I.F.MalovPushchino Radio Astronomy Observatory, Lebedev Physical Institute

RUSSIAmalov@prao.ru

Do «magnetars» really exist?

AXPs and SGRs

Magnetars

(dPdr/dt)-11

Р(sec)=8.32x10-2 [ —————————]2/5 , (Lx)34 (W/Pdr)

2 Pdr ƒpl

  

P (dPdr/dt)

dP/dt = ——————, 2 Pdr

 

B (G) = 22.45 Pdr/Р2

Drift waves

CONCLUSIONS

1) There is no one criterion defining the magnetar type.

The answer the question in the title must be negative, as we believe.

What the word “magnetar” means ?

1) Is the supercritical dipole magnetic field ? But magnetic field of SGR 0418+5729 is less than 7.5 x 1012 G

2)Is the bursting behaviour? Normal pulsars have the burst components and giant pulses.

3) Is the low rotational power with respect to their X-ray luminosity? The young pulsar PSR J1846-0258 in the SNR Kes 75 (τ = 884 years), P = 326 msec show X-ray bursts, similar to АХРs and SGRs. However its X-ray luminosity L

x = 4.1 x 1034 erg/sec can be provided by the losses of

the rotation energy dE/dt = 8.1x1036 erg/sec.

4) Is the black body plus power-law X-ray spectrum? Normal radio pulsars emit thermal and non-thermal radiation outside the radio range.

5) Is the erratic radio pulse behaviour? Individual pulses of radio pulsars have different forms and spectra.

So, there is no one criterion defining the magnetar type.

Energy of a giant burst must be equal to magnetic energy:

B2 4 π R0

3 B2 R0

3

—————— = ——— =1046 erg

8 π 3 6

It is necessary to draw through the crust a sphere with R0

~ 1 km, i.e. 0.1 R* if an efficiency of transformation of

magnetic energy to radiation is 100 %. Such an event must cause some catastrofic changes in the neutron star. There are no observational evidences of these changes.

The geometry of the magnetosphere considered

The oscillating behaviour of the angle between the axis of the emission cone and the line of sight

For this model the angle β between the rotation axis and the magnetic moment must be small. Indeed our calculations have shown that in PSR J1642-4950 β = 150. 6, in AXP J1810-197 and 1E 1547.0-5408 β < 200.

2) The detection of SGR 0418+5729 with magnetic field of order of 7.5 x 1012 G gives birth doubts on the supercritical magnetic fields as the main peculiarity of АХРs and SGRs.

3) It is not enough to have magnetic fields ~1016 G to provide bursts with energies ~1046 erg.

4) The angle between magnetic and rotation axes in АХР PSR J1642-4950 is equal to 150.6. This gives the possibility to use the drift model for the description of AXPs.

5) In the frames of this model parameters of PSR J1642-4950 are the rotation period Р = 0.32 sec, the strength of magnetic field in the region of generation of observed emission В = 950 G and at the surface of the neutron star B

s = 3.39 x 1012 G.

6) It is shown that the cyclotron instability near the light cylinder of the PSR J1642-4950 can cause the generation of radio radiation. This radiation must be located in the narrow laye near the light cylindrr and the flux at low frequences ( ~100 MHz) is expected much more intense than at higher frequences.

In the frame of the drift model we estimate the rotation period Р = 0.32 sec, dP/dt = 6.29 x 10-13 , logB

s = 12.53

for PSR J1642-4950.

The cyclotron instability causes the generation of transverse waves at the frequency

4 ωB

3 γp

3

ω = ————— ,

ωp

2 γb

where

e B 8 π np e2

ωB = —— is the cyclotron frequency, ω

p = ————

m c m

plasma frequency , γp Lorentz-factor of the secondary plasma, γ

b

Lorentz-factor of the primary beam.

The distance of generation of radio waves

r r e2 B

s

2 γp

4 P r

—— = ( ————————— ) 1 / 6 —— = 1,76 103 ν8 -1/6

R* 2π2 m2 c2 γb 2 ν R*

is of order of the light cylinder radius. The increment of the cyclotron instability

π ω 2

p res

Гс = ―――――

ω γT

2 π e Bs γ

b ( R* / r )3

Гсt = ―――――――――― = А

2 ( R* / r )3 ν -1

m c P ν γT

γt

gives the amplification of waves with

dr 3 А2 R*3 τ = ∫ Г ―― = ―――――― = 62.6 ν

8 -1

c 8 с rLC

2 ν

This amplification must be effective at low frequencies. So, we must expect high fluxes at ν* ~ 100 MHz

and much less at ν >> ν*.