  The Be/X-ray binary A 0535+26 showed a normal (type I) outburst in
August/September 2005, which reached a maximum X-ray flux of 400mCrab in the
5-100keV range. The outburst was observed by INTEGRAL and RXTE. The energy of
the fundamental cyclotron line has been measured with INTEGRAL and RXTE at
~45keV. Flaring activity was observed during the rise to the peak of the
outburst. RXTE observations during one of these flares found the energy of the
fundamental cyclotron line shifted to a significantly higher position than
during the rest of the outburst, where it remains constant. Also, the
energy-dependent pulse profiles during the flare differ significantly from the
rest of the outburst. These differences have been interpreted with the presence
of magnetospheric instabilities at the onset of the accretion.
  A decomposition method is applied to A 0535+26 pulse profiles. Basic
assumptions of the method are that the asymmetry observed in the pulse profiles
is caused by a distorted magnetic dipole field, and that the emission regions
have axisymmetric beam patterns. Using pulse profiles obtained from RXTE
observations, the contribution of the two emission regions has been
disentangled. Constraints on geometry of the pulsar and a possible solution of
the beam pattern are given. First results of the comparison of the
reconstructed beam pattern with a geometrical model that includes relativistic
light deflection are presented.
