GRB 050801.769 : Optical photometry and decay index

GRB 050801.769 :

Left: Finding chart for GRB 050801.769.
        R:3x600s image taken at Aug 2.0, 2005 UT, (FWHM~1.2").
        The WCS-solution is calibrated to 12 nearby 2MASS-stars, with an uncertainity of +-0.1".
Right: R-band lightcurve for GRB 050801.769
        The first measurement (open circle at t=0.02d) is the last ROTSE-IIIc detection
        reported by Rykoff et al. (GCN#3726).
        The three measurements at t=0.2d (closed circles) are from Fynbo et al. (GCN#3735),
        the measurement at t=1.2d (closed circle) is from Fynbo et al. (GCN#3743).

NUMBER:  3743
SUBJECT: GRB050801.769: Unchanged decay slope
DATE:    05/08/03 10:00:32 GMT

J. P. U. Fynbo, B. L. Jensen, J. Hjorth, K. G. Woller, D. Watson, J. Sollerman (Niels Bohr Institute), P. Fouque (Obs-MiP, Toulouse), M. I. Andersen (Potsdam, AIP) report on behalf of the DARK Cosmology Centre:

"We have obtained additional DK-1.5m R-band imaging (Aug 3.0 UT) of the optical afterglow (Rykoff et al. GCN#3726) of GRB 050801.769 (Band et al. GCN#3725). Extending the fit from Fynbo et al. (GCN#3726) yields a smooth well-fitting power-law from t-t0=0.44h to 29.5h, with an R-band decay slope of -1.31 +- 0.04.

The lightcurve is shown at:

http://www.astro.ku.dk/~brian_j/grb/grb050801.769/ "

NUMBER:  3735
SUBJECT: GRB050801.769 : Optical photometry and decay index
DATE:    05/08/02 15:01:05 GMT

J. P. U. Fynbo, B. L. Jensen, J. Hjorth, K. G. Woller, D. Watson (Niels Bohr Institute), P. Fouque (Obs-MiP, Toulouse), M. I. Andersen (Potsdam, AIP) report on behalf of the DARK Cosmology Centre:

"We obtained BVR-band imaging of the XRT error circle of GRB050801.769 (Band et al. GCN#3725, Perri et al. GCN#3731) with the Danish 1.5m (La Silla) on Aug. 2.0 UT (approx. 6hr after the burst). We detect the optical afterglow candidate source reported by Rykoff et al. (GCN#3726), with position (RA, Dec)(J2000.0)

13:36:35.363, -21:55:42.03

Based on a preliminary std. star calibration, we obtain the following photometry of the afterglow candidate:

Date (UT):  Filter: Exptime: Mag.
Aug 1.997   B       600s     22.36+-0.05
Aug 2.012   V       600s     21.03+-0.05
Aug 1.989   R       600s     20.75+-0.04
Aug 2.005   R       600s     20.87+-0.04
Aug 2.020   R       600s     20.94+-0.05

(in this calibration, we obtain B=20.95, V=19.74, R=19.63 for the star at:

(RA, Dec) = (13:36:33.657, -21:55:29.55)).

Fitting a power-law to our three R-band data points gives a lightcurve, which intersects the R=17.29 ROTSE-III (Rykoff et al. GCN#3726) data point at t-t0=1590s, to within the errors of that data point. Including the ROTSE-III data point in the fit, we find an R-band decay slope of -1.29 +-0.05.

A findingchart of the field is shown at:

http://www.astro.ku.dk/~brian_j/grb/grb050801.769/ "

Last updated on August 03, 2005, by Brian Lindgren Jensen