March 2    (posted on March 2)
 
 

(click on the image to zoom) This is a combination of two 10 mn images  using MOS in imaging mode  (EEV detector 0.28"/pixel - seeing ~0.8") The OT is in the center of the image

 

GCN #1003

GRB010222 - Optical observation and decay

The optical counterpart of GRB010222 has been observed using the
CFHT Multi Object Spectrograph in imaging mode at the Cassegrain
focus of the 3.6-m CFH Telescope on the night of March 1 to 2.

Two 10 mn images were obtained with a seeing of about 0.8".

Photometric reduction made as outlined on GCN #1000 leads to:

Mar. 2.641   R = 23.10 +/- 0.10

The index of the power law decay fitting the R light curve data
since 0.6 days after the burst (including the revised and new
measurements by Holland et al. in GCN #1002) is 1.25 +/- 0.03,
the same as our previous determination (Veillet, GCN #1000) and
not significantly different from the GCN #1002 value.

While a few objects are now seen in a radius of 4", the OT is
still a point like object.

More information (with the new images of the OT) can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html

M. Pakull, L. Mirioni, and J. McDonald are acknowledged for their
help  in this observation.

This message may be cited.
 
 

March 1    (posted on March 1)
 

(click on the image to zoom and get a larger field) This is a combination of two 10 mn images  using MOS in imaging mode  (EEV detector 0.28"/pixel - seeing ~0.8") The OT is in the center of the image... 1 is the star like object used for overall consistency check  of the field with Henden's list (GCN #987). 2 is the object used for faint object photometry quality.

GCN #1000

GRB010222 - Optical observation and decay

The optical counterpart of GRB010222 has been observed using the
CFHT Multi Object Spectrograph in imaging mode at the Cassegrain
focus of the 3.6-m CFH Telescope on the night of Feb. 28 to March 1.

Two 10 mn images were obtained in much better conditions than
the night before (GCN #998) with a seeing of about 0.8".  There are
only a few point like sources in the vicinity of the OT. A star like
object ~11" S of the OT has been carefully measured with respect
to the two stars used in GCN #998 and has a very consistent R
magnitude on the MOS exposures (R = 20.13 +/- 0.02). A fainter
object 8" from the OT is used for internal consistency checks at
R = 22.35.

Precise reduction of the images from Feb. 28 and March 1 gives the
following results:

Feb. 28.653 UTC   R = 22.73 +/- 0.10
Mar. 01.628 UTC   R = 22.96 +/- 0.10

The index of the power law decay given in GCN #998 is not
significantly modified and found as 1.25 +/- 0.06.

There is not structure found on the OT, which is still seen as a
point source on the March 1 combined image.

More information (with the new images of the OT) can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html

M. Pakull, L. Mirioni, and J. McDonald are acknowledged for their
help  in this observation.

This message may be cited.

(click on the image for a larger field) One image has  been taken at the end of the night (10 mn in R) using MOS in imaging mode  (EEV detector 0.28"/pixel - seeing ~1.5") The OT is in the center of the image...

GCN #998

GRB010222 - Optical observation and decay

The optical counterpart of GRB010222 has been observed using the
CFHT Multi Object Spectrograph in imaging mode at the Cassegrain
focus of the 3.6-m CFH Telescope on the night of Feb. 27 to 28.

One image was obtained in relatively poor conditions (seeing ~ 1.5").
A preliminary reduction using stars (223.008250,43.006507) and
(223.098277,42.994077) from Henden's list (GCN #987) gives:

Feb. 28.653 UTC   R = 22.60 +/- 0.15

The relative photometry of the two stars used is consistent
with our image within 0.02 magnitudes. Using all the measurements
of the R magnitude of the OT published in the GCN's (corrected if
needed to put them back in the photometric system of Henden's list),
the R magnitude is following a nice power law decay with an index of
1.20 +/- 0.07 since 0.6 days after the burst.

An image of the OT and a graph of the decay are available at
http://www.cfht.hawaii.edu/~veillet/grb.html

S. Lilly and J. McDonald are acknowledged for their help in
this observation.

This message may be cited.