The millisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397 shows
radio eclipses over ~40% of its binary orbit. A first Chandra observation
revealed indications for the X-ray flux being orbit dependent as well. In this
work we analysed five data sets of archival Chandra data taken between 2000 and
2007 in order to investigate the emission across the pulsar's binary orbit.
Utilizing archival Chandra observations of PSR J1740-5340, we have performed a
systematic timing and spectral analysis of this binary system. Using a
chi-square-test the significance for intra-binary orbital modulation is found
to be between 88.5% and 99.6%, depending on the number of phase bins used to
construct the light curve. Applying the unbiased statistical Kolmogorov-Smirnov
(KS) test did not indicate any significant intra-binary orbital modulation,
though. However, comparing the counting rates observed at different epochs a
flux variability on times scales of days to years is indicated. The possible
origin of the X-ray emission is discussed in a number of different scenarios.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysic
