The gamma-ray spectrum of the pulsar Outer-Gap J.Takata & - - PDF document

The gamma-ray spectrum of the pulsar Outer-Gap

J.Takata & S.Shibata Yamagata Univ.

Contents

1, The gamma-ray emission from

Outer-Gap.

2, The TeV emission from the pulsar

magnetosphere and the pulsar wind

• region. – the possibility of the origin for

TeV component from B1706-44.

gamma- ray pulsars (7 pulsars)

• Where and How are the particles accelerated and

gamma-rays radiated in the pulsar magnetosphere?

Gamma-ray

radio

• ptical

X-ray 1, Introduction:

The acceleration of particles in the magnetosphere

* The electric field along the magnetic field accelerates the particles. The pulsar is the electric dynamo with about * This grow up in the region (gap) , where the charge disagree with the Goldreich-Julian density. * The gamma-rays are radiated by the curvature, inverse-Compton processes Polar Cap Outer Gap 1, Introduction:

Outer-Gap model (previous works)

* Romani (1996)

• three dimensional model(pulse shape,phase resolve spectra)
• assuming electric field

* Hirotani & Shibata (1999, HS model)

• solved the electric field with curvature radiation

and pair-creation process self-consistently

• one dimensional model along the magnetic field line
• the spectrum is consistent with observation in GeV bands

I improve the spectrum of HS model by taking account of the radiation from outside of the gap 1, Introduction:

The electrodynamics in the gap

* the accelerated electrons (positrons) control the accelerating field * the distribution of particles is determined by the pair-creation rate of the gamma-rays with X- rays

* the distribution of the gamma-rays is

determined by the emissivity of radiation and the

2, Outer-gap model:

The radiation from outside of the gap

* The gap width is characterized by the pair-creation mean free path. * Particles escape from the gap with

* Particles can radiate the curvature

photons at the outside of the gap as well as in the gap. Gap width The original HS model thought the gap emission, only But.., 2, Outer-Gap model:

The gamma-ray spectrum of the

• ne-dimensional model(Vela)

* Gap emission is consistent with

• bservation in GeV bands, but

is inconsistent in MeV bands * The total spectra is consistent with observation above 100MeV * The ~ 1MeV emissions are synchrotron radiation, probably

The assumed the current in the gap, inclination angle and the cross section area

Model parameter

2, Outer-Gap model:

νFν spectrum

Vela .vs. B1706-44

* Vela and B1706-44 are similar pulsars * The spectral peek energies are ~ 1GeV (B1706-44) and ~ 3GeV (Vela) * The difference of rotational speed produce the difference of

• the distance to the gap (and the light

cylinder) from the surface

• the strength of magnetic field in the gap

Our model can explain the observed spectral features 2, Outer-Gap model:

• this difference is produced in the result
• f our model, naturally

The TeV gamma-rays from B1706-44

* The CANGAROO group observed the TeV gamma-ray in the direction

• f B1706-44
• it is also difficult to the explain by

the gap emission

• can not explain the ordinary synchrotron
• inverse Compton process of the

synchrotron nebula (Kushida et. al. 2002)

* I calculated the TeV emission from the Outer-Gap.

• small the soft-photon density around

the gap (following discussion)

3, TeV emission from around pulsar: It may be the another origin.

Pulsar Wind

The possibility of the another radiation region * The wind particles are accelerated at somewhere * This region may bright at TeV bands by IC process * The wind particle carry out the almost the spin down luminosity of the pulsar ?

IC IC OG

Wind particles are accelera- ted to the Lorentz factor of 3・ 106 at light cylinder. assumption 3, TeV emission from around pulsar:

The luminosity of IC process

* The inverse Compton luminosity

ability probability

• Gap region
• Wind region

3, TeV emission from around pulsar:

* The TeV luminosity at the each regions

PSR B1706-44

* The needed soft-photon density to obtain the observed luminosity is * The CANGAROO observation (Kushida,2002) at d= 2.5 kpc

3, TeV emission from around pulsar: We compare this needed density with the predicted density (in the gap) ( in the wind region)

The predicted photon-field around B1706-44

* The soft- photon energy : Infrared

* The Rayleigh-Jeans region of surface black body: kT= 143eV * The non-thermal radiation

• no available observations for Infrared
• the observations for pulsed X-ray and optical

(upper limited point) can be interpreted as The predicted spectral

3, TeV emission from around pulsar:

* The gap region

too small

• the scattering photon energy~ 0.01eV

* The wind region

too small

• the scattering photon energy~ 0.1eV

the needed soft photon density

small This TeV component may have the origin of the pulsar wind

Result

3, TeV emission from around pulsar: OK

Summary (1)

• By taking account of the radiation from outside
• f the gap to the HS model, the spectrum is

consistent with observation above 100MeV

• The our Outer-Gap model explain the observed

spectral peak energies and features of Vela and B1706-44, naturally.

To compare the more detail observations, for example the phase resolved spectra, we are now extending the one-dimensional model to the two- dimensional.

Summary (2)

It is difficult to explain the TeV gamma-rays

from the B1706-44 by the out-gap emission.

If the pulsar wind particles are accelerated at

near the light cylinder, this TeV component may be the detection of the emission from the pulsar wind.

If this component is the detection of the wind

component, it is the first directly observation for the pulsar wind.