COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 2948

                                                 Konkoly Observatory
                                                 Budapest
                                                 24 October 1986

                                                 HU ISSN 0374 - 0676


       POSSIBLE OPTICAL COUNTERPART TO THE GRBS
                1979 MARCH 25B (1810+31)

A preliminary evaluation of the data obtained by checking
1733 plates from the Sonneberg Observatory collection
(Central Institute for Astrophysics of the Academy of
Sciences of the GDR) has revealed a possible optical
counterpart to the gamma ray burst source (GRBS) 1979
March 25b. The data represents about 1807 hours (nearly
0.2 year) of cumulative exposure.
   The object was detected on 3 different plates at the
same position. The preliminary coordinates are RA =
18h09m27 +- 3 s, d = + 31d23.0' +- 0.5' ( 1950.0 ). The plates
were taken on 1946 March 27, 1946 August 31 and 1954 April
27. In all three cases, the images of the object exhibit
structure somewhat different from those of stars, indicating
short flash as a possible explanation of these images. The
position of the object is closely outside (about 6.5 arcmin
away from the centre) the error box given by Laros et al.
(1985).
   Preliminary estimated blue magnitudes for 1 sec optical
flash lie in the range 4-7, resulting in possible gamma
ray to optical fluency ratios E_gamma/E_o of order 10^2 to 10^3
   The position of the object proved to be empty on the POSS prints
indicating enormous amplitude of brightening and, consequently,
eliminating the possibility that the object is a classical
variable star.
   As the object appears on 3 independent plates at the same
position, its reality seems to be considerably more certain
than the reality of images found previously by other authors
on only one plate. Nevertheless, great variety of properties
of photographic emulsion being taken into account, we cannot
yet be absolutely sure that the images detected indeed represent
the true optical counterparts to GRBS.


                         R. HUDEC

                Department of Space Astroph.
                   Astronomical Institute
                      251 65 Ondrejov
                      Czechoslovakia



Reference:

Laros, J. et al., 1985, Ap. J. 290, 728. [BIBCODE 1985ApJ...290..728L ]