  The broad-band X-ray observations of the youngest known galactic supernova
remnant, G1.9+0.3, provide unique information about the particle acceleration
at the early stages of evolution of supernova remnants. Based on the publicly
available X-ray data obtained with the Chandra and NuSTAR satellites over two
decades in energy, we derived the energy distribution of relativistic electrons
under the assumption that detected X-rays are of entirely synchrotron origin.
The acceleration of electrons was found to be an order of magnitude slower than
the maximum rate provided by the shock acceleration in the nominal Bohm
diffusion regime. We discuss the implications of this result in the context of
contribution of SNRs to the Galactic Cosmic Rays at PeV energies.
