Pulsar modeling and simulations

Gamma-ray Large Area Space Gamma-ray Large Area Space TelescopeTelescope

Massimiliano RazzanoNicola 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;

PulsarSpectrum simulator

Crab and Geminga seen by EGRET

Simulation of Crab and 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 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 pulsars starts by perfoming the barycentering, i.e. transform the photon arrival times at the spacecraft to the Solar System Barycenter, located near the surface of 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

ecti

on

(s.)

Period change with time

Phase assignment in analysis:•# of rotations:

•Integrating and taking the fractional part:

ttttftttftfttf d...))((2

1))(()(d)(dN 2

00000

...)(6

1)(

2

1)()φ()φ( 3

022

01000 ttfttfttftt

)( 00 tff )( 01 tff )( 02 tff )(

1)(

tPtf

We know that pulsar period changes with time because of loss of rotational energy:

We must take this effect into account

The interval between 2 photons is expanded according to the period variation.

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 compatible with 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 general parameters 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 as in 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 to DC2 we have

updated EGRET pulsars with

more detailed data

First results on simulated Vela

Plotting the PULSE_PHASE entries in the Vela_1week_bari.fits

(after barycentering and phase assignment)

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

Analysis of simulated data:CrabCut of 2° around Crab position

After applying barycentric corrections and phase assigment

EGRET lightcurve

(from J.M.Fierro thesis,1995)

For all these pulsars we perform periodicity tests

Analysis of simulated data:Geminga

After applying barycentric corrections and phase assigment

EGRET lightcurve

(from J.M.Fierro thesis,1995)

Cut of 2° around Geminga position

Simulating pulsar catalogsPulsarSpectrum can also simulate different pulsars placed in the sky.

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

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

1-day catalog simulation of a catalog

We designed a tool that manage catalog of pulsars and can be interfaced with PulsarSpectrum. This will be useful for several purposes:

•Create catalogs for checkouts and for the next Data Challenge;

•Provide synthetic catalogs from existing ones;

•Make studies on LAT pulsar capabilities;

An example of Pulsar Catalog

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

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

Synthetized pulsars

Starting from an observed population we extract the characteristic of the population we want to simulate.

Galactic positions

(The distribution of distance in the galaxy are also considered)

Period-Pdot diagram

Also the period vs. period derivative is derived

(Here we didn’t show the millisecond pulsars)

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

radio quiet pulsars.

ATNF pulsars

Synthetized pulsars

Spectral modeling

Spectrum and flux depends on the

theoretical model you choose 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 an estimate of the cutoff energy for the power law.

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

LAT sensitivity

EGRET sensitivity

This is very,very,…,very

preliminar estimate!

Rumors from 3° Checkout…

Some pulsars in the 3° Checkout will be near EGRET sources…

…and much more surprises have to come!

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;