Gamma-ray pulsars discovery by Fermi Space Observatory

Sergei Popov(SAI MSU)

Plan

1. General intro2. Pulsar models3. Population synthesis4. Summary of discoveries

EGRET legacy

Just 6 pulsars:

• Crab• Geminga• Vela• PSR B1055-52• PSR B1706-44 • PSR B1951+32

Nolan et al. 1996astro-ph/9607079

(plus one by COMPTEL)

Fermi PSR light curves

The first catalogue of Fermi pulsars: arXiv:0910.1608

Galactic map

arXiv:0910.1608

Luminosity vs Edot

arXiv:0910.1608

Spectra

arXiv:0910.1608 arXiv: 1007.1142

Geminga

Light cylinder magnetic field vs. age

Caraveo arXiv: 1009.2421

Total of 46 pulsars 29 of which detected in radio (further divided between 8 mPSRs and 21 “classical” pulsars) and 17 selected in gamma-rays (i.e. 16 discovered by LAT + Geminga)

Emission geometry

D. Thomson, NASA/GSFC)From Encyclopedia article 'Gamma-ray astronomy'

gsfc.nasa.gov

Crab pulsar profile

arXiv: 1007.2183Gamma pulse is shiftedrelative to the radio pulse

Now there are examplesthat radio and gammapulses can be both:at nearly the same positions andsignificantly shifted.

Gamma – OG,Radio – TPC?

Several models

• Polar cap (inner gap or space-charge limited flow)• Outer gap• Slot gap and TPC• Striped wind

Inner gap (polar cap) model

Outer gap model

Slot gap and TPC model

Gonthier et al. 2004 Dyks, Rudak 2003

Polar vs. Slot (TPC) gap

Harding arXiv:0710.3517

In brief

Fermi data favors outer gap

Population synthesis of gamma-ray PSRs

(following Gonthier et al astro-ph/0312565)

Ingredients1. Geometry of radio and gamma beam2. Period evolution3. Magnetic field evolution4. Initial spatial distribution5. Initial velocity distribution6. Radio and gamma spectra7. Radio and gamma luminosity8. Properties of gamma detectors9. Radio surveys to compare with.

Tasks

1. To test models2. To make predictions for GLAST and AGILE

Beams

1. Radio beam

2. Gamma beam.

Geometry of gamma-ray beam was adapted from the slot gap model (Muslimov, Harding 2003)

Other properties• Pulsars are initially distributed in an exponential (in R and z) disc,

following Paczynski (1990).• Birthrate is 1.38 per century• Velocity distribution from Arzoumanian, Chernoff and Cordes (2002).• Dispersion measure is calculated with the new model by Cordes and Lazio• Initial period distribution is taken to be flat from 0 to 150 ms.• Magnetic field decays with the time scale 2.8 Myrs

(note, that it can be mimicked by the evolution of the inclination angle between spin and magnetic axis).

The code is run till the number of detected (artificially) pulsars is 10 timeslarger than the number of really detected objects.

Results are compared with nine surveys (including PMBPS)

Drawbacks of the scenario• Simplified initial spatial distribution (no spiral arms)• Uncertainties in beaming at different energies• Uncertainties and manipulations with luminosity• Unknown correlations between parameters

P-Pdot diagrams

Detected Simulated

Comparison of distributions

Shaded – detected, plain - simulated

Distributions on the sky

Results for Fermi

Crosses – radio-quietDots – radio-loud

Examples of pulse profiles

Predictions for Fermi and AGILE

(prediction just for detection as a source, not as a pulsating sources!)

Spatial distribution of gamma sources

New population synthesis

Watters, Romani arXiv: 1009.5305

Outer gap model is prefered

Another one

Takata et al. arXiv: 1010.5870

Outer gap

The first Fermi catalogue56 pulsating sources out from 1451 sources in total

arXiv: 1002.2280

Blind searches

arXiv: 1007.2183

PSR J1957+5033

24 PSRs found in blind searches.

See details in arXiv: 1009.0748 and arXiv: 1006.2134

Blind search

arXiv: 1009.0748

Up to now few (3) are foundalso in radio, but it is not easy!

Pulsar timing

arXiv: 1007.2183

PSR J1836+592518 months timing

Millisecond pulsars

PSR J0218+4232 was probably detected by EGRET.With Fermi we now have 11+18 clearly detected in gamma mPSRs.Many “black widows”.No radio-quiet mPSR, yet.Plus, there are 8 gamma-sources coincident with globular clusters.

More are coming.

P-Pdot diagram

arXiv: 1007.2183

63 PSRs detected by Fermi

Bottom line

- 63 clearly detected pulsating PSRs: ~20 radio selected (with 7 known from CGRO time) 24 – in blind searches (several detected also in radio) 27 - mPSRs

- 18 mPSRs candidates from radio (non-pulsating in gamma)

About radio pulsar populationsee Lorimer arXiv: 1008.1928

The outer gap models seems to bemore probable on the base of Fermi data.