GRB000301C observations |
April 4 (posted on Apr. 4))
The candidate for the optical transient (OT) associated with the
gamma ray burst GBR000301C has been observed using the CFH12K mosaic camera
at the prime focus of the CFH Telescope.
Click on the image for a composite of three 12mn exposures in R
and a comparison with the field on March 11.
Photometry and considerations on the decay are in the following circular.
GCN 623
GRB000301C - R magnitude lower limit
The candidate for the optical transient (OT) associated
with the gamma
ray burst GRB000301C has been observed
using the CFH12K CCD mosaic
camera at the prime focus of the 3.6-m CFH Telescope
in the course of
the French GRB follow-up program
at CFHT (M. Boer, CESR, C. Veillet,
CFHT).
Three 12mn exposures with moderate seeing (image
quality around 0.9") have
been coadded.
There is nothing visible at the location of the
OT. The nearby galaxy
(thought to be the host for some time before
the HST observations) has a
magnitude of R= 24.5 +-0.1, confirming the previous
determinations (GCN 592
- GCN598).
The faintest objects detected in the neighborhood
are at around R=26.
We can infer the following lower limit:
R > 26.0 on 2000 April 4.6
It is compatible with the alpha = -2.7 power law
decay given in GCN611, and
not with alpha = -2.1 given earlier, which
would lead to R~25.6 at the
same epoch.
Further imaging is planned if the seeing gets better.
Jean-Charles Cuillandre is acknowledged for his help in this observation.
This message may be cited.
The candidate for the optical transient (OT) associated with the gamma ray burst GBR000301C has been observed using a STSIS2 detector on OSIS (the Optically Stabilized Imager and Spectrograph) at the Cassegrain focus of the 3.6-m Telescope.
Two 30mn images in R and one 55mn image in B have been taken, using again OSIS in imaging mode. Seeing was still decent (0.7 to 0.8").
This graph shows the two power laws which fit
reasonably well the data published so far.
What to include in a given phase is a choice
which impacts strongly on the values of the power law exponent alpha...
It is clear however that a more accurate processing
of the data would allow a better study of the behaviour of this GRB, which
is probably not described with only two power laws anyway!
Photometry and considerations on the decay are in the following circular.
GCN 611
GRB000301C - B and R photometry
The candidate for the optical transient (OT)
associated with the gamma ray burst
GRB000301C has been observed in imaging mode
with OSIS on the 3.6-m CFH Telescope
in the course of the French GRB follow-up
program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
The OT has the following magnitude, using star A (GCN573) photometry (GCN583):
R = 23.82 +/- 0.10 2000 March
14.60 (UTC)
(two 30mn exposures)
B = 24.83 +/- 0.12 2000 March
14.60 (UTC)
(one 55mn exposure)
The power-law decay described with alpha =
-2.1 +/- 0.1 (GCN610) is not sufficient
to account properly for the last four measurements
(GCN598, 604, 610 and this GCN),
which are better fit with alpha = -2.7 +/-
0.1 . The first phase of the decay would
cover the first four days after the burst,
with alpha = -0.91 +/- 0.08.
A graph with these two consecutive power
laws, as well at the new images, are at
http://www.cfht.hawaii.edu/~veillet/grb.html
As for the apparent B-R, the error bars are
large enough to make it identical
to the value determined using MOS on March
3.5 (0.86 +/- 0.06) or the one
published by Halpern (0.77 +/- 0.06 in GCN585
a week ago).
As the GRB is still steadily decaying, it's
unlikely to have the underlying galaxy
contributing significantly to the measured
flux. This galaxy should probably be
fainter than R = 24.5, confirming the comment
by Fruchter et al. (GCN602) from HST
imaging data (R >~ 24).
A 20 micron camera will be installed on the
telescope today for 10 nights. No new
data on this GRB will be acquired during
this period.
Aloha from Hawaii!
I. Gable is acknowledged for his help in this observation.
This message may be cited.
The candidate for the optical transient (OT) associated with the gamma ray burst GBR000301C has been observed using a STSIS2 detector on OSIS (the Optically Stabilized Imager and Spectrograph) at the Cassegrain focus of the 3.6-m Telescope.
One image in R has been taken with a good seeing (0.6"). Note that the instrument is now OSIS instead of MOS. Scale is 0.15"/pixel (instead of 0.4"/pixel on MOS).
Photometry and considerations on the decay are in the following circular.
GCN 610
GRB000301C - R photometry
The candidate for the optical transient (OT)
associated with the gamma ray burst
GRB000301C has been observed in imaging mode
with OSIS on the 3.6-m CFH Telescope
in the course of the French GRB follow-up
program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
The OT has the following magnitude, using star A (GCN573) photometry (GCN583):
R = 23.02 +/- 0.10 2000 March 11.63 (UTC)
The power-law decay observed lately (after
4 days after the burst, as described
by Halpern et al. GCN604) can now be described
with alpha = 2.1 +/- 0.1.
Note that alpha is dependent on the choice
of the start of the "new decay" and
on the inclusion or not of some of the measurements
from Bernabei et al.(GCN599).
In case you read the introduction too fast,
the instrument used is no longer MOS,
but OSIS. The detector is the same though
(STIS2).
The new image is available at
http://www.cfht.hawaii.edu/~veillet/grb.html
.
M. Pakkul is acknowledged for his help in this observation.
This message may be cited.
The candidate for the optical transient (OT) associated with the gamma ray burst GBR000301C has been observed using a STSIS2 detector on MOS at the Cassegrain focus of the 3.6-m Telescope.
One image has been made in R in reasonably good seeing conditions (around 1 arcsecond).
The faint source found on March 5 is clearly seen at the same position on its new image.
A composite image of the two 600s exposures taken on March 5
and 7...
Photometry of the OT and considerations on the faint source are given
in the following circular.
GCN 598
GRB000301c - R photometry and nearby faint source confirmation
The candidate for the optical transient (OT)
associated with the gamma ray burst
GRB000301c has been observed in imaging mode
with MOS on the 3.6-m CFH Telescope
in the course of the French GRB follow-up
program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
The OT has the following magnitude, using star A (GCN573) photometry (GCN583):
R = 21.70 +/- 0.07 2000 March 7.65 (UTC)
This value does not fit very well with the
the R magnitudes published in the
previous GCN, in particular by Mohan(595),
if we assume a power law common
to all observations. In fact, the best fit
of the data published so far is
obtained with a linear magnitude decay
of 0.32 +/- 0.02 mg/day...
The acceleration in the decay in K (GCN596)
seems also to be seen in R.
More data, as well as a careful reanalysis
of the existing images, are
clearly needed!
The faint source found on March 5 (GCN592),
recognized in GCN594 as identical
to the one detected in IR at NASA IRTF, is
definitely there also
on the March 7 image. A composite of the
two images is available at
Its R magnitude is measured as 24.3 +/- 0.3
, to be refined with further
analysis.
S. Lilly is acknowledged for his help in this observation.
This message may be cited.
The candidate for the optical transient (OT) associated with the gamma ray burst GBR000301c has been observed using a STSIS2 detector on MOS at the Cassegrain focus of the 3.6-m Telescope.
One image has been made in R in good seeing conditions (seeing better than 0.8 arcsecond).
Corresponding photometry and considerations
on host galaxy detection have
been summarized in the following two GCN circulars.
GCN 592
GRB000301c - Host galaxy not detected in R (?)
The candidate for the optical transient (OT)
associated with the gamma ray burst
GRB000301c has been observed in imaging mode
with MOS on the 3.6-m CFH Telescope
in the course of the French GRB follow-up
program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
The R image mentioned in GCN588 has been examined
for a possible detection
of the galaxy observed in the near IR (GCN586-587).
Nothing is detected at the reported position
(1"E 2"N). The detection limit in
this area of the field is at R~25.
The OT itself has no significant elongation compared to nearby stars.
"Something" is detected at -1"E 2"N though,
which could only be catalogued
as a real object through another exposure.
It was not visible on the
previous R image taken on March 3.5 due to
a much poorer seeing (~1.5").
Its magnitude (if real) is 24.7 +/- .3 .
Should I add thet deeper imaging is needed?...
D. Elbaz and H. Flores are acknowledged for their help in these observations.
This message may be cited.
GCN 588
GRB000301c optical observations
The candidate for the optical transient (OT)
associated with the gamma ray burst
GRB000301c has been observed in imaging mode
with MOS on the 3.6-m CFH Telescope
in the course of the French GRB follow-up
program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
An R image has been taken with a good seeing
(better then 0.8 arcsecond).
Relative photometry with respect to the reference
star A (GCN573) using
GCN583 photometry is as following
R = 20.86 +/- 0.04 2000 March 5.63 (UTC)
It is significantly different from the prediction
based on a temporal decay
slope alpha = -1.07 +/- 0.09 (GCB581) and
seems to confirm the flattening of the
decay rate suggested in the same circular.
More data would be welcome though!
The relative photometry in B and R published
in GCN575 becomes, using GCN583 data:
B = 21.11 +/- 0.04 2000 March
3.50 (UTC)
R = 20.27 +/- 0.04 2000 March
3.51 (UTC)
and B-R = 0.84 +/- 0.06 at the same date,
to be compared with 0.77 +/- 0.06
on March 4.52 (GCN585).
D. Elbaz and H. Flores are acknowledged for their help in these observations.
This message may be cited.
The candidate for the optical transient (OT) associated with the gamma ray burst GBR000301c has been observed using a STSIS2 detector on MOS at the Cassegrain focus of the 3.6-m Telescope.
Two images have been made (900s in B and 600s in R).
Message sent for publication in the GCN series
GRB000301c optical observations
The candidate for the optical transient (OT)
associated with the gamma ray burst
GRB000301c has been observed in imaging mode
with MOS on the 3.6-m CFH Telescope
in the course of the French GRB follow-up
program at CFHT (M. Boer, CESR,
C. Veillet, CFHT).
Relative photometry in B and R with respect
to the reference star A (GCN573)
is as following:
delta B = 1.29 +/- 0.05
2000 March 3.50 (UTC)
delta R = 2.19 +/- 0.05
2000 March 3.51 (UTC)
The R magnitude inferred from star A magnitude
determination in GCN573
is 20.24 +/-.07, in good agreement with the
GCN 573 value of R = 20.28 +\- 0.05
measured at the same epoch.
B and R images can be found at
http://www.cfht.hawaii.edu/~veillet/grb.html
B calibrations will be made tonight if no
multicolor photometry is made available
for reference stars in the field.
D. Elbaz and H. Flores are acknowledged for their help in these observations.
This message may be cited.
GRB990123 observations are here...