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[vsnet-grb-info 416] XRF020903: TNG and Asiago photometry
TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 1563
SUBJECT: XRF020903: TNG and Asiago photometry
DATE: 02/10/03 08:43:21 GMT
FROM: Stefano Covino at Brera Astronomical Observatory <covino@merate.mi.astro.it>
Covino S., Malesani D., Ghisellini G., Stefanon M., Tavecchio F. (INAF-OAB),
Covone G., Fugazza D. (INAF-TNG), Di Paola A., Israel G.L. (INAF-OAR),
Mannucci F. (IRA-CNR), Masetti N. (IASF-CNR), Pian E. ((INAF-OAT), on behalf
of a larger Italian collaboration, report:
We observed the varying source (VS) in the field of XRF 020903 (Ricker et al.,
GCN 1530; Soderberg et al., GCN 1554) on Oct 1.9 UT, with the Italian 3.5m
TNG telescope, using BVRI filters. Seeing conditions were moderate (about 1.5
arcsec) and airmass about 1.6. Magnitudes were derived by PSF fitting
photometry. One standard star field was also observed under clear (but not
photometric) conditions; therefore a small zeropoint offset is still
possible. The magnitudes for the VS are the following:
Filter UT Magnitude
-----------------------------
B 1.941 21.87 +- 0.06
V 1.932 21.14 +- 0.04
R 1.916 20.60 +- 0.09
I 1.919 20.29 +- 0.07
For comparison, we also report the magnitudes of some nearby USNO stars;
U0675_37142330 is named "star 1" in Soderberg et al. finding chart.
U0675_37143953 U0675_37141960 U0675_37142330
----------------------------------------------
B 18.54 +- 0.02 19.51 +- 0.02 17.14 +- 0.01
V 17.77 +- 0.01 19.02 +- 0.01 16.40 +- 0.01
R 17.21 +- 0.04 18.63 +- 0.04 15.92 +- 0.03
I 16.81 +- 0.03 18.36 +- 0.03 15.58 +- 0.03
Based on the photometry performed at the TNG, we re-analyzed data obtained on
Sep., 29.9 UT with the Asiago telescope (GCN 1561). Seeing conditions were
mediocre (about 2 arcsec) and airmass about 2. Magnitudes were again derived
by PSF fitting photometry. We report the following results for the VS:
Filter UT Magnitude
-----------------------------
V 29.923 20.94 +- 0.12
R 29.931 20.42 +- 0.10
I 29.937 19.98 +- 0.13
The source has simultaneously faded by about 0.2 mag in all V, R and I bands
between Sep 29.9 and Oct 1.9. Comparing with the R-band measurement by
Soderberg et al. on Sep 28.3, the source appears fainter by more than 1
magnitude.
A color-color diagram, together with a BVRI spectrum and a light curve are
shown at the web page: http://www.merate.mi.astro.it/~malesani/XRF020903 .
The values reported here supersede those in our GCN 1561, that were based on a
misidentification of the reference star. We apologize for any inconvenience
this may have caused.
Detailed analsys of these data is still in progress, and more observations
will be performed in the next few days.
This message may be cited.
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