Pulsation searches

Note

For a general introduction to HENDRICS’s workflow, please read the Introductory concepts and example analysis tutorial

We have a pulsar observation with, e.g., NuSTAR and we want to find pulsations on it. The general procedure is looking for pulsations using a power density spectrum (see Introductory concepts and example analysis) or similar methods, and if we do find a promising candidate frequency, investigate more with the Epoch Folding or the Z search.

Let’s say we have found a peak in the power density spectrum at about 0.101 seconds, or 9.9 Hz, and we want to investigate more.

We start from the _event_ file. If we have run HENreadevents on the original mission-specific event file, we have a HENRICS-format event file (ending with _ev.nc or _ev.p), e.g.

$ ls
002A.evt 002A_ev.nc

To look for pulsations with the epoch folding around the candidate frequency 9.9 Hz, we can run HENefsearch as such:

$ HENefsearch -f 9.85 -F 9.95 -n 64 --fit-candidates

where the options -f and -F give the minimum and maximum frequencies to search, -n the number of bins in the pulsed profile and with --fit-candidates we specify to not limit the search to the epoch folding, but also look for peaks and fit them to find their centroids.

The output of the search is in a file ending with _EF.nc or _EF.p, while the best-fit model is recorded in pickle files

$ ls
    002A.evt 002A_ev.nc 002A_EF.nc 002A_EF__mod0__.p

To use the Z search, we can use the HENzsearch script with very similar options:

$ HENzsearch -f 9.85 -F 9.95 -N 2 --fit-candidates

where the -N option specifies the number of harmonics to use for the search.

The output of the search and the fit is recorded in similar files as Epoch folding

$ ls
    002A.evt 002A_ev.nc 002A_Z2n.nc 002A_Z2n__mod0__.p

We can plot the results of this search with HENplot, as such:

$ HENplot 002A_Z2n.nc

zn_search.png

Searching for pulsars and measuring frequency derivatives interactively

HENphaseogram is an interactive phaseogram to adjust the values of the frequency and frequency derivatives of pulsars.

phaseogram1.png

phaseogram2.png