One of the science goal of the Athena mission is to detect and characterise, in the X-ray domain, transits of
hot Jupiter-like planets orbiting their parent stars. To date, the only candidate for this kind of studies is HD
189733b, a Jupiter-size planet in a 2d orbit, for which a transit depth of 6-8% has been observed accumulating
several Chandra and XMM-Newton observations.
We simulate in this work realistic light curves of exoplanet transits using the Athena end-to-end simulator,
SIXTE, and derive the expected signal-to-noise ratios (SNR) for different instrument configurations and planetary
system parameters. We first produce
at light curves for the currently existing WFI instrument designs and
for different source fluxes to extract the expected (white noise) standard deviation. Next, moderate levels of
correlated noise and transits of different depths are added to the light curves.
As expected, for pure white noise the SNR is proportional to the square root of the flux, to the light curve
bin size and to the number of co-added transits, and by definition proportional to the transit depth. When
correlated noise starts to be significant, rebinning the data will only slightly increase the SNR, depending on the
noise characteristics. Considering only white noise, a transit observed in a source like HD 189733, that has a flux around 5x10-13 erg s-1 cm-2 and a transit depth of about 5% can be detected with a SNR>3 in a unique
transit. With correlated noise, several transits might be necessary.
We also simulate trapezoidal shaped transits and try to recover the ingress/egress times after addition of
noise. The relative error on the fitted ingress times is below 10% for most of the light curves with SNR>1.