Gamma-ray pulsars discovery by Fermi Space Observatory

Gamma-ray pulsars discovery
by Fermi Space Observatory
Sergei Popov
General intro
Pulsar models
Population synthesis
Summary of discoveries
EGRET legacy
Just 6 pulsars:
• Crab
• Geminga
• Vela
• PSR B1055-52
• PSR B1706-44
• PSR B1951+32
(plus one by COMPTEL)
Nolan et al. 1996
Fermi PSR light curves
The first catalogue of Fermi pulsars: arXiv:0910.1608
Galactic map
Luminosity vs Edot
arXiv: 1007.1142
Light cylinder magnetic field vs. age
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)
Caraveo arXiv: 1009.2421
Emission geometry
D. Thomson, NASA/GSFC)
From Encyclopedia article
'Gamma-ray astronomy'
Crab pulsar profile
Now there are examples
that radio and gamma
pulses can be both:
at nearly the same
positions and
significantly shifted.
Gamma – OG,
Radio – TPC?
Gamma pulse is shifted
relative to the radio pulse
arXiv: 1007.2183
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
In brief
Fermi data favors outer gap
Population synthesis of gamma-ray PSRs
Geometry of radio and gamma beam
Period evolution
Magnetic field evolution
Initial spatial distribution
Initial velocity distribution
Radio and gamma spectra
Radio and gamma luminosity
Properties of gamma detectors
Radio surveys to compare with.
1. To test models
2. To make predictions for GLAST and AGILE
(following Gonthier et al astro-ph/0312565)
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 times
larger 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
Comparison of distributions
Shaded – detected, plain - simulated
Distributions on the sky
Results for Fermi
Crosses – radio-quiet
Dots – 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
New population synthesis
Outer gap model is prefered
Watters, Romani arXiv: 1009.5305
Another one
Outer gap
The first Fermi catalogue
56 pulsating sources out from 1451 sources in total
arXiv: 1002.2280
Blind searches
24 PSRs found in blind searches.
PSR J1957+5033
arXiv: 1007.2183
See details in arXiv: 1009.0748 and arXiv: 1006.2134
Blind search
Up to now few (3) are found
also in radio, but it is not easy!
arXiv: 1009.0748
Pulsar timing
PSR J1836+5925
18 months timing
arXiv: 1007.2183
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
63 PSRs detected by Fermi
arXiv: 1007.2183
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)
The outer gap models seems to be
more probable on the base of Fermi data.
About radio pulsar population
see Lorimer arXiv: 1008.1928

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