Pulsar modeling and simulations

GammaGamma --ray Large Area Space ray Large Area Space TelescopeTelescope

Massimiliano Razzano

Nicola Omodei

LAT Collaboration Meeting(SLAC, August 29th- September 1th 2005)

Outline

• The PulsarSpectrum simulator;• The phenomenological model;• The EGRET pulsars: some first analysis of

simulated data;• Simulation and generation of pulsar catalogs;• Some first results on catalogs;• Conclusions and future developments;

PulsarSpectrumsimulator

Crab and Gemingaseen by EGRET

Simulation of Craband Geminga

Key features:

�The simulator engine is designed to make easy the creation of pulsar sources;

�Spectra and lightcurves are simulated according to observed pulsars through a phenomenological model;�Simulation of timing effects due to period changes and motion of GLAST and Earth in the Solar System;

�Interface with a new tool for creating catalog of pulsars�Compatibily with LAT software (Gleam, observationSim);

An overview of PulsarSpectrum

Pulsar model

Simulator Engine

Model parameters(phenomenological, physical)

( XML File )

Pulsar Data(Flux,Period,…)

(Ascii datafile)Standalone

LAT software(ObsSim,Gleam)

2Dim ROOT hist

The simulation of the lightcurves

Lightcurves can be random generated or read from a profile

�Random curves (Lorentz peaks);�Existing TimeProfiles are useful for simulating known pulsars;

Random peaks

Vela Time Profile

Crab Time ProfileThe current default model is

a phenomenological one

The simulation of spectra

We choose this analytical spectral shape:(Nel and De Jager,1995):

�Description of the high energy cutoff; �Parameters are obtained from fits on the known γ ray pulsars (e.g. ref. N,DJ95, and DJ 2003);�Flux normalisation based on 3rdEGRET catalog (ph/cm2/s, E>100MeV);

Example for Vela-like PSRF(E>100) ~9*10-6 ph/cm2/s,

•En=1GeV,E0=8GeV;

•g=1.62

B=1.7

Data fit

b=1

Different scenarios

b=2

We combine lightcurve and spectrum:

���� TH2D ROOT histogram

Now multiplication, but more complex combination laws are not too difficult to simulate;(goal for phase-resolved analysis)

The phenomenological model (III)the final product

According to the flux the photons are extracted and then the photon arrival times are de-corrected

Lightcurve Spectrum

Barycentric decorretionsThe analysis procedure on pulsarsstarts by perfoming the barycentering, i.e. transform the photon arrival timesat the spacecraft to the Solar System Barycenter, located near the surfaceof the Sun

In order to be more realistic for the simulations we then must de-correct

Several effects that contribute to the barycentering, mainly:

� Geometrical delays (due to light propagation);

�Relativistic effects (i.e “Shapiro delay” due to gravitational wall of Sun)

Contribution to the geometrical delay due to SC orbit

-0,01

-0,005

0

0,005

0,01

0,015

0,02

0 200 400 600 800 1000

t from start (min.)

corr

ectio

n(s.

)

Period change with time

Phase assignment in analysis:•# of rotations:

•Integrating and taking the fractional part:

ttttftttftfttf d...))((2

1))(()(d)(dN 200000

+−+−+== &&&

...)(6

1)(

2

1)()φ()φ( 302201000 +−+−+−+= ttfttfttftt

)( 00 tff =)( 01 tff &= )( 02 tff &&=)(

1)(

tPtf =

We know that pulsar period changeswith time because of loss of rotationalenergy:

We must take this effect into account

The interval between 2 photons isexpanded according to the periodvariation.

�We switch between the “reference systems”

S (Pdot is = 0, period constant)

S~ (Pdot is not 0, period not constant, the real world)

Pulsar databasePulsarDataList XML file

For each pulsar simulated in DC2 there must be an entry in the pulsar database (D4)

PulsarSpectrum creates an output file that can be converted through gtpulsardb to a FITS file compatiblewith the D4 database

PulsarSpectrum

ASCII ephem file

gtpulsardb

Ephemerides

fits file

AdvertisementCreate your own pulsar with only 2 easy steps!

1 - Edit the PulsarDataList.txt file (located in /Pulsar/vXrYpZ/data), where are stored the generalparameters of the pulsars know by the simulator

Flux E>100MeV Ephem. validity range T(>t0) where phi(t) = 0.0Period (or frequency) and derivatives

For more informations, please see at: www.pi.infn.it/ ~razzanoPulsar/PulsarSpTutor/PulsarSpTutor.htm

2 – Create an XML source entry in a xml file , where are stored the position, energy range and model-dependent parameters of the pulsar

Name asin Datalist Emax,Emin

RA,dec

Model (=1) & random seed

Model parameters

An example of simulation:the EGRET pulsars

This is a one-week simulation of:

• EGRET pulsars;• galactic diffuse emission;• extragalactic background;

GemingaCrab

Vela B1706-44B1055-52

B1951+32

On the road toDC2 we have

updated EGRET pulsars with

more detaileddata

First results on simulated Vela

Plotting the PULSE_PHASE entries in the Vela_1week_bari.fits

(after barycentering and phase assignment)

The real Vela observedby Egret(Kanbach et al. ,1994)

Analysis of simulated data:CrabCut of 2° aroundCrab position

After applying barycentriccorrections and phase assigment

EGRET lightcurve

(fromJ.M.Fierrothesis,1995)

For all these pulsars weperform periodicity tests

Analysis of simulated data:Geminga

After applying barycentriccorrections and phase assigment

EGRET lightcurve

(fromJ.M.Fierrothesis,1995)

Cut of 2° aroundGeminga position

Simulating pulsar catalogsPulsarSpectrum can alsosimulate different pulsarsplaced in the sky.

For each pulsar a log file isproduced in order to keep track of the simulated pulsars

This tool is now at a goodpoint of development and it’s working with basic features

1-day catalog simulation of a catalog

We designed a tool that managecatalog of pulsars and can beinterfaced with PulsarSpectrum. This will be useful for severalpurposes:

•Create catalogs for checkouts and forthe next Data Challenge;

•Provide synthetic catalogs fromexisting ones;

•Make studies on LAT pulsar capabilities;

An example of Pulsar Catalog

We started to take pulsar data from the database of the Australian TelescopeNational Facility.

http://www.atnf.csiro.au/research/pulsar/

Synthetized pulsars

Starting from an observedpopulation we extract the characteristic of the population we want tosimulate.

Galactic positions

(The distribution of distancein the galaxy are alsoconsidered)

Period-Pdot diagram

Also the period vs. periodderivative is derived

(Here we didn’t show the millisecond pulsars)

This first approach has a limitation: our empirical catalogdidn’t mimic the distribution of

radio quiet pulsars.

ATNF pulsars

Synthetized pulsars

Spectral modeling

Spectrum and fluxdepends on the

theoretical model youchoose to adopt

We start from Polar Cap model, as in Harding & Zhang (2000), and Gonthier et al. (2002)

We obtain the luminosity Lgamma, the spectral index and anestimate of the cutoff energy forthe power law.

Then we slightly modify the spectra in order to have anexponential cutoff of ≈2.

LAT sensitivity

EGRET sensitivity

Thisis ve

ry,very,

…,very

prelimin

ar estim

ate!

Rumors from 3° Checkout…

Some pulsars in the 3° Checkoutwill be nearEGRET sources…

…and much more surprises have tocome!

ConclusionsWhere we are…

�The PulsarSpectrum simulator is stable and working;�The phenomenological model included can reproduce observed pulsars and used with theoretical models;�Most of the timing effects are simulated (i.e. barycentering);�An updated set of data for simulating EGRET pulsars is now available; �PulsarSpectrum is being used during Science Tools Checkouts for testing the Pulsar Analysis Tools;�A tool for managing and simulating pulsar catalogs is under development, we will include more theoretical models;�All this tools are suitable for modeling pulsars for DC2 and to study pulsar science with LAT;

…and where we go!�Include more realistic timing effects (timing noise, glitches,etc.);�Develop the simulation of binary pulsar systems;�Add more theoretical model to the simulations (i.e. outer gap);�Develop and optimize the simulated catalogs managers; �Provide a set of pulsars for DC2 and the relative ephemerides database;