http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/November 8, 2005 GLAST Users’ Committee Meeting — 1

Overview of Pulsar Tools

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

November 8, 2005 GLAST Users’ Committee Meeting — 2http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/

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

Plot by D.J. Thompson

November 8, 2005 GLAST Users’ Committee Meeting — 3http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/

Typical Pulsar Analysis

1. Download data and screen events.2. Barycentric correction. gtbary

To cancel Doppler effect resulting from the orbital motions of the Earth and the spacecraft.

3. Find pulsar ephemeris at the time of observation. gtephcompOption 1: Use a radio ephemeris as is.Option 2: Scan pulse frequencies around extrapolation

of radio ephemeris. gtpsearch Option 3: Search for pulsations even if no radio

ephemeris is available. (New tool gtpsd).

4. Calculate pulse phase for each photon. gtpphase1. Epoch folding (pulse shape) using fv, fplot, etc.2. Phase-resolved spectrum (or image) gtselect, gtlike

http://glast-ground.slac.stanford.edu/workbook/science-tools/sciTools_Home.htm

November 8, 2005 GLAST Users’ Committee Meeting — 4http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/

Pulsar Tools In Action

Pulsarephemerides (D4)

Satellite positionhistory (FT2)

Pulsar periodsearch (A4)

Pulsar phaseassign (U12)

Periodicitytest (A3)

Arrival timecorrection (U10)

Ephemerisextract (U11)

TIME • • • • • PULSE_PHASE • • •

Event SummaryFITS File (FT1)

Data sub-selection (U2)

Likelihood (A1)

Pulseprofile (A3)

gtpulsardb

gtpphase

gtbary

gtpsearch

fv

gtpsd

November 8, 2005 GLAST Users’ Committee Meeting — 5http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/

GUC Action Item 18

• The methodology will be described for the simple pulsar search tool provided by the standard analysis environment.

• Standard Analysis Environment identifies two tools:– Periodicity tests (A3) gtpsearch already implemented

• Previous measurements provide an estimate of the frequency that may not be accurate for the current data.

– Blind period search (A4) gtpsd? under consideration• Source has not been identified as a pulsar.

• Blind search methodologies are open ended and many are outside the scope of SAE.– Many techniques exist and are still being developed.– Best technique depends strongly on the scientific goal,

and on personal preference.– Powerful techniques are too computationally intensive.

November 8, 2005 GLAST Users’ Committee Meeting — 6http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/

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, A&A 128, 245) – Rayleigh test (equivalent to Zn2 test for n = 1) – H test (De Jager et al. 1989, A&A 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, Ap&SS 39,

447; Scargle 1982, ApJ 263, 835; Press & Rybicki 1989, ApJ 338, 277)

November 8, 2005 GLAST Users’ Committee Meeting — 7http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/

Pulsar period search tool (A4)

• Searches for periodic emission from a point source. – Position of the source is well-known.– No prior knowledge on pulse frequency.– The source is either not in a binary system, or

in a binary system whose binary parameters are known.

Example case: Search for pulsations from EGRET un-identified sources.

• Recommended algorithm for period search.– Discrete Fourier transforms (Ransom 2002, AJ 124,

1788)– Implementation is FFTW (Fastest Fourier Transform

in the West) http://www.fftw.org/

http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/November 8, 2005 GLAST Users’ Committee Meeting — 8

Backup Slides

November 8, 2005 GLAST Users’ Committee Meeting — 9http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/

Utility Tools

• Ephemeris computer gtephcomp– 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).

• Orbital phase assignment gtophase– 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.

• Pulsar ephemerides extraction tool gtpulsardb– To sub-select pulsar ephemerides from a master

database.– Also, used to create, modify, merge pulsar

ephemerides database.

November 8, 2005 GLAST Users’ Committee Meeting — 10http://glast.gsfc.nasa.gov/ssc/dev/psr_tools/

Pulsar ToolsPulsar

ephem. (D4)

Level 1 (D1)

LAT Point sourcecatalog (D5)

Interstellar em.model (U5)

Pointing/livetimehistory (D2) Astron.

catalogs (D6)

Level 0.5

IRFs (D3)

Alternative source for testing high-level analysis

Alternative for making additional cuts on already-retrieved event data

Pt.ing/livetimesimulator (O1)

Observationsimulator (O2)

Pt.ing/livetimeextractor (U3)

Data sub-selection (U2)

Data extract(U1)

Exposurecalc. (U4)

Likelihood (A1)

Map gen(U6)

Src. ID (A2)

Eventdisplay (UI1) Pulsar

profiles (A3)1

CatalogAccess (U9)

Pt.ing/livetimeextractor (U3)

Pulsar phaseassign (U12)

Pulsar periodsearch (A4)

GRB spectral-temporalmodeling (A10)

Source modeldef. tool (U7)

Arrival timecorrection (U10)

GRB temporalanalysis (A7)2

GRB LAT DRMgen. (U14)

GRB spectralanalysis (A8)2

GRB eventbinning (A5)

GRB unbinnedspectral analysis (A9)

GRB visual-ization (U13)

IRF visual-ization (U8)

Ephemerisextract (U11)

GRB rebinning(A6)2

Data in