Science capabilities of EP:
- Monitoring a large fraction of the whole sky at high cadences in soft X-rays.
- Detection and classification of transients by real-time processing of WXT data on-board.
- Triggering the satellite to slew to positions where the transients are centered to the FoV of FXT to perform follow-up observations automatically.
- Fast downlink of transient alert data.
- Pointed observations of targets of opportunity triggered by other facilities.
TABLE 1 Some of the specifications
|Number of modules||8||1|
|Focal length (mm)||375||1,400|
|Angular resolution (arcmin)||＜5||＜5|
|Banpass (keV)||0.5-4 keV||0.5-4 keV|
|Energy resolution @1keV||40%||100eV|
|Effective area (central focus) (cm^2)||3 @0.7KEV||60 @1keV|
|Sensitivity (erg/s/cm^2 @1ks)||~ 1e-11||~ 3e-12|
The estimated sensitivity of WXT is shown in Figure 1. The sensitivity is calculated based on the effective area of WXT, assuming a power-law X-ray spectrum with a photon index gamma=2 and Galactic absorption of the column density NH=3E20/cm^2. The effective area is obtained by simulations, using the Q-software developed by the SRC at Leicester University, for the Lobster-eye type optics with a focal length of 375 mm and gas detectors of the GEM (Gas-electron multiplier) type with an entrance window of 1 μm thick polyimide. The grasp (FoV*effective area) of WXT is shown in Figure 2, which is the highest among the previous, current and future missions with focusing X-ray optics.
Figure 1 Sensitivity curves of EP/WXT as a function of integration time for X-ray sources with an assumed power-law photon spectral index of 2 (blue) and 3, respectively (bandpass: 0.5-4.keV; Galactic absorption column density of 3E20 atom/cm^2 is assumed). The shaded area denotes the detecting sensitivity of the ROSAT All-Sky Survey (RASS) in a similar band (0.1-2.4keV).
Figure 2 Grasp of EP/WXT (solid line) and comparison with some other missions of focusing X-ray optics.