The influence of the Insight-HXMT/LE time response on timing analysis

Abstract

The LE is the low energy telescope that is carried on Insight-HXMT. It uses swept charge devices (SCDs) to detect soft X-ray photons. LE’s time response is caused by the structure of the SCDs. With theoretical analysis and Monte Carlo simulations we discuss the influence of LE time response (LTR) on the timing analysis from three aspects: the power spectral density, the pulse profile and the time lag. After the LTR, the value of power spectral density monotonously decreases with the increasing frequency. The power spectral density of a sinusoidal signal reduces by a half at frequency 536 Hz. The corresponding frequency for quasi-periodic oscillation (QPO) signals is 458 Hz. The root mean square (RMS) of QPOs holds a similar behaviour. After the LTR, the centroid frequency and full width at half maxima (FWHM) of QPOs signals do not change. The LTR reduces the RMS of pulse profiles and shifts the pulse phase. In the time domain, the LTR only reduces the peak value of the cross-correlation function while it does not change the peak position; thus it will not affect the result of the time lag. When considering the time lag obtained from two instruments and one among them is LE, a 1.18 ms lag is expected caused by the LTR. The time lag calculated in the frequency domain is the same as that in the time domain.