Gamma Ray Burst optical follow-up program
    C. Veillet (CFHT)  - M. Boer  (CESR)


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.

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March 14   (posted on Mar. 14)

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.

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March 11   (posted on Mar. 11)

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.

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March 7   (posted on Mar. 7)

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.

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March 5   (posted on Mar. 5)

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).


R image - 600s
 

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.

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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.

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March 3   (posted on Mar. 3)

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).

  B image - 900s

R image - 600s
 
 

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.

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GRB990123 observations are here...