- GCN notice #801
K. Hurley, on behalf of the Ulysses GRB team, E. Mazets and
S. Golenetskii, on behalf of the Konus-Wind GRB team, and
T. Cline, on behalf of the Konus-Wind and NEAR GRB teams, report:
Ulysses, Konus, and NEAR observed this burst at 85773 s. As observed
by Ulysses, it had a duration ~25 s, a 25-100 keV fluence of
We have triangulated it to a preliminary, 3 sigma error box whose
area is approximately 35 sq. arcmin. and whose coordinates are
RA(2000) DEC(2000)
17 h 4 m 15.05 s 51 o 46 ' 34.93 " (CENTER)
17 h 4 m 2.88 s 51 o 46 ' 10.91 " (CORNER)
17 h 4 m 31.05 s 51 o 38 ' 13.48 " (CORNER)
17 h 3 m 59.06 s 51 o 54 ' 56.51 " (CORNER)
17 h 4 m 27.22 s 51 o 46 ' 58.88 " (CORNER)
This box may be improved.
- GCN notice #802
K. Hurley reports:
Because I am logged in from an unfamiliar terminal, the
tilde characters caused a line to be erased from the
previous message (GCN 801). The 25-100 keV fluence
was approx. 2.2E-5 erg/cm^2, and the peak flux over
0.25 s was approx. 1.3E-6 erg/cm^2 s.
- GCN notice #803
J. Gorosabel (DSRI, Copenhagen),
J.M. Castro Ceron (ROA, San Fernando),
A.J. Castro-Tirado (IAA-CSIC, Granada),
J. Greiner (AIP, Potsdam)
Starting at 27.859UT SEP 2000 we obtained R- ,V-, I- and B-band images
of the IPN error box for GRB 000926 (Hurley et al., GCN #801) with the
2.2m. telescope at the Calar Alto Observatory. A comparison with the
Digital Sky Survey-2 revealed a new bright point-like source located
at:
RA(J2000)= 17h 04m 09.70s
DEC(J2000)= +51o 47' 10.2"
Our uncertainty is 2". These object's coordinates agree with the ones
reported independently by Dall et al. It is clearly detected in the
R-, V-, and I-bands. We derive a preliminary magnitude of 19.5 +/- 0.3
based on a zero point calculated with USNO-2.0 stars in the field.
Further multicolour imaging is in progress.
- GCN notice #804
T. Dall (NOT and University of Aarhus), J.P.U. Fynbo (ESO),
H. Pedersen, B.L. Jensen, J. Hjorth (U. of Copenhagen) and
J. Gorosabel (DSRI, Copenhagen)
report on behalf of a larger European GRB Collaboration:
Using the ALFOSC on the 2.5m Nordic Optical Telescope, we have
obtained U,B,R and I-band imaging of the field of GRB 000926
(Hurley et al., GCN #801) on 2000 September 27.8-28.1 UT.
Comparing with DSS-2 (red) we find a bright point source
not visible on the DSS-2 exposure.
The coordinates of this object are:
RA(J2000) : 17 04 09.62
Dec(J2000) : +51 47 11.2
(with an uncertainty of about 2")
These coordinates are consistent with those reported
independently by Gorosabel et al.
This object is detected in both U,B,R and I-band images.
A 1hr spectrum covering the region 3500AA-7000AA has been obtained
showing a blue spectrum with strong absorption lines. The redshift
has not yet been determined.
A preliminary magnitude for the object is: R=19.3 +- 0.2.
Ingvar Svaerdh and Charlotte Moeller are acknowledged for help
with the observations.
- GCN notice #805
D. A. Frail (NRAO) and E. Berger (Caltech) report on behalf of a
larger collaboration:
Beginning on September 28.16 we observed the IPN error box of
GRB000926 (GCN #801) with the VLA at 8.46 GHz and 4.86 GHz. A
quick-look analysis of the 8.46 GHz data reveals a ~0.5 mJy radio
source positionally coincident with the optical candidate reported by
Gorosabel et al. (GCN #803) and Dall et al. (GCN #804). Further
observations are planned.
- GCN notice #806
J. P. Halpern, N. Mirabal (Columbia U.), D. Turnshek
& J. Busche (U. Pittsburgh) report on behalf of the
MDM Observatory GRB follow-up team:
We observed the optical candidate for GRB 000926
(Gorosabel et al. GCN #803; Dall et al. GCN #804)
in R and B on Sep. 28.177 UT using the MDM 2.4m.
We measure the position of the optical candidate to be
(J2000) RA 17:04:09.749, Dec +51:47:09.97 in the Guide
Star Catalog system, relative to eight stars having an
rms dispersion of 0".15.
A preliminary magnitude for the optical candidate is
measured as R = 19.89 +/- 0.02, referenced to a USNO-A2.0
star at (J2000) RA 17:04:01.206, Dec +51:46:19.88 which
is listed as having R = 17.1. Since this measurement was
made from an unprocessed image, it is subject to additional
systematic error, and should not be used in serious analyses.
The decay rate is therefore still unknown.
- GCN notice #807
J. P. U. Fynbo, P. Moller (ESO), T. Dall (NOT and U. of Aarhus),
H. Pedersen, B. L. Jensen, J. Hjorth (U. of Copenhagen) and J. Gorosabel
(DSRI, Copenhagen) report on behalf of a larger European GRB Collaboration:
We have analysed the spectrum of the optical afterglow of GRB 000926
(GCN #803, GCN #804) reported by Dall et al. (GCN #804). The spectrum
was obtained 22.2 hours after the burst with ALFOSC at the Nordic Optical
Telescope and covered the wavelength range from the atmospheric cut-off
to 8800 A. We find two significant absorption systems: One at z = 1.378
(based on Al II 1670, Fe II 2344, Fe II 2374, Fe II 2382, Fe II 2586) and
one at z = 2.066 (based on Ly alpha 1215, Si IV 1393, Si IV 1402, C IV
1548/1550, Fe II 1608, Al II 1670). The redshift of GRB 000926 is likely
to be z = 2.066 due to the high column density of this absorption system.
In an Omega_m = 0.3, Omega_Lambda = 0.7, H_0 = 65 km s^-1 Mpc^-1 cosmology
the 25 - 100 keV fluence of 2.2 10^-5 erg cm^-2 (Hurley et al. GCN #801,
GCN #802) corresponds to an isotropic energy release of 2.6 10^53 erg.
- GCN notice #808
S. Kulkarni, on behalf of a large international GRB collaboration reports:
This note is to inform you that, under the aegis of our AO-9
program, we have requested observations of GRB 000926 (GCN 801) with the
Hubble Space Telescope and Chandra X-ray Observatory. This burst with
a bright optical (GC 803, 804) and radio (GCN 805) afterglow appears
to be particularly well suited for detailed studies of the afterglow
and the circumburst medium.
We encourage intensive ground based observations of this burst so that
it will become a very well studied GRB. Particularly valuable are
intensive lightcurves at early times since the earliest HST observation
is at least a week away (as is the requested Chandra observation). We
ourselves are planning to supplement the HST and CXO observations with
detailed multiwavelength observations at facilities to which our group
has access (e.g. Keck, Palomar, MDM, HET). In the radio, we will be
undertaking observations at VLA and OVRO and possibly other facilities
as well.
- GCN notice #809
J. Hjorth, B. L. Jensen, and H. Pedersen (U. of Copenhagen),
J. U. P. Fynbo and P. Moller (ESO), J. Gorosabel (DSRI, Copenhagen)
report on behalf of a larger European GRB collaboration:
"Using the ALFOSC on the 2.56-m Nordic Optical Telescope we have
obtained R-band imaging of the optical afterglow of GRB 000926
(GCN #801-#808) on 2000 September 27.8-28.9 UT. We find the
following preliminary R-band magnitudes of the object using the
reference star of Halpern et al. (GCN #806) :
Sept. 2000 UT R 1 sigma
--------------------------------
27.8547 19.414 0.015
27.8594 19.428 0.011
27.8639 19.411 0.011
27.8684 19.433 0.008
27.8729 19.437 0.011
27.8774 19.453 0.010
27.8820 19.441 0.010
27.9658 19.618 0.011
27.9705 19.595 0.014
27.9750 19.641 0.015
27.9795 19.609 0.017
27.9840 19.619 0.021
28.8356 20.778 0.023
28.8911 20.834 0.034
These magnitudes show that the object identified as the optical afterglow
is decaying. The temporal power-law decay index appears to progressively
steepen from -1.2 on Sep 27.85 to -1.85 between Sep 28.2 (GCN #806) and
Sep 28.9, indicating a 'break' in the lightcurve.
- GCN notice #810
R. J. Nemiroff, D. Perez-Ramirez, J. B. Rafert,
W. E. Pereira, C. Ftaclas, and J. Fernandez
(Michigan Tech) report on behalf of the CONCAM collaboration:
The CONtinuous CAMera (CONCAM) operating on the roof of the
RMT building at Kitt Peak National Observatory in Arizona has
recorded data that provides very crude limits on the attributes
of the OT through non-detection.
Before the GRB Trigger:
From (2000 September 26.135) to (2000 September 26.263), spanning from
roughly 20.6 hours to 17.5 hours before the Konus trigger, no obvious
optical transient brighter than visual magnitude 4 was recorded.
These above results were derived from a visual inspection of a series
of two-minute exposures of the nearly 2 pi steradian CONCAM field.
A more detailed inspection of the data might improve these magnitude
limits to approximately visual magnitude 6. Data remains freely
available at
http://concam.net
- GCN notice #811
P.A. Price, O. Pevunova, B.F. Madore, A. Diercks and J.S. Bloom (Caltech)
report on behalf of a larger collaboration:
We have observed the optical transient candidate of Dall et. al. (GCN #804)
and Gorosabel et. al. (GCN #803) with the Palomar 60-inch telescope in
B, R and I. Photometry was performed relative to the USNO-A2.0 star
U1350_09071131 at J2000 coordinates RA 17:04:01.21, Dec +51:46:19.9 (as per
Halpern et. al., GCN #806). Results are as follows:
Filter Epoch Relative Reference Magnitude
B Sep 28.193 2.427 +/- 0.049 mag 17.8 mag 20.227 +/- 0.049
R Sep 28.213 2.934 +/- 0.037 mag 17.1 mag 20.034 +/- 0.037
I Sep 28.173 2.917 +/- 0.052 mag Unknown
(Errors are statistical only.)
Further observations are planned.
- BeppoSAX MAIL n. 00/21
A BeppoSAX TOO observation (20 ksec) of GB000926 has started on Sept.
28.979, i.e. about 2 days after the GRB.
Preliminary analysis of the first three orbits shown a
relatively bright (flux about 0.5 10**-12 erg/cm2/s) unknown source
in the MECS(1.6-10 keV) image.
The position is:
RA=256.029
Delta=51.797
which is 0.7' from the optical counterpart and consistent with it within
our errors. We identify this new X-ray source as the X-ray afterglow
of GB000926.
L. Piro
- GCN notice #812
L. Piro (BeppoSAX Mission Scientist) on behalf of a large collaboration
reports:
A BeppoSAX TOO observation of GB000926 has started on Sept. 28.979, i.e.
about 2 days after the GRB. Preliminary analysis of the first three orbits
shows a relatively bright (flux about 0.5 10**-12 erg/cm2/s) unknown
source in the MECS(1.6-10 keV) image.
The position is
RA(2000)=17h 04m 07s Decl.(2000)= +51 47' 42"
which is 0.7' from the optical counterpart (Gorosabel et al. GCN 803, Dall
et al. GCN 804, Halpern et al. GCN 806) and consistent with it within our
errors. We identify this new X-ray source (1SAXJ1704.1+5147) as the X-ray
afterglow of GB000926.
This is an updated status of X-ray observations programmed on this
source:
1- This BeppoSAX observation will last upto Sept. 29.046 (T_GRB+2 days)
2- A fast Chandra TOO (Cycle 1 program by Piro et al) has been scheduled
for Sept. 29.67 (T_GRB+2.7 days)
3- On the basis of the results of these 2 observation we will decide
whether to plan another BeppoSAX observation around T_GRB+6 days
4- Another Chandra observation should be performed by Kulkarni et al
(GCN808) at later times
- GCN notice #813
Taichi Kato at Kyoto Univ. reports
The following observation has been reported to vsnet-grb No. 14
(http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-grb/maillist.html)
Subject: [vsnet-grb 14] Re: GRB 000926, Oksanen's image
Re: GRB 000926, Oksanen's image
>On Oksanen's image, a very faint source near the position of the
>candidate of the afterglow of GRB 000926 (vsnet-grb 10) is shown.
>It is not shown in the DSS 2 R image. Further analysis is
>undergoing.
The precise astrometry using 43 USNO_A2.0 stars yields:
R.A. = 17h04m09s.71 +/- 0s.05, Decl. = +51o47'10".0 +/- 0".5
(2000.0), which shows quite good agreement with the reported
positions. Oksanen reports that every POSS scan examined at USNO
server does not show this object. Thus it is highly probable that
this object is the same object as a candidate of the afterglow of GRB
000926.
The magnitude was about 20.0CR at Sept. 28.8 UT
(comparison star is USNO_A2.0 star at 17h04m01s.21, +51o46'19".9
(2000.0), rmag = 17.1, same as Halpern et al. (GCN 806)).
Note that it is somewhat brighter than Hjorth et al. (GCN 809) report.
Sincerely Yours,
Hitoshi Yamaoka, Kyushu Univ., Japan
yamaoka@rc.kyushu-u.ac.jp
- GCN notice #814
J. Hjorth, B. L. Jensen, and H. Pedersen (U. of Copenhagen),
J. U. P. Fynbo and P. Moller (ESO), J. Gorosabel (DSRI, Copenhagen)
report on behalf of a larger European GRB collaboration:
Further to GCN #809, we report an additional NOT R-band data point
obtained on Sept. 28.9595 UT: R=20.889+-0.035. We note that if we
exclude the preliminary data point of Halpern et al. (GCN #806) and
include the data point of Price et al. (GCN #811) the lightcurve is
consistent with a pure power law decay with a decay index of
-1.66 +- 0.02. Further monitoring of the optical afterglow is needed
to distinguish a pure power law and a broken power law decay. A
finding chart, a lightcurve and predictions for the coming days are
posted at
http://www.astro.ku.dk/~brian_j/grb/grb000926/
and reproduced below:
- GCN notice #816
A. Di Paola, R. Speziali, L.A. Antonelli, F. Pedichini, F. D'Alessio,
G.L. Israel, D. Lorenzetti, L. Stella, Osservatorio Astronomico di Roma,
Italy, on behalf of a larger collaboration report:
"We observed the optical transient candidate of GRB 000926 (Gorosabel
et al., GCN #803; Dall et. al., GCN #804) with the AZT-24 1.1-meter
telescope at Campo Imperatore (AQ).
The J-band observation started at September 28.8481 UT and the field
was imaged for a total exposure time of 1800 sec. We observed a source
at a position:
RA(J2000)= 17h 04m 09.11s
DEC(J2000)= +51o 47' 09.3"
(uncertainty is 2")
consistent with the optical transient of GRB 000926 (GCN #803) having
a magnitude of J=18.6+/-0.3 mag with a S/N=5.
The K-band observation started at Sep. 28.9345 UT and the field was
imaged for a total exposure time of 1800 sec. The limiting magnitude
reached in the K-band was K=17.0 mag (S/N=3) with an average FWHM of
2.5", no sources were detected at the above position.
The J-band image is posted at
http://argos.mporzio.astro.it/angelo/grb000926/
- GCN notice #817
Taichi Kato at Kyoto Univ. reports:
Addendum to GCN No. 813:
Important information was missing, sorry.
The observation referred in GCN 813 was done by Arto Oksanen,
Nyrola Observatory, Finland.
(
http://www.ursa.fi/sirius/nytt/nytt_info.html)
The observation was done using a 40-cm f6.3 SCT telescope. The image
was combined from 17 240s unfiltered exposures around September 28 19:00 UT.
- GCN notice #818
The optical counterpart of GRB000926 has been observed using the
CFH12K CCD mosaic camera at the prime focus of the 3.6-m CFH
Telescope.
One 600s exposure with moderate seeing (image quality between 0.9"
and 1.0") has been obtained and a preliminary reduction using
the reference star of Halpern et al. (GCN #806) with R=17.1 gives
the following measurement for GRB000926:
Sept. 29.3075 R = 21.23 +/- 0.05
Added to the R-band data points used in the analysis by Hjorth et al.
(GCN #814), this new point confirms a pure power law decay with
a decay value of 1.69 +/- 0.03, which is not significantly different
from Hjorth et al.'s determination.
An image of the area around the GRB can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html
Kocevski, Donovan and G. Luppino are acknowledged for their help in
this observation.
- GCN notice #819
On behalf of the USNO GRB team, F. Vrba and B. Canzian, report
two additional R-band photometric measurements of the GRB 000926
optical counterpart, discovered by Gorosabel et al. (GCN 803)
and Dall et al. (GCN 804). Our observations were obtained with
the USNO, Flagstaff Station, 1.0-m telescope. These measurements
are based on a preliminary photometric calibration from a limited
number of standard stars.
UT Date Magnitude
Sep 28.097 R = 19.70 +/- .03
Sep 29.146 R = 21.05 +/- .04
If weather permits at a later date, we will produce a fully-calibrated
UBVRI standard sequence, as we have for several earlier GRB fields.
- GCN notice #820
J. P. U. Fynbo, P. Moller (ESO), J. Gorosabel (DSRI, Copenhagen),
J. Hjorth, B. L. Jensen, and H. Pedersen (U. of Copenhagen),
report on behalf of a larger European GRB Collaboration:
Using the ALFOSC on the 2.5m Nordic Optical Telescope, we have
obtained further R-band imaging of the Optical Transient (OT) of
GRB 000926 (GCN #801, #803, #804) on 2000 September
29.84-29.95 UT.
We find the following R-band magnitudes of the OT using the
reference star of Halpern et al. (GCN #806) :
UT R-band 1sigma
-----------------------------
29.8414 21.779 0.042
29.9478 21.890 0.082
An updated lightcurve including the NOT measurements (black circles)
and the measurements of Halpern et al. (GCN #806), Price et al. (#811)
and Veillet (GCN ~818) (open diamonds) can be seen at
www.obs.aau.dk/~jfynbo/grb/grb000926/lightcurve.gif. The new NOT
measurements fall below the extrapolation of the power-law decline
found at earlier epochs. We conclude therefore that the decay slope
of the afterglow is increasing.
- GCN notice #821
Naoto Kobayashi, Miwa Goto, Hiroshi Terada, Daigo Tomono
(Subaru Telescope, National Astronomical Observatory of Japan),
reported on behalf of SUBARU Telescope team and SUBARU IRCS team
On 29 Sept, 5:20-6:00 UT (29.24 UT), we have obtained 1800-sec K'
image of the field around the proposed optical transient (OT) of
GRB000926 (GCNC #803, Gorosabel et al.). We used the Subaru 8.2m
Telescope atop Mauna kea with a near-infrared camera and spectrograph
(IRCS) during its second engineering run. The candidate OT was clearly
detected in our image.
http://www.SubaruTelescope.org/Latestnews/200010/GRB/grb000926.jpg
Seeing was about 0".7 in the K'-band. No associated host galaxy was
detected in our image. Since we did not have time to observe
standards, here we just show the relative magnitudes of the OT to a
number of field stars:
relative relative
position K'-magnitude
to OT
OT 0.00 +- 0.04
StarA 42"E -0.45 +- 0.03
StarB 30"E,34"S -2.06 +- 0.01
StarC 32"W -0.80 +- 0.03
Assuming a probable V-K color of StarB (US170412+514636,
R=18.6,B=20.9), we have estimated rough K'-magnitude of the OT at
about K'=19 mag.
We have also uploaded the co-added fits image on the same web site
shown above.
http://www.SubaruTelescope.org/Latestnews/200010/GRB/grb000926.fits
Please feel free to use it for detailed photometry if you have
any information on K'-magnitudes of the field stars. The original
pixel scale of our image is 0.058 arcsec/pix, but the posted image is
binned by 4-pix and the resultant pixel scale should be 0.233
arcsec/pix. North is to the top, East is to the left.
- GCN notice #823
The optical counterpart of GRB000926 has been observed using the
CFH12K CCD mosaic camera at the prime focus of the 3.6-m CFH
Telescope.
One 600s exposure with moderate seeing (image quality 0.8")
has been obtained and a preliminary reduction using the reference
star of Halpern et al. (GCN #806) with R=17.1 gives the following
measurement for GRB000926:
Sept. 30.3075 R = 22.19 +/- 0.06
Added to the R-band data points used in the analysis by Hjorth et al.
(GCN #814), to the previous CFHT observation and to the last data
by Fynbo et al. (GCN #820), this new point confirms the change in decay
rate announced in GCN #820.
The decay value is now 2.44 +/- 0.07, using data past Sept 29.2, while
the decay is 1.67 +/- 0.04 with data prior to Sept 29.2.
A graph of the light curve in R with the linear fits can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html
D. Kocevski, D. Donovan and G. Luppino are acknowledged for their
help in this observation.
- GCN notice #824
J. P. Halpern, N. Mirabal (Columbia U.), D. Turnshek
& J. Busche (U. Pittsburgh) report on behalf of the
MDM Observatory GRB follow-up team:
We processed and calibrated the MDM R and B data reported
previously in GCN #806, now using Landolt standard stars,
and we acquired new R and B observations on the MDM 2.4.
The comparison star at (J2000) RA 17:04:01.21, Dec +51:46:19.9,
previously assumed to have R = 17.1, is now measured at
R = 17.06, B = 18.50. In this new system, we find the
following magnitudes for the OT:
Sep. 28.183 B = 20.89 +/- 0.04
Sep. 28.177 R = 19.86 +/- 0.02
Sep. 29.176 B = 22.11 +/- 0.09
Sep. 29.196 R = 21.14 +/- 0.03
Sep. 30.179 B = 23.07 +/- 0.06
Sep. 30.211 R = 22.11 +/- 0.06
Correcting the observed B-R for the Galactic extinction
A_B = 0.101, A_R = 0.063 of Schlegel et al., we find that
B-R = 0.95 +/- 0.05 consistently for these three nights.
This color corresponds to spectral slope beta = -1.51 +/- 0.12,
which indicates that there may be intrinsic extinction.
Our latest R-band measurement confirms the steepening of the
decay reported by Fynbo et al. (GCN #820) and Veillet (GCN #823).
For the first 2 days the decay slope was consistent with
alpha = -1.65 +/- 0.02. After 2.2 days, alpha = -2.51 +/- 0.17.
Images of this field and an updated decay curve are posted at
http://www.astro.columbia.edu/~jules/grb/000926
- GCN notice #825
J. P. U. Fynbo, P. Moller (ESO), J. Gorosabel (DSRI, Copenhagen)
J. Hjorth, B. L. Jensen, and H. Pedersen (U. of Copenhagen),
report on behalf of a larger European GRB Collaboration:
Using the ALFOSC on the 2.5m Nordic Optical Telescope, we have
obtained further R-band imaging of the Optical Transient
(OT) of GRB 000926 (GCN #801, #803, #804) on 2000 September
30.83 UT. We also report the results of B-band imaging on
2000 September UT 27.88 - 30.85.
We find the following magnitudes of the OT using R=17.06 and
B=18.50 for the reference star of Halpern et al. (GCN #806,
#824) :
UT
--------------------------
30.83 R=22.45+-0.05
27.89 B=20.41+-0.03
29.86 B=22.83+-0.08
30.85 B=23.46+-0.10
We note that the colour of the OT, B-R=0.95+-0.05 (Halpern
et al., GCN #824), is similar to that of the OT of GRB 000301C
at z=2.04, B-R=0.91+-0.03 (Jensen et al., astro-ph/0005609).
The estimated intrinsic extinction for this OT was in the range
A(V)=0.11-0.35.
- GCN notice #826
The optical counterpart of GRB000926 has been observed using the
CFH12K CCD mosaic camera at the prime focus of the 3.6-m CFH
Telescope for the third night.
One 600s exposure has been obtained with an excellent seeing
(0.5"). Using the new R magnitude of 17.06 by Halpern et al.
(GCN #824) for the reference star, the three R magnitudes of
the GRB for our observations are:
Sept. 29.3075 R = 21.19 +/- 0.05
Sept. 30.3075 R = 22.15 +/- 0.06
Oct. 01.2593 R = 22.57 +/- 0.08
The last observation by Fynbo et al. (GCN #825) and this new
CFHT data point sugest that the GRB is no longer on the decay
reported by Fynbo et al. (GCN #820), Veillet (GCN #823) and
Halpern et al. (GCN #824). We could see a flare out as
suggested by Dar in a private communication (see also
astro-ph/0008474), though more observations would definitely
be welcome at this stage...
A new graph of the light curve in R can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html
D. Kocevski, D. Donovan and G. Luppino are acknowledged for their
help in this observation.
- GCN notice #827
The optical counterpart of GRB000926 has been observed using the
CFH12K CCD mosaic camera at the prime focus of the 3.6-m CFH
Telescope for the fourth night.
One 600s exposure has been obtained with a decent seeing
(0.7"). Using the new R magnitude of 17.06 by Halpern et al.
(GCN #824) for the reference star, the R magnitude of
the GRB is found as:
Oct. 02.2626 R = 22.82 +/- 0.08
The last two days of data from Halpern et al. (GCN #284),
Fynbo et al. (GCN #825), and the previous CFHT measurement
(GCN #826) suggest a new decay phase with a decay rate
of 1.47 +/- 0.10 .
A new graph of the light curve in R can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html
D. Kocevski, D. Donovan and G. Luppino are acknowledged for their
help in this observation.
- GCN notice #829
J. P. Halpern, N. Mirabal (Columbia U.), D. Turnshek
& J. Busche (U. Pittsburgh) report on behalf of the
MDM Observatory GRB follow-up team:
Using the MDM 2.4m, we obtained 5x900 s exposures in the
R band centered on Oct. 2.16 UT. Using the comparison star
previously measured at R = 17.06 (GCN #824), we find for the
OT R = 23.17 +/- 0.09 (1 sigma). This is significantly fainter
than the measurement made by Veillet just after ours (GCN #827,
R = 22.82 +/- 0.08 on Oct. 2.26), which constitutes an interesting
discrepancy. Our own measurement is consistent with a constant
decay slope alpha = -2.33 +/- 0.07 after day 2, and would predict
that R = 23.9 +/- 0.1 on Oct. 4.0 UT.
This image and an updated decay curve are posted at
http://www.astro.columbia.edu/~jules/grb/000926
- GCN notice #830
The optical counterpart of GRB000926 has been observed using the
CFH12K CCD mosaic camera at the prime focus of the 3.6-m CFH
Telescope for the fifth night on Oct. 3.2304 .
Following GCN #829 by Halpern et al., a more accurate reduction of the
CFHT data has been made, with the problems encountered when none of the
observations is made in photometric reduction.
A fist full reduction of the images leads to a more constant slope.
The change seen previously in the decay rate (GCN #825, #826 and #827) doesn't
seem to be real. Even if there are still discrepancies between the MDM and
CFHT data, there are now smaller, thanks to the work on the secondary
reference stars made by F. Vrba (USNO).
The 5 nights of observations at CFHT lead to a decay slope of 2.16 +/- 0.03
but it's not really possible to link accurately the CFHT magnitudes to others
as long as there is no calibration of the field stars made.
A graph of the light curve in R from CFHT observations can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html
where more information on the photometric reductions can be found.
An accurate photometric calibration of stars 1 and 2 (see the image
on the web page) is definitely needed.
L. Wells, D. Woodworth and J. Luthe are acknowledged for their
help in this observation.
- GCN notice #831
The optical counterpart of GRB000926 has been observed using the
CFH12K CCD mosaic camera at the prime focus of the 3.6-m CFH
Telescope for the sixth night on Oct. 4.25 .
The two images were with variable transparency and poor seeing conditions
(0.9 to 1").
Star 2 (see GCN #830 and the web page referenced below) is used as a
reference with R=20.36 for the following photometric data:
Sept. 29.3075 21.23 0.03
30.3075 22.10 0.04
Oct. 1.2593 22.71 0.04
2.2626 23.13 0.08
3.2304 23.45 0.10
4.2500 23.73 0.15
T is in UTC days after Sept. 0 . R magnitudes are given with their uncertainty.
A photometric check on stars 1 and 2 leads to mg1 - mg2 = 0.658 +/- 0.01
over the 6 nights of observations.
A graph of the light curve in R from CFHT observations can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html
as well as the last image of the OT vanishing in the background...
We are done at CFHT with the observations of the OT itself. The observing
time used for GRB000926 has been taken from allocated time to
colleagues from Canada and Hawaii who are once more acknowledged,
with for last night special thanks to M. Brodwin.
The field will be imaged again when CFH12K will be on the telescope for
a final photometric calibration before running the last analysis and
publishing the data.
This run has been more hectic than the one on GRB000301C. Sorry for that...
Aloha!
- GCN notice #832 = BeppoSAX mail 00/21
L. Piro (BeppoSAX Mission Scientist, IAS/CNR Roma) & L. A. Antonelli (OaR)
report on behalf of the BeppoSAX team:
A BeppoSAX TOO observation of GB000926 started on Sept. 29.00, i.e.
2 days after the GRB and lasted for 12 hrs.
Effective exposure times were MECS(1.6-10 keV): 20 ksec, LECS(0.1-10
keV):5 ksec.
We confirm the relatively bright unknown source identified as the X-ray
afterglow by Piro (GCN 812)
The revised position is:
RA(2000)=17h 04m 07s Decl.(2000)= +51 47' 18"
with an error radius of 50", consistent with the previous preliminary
position distributed in GCN 812 and with the optical counterpart
(Gorosabel et al. GCN 803, Dall et al. GCN 804, Halpern et al. GCN 806).
The average flux of the source in the MECS(1.6-10 keV) is (4.1+/-0.6)
10^-3 cts/s, corresponding to a F(1.6-10 keV)=(4.8+-0.7) 10^-13 erg/cm2/s.
The spectrum is consistent with a power law with photon index=(1.9+/-0.7)
and absorption by our Galaxy (NH=2.7 10^20 cm-2).
The BeppoSAX observation occured in coincidence with the break of the
optical light curve reported e.g by Fynbo (GCN820), Veillet (GCN 823) and
Halpern et al (GCN824). In the X-ray band the source exhibits a
substantial decay, decreasing by a factor of (1.7+/-0.5) in 6 hours. This
would correspond to a power law decay F= c(T-T0)^d_X (where T0=26.99)
with slope d_X=-4.3+/-1, i.e. steeper that that measured in the
optical after the break (d_O=-2.5+/-0.2, Halpern et al., GCN 824).
This behaviour is not immediately consistent with a jet-expansion, that
predicts d_X=d_O. Chandra data, taken few hours after the end of the
BeppoSAX observation, shall be crucial in confirming the X-ray light
curve.
- GCN notice #833 = BeppoSAX mail n.00/23
L. Piro (BeppoSAX Mission Scientist, IAS/CNR Roma) & L. A. Antonelli (OaR)
report on behalf of the BeppoSAX team:
We have found an error in the application of a conversion factor which
underestimates the fluxes distributed in GCN n.832
The correct value of the average flux (at T=29.25) is
F(1.6-10 keV)= (2.6+\-0.6) 10^-13 erg/cm2/s
We have also carefully checked different background subtraction methods,
finding that the corresponding systematic effect amouts to less than about
15%. This has been included in the flux error quoted above.
All the other results on the fading behaviour and on the spectral
shape presented in GCN 832 remain unaffected.
- GCN notice #834 = BeppoSAX mail n.00/24
L. Piro (BeppoSAX Mission Scientist) reports:
The observation of the X-ray afterglow of GRB000926 reported by Piro et
al. in BeppoSAX mails n. 00/21, 00/22, 00/23 and GCN n. 812 , 832, 833 was
performed as a BeppoSAX Project TOO (i.e. the equivalent of Director
Discretionary Time) and as such falls under the responsibility of the
BeppoSAX Mission Scientist. These data are usually property of the
BeppoSAX team.
However, taking into account the considerable interest of this GRB, we
have decided to make these data immediately public to the scientific
community.
Reduced data sets (image, spectrum, light curve) and cleaned photon list
can be accessed through the BeppoSAX archive at:
http://www.sdc.asi.it/archive/00000059/
- GCN notice #836
G. Garmire and A. Garmire (Penn State U), L. Piro ( IAS/CNR Roma) and M.R.
Garcia (CfA):
A Chandra X-ray Observatory TOO observation of the afterglow from GRB000926
began September 29.67375 and ended
on 29.85125, but with a total good time of observation of 9979s.
The source position determined by CXO is:
RA(2000)=17h 04m 09.6s Decl. (2000)= +51 47' 8.6"
with an uncertainty of ~2", consistant with the optical position by Gorosabel
et al. GCN 803, Dall et al. GCN 804, Halpern et al. GCN 806.
The average flux of the source is (3.08+/-.017) 10^-2 cts/s, corresponding to a
flux F(1.6-10 keV)=(9.4+/-0.95)10^-14 erg/cm2/s.
The spectrum is found to fit a powerlaw with powerlaw index =(1.76+/-0.2)
consistant with
the slope of Piro et al. GCN 832, and the absorption by our Galaxy
(NH=2.7 10^20 cm-2).
This very large decrease in flux in such a short time is unprecedented,
decreasing by a factor of ~3 in only ~12 hours from the BeppoSAX measurement!
To obtain a better measure of the slope with time for a law of the
form F=c(T-T0)^d_X with T0=26.99 will require a more refined analysis,
since taking average values leads to a slope of -5!
- GCN notice #840
J. P. U. Fynbo (ESO), M. I. Andersen (University of Oulu),
J. Gorosabel (DSRI, Copenhagen),
J. Hjorth, B. L. Jensen, H. Pedersen (University of Copenhagen),
T. Pursimo, M.T. Hanski (University of Turku),
R. Oestensen, J.-E. Solheim (University of Tromsoe) report:
Using the ALFOSC on the 2.5m Nordic Optical Telescope we have obtained
further R-band imaging of the Optical Transient (OT) of GRB 000926
(GCN #801, #803, #804) on 2000 October 2.84 and 6.87 UT.
We find the following magnitudes of the OT using R = 17.06 for the
reference star of Halpern et al. (GCN #806, #824):
Date (UT) R
------------------------------
Oct 2.84 23.28 +- 0.13
Oct 6.87 23.87 +- 0.25
The emission at the position of the OT in the Oct 6.87 image is (although
at low signal-to-noise ratio) significantly elongated with a position angle
of about 90 degrees. This indicates a contribution from a galaxy, possibly
the GRB host. The light-curve shape also indicates a flattening consistent
with a late time decay slope of alpha=2.5+-0.15 and an underlying galaxy
with a magnitude of about R=24. An updated light-curve based on the NOT
points only can be found at:
http://www.ifa.au.dk/~jfynbo/grb/grb000926/GRB000926_lc.gif
- GCN notice #844
Janet A. Mattei, AAVSO Director, reports:
On the evening of September 28 UT, in response to an alert on the
AAVSO's GRB mailing list, Joe Dellinger, Fort Bend Astronomy Club
(FBAC), Texas, took a sequence of unfiltered CCD images of the
GRB000926 field. He used the FBAC's 46 cm reflector at the Houston
Museum of Natural Science's George Observatory, and an SBIG ST-9e
camera on generous loan from Rice University. He could not see any
optical transients on individual four-minute images when comparing
them with a DSS-derived finder chart.
Fellow FBAC member Bill Dillon combined the best seven of Joe's
four-minute images into an equivalent 28 minute image. The combined
image's UT mid-point time was 03:16:16. From positions and annotated
images reported by professional astronomers, he realized that the OT had
been imaged, near the threshold of detection. Using Astrometrica and
the USNO-A2.0 catalog, the OT's position was measured at:
RA 17h 04m 09.76s,
DEC +51d 47' 10.6"
with a magnitude of roughly 19.1.
On the evening of October 3 UT, Randy Pepper and Bill Dillon did
follow-up imaging of the GRB000926 field using the same telescope and
camera. The OT had faded below detectability on a image made by
combining 31 one-minute exposures.
Joe, Bill, and Randy are all members of the FBAC's Gamma Ray Burst
Extended Team, formed as the result of the NASA-MSFC/AAVSO High Energy
Astrophysics Workshop held this April in Huntsville, Alabama.
More information and imagery associated with this detection are
available at
http://www.geocities.com/amicustellarum/grb/grb000926.html
- GCN notice #850
E. Rol, P. M. Vreeswijk (U. of Amsterdam) and N. Tanvir (U. of
Hertfordshire), on behalf of a larger collaboration, report:
We have obtained Sloan i and Harris R & V band images of the field of
GRB 000926 (GCN #801), using the Wide Field Camera on the 2.5m Isaac
Newton Telescope at La Palma. Using aperture photometry (with a radius
twice the FWHM), we find the magnitude of the OT, relative
to the reference star of Halpern et al. (GCN #824), to be as follows:
date (UT) filter rel-mag error exp-time
(Sept 2000) (secs)
- ------------------------------------------------
27.919 i 2.406 0.007 300
27.924 i 2.439 0.007 300
27.929 i 2.454 0.008 300
30.850 i 5.403 0.009 600
27.892 R 2.369 0.007 300
27.896 R 2.386 0.007 300
27.901 R 2.396 0.008 300
27.906 V 2.271 0.009 300
27.910 V 2.298 0.009 300
27.915 V 2.301 0.010 300
30.839 V 5.352 0.096 600
(errors are statistical only)
We have fitted the R band data, together with all published data (GCNs
#809, #814, #816, #819, #820, #824, #825, GCN #829, #831, #840), with a
smoothly broken power-law, and a constant flux (presumably from the
underlying host galaxy). The fitted function is
F(t) = { F_1^(-n) + F_2^(-n) }^(-1/n) + F_host,
with F_i = k_i t ^(-a_i), n > 0; i = 1, 2.
a_1 and a_2 correspond to the early and late time power-law indices,
respectively. The break time t_0 corresponds to the time when F_1 = F_2.
(see e.g. Beuermann, K., et al 1999, A&A, 352, L26-L30)
We obtain the following parameters for the R band data, with n fixed at 1:
a_1 = 1.1 +- 0.2
a_2 = 3.2 +- 0.4
t_0 = 2.0 +- 0.4
host: R = 24.2 +- 0.3
Errors are 1 sigma; chi^2/DOF = 69/31. Excluding the host,
we find a chi^2/DOF = 83/32.
The fit shows a rather large increase in the decay-rate of the OT flux
around two days after the burst (from a power-law index of 1.1 to
3.2). Fitting for n as well (which can be used to define the
sharpness of the break) gives the same results as above, with n = 1.1
+- 0.8.
Graphs of these fits can be found at
http://www.astro.uva.nl/~evert/grb000926/ (and reproduced below)
We acknowledge the help of the observers Chris Blake and Steve Rawlings
(U. of Oxford), and the ING staff.
Our R band data (filled circles), together with R band data collected from
literature (GCNs #809, #814, #816, #819, #820, #824, #825, #829, #831, #840).
A smoothly broken power-law fit with an underlying host-galaxy is indicated as
the continous line in the graph. The dashed line shows the decay of the OT
only.
- GCN notice #851
Sandra M. Castro, S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, T. J. Galama,
F. A. Harrison (Caltech), and D. A. Frail (NRAO), report on behalf of a
large collaboration:
We analysed high-resolution spectra of the optical afterglow of GRB 000926
kindly obtained at the WMKO Keck-II telescope by L. Cowie, A. Barger, et al.
on UT 2000 September 29.26, using the ESI instrument (an Echelle spectrograph).
Our preliminary analysis yields a single absorption system including the
following lines: Si II 1526.7, C IV 1548.2 and 1550.5, Al II 1670.8, Si II
1808.0, Al III 1854.7 and 1862.8, Zn II 2026.1, Fe II 2344.2, 2373.7, 2382.8,
2586.6, and 2600.2, Mg II 2796.3 and 2803.5, and Mg I 2853.0. The mean
redshift is z = 2.0369 +- 0.0007, presumably corresponding to the system
identified by Fynbo et al. (GCN 807) as having z ~ 2.066. However, we see
no evidence for any other absorption systems in these data; in particular,
the ostensible system at z = 1.378 proposed by Fynbo et al. is likely due to
line misidentifications.
We note that the line equivalent widths appear to be unusually strong in
comparison to the general population of metallic line absorbers seen in the
spectra of quasars, suggesting a high column density and/or metallicity of
the intervening gas. A more detailed analysis is in progress.
- GCN notice #871
J. P. U. Fynbo, P. Moller (ESO, Garching)
I. Burud (University of Liege), M. I. Andersen (University of Oulu),
J. Gorosabel (DSRI, Copenhagen),
J. Hjorth, B. L. Jensen, H. Pedersen (U. of Copenhagen) report :
Using the ALFOSC on the 2.5m Nordic Optical Telescope, we have
obtained 4700sec of further R-band imaging of the Optical Transient
(OT) of GRB 000926 (GCN #801, #803, #804) on 2000 October 27.
The seeing was 1.1 arcsec.
Near the position of the OT we detect extended emission, which most
likely is from the host galaxy of GRB000926. There are several knots of
emission. One of these knots coincides with the precise position of the
OT. The magnitude of the galaxy measured in a circular aperture with
diameter 5.7 arcsec is about R=23.9 in good agreement with estimates
based on the flattening of the OT light-curve (GCN #840, #850).
A 10.5x10.5 arcsec^2 section of the combined R-band image centred on
the position of the OT (marked by a circle) can be seen at
http://www.astro.ku.dk/~brian_j/grb/grb000926.
- GCN notice #1088
F. A. Harrison, T. J. Galama, J. S. Bloom, S. M. Castro,
S. R. Kulkarni (Caltech) report on behalf of the CIT-NRAO-CARA
collaboration:
"We have obtained HST WFPC2 images of the host of GRB 000926 in three
filters. The observations spanned from UT May 19 19.63 - 19.86 2001, 238
days after the event. The images reaveal a compact knot of emission the
center of which is consistent with the location of the optical transient.
We interpret this to be the host galaxy of GRB 000926. The knot is
reasonably bright, corresponding to about 25 mag in R, and appears to be
marginally extended, with a FWHM of 0.3 arcsec."
An image of the host may be found at:
http://www.srl.caltech.edu/~fiona/grb000926host.eps
This message may be cited.
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