We studied the effect of the external magnetic field and photon flux on
timing jitter in photon detection by straight superconducting NbN nanowires. At
two wavelengths 800 and 1560 nm, statistical distribution in the appearance
time of the photon count exhibits Gaussian shape at small times and exponential
tail at large times. The characteristic exponential time is larger for photons
with smaller energy and increases with external magnetic field while variations
in the Gaussian part of the distribution are less pronounced. Increasing photon
flux drives the nanowire from quantum detection mode to the bolometric mode
that averages out fluctuations of the total number of nonequilibrium electrons
created by the photon and drastically reduces jitter. The difference between
Gaussian parts of distributions for these two modes provides the measure for
the electron-number fluctuations. Corresponding standard deviation increases
with the photon energy. We show that the two-dimensional hot-spot detection
model explains qualitatively the effect of magnetic field