DC2 Software Workshop

1
Progress on Pulsar Tools Development

• Masaharu Hirayama (GLAST SSC, GSFC/UMBC)
• James Peachey (GLAST SSC, HEASARC)

2
Typical Pulsar Analysis

• Download data and screen events.
• For maximum pulse-detection sensitivity, select
  only events within a small region, typically size
  of a couple of PSFs.
• Correct event times barycentric correction.
• To cancel Doppler effect resulting from the
  orbital motions of the Earth and the spacecraft.
• Find pulsar ephemeris at the time of observation.
• Option 1 Use a radio ephemeris as is.
• Option 2 Scan pulse frequencies around
  extrapolation of radio ephemeris.
• Option 3 Search for pulsations even if no radio
  ephemeris is available.
• Calculate pulse phase for each photon.
• Use pulse phases in your analysis.
• Pulse shape (or pulse profile)
• Phase-resolved spectrum
• Phase-resolved image

3
Pulsar Tools Components

• Pulsar ephemerides database (D4)
• List of pulsar timing solution maintained during
  the mission for potential LAT sources.
• Downloadable as a FITS file.
• Pulsar ephemeris extractor gtpsearch (U11)
• Basic front end to the pulsar ephemerides
  database.
• Photon arrival time converter glbary/gtbary (U10)
• Converts photon arrival times in a photon list to
  those at the solar system barycenter.
• Pulsar phase assignment pulsePhase/gtpulsephase
  (U12)
• Assigns pulse phase to each photon in a photon
  list.
• Pulsar profile periodicity tests gtpsearch (A3)
• Epoch-folds photon arrival times at trial pulse
  frequencies and estimate significance of
  pulsation at each frequency.
• Pulsar period search gt??? (A4)
• Searches for periodic emission from a point
  source.

4
Pulsar Tools In Action
gtpulsardb
Ephemeris extract (U11)
Pulsar ephemerides (D4)
gtpulsephase
Pulsar phase assign (U12)
fv
Satellite position history (D2)
Pulse profile (A3)
TIME PULSE_PHASE

Arrival time correction (U10)
gtbary
Data sub- selection (U2)
Event Summary FITS File (D1)
Likelihood (A1)
Pulsar period search (A4)
Periodicity test (A3)
gtpsearch
gt???
5
Major Design Changes Since 9/2002 Review

• Binary demodulation (arrival time correction for
  binary pulsars) will be performed on the fly.
• Originally this task was assigned to photon
  arrival time converter (U10). This had the
  following problems
• The FITS standards for photon lists have no
  support for binary-demodulated times.
• For U10 an existing tool (FAXBARY in FTOOLS) was
  adopted for use with GLAST data, and it does not
  support binary demodulation.
• As of the end of build 9 it is performed in pulse
  phase assignment (U12), periodicity tests (A3),
  and period search (A4).
• Single TIME column in an event file.
• Original plan was to include multiple time
  columns in event files, in order to preserve
  original event times while performing time
  corrections. This had the following problems
• The HEASARC standards for an event file assume a
  single time column. (Desired HEASARC compliance).
• Existing analysis tools may recognize TIME column
  only.

6
Current Status of Development
Design Existing counterparts Implementation Testing
Ephemerides database Defined in detail Identified Examples available Used in ST checkout 2
Ephemeris extractor Complete None Complete Done
Arrival time converter Algorithms identified Identified Complete Done
Phase assignment Algorithms identified Identified Complete for solitary pulsars Done
Pulse profile period scan Algorithms identified Identified Complete for solitary pulsars Done
Period search Algorithms identified Identified After DC2 Not yet
7
Data Challenge 2

• Ready for Data Challenge 2
• Pulsar ephemerides database (D4)
• Database format defined and examples available.
• Ingest protocol defined.
• Extractor (U11) available.
• Photon arrival time converter (U10)
• Pulse phase assignment (U12) for solitary pulsars
• Pulsar periodicity tests (A3) for solitary
  pulsars
• Will be ready by Data Challenge 2
• Arrival time corrections for binary pulsars
• Pulsar periodicity tests (A3)
• Pulse phase assignment (U12)
• Major tasks beyond Data Challenge 2
• Pulsar period search (A4) re-use of FTOOLS
  counterparts?
• Bayesian approach for periodicity tests (A3)

8
Further Developments

• Ephemeris computer
• Reads pulsar ephemerides database (D4) and
  compute pulsar-related parameters (such as pulse
  frequency) at a given moment in time.
• Also serves as a sanity checker for first-time
  users of our pulsar ephemerides database (D4).
• User-interface
• GUI under development for all SAE tools.
• Web interface for database extractor?
• Orbital phase assignment
• To assign an orbital phase to each photon (just
  like a pulse phase for each photon).
• Pulse phase assignment tool (U12) is a natural
  candidate to do this task.

9
Backup Slides
10
Pulsar Tools
Pulsar ephem. (D4)
Data in
Pulsar period search (A4)
Ephemeris extract (U11)
Event display (UI1)
Level 0.5
Pulsar profiles (A3)1
LAT Point source catalog (D5)
Pulsar phase assign (U12)
Arrival time correction (U10)
Data extract (U1)
Level 1 (D1)
Source model def. tool (U7)
Src. ID (A2)
Catalog Access (U9)
Exposure calc. (U4)
Pt.ing/livetime extractor (U3)
Pointing/livetime history (D2)
Likelihood (A1)
Astron. catalogs (D6)
Alternative source for testing high-level analysis
Alternative for making additional cuts on
already-retrieved event data
Interstellar em. model (U5)
Map gen(U6)
IRFs (D3)
Observation simulator (O2)
Data sub- selection (U2)
GRB unbinned spectral analysis (A9)
IRF visual- ization (U8)
Pt.ing/livetime simulator (O1)
Pt.ing/livetime extractor (U3)
GRB spectral-temporal modeling (A10)
GRB LAT DRM gen. (U14)
GRB spectral analysis (A8)2
GRB visual- ization (U13)
GRB rebinning (A6)2
GRB temporal analysis (A7)2
GRB event binning (A5)
11
Algorithms

• Periodicity tests
• Chi-squared test (Leahy et al. 1983, ApJ 266,
  160 Vaughan et al. 1994, ApJ 435, 362)
• Zn2 test (Buccheri et al. 1983, AA 128, 245)
• Rayleigh test (equivalent to Zn2 test for n 1)
• H test (De Jager et al. 1989, AA 221, 180)
• Bayesian approach (Gregory and Loredo 1992, ApJ
  398, 146 Gregory and Loredo 1996, ApJ 473, 1059)
  
• Period search
• Discrete Fourier transforms (Ransom 2002, AJ 124,
  1788)
• Lomb-Scargle periodogram (Lomb 1976, ApSS 39,
  447 Scargle 1982, ApJ 263, 835 Press Rybicki
  1989, ApJ 338, 277)

12
Pulsar Ephemerides Database (D4, U11)

• Full definition of D4 FITS file complete.
• Similar to the CGRO catalog, with some
  improvements.
• Ephemerides ingest protocol defined.
• Ephemerides extractor tool (U11) available.
• Examples of D4 FITS file available.
• Contents based on the CGRO catalog.
• To be used in Data Challenge 2.
• Action items
• Discuss on ephemerides data ingest with the
  pulsar IDS.

13
Photon Arrival Time Converter (U10)

• Existing counterparts identified.
• FAXBARY seems to be re-usable for GLAST.
• FAXBARY FTOOLS originally developed for XTE, now
  available for other missions such as Swift.
• FAXBARY modified to adopt to GLAST data.
• Tested with simulated data in Science Tools
  checkout 2.
• To be used in Data Challenge 2.
• Action items
• Deliver to the LAT team as a part of the HEADAS
  package.

14
Pulsar Phase Assignment (U12)

• Basic functionality implemented and tested.
• Single set of frequency ephemeris can be given.
• Multiple ephemerides can be read from database
  (D4).
• Probably already good enough for Data Challenge
  2.
• To be used in Data Challenge 2.
• Action items
• Implement arrival time corrections for binary
  pulsars.

15
Pulsar Profile Periodicity Tests (A3)

• Basic functionality implemented and tested.
• Single set of initial frequency ephemeris can be
  given by a user or read from database (D4).
• Good enough for Data Challenge 2.
• To be used in Data Challenge 2.
• Most of periodicity tests implemented and tested.
• Chi-squared test (Leahy et al. 1983, ApJ 266,
  160 Vaughan et al. 1994, ApJ 435, 362)
• Zn2 test (Buccheri et al. 1983, AA 128, 245)
• Rayleigh test (equivalent to Zn2 test for n 1)
• H test (De Jager et al. 1989, AA 221, 180)
• Action items
• Implement arrival time corrections for binary
  pulsars.
• Identify periodicity tests to be implemented (if
  any).

16
Pulsar Period Search (A4)

• Suggested algorithms for period search.
• Discrete Fourier transforms (Ransom 2002, AJ 124,
  1788)
• Lomb-Scargle periodogram (Lomb 1976, ApSS 39,
  447 Scargle 1982, ApJ 263, 835 Press Rybicki
  1989, ApJ 338, 277)
• Existing counterparts identified.
• powspec (XRONOS) calculates power spectrum
  density
• perdgrm (FTOOLS) computes Lomb-Scargle
  periodogram
• Action items
• Test existing tools with GLAST data format.
• Implement Python wrapper if needed.

17
Pulsars for GLAST LAT

• Pulsars are point sources
• GLAST expected to detect pulsations from 50-100
  pulsars
• 10-50 are predicted to be radio quiet like
  Geminga
• Most need 1 year exposure for detection
• Sparse data
• One photon per 500 pulses (Crab 30 MeV 300 GeV)
• Scanning with large FOV
• All sources get some exposure every day
  throughout a year
• Large number of short observations

18
What Pulsar Tools Are Needed?

• Barycentric corrector
• Photon arrival time converter glbary/gtbary (U10)
• Pulsar ephemeris finder
• Case 1 use a radio ephemeris as is.
• Pulsar ephemerides database (D4)
• Pulsar ephemeris extractor gtpulsardb (U11)
• Case 2 scan around a radio ephemeris.
• Pulsar profile periodicity tests gtpsearch
  (A3)
• Case 3 search for pulsations.
• Pulsar period search gt??? (A4)
• Pulse phase calculator
• Pulsar phase assignment pulsePhase/gtpulsephase
  (U12)