XMM-Newton Science Analysis System


phasecalc (dscalc-2.9) [xmmsas_20230412_1735-21.0.0]

Description

Given an ephemeris and a list of event tables, phasecalc calculates the phase of each event in each of the tables. The calculated values are stored in a column named PHASE. If the column exists it is overwritten.

phasecalc relies on the event table having a TIME column and the two attributes MJDREF and TIMEZERO.

• MJDREF is the Modified Julian Day from which times are calculated.

• TIMEZERO is the clock correction at the start of the observation in seconds.

• phasecalc also uses the TIMESYS keyword to determine the Time System (UTC, TT, TAI) used in event table. If the TIMESYS keyword is not UTC, the Reference Epoch time of the ephemeris is converted to the appropriate Time System. In the absence of this keyword TT (XMM Time) is assumed.

The time of event n is then:

  $$t(n) = \texttt{MJDREF} * 86400 + \texttt{TIMEZERO} + \texttt{TIME}[n]$$ (1)

where $\texttt{TIME}[n]$ is the value stored in the TIME column.

An ephemeris is specified in terms of four quantities:

• reference epoch $t_0$; This is UTC.
• reference phase $\phi_0$;
• frequency $\nu$ in Hz;
• frequency time derivative $\dot{\nu}$ in Hz/s.

The phase of event n is defined as:

  $$\phi(n) = \phi_0 + \{ t(n) - t_0 \} \times \nu + \frac{1}{2} \{ t(n) - t_0 \}^2 \times \dot{\nu}\,.$$ (2)