booklet format - inaf iasf bologna

A.A. 2011/2012
Temporal Data Analysis
Figure B.4: The Cen X–3 pulse profile, obtained by folding the original data with the best trial
period.
B.4 Variability in the Pulse Period
Up to now we have assumed that the pulse period is constant, but this is not always true! Indeed,
many X–ray pulsars show changes of their spin period as a function of time, and this effect
must be taken into account when determining the best pulse period. We will study this effect
on the X–ray binary pulsar XTE J1946+274, observed by the Indian X–ray satellite IXAE. First, let
us find the pulse period by means of the efsearch program without any period derivative (as
we did in the previous example on Cen X–3).
orma> efsearch
efsearch 1.1 (xronos5.22)
Ser. 1 filename +options (or @file of filenames +options)[] XTE_1946+274_ixae.lc
Series 1 file 1:XTE_1946+274_ixae.lc
WARNING: Defaulting to first FITS extension
Selected FITS extensions: 1 - RATE TABLE;
Source ............ Start Time (d) .... 11723 18:03:40.786
FITS Extension .... 1 - ‘ ‘ Stop Time (d) ..... 11732 16:47:25.887
No. of Rows ....... 32469 Bin Time (s) ...... 1.020
M.Orlandini 143