GRB 040924
GCN Circular 2833
Subject
GRB 040924: Afterglow Color
Date
2004-11-08T17:34:49Z (21 years ago)
From
Matt Bayliss at UNC,Chapel Hill <mbayliss@physics.unc.edu>
J. Silvey, D. Allen, M. Bayliss, M. Nysewander, T. Tilleman, A. Henden, M.
Leake, A. Homewood, R. Canterna, D. Reichart, D. H. Hartmann, and M.
Schwartz report on behalf of the U. Wyoming, U. North Carolina, USNO, and
SARA GRB teams of the FUN GRB collaboration:
We observed the afterglow location (Fox & Moon, GCN 2734) of the short/soft
GRB 040924 (Fenimore et al., GCN 2735) in VRcIcH beginning 16.2 hours after
the burst. Using the field calibrations of Henden (GCN 2811) and 2MASS, we
report the following magnitudes:
Start Mean Time Filter Exposure Magnitude Telescope
Date Since GRB Time (sec) (1)
(hours) x Exposures
Sep 25.171 16.44 Rc 300 x 4 >18.9 0.9m SARA
Sep 25.191 16.89 Ic 300 x 4 >20.6 0.9m SARA
Sep 25.209 17.31 V 300 x 4 >19.6 0.9m SARA
Sep 25.228 18.32 H 800 x 4 >19.5 1.55m NOFS
Sep 25.328 21.18 Ic 300 x 24 >21.7 0.8m TII(2)
Sep 25.391 21.86 Rc 300 x 3 22.68+/-0.07 2.3m WIRO
Sep 25.395 21.96 V 300 x 3 23.06+/-0.07 2.3m WIRO
(1) Limiting magnitudes are 2 sigma.
(2) Tenagra II
Compared to the R observations of Fox (GCN 2741) and Pavlenko et al. (GCN
2753), our Rc observation is generally consistent with a temporal index of
approx. -1.
Assuming a temporal index of -1.16 (Khamitov et al., GCN 2749) and using
this index to scale our observations and the K' observation of Terada et
al. (GCN 2750) to 21.9 hours after the burst, and correcting for Galactic
extinction along the line of sight assuming that R_V = 3.1, yields a
spectral index of -0.61 +/- 0.08:
www.physics.unc.edu/~mbayliss/grbdata/grb040924spec.eps
If source-frame extinction is negligible, this is consistent with either a
constant-density or wind-swept medium with the cooling break blueward of
the observed bands. It is inconsistent with either a constant-density or
wind-swept medium with the cooling break redward of the observed bands
(e.g., Sari, Piran & Narayan 1998, ApJ, 497, L17; Chevalier & Li 2000; ApJ,
536, 195).
However, if source-frame extinction is non-negligible this is only
consistent with a wind-swept medium with the cooling break blueward of the
observed bands.
GCN Circular 2811
Subject
GRB040924, BVRcIc field calibration
Date
2004-10-16T02:36:15Z (21 years ago)
From
Arne A. Henden at USNO/USRA <aah@nofs.navy.mil>
A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:
We have acquired BVRcIc all-sky photometry for
a 11x11 arcmin field centered on the afterglow coordinates
(Fox and Moon, GCN 2734) for the HETE burst GRB040924
(trigger 3564; Fenimore et al., GCN 2735)
with the USNOFS 1.0-m telescope on one photometric
night. Stars brighter than V=14 are saturated and
should be used with care. We have placed the photometric data
on our anonymous ftp site:
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb040924.dat
The astrometry in this file is based on linear plate solutions
with respect to UCAC2. The external errors are less than 100mas.
The estimated external photometric error is about 0.03mag
and will be improved with additional calibration nights
later this week, weather permitting.
As always, you should check the dates on the .dat file prior to
final publication to get the latest photometry. There is
a README file on the ftp directory to give you information
about the procedures used to calibrate these fields.
GCN Circular 2800
Subject
GRB 040924: VLT spectroscopy
Date
2004-10-13T14:54:11Z (21 years ago)
From
Rhaana Starling at GRACE/U of Amsterdam <starling@science.uva.nl>
Klaas Wiersema (University of Amsterdam), Rhaana L.C. Starling
(University of Amsterdam), Evert Rol (University of Leicester),
Paul Vreeswijk (ESO), Ralph A.M.J. Wijers (University of Amsterdam)
report on behalf of the GRACE collaboration:
"We have obtained two spectra of the host galaxy of GRB 040924
(GCN #2735, 2734) with the FORS2 long slit spectrograph on the
ESO VLT (Antu) on 10 October 2004, approx. 15.75 days after burst.
The first spectrum was taken at 05:10 UT using the 300V grism, with
an exposure time of 1800 s; the second spectrum was taken at 05:48 UT
using the 300I grism, again with an exposure time of 1800 s. We used
a 1 arcsec slit. The total wavelength range is approx. 400 - 950 nm.
We find weak emission lines in the spectra, which we identify with
[OII] 3727, [NeIII] 3968.9, H gamma, H beta and [OIII] 4959,5007.
All of these lines are consistent with a redshift z = 0.859.
The presence of [NeIII] implies a galaxy with a significant
population of massive stars. The isotropic energy of the burst is
E_iso=1.48x10^52 erg, using the 25-100 keV fluence value from HETE
and a cosmology with H_0=70 km/s/Mpc, Omega_matter=0.3 and
Omega_lambda=0.7. As the lightcurve breaks fairly early on, the true
energy is likely to be much lower.
The presence of continuum features relating to a supernova
can only be determined after further analysis: a SN1998bw-like bump
would be expected to peak at approximately t_V~23.5 days, t_R~25 days and
t_I~26 days with magnitudes V~25.4, R~24.6 and I~23.8.
We acknowledge excellent support from the staff of Paranal Observatory
and ESO's PSO and USG."
GCN Circular 2759
Subject
GRB 040924: Second Epoch WSRT Radio Observations
Date
2004-10-01T12:49:59Z (21 years ago)
From
Alexander van der Horst at U of Amsterdam <avdhorst@science.uva.nl>
A.J. van der Horst (University of Amsterdam), E. Rol (University of
Leicester) and R.A.M.J. Wijers (University of Amsterdam) report on behalf
of a larger collaboration:
"We reobserved the position of the GRB 040924 afterglow at 4.9 GHz with
the Westerbork Synthesis Radio Telescope from September 29 19.06 UT to
September 30 6.81 UT, i.e. 5.30 - 5.79 days after the burst (GCN 2735).
The rms noise in het map around that position is 30 microJy per beam. The
formal flux measurement for a point source at the location of the optical
afterglow (GCN 2734) is 11 +/- 30 microJy.
In conclusion, we do not detect a source at the optical position, in
agreement with our previous WSRT measurements (GCN 2746) and the VLA
measurements (GCN 2758).
No further observations are planned."
This message may be cited.
GCN Circular 2758
Subject
radio observations, GRB 040924
Date
2004-09-30T21:16:19Z (21 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>