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HRDuration Correlation
Another result confirming a propery already known from the BATSE catalog
is the correlation between hardness ratio (HR) and duration: in particular,
short GRBs look harder than long ones, as it can be seen from
fig. .
In the GRBM case, the HR here considered, is the weighted average
of the HRs of the single GRBM units (eq. ),
where each HR expresses the
ratio of the 100 keV counts over the 40700 keV counts;
although these bands are strongly correlated (owing to the common
100700 keV counts),
nevertheless short GRBs are significantly harder, as
it can be seen in fig. ; in this figure, the error bars
have been omitted for clarity. In fig. ,
only the GRBs with HR at least significant and with
HR uncertainties lower than have been included;
here the error bars are reported as well.
Figure:
HRDuration Correlation of 501 () and 497 ()
GRBM bursts. In the upper panel, duration is expressed in terms
of , while has been used in the lower panel.

The mean HR has been computed for the different duration classes: the
mean HR is
and
for short and
long GRBs, respectively.
This property, originally discovered by BATSE, is therefore confirmed
independently by the GRBM catalog.
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Cristiano Guidorzi
20030731