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.