Deep Chandra observations of TeV binaries I: LSI +61 303
  We report on a 95ks Chandra observation of the TeV emitting High Mass X-ray
Binary LSI +61 303, using the ACIS-S camera in Continuos Clocking mode to
search for a possible X-ray pulsar in this system. The observation was
performed while the compact object was passing from phase 0.94 to 0.98 in its
orbit around the Be companion star (hence close to the apastron passage). We
did not find any periodic or quasi-periodic signal (at this orbital phase) in a
frequency range of 0.005-175 Hz. We derived an average pulsed fraction 3 sigma
upper limit for the presence of a periodic signal of ~10% (although this limit
is strongly dependent on the frequency and the energy band), the deepest limit
ever reached for this object. Furthermore, the source appears highly variable
in flux and spectrum even in this very small orbital phase range, in particular
we detect two flares, lasting thousands of seconds, with a very hard X-ray
spectrum with respect to the average source spectral distribution. The X-ray
pulsed fraction limits we derived are lower than the pulsed fraction of any
isolated rotational-powered pulsar, in particular having a TeV counterpart. In
this scenario most of the X-ray emission of LSI +61 303 should necessarily come
from the interwind or inner-pulsar wind zone shock rather than from the
magnetosphere of the putative pulsar. Furthermore, we did not find evidence for
the previously suggested extended X-ray emission (abridged).
