Discovery of Temporal Changes in the Torus around PSR B1509-58

Y. Yatsu, N. Kawai, T. Nakamori, & H. Nakajima Tokyo Institute of Technology

2009 July 8th

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Contents of this talk

Introduction

Data Analysis and Results

Discussion

Conclusion

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Temporal studies of PWNe

We would like to find the temporal changes on the torus of PSR B1509-58 as seen in the Crab nebula.

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- Crab nebula (Mori et al. 2004)- Vela Pulsar (Pavlov et al. 2003)- PSR B1509-58 (DeLaney et al. 2006)- G11.2-0.3 (Roberts et al. 2003)- PSR B0540-69 (DeLuca et al. 2007)

Providing the information of plasma dynamics directly!

PSR B1509-58

Young and Energetic Pulsar

D = 5.2 +/- 1.4 kpc

P = 150 ms (c 1700 yr)

Lspin = 1.8 x 1037 ergs s-1

Surrounding Radio shell (MSH15-52)

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We focused on the torus within 30” from the pulsar.

PSR B1509-58

10 arcmin

5Very fine structures at the pulsar vicinity

Nested tori-Inner arc-Outer arcGaensler et al. +02DeLaney et al. +06

Inner ringYatsu et al. +09

Outer arc: 30~60”

Inner arc: ~30”

South Jet

Inner Ring R~10”

1 arcmin

Observations

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We used archive data of

four times monitoring observation.

ObsID Date ExpTime5534 2004,12,28 (T=0) 50 ks

5535 T = 41 days 43 ks

6116 T = 122 days 48 ks

6117 T = 294 days 46 ks

Region selection

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vflow = c/3

(I = 50deg)

In order to investigate the torus, the jet region was excluded.

The funnel were divided into

80 sectors with a width of 0.5”.

Jet

Torus

Variations of radial profile

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41 days81 days

172 days

0 5 10 15 20 25 30Distance from the Pulsar [arcsec]

Sur

face

Brig

htne

ss

We searched moving features by using cross correlation function.

We detected moving features on the torusrunning at 10.5 arcsec/yr outward from the pulsar !

Radial profileVapp ~ 10.5 arcsec yr -1

(~ 0.86c for D=5.2 kpc)

Calculation of the moving velocity

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Considering the superluminal motion effect,

v ~ 0.65c (30° < i < 50°) is required for vapp = 0.86c.

i

Torusi =

40°

0 0.2 0.4 0.6 0.8 1.0Velocity [c]

1.0

0.8

0.6

0.4

0.2

Vapp = 0.86ci =

30°i = 5

0°

What’s moving? (1)“Actual motion of the pulsar wind”

Based on the brightness distribution of the torus

(Pelling et al. 1987)

Vflow ≤ 0.6c (for i ≥ 30 deg)

From the KC-model （ Kennnel & Coroniti 1984 ）…

Vflow = c/3(rTS/r)2 ≤ c/3

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It is difficult to explain the proper motion by the actual flow velocity of the pulsar wind.

What’s moving? (2)“Propagation of magneto-sonic wave”

Velocity of the Fast-mode magneto-sonic wave

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€

VA =c

1+ 4π (ρc 2 + 4 p)[ ] /B2≈ c1+ (16πU /3B2)

= 0.63c

€ €

VF =VA

2 + cs2

1+ (VA /c)2~ 0.7c

€

cs ≤13

c ~ 0.58c

(Delaney et al. 2006)

The Fast mod magneto-sonic wave can explain the observed proper motion.

Summary

We studied the temporal variation on the torus around PSR B1509-58 using Chandra.

We found temporal changes on the torus propagating at 10.5 arcsec yr -1, analogous to the “moving wisp” as seen in the Crab nebula.

The observed proper motion can be explained by the magnetosonic wave propagating at ~ 0.7c .

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Cross Correlation Function

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CC

FC

CF

41 days81 days

172 days

0 5 10 15 20 25 30

Sur

face

Brig

htne

ss

Radial profile

0 2 4 6 8 10

Travel Distance [arcsec]

CC

F

ΔT = 41 day

ΔT = 81 day

ΔT = 172 day

CC

F ΔT = 122 day

€

CCF(Δr) =E [a(r) − a ]⋅[b(r + Δr) −b ]{ }

σ aσ b

Inclination angle vs Flow velocity

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i = 30° i = 50°i = 40°