  Despite over 50 years of research, many open questions remain about the
origin and nature of GRBs. Polarization measurements of the prompt emission of
these extreme phenomena have long been thought to be the key to answering a
range of these questions. The POLAR detector was designed to produce the first
set of detailed and reliable polarization measurements in an energy range of
approximately 50-500 keV. During late 2016 and early 2017, POLAR detected a
total of 55 GRBs. Analysis results of 5 of these GRBs have been reported in the
past. The results were found to be consistent with a low or unpolarized flux.
However, previous reports by other collaborations found high levels of
polarization. We study the polarization for all the 14 GRBs observed by POLAR
for which statistically robust inferences are possible. Additionally,
time-resolved polarization studies are performed on GRBs with sufficient
apparent flux. A publicly available polarization analysis tool, developed
within the 3ML framework, was used to produce statistically robust results. The
method allows to combine spectral and polarimetric data from POLAR with
spectral data from the Fermi GBM and Swift-BAT to jointly model the spectral
and polarimetric parameters. The time integrated analysis finds all results to
be compatible with a low or zero polarization with the caveat that, when
time-resolved analysis is possible within individual pulses, we observe
moderate polarization with a rapidly changing polarization angle. Thus,
time-integrated polarization results, while pointing to lower polarization are
potentially an artifact of summing over the changing polarization signal and
thus, washing out the true moderate polarization. Therefore, we caution against
over interpretation of any time-integrated results and encourage one to wait
for more detailed polarization measurements from forthcoming missions such as
POLAR-2 and LEAP.
