Abstract
Recently, the Large High Altitude Air Shower Observatory (LHAASO) reported
the discovery of 12 ultrahigh-energy (UHE; $\mathrm{\varepsilon} \ge 100$ TeV)
gamma-ray sources located in the Galactic plane. A few of these UHE gamma-ray
emitting regions are in spatial coincidence with pulsar wind nebulae (PWNe). We
consider a sample of five sources; two of them are LHAASO sources (LHAASO
J1908+0621 and LHAASO J2226+6057) and the remaining three are GeV-TeV gamma-ray
emitters. In addition, X-rays, radio observations, or upper limits are also
available for these objects. We study multiwavelength radiation from these
sources by considering a PWN origin, where the emission is powered by the
spin-down luminosity of the associated pulsars. In this leptonic emission
model, the electron population is calculated at different times under the
radiative (synchrotron and inverse-Compton) and adiabatic cooling. We also
include the onset of the reverberation phase for the PWN, by assuming radially
symmetric expansion. However, in this work, we find that multiwavelength
emission can be interpreted before the onset of this phase. The maximum energy
of the electrons based on the spectral fit is found to be above 0.1 PeV and
close to 1 PeV. For LHAASO J2226+6057, using its observations in radio to UHE
gamma-rays, we find that UHE gamma-rays can be interpreted using electrons with
maximum energy of 1 PeV. We estimate the upper limits on the minimum Lorentz
factor of the electrons and it also infers the minimum value of the
pair-multiplicity of charged pairs.