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.77 +- 0.12. The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+202.83 sec in the 15-150 keV band
is 2.1 +- 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/326115/BA/
GCN Circular 8296
Subject
GRB 080928: GROND DETECTION
Date
2008-09-29T12:02:04Z (17 years ago)
From
Andrea Rossi at TLS Tautenburg <rossi@tls-tautenburg.de>
A. Rossi (Tautenburg Obs.), C. Clemens, J. Greiner, A. Yoldas, T. Kruehler,
R. Filgas (all MPE Garching), A. Kupcu Yoldas (ESO) and
G. Szokoly (Eoetvoes Univ., Budapest) report on behalf of the GROND team:
GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI
telescope at La Silla Observatory (Chile), started observations of the
field of GRB 080928 (Sakamoto et al. GCN #8292) in g'r'i'z'JHK at
04:46:00 UT on 2008-09-29, 13.5 hours after the burst trigger.
We clearly detect the optical afterglow detected by UVOT (Sakamoto et al.
GCN #8292) and ROTSE telescope (Rykoff et al. GCN #8293) in
all optical bands, implying a redshift z<3.5.
Observations continued for 90 min and were repeated at the mid-time
06:00 UT for a total 90 min. Both observations were done during strong wind
and bad seeing (>2").
Calibrating the field on the SDSS standard SA95-149, we derive the following
r' band observed magnitudes:
midtime(s) r' err
------------------------
50507 20.57 0.04
65807 21.36 0.06
Our data, when compared to the reported brightness of the afterglow
reported by UVOT, suggest a break between the UVOT and the GROND
measurements.
GCN Circular 8295
Subject
GRB 080928: Enhanced Swift-XRT position
Date
2008-09-28T23:23:00Z (17 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 5367 s of XRT Photon Counting mode data and 8 UVOT
images for GRB 080928, 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 = 95.07029, -55.19958 which is equivalent
to:
RA (J2000): 06h 20m 16.87s
Dec (J2000): -55d 11' 58.5"
with an uncertainty of 1.4 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 8294
Subject
GRB 080928, Swift-BAT initial refined analysis
Date
2008-09-28T23:18:56Z (17 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), C. Guidorzi (INAF-OAB),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
K. L. Page (U Leicester), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+323 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 080928 (trigger #326115)
(Sakamoto, et al., GCN Circ. 8292). The BAT ground-calculated position is
RA, Dec = 95.063, -55.175 deg, which is
RA(J2000) = 06h 20m 15.1s
Dec(J2000) = -55d 10' 29.5"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 84%.
The mask-weighted light curve shows that BAT triggered on a weak blip
that occurred long before the main emission of this burst. The initial
peak started at ~T-10 sec, peaked at ~T_zero, and returned to baseline
around T+30 sec. Then a second, slightly larger peak, started at ~T+50
and ended at ~T+130 sec. Then the main emission started at ~T+170, with
a pair of peaks at ~T+205 and ~T+215 sec. We currently only have data
downlinked out to T+325 sec and the mask-weighted lightcurve shows
continued emission out to this time. The flight-generated mask-weighted
lightcurve (lower resolution) shows no further peaks beyond T+325 sec.
The main peak at ~T+210 sec coincides with the peak emission in the
prompt XRT TDRSS lightcurve.
The time-averaged spectrum from T+51.1 to T+255.3 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.80 +- 0.12. The fluence in the 15-150 keV band is 2.1 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+202.83 sec in the 15-150 keV band
is 2.1 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
When we get the remainder of the event-by-event data downlinked,
we will issue revised spectral fit results and a T90.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/326115/BA/
GCN Circular 8292
Subject
GRB 080928: Swift detection of a burst with an optical counterpart
Date
2008-09-28T15:16:04Z (17 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
T. Sakamoto (NASA/UMBC), S. D. Barthelmy (GSFC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC), C. Gronwall (PSU),
C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC),
J. Mao (INAF-OAB), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:
At 15:01:32 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080928 (trigger=326115). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 95.084, -55.173 which is
RA(J2000) = 06h 20m 20s
Dec(J2000) = -55d 10' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). This is an image trigger so as usual
the BAT lightcurve shows nothing.
The XRT began observing the field at 15:04:22.6 UT, 169.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 95.0691, -55.1997 which is equivalent to:
RA(J2000) = 06h 20m 16.58s
Dec(J2000) = -55d 11' 58.9"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 100 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy.
The initial flux in the 2.5 s image was 5.77e-09 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 179 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 06:20:16.85 = 95.0702
DEC(J2000) = -55:11:59.3 = -55.1998
with a 1-sigma error radius of about 0.5 arc sec. This position is 2.3 arc sec.
from the center of the XRT error circle. The estimated magnitude is 19.2 with a
1-sigma error of about 0.5 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.07.
Burst Advocate for this burst is T. Sakamoto (Taka.Sakamoto AT nasa.gov).
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.)