The Excess Density of Field Galaxies near z=0.56 around the Gamma-Ray
  Burst GRB021004 Position
  We test for reliability any signatures of field galaxies clustering in the
GRB 021004 line of sight. The first signature is the GRB 021004 field
photometric redshifts distribution based on the 6-m telescope of the Special
Astrophysical Observatory of the Russian Academy of Sciences observations with
a peak near z = 0.56 estimated from multicolor photometry in the GRB direction.
The second signature is the Mg II 2796, 2803AA absorption doublet at z = 0.56
in VLT/UVES spectra obtained for the GRB 021004 afterglow. The third signature
is the galaxy clustering in a larger (of about 3 sq.deg.) area around GRB
021004 with an effective peak near z = 0.56 for both the spectral and
photometric redshifts from a few catalogs of clusters based on the Sloan
Digital Sky Survey (SDSS) and Baryon Oscillation Spectroscopic Survey (BOSS) as
a part of SDSS-III. From catalog data the size of the whole inhomogeneity in
distribution of the galaxy cluster with the peak near z = 0.56 was also
estimated as about 6--8 deg. or 140--190 Mpc. A possibility of inhomogeneity (a
galaxy cluster) near the GRB 021004 direction can be also confirmed by an
inhomogeneity in cosmic microwave background related with the Sunyaev-Zeldovich
effect.
