TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  871
SUBJECT: GRB 000926 : R-image of the host galaxy 
DATE:    00/11/01 17:23:20 GMT

J. P. U. Fynbo, P. Moller (ESO, Garching)

"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 Oktober 27.

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"

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  840
SUBJECT: GRB 000926 : the host galaxy
DATE:    00/10/09 17:12:45 GMT

J. P. U. Fynbo (ESO), M. I. Andersen (University of Oulu),

"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"

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  825
SUBJECT: GRB 000926: optical observations
DATE:    00/10/01 01:16:56 GMT

J. P. U. Fynbo, P. Moller (ESO), J. Gorosabel (DSRI, Copenhagen)

"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."

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  820
SUBJECT: GRB000926 : increasing optical decay slope
DATE:    00/09/30 00:47:57 GMT
FROM:    Johan U. Fynbo at ESO,Garching  

J. P. U. Fynbo, P. Moller (ESO), J. Gorosabel (DSRI, Copenhagen),

"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 http://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.

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  814
SUBJECT: GRB 000926: Lightcurve Update and Predictions
DATE:    00/09/29 13:00:56 GMT

J. Hjorth, B. L. Jensen, and H. Pedersen (U. of Copenhagen),

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/ ."

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  809
SUBJECT: GRB 000926: Preliminary R-band Lightcurve
DATE:    00/09/28 22:35:11 GMT

J. Hjorth, B. L. Jensen, and H. Pedersen (U. of Copenhagen),

"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."

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  807
SUBJECT: Spectroscopic Redshift of GRB 000926
DATE:    00/09/28 14:03:26 GMT

J. P. U. Fynbo, P. Moller (ESO), T. Dall (NOT and U. of Aarhus),

"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".

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  804
SUBJECT: GRB 000926: Optical candidate
DATE:    00/09/28 00:41:00 GMT

T. Dall (NOT and University of Aarhus), J.P.U. Fynbo (ESO),

"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.

RA(J2000)  :  17 04 09.62
Dec(J2000) : +51 47 11.2

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.

Ingvar Svaerdh and Charlotte Moeller are acknowledged for help with the observations."