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\IBVShead{4496}{16 July 1997}

\title{Observation of the optical counterpart of}\\
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\title{the GRB 970508 source}

\begintext

  With the aid of the 60/90/180 cm Schmidt telescope of the Konkoly Observatory
we obtained CCD images of the gamma ray source which was detected by the 
BeppoSAX Gamma-Ray Burst Monitor on May 8.904 UT, 1997. We used a Photometrics, 
AT200 CCD camera having a 1536 x 1024 pixel KAF 1600 MCII coated CCD chip 
displaying a 29 arcminute x 18 arcminute area of the sky with an angular 
resolution of nearly 1 arcsecond/pixel. The images were taken on the nights 
15/16 May 1997 (5 frames each 10 minutes exp. time)  and 31 May/01 June 1997  (6 frames each 15 minutes exp. time).  
  
In order to reduce the background noise and to reach as faint limiting
magnitude as possible we coadded the frames taken on one particular night 
(Figure 1 and Figure 2). 
Filters were not used for the imaging. Based on the spectral 
sensitivity distribution of the chip, the brightness values represent
close to R magnitudes. To estimate the brightness of the optical counterpart 
of the GRB 970508 we compared its intensity to the nearby star 13 arcsec north,
R=19.7 (Schaefer et al., 1997) marked as ``c" in Figures 1 and 2.  
  

During our observations we made positive identification of the source on the 
night 15/16 May 1997 and a negative one on the night 31 May/01 June 1997, 
which means that we could not identify any visible object in the 
previous position of the optical counterpart imaged two weeks before. 
Because the limiting magnitude of our coadded frame was 23.5 $\pm$ 0.2 magnitude 
we conclude that the object has faded below this brightness level.

The light curve based on the data listed in Table 1 is shown in Figure 3.

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Figure 1.
CCD image of the optical counterpart of the GRB 970508. 
Date of the exposure for the coadded image is 15.994 May 1997 
(J.D. 2450584.494)
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\centerline{2}
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Figure 2. CCD image of the optical counterpart of the GRB 970508.  
Date of the exposure for the coadded image is 01.001 Jun. 1997
(J.D. 2450600.501)
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Figure 3. R lightcurve of the optical counterpart of the GRB 970508 based 
on the brightness data published in the IAU Circulars (see References). 
The x represents the brightness estimation made at the Konkoly Observatory
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\centerline{3}
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\centerline{Table 1. Brightness data of the GRB 970508 in the R band} 
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\begin{tabular}{lllll}
\hline
Date UT. &     J.D.  &           m(R) &     err. &        source\\
(1997 May)&  2450000+&                &           &              \\
\hline            
   09      & 577.500         &   21.2   &   .1  &          Galama et al., 1997\\
   09      & 577.500         &   21.4   &   .05 &          Schaefer et al., 1997\\
   09.128  & 577.628         &   20.8   &   .2  &          Castro-Tirado et al., 1997\\
   09.19   & 577.690 (Gunn r)&   21.33  &   .1  &          Djorgovski et al., 1997a\\
   09.195  & 577.695 (Gunn r)&   21.2   &   .15 &          Djorgovski et al., 1997b\\
   09.89   & 578.390         &   21.1   &   .15 &          Kopylov et al., 1997\\
   09.899  & 578.399         &   20.8   &   .2  &          Castro-Tirado et al., 1997\\
   10      & 578.500         &   20.3   &   .02 &          Schaefer et al., 1997\\
   10      & 578.500         &   20.35  &   .1  &          Galama et al., 1997\\
   10.178  & 578.678 (Gunn r)&   20.18  &   .07 &          Djorgovski et al., 1997b\\
   10.23   & 578.730 (Gunn r)&   20.17  &   .05 &          Djorgovski et al., 1997a\\
   10.77   & 579.270         &   19.87  &   .08 &          Kopylov et al., 1997\\
   10.85   & 579.350         &   19.78  &   .05 &          Mignoli et al., 1997\\
   10.872  & 579.372         &   19.6   &   .2  &          Castro-Tirado et al., 1997\\
   10.93   & 579.430         &   19.92  &   .08 &          Kopylov et al., 1997\\
   11      & 579.500         &   20.0   &   .1  &          Galama et al., 1997\\
   11      & 579.500         &   20.47  &   .03 &          Schaefer et al., 1997\\
   11.198  & 579.698 (Gunn r)&   20.16  &   .06 &          Djorgovski et al., 1997b\\
   11.21   & 579.710 (Gunn r)&   20.15  &   .05 &          Djorgovski et al., 1997a\\
   11.76   & 580.260         &   20.18  &   .08 &          Kopylov et al., 1997\\
   11.868  & 580.368         &   20.4   &   .2  &          Castro-Tirado et al., 1997\\
   12.03   & 580.530         &   20.2   &   .1  &          Groot et al., 1997\\
   12.195  & 580.695 (Gunn r)&   20.53  &   .06 &          Djorgovski et al., 1997b\\
   12.21   & 580.710         &   20.47  &   .09 &          Garcia et al., 1997\\
   12.87   & 581.370         &   20.77  &   .08 &          Kopylov et al., 1997\\
   13.18   & 581.680 (Gunn r)&   20.76  &   .15 &          Djorgovski et al., 1997c\\
   13.88   & 582.380         &   21.01  &   .08 &          Kopylov et al., 1997\\
   14.40   & 582.900         &   21.1   &   .2  &          Chevalier et al., 1997\\
   15.99   & 584.494         &   21.5   &   .2  &          present paper\\
Jun 1.00   & 600.501         &   23.5   &   .2  &          present paper (upper limit)\\
\hline
\end{tabular}
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\beginauthors
\authorsrightcol
J\'anos KELEMEN
Konkoly Observatory
H-1525 Budapest, Box 67
\endauthors
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\references

Castro-Tirado, A.J.  et al., 1997, {\it IAU Circular}, No.\,6657

Chevalier, C. et al., 1997, {\it IAU Circular}, No.\,6663

Djorgovski, S.G. et al., 1997a, {\it IAU Circular}, No.\,6655

Djorgovski, S.G. et al., 1997b, {\it IAU Circular}, No.\,6658

Djorgovski, S.G. et al., 1997c, {\it IAU Circular}, No.\,6660

Galama, T.J. et al., 1997, {\it IAU Circular}, No.\,6655

Garcia, M. et al., 1997, {\it IAU Circular}, No.\,6661

Groot, P.J. et al., 1997, {\it IAU Circular}, No.\,6660

Kopylov, A.I. et al., 1997, {\it IAU Circular}, No.\,6663

Mignoli, M. et al., 1997, {\it IAU Circular}, No.\,6661

Schaefer, B. et al., 1997, {\it IAU Circular}, No.\,6658


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\centerline{4}
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\centerline{\ft CORRIGENDA}
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Correction to IBVS No.\,4418:
In order to bring to accordance Table 1 and Figure 2, it is necessary to
interchange star's Nos.\,4 and 5 in Table 1 and to attribute No.\,6 to 
that one of two stars with number 5 in Figure 2 that has coordinates Xpixel=359 and Ypixel=341.
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\hfill Y. Malakhova

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The eclipsing binary nature of NSV\,07457 (see IBVS No.\,4365) was 
discovered earlier by J. Vandenbroere (IBVS No.\,3946), see also
Diethelm's note published in IBVS No.\,4011.
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\hfill The Editors


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