Deep Chandra observations of TeV binaries - II. LS 5039

We report on Chandra observations of the TeV-emitting high-mass X-ray binary LS 5039 , for a total exposure of ∼70 ks, using the ACIS-S camera in continuous clocking mode to search for a possible X-ray pulsar in this system. We did not find any periodic or quasi-periodic signal in the 0.3-0.4 and 0.75-0.9 orbital phases, and in a frequency range of 0.005-175 Hz. We derived an average pulsed fraction 3σ upper limit for the presence of a periodic signal of ≲15 per cent (depending on the frequency and the energy band), the deepest limit ever reached for this object. If the X-ray emission of LS 5039 is due (at least in part) to a rotational powered pulsar, the latter is either spinning faster than ∼5.6 ms, or having a beam pointing away from our line of sight, or contributing to ≲15 per cent of the total X-ray emission of the system in the orbital phases we observed