*7.2. Instrumental Selection Effects*

A still open issue is the instrumental selection effects that may affect the observed GRB energy or luminosity correlations. There are at least two kinds of issues due to (a) the trigger threshold, i.e., the minimum photon peak flux that a burst must have in order to be detected by a given instrument, and (b) the spectral analysis threshold, i.e., the minimum fluence to perform a reliable spectral analysis and determine the SED parameters.

Several analyses have been performed in the literature, using different samples and correlations of GRBs and searching for outliers and inconsistent GRBs. Several conclusions were drawn: (a) some correlations may exist, though due to selection effects; (b) other correlations may exist when accounting for the intrinsic scatter; and (c) some correlations may have statistical significance, though affected by the thresholds of GRB detectors, etc. See Ref. [144], for more details. Interestingly, using the time-resolved spectra, similar correlations were found in individual bursts, strongly supporting the fact that the correlations may be physical [64].
