**2.11. Correlations with Abell Clusters, Quasars and Supernovae**

Various attempts to search for a correlation between GRBs and other astronomical objects led to null result. For example, Blumenthal & Hartmann [172] found no angular correlation between GRBs and nearby galaxies. They concluded that if GRBs are cosmological then they must be located at distances larger than 100 Mpc. Otherwise, they would have shown a positive correlation with the galaxy distribution.

The only exception is the correlation (at 95% confidence level)
between GRBs at the 3B catalog and Abell clusters
[77,
173].
This correlation has been recently confirmed by Kompaneetz & Stern
[174].
The correlation is
strongest for a subgroup of strong GRBs whose position is accurately
known. Comparison of the rich clusters auto-correlation with the
cross-correlation found suggests that ~ 26 ± 15% of the
accurate position GRBs sub-sample members are located within
600 *h*^{-1} Mpc. Recently Schartel *et al. *
[176]
found that a group of 134 GRBs with position error radius smaller than
1.8° are correlated with radio quiet quasars. The probability of
of such correlation by chance coincidence is less than 0.3%.

It should be stressed that this correlation does not imply that there is a direct association between GRBs and Abell clusters, such as would have been if GRBs would have emerged from Abell clusters. All that it means is that GRBs are distributed in space like the large scale structure of the universe. Since Abell clusters are the best tracers of this structure they are correlated with GRBs. Therefore the lack of excess Abell Clusters in IPN error boxes (which are much smaller than BATSE's error boxes) [175] does not rule out this correlation.