  In this work, we study theoretical and observational issues about pulsars
(PSRs), pulsar wind nebulae (PWNe) and supernova remnants (SNRs). In
particular, the spectral modeling of young PWNe and the X-ray analysis of SNRs
with magnetars comparing their characteristics with those remnants surrounding
canonical pulsars.
  The spectra of PWNe range from radio to $\gamma$-rays. They are the largest
class of identified Galactic sources in $\gamma$-rays increasing the number
from 1 to $\sim$30 during the last years. We have developed a detailed spectral
code which reproduces the electromagnetic spectrum of PWNe in free expansion
($t_{age} \lesssim$10 kyr). We shed light and try to understand issues on time
evolution of the spectra, the synchrotron self-Compton dominance in the Crab
Nebula, the particle dominance in PWNe detected at TeV energies and how
physical parameters constrain the detectability of PWNe at TeV. We make a
systematic study of all Galactic, TeV-detected, young PWNe which allows to find
correlations and trends between parameters. We also discuss about the spectrum
of those PWNe not detected at TeV and if models with low magnetized nebulae can
explain the lack of detection or, on the contrary, high-magnetization models
are more favorable.
  Regarding the X-ray analysis of SNRs, we use X-ray spectroscopy in SNRs with
magnetars to discuss about the formation mechanism of such extremely magnetized
PSRs. The alpha-dynamo mechanism proposed in the 1990's produces an energy
release that should have influence in the energy of the SN explosion. We extend
the work done previously done by \cite{vink06} about the energetics of the SN
explosion looking for this energy release and we look for the element
ionization and the X-ray luminosity and we compare our results with other SNRs
with an associated central source.
