Pulsars:Pulsars: The Unexplored The Unexplored GeVGeV--TeV TeV Energy BandEnergy Band

Alice K. Harding NASA Goddard Space Flight Center

• CGRO pulsars: • High-energy cutoffs• No pulsed TeV emission detected

• Millisecond pulsars: • Only one detected (PSR J0218+4232)• Where are the nearby sources?

• AXPs: Where do the hard components end?

• Power peaked in γ-rays

• No pulsed emission detected above 20 GeV

• High-energy turnover

• Increase in hardness with age

Broad-band spectra

Changes in profile at highest energies (> 5 Changes in profile at highest energies (> 5 GeVGeV))Thompson 2001

Pulsar highPulsar high--energy emission modelsenergy emission models

ΩBαLight

Cylinder

closed fieldregion

polarcap

null charge surfaceΩ . B = 0

outergap

|| 41/ 20c sin coss

2olowE θ η α φκ α

η−∝ +

3

IR

κ ∝

slot gap

Pair plasma

µ

slot

gap

Pairformation

front

∆ ξSG

Closed field region

|| 0E =

Pair attenuation cutoff for normal pulsarsPair attenuation cutoff for normal pulsars7 / 2

1/ 2 1max 122esc

rE E GeV P BR

− ⎛ ⎞= ≈ ⎜ ⎟⎝ ⎠

1011 1012 1013 1014

B0 (Gauss)

10-3

10-2

10-1

100

101

102

103H

igh

Ene

rgy

Cut

off (

GeV

)

P =

0.1

- 5 s

3R019

51+3

2

20 GeV

2R0

R0

1055

-52

Vel

aC

rab

1509

-58

Gem

inga

1706

-44

0656

+14

100 GeV

Sensitivity of H.E.S.S. to pulsar emissionSensitivity of H.E.S.S. to pulsar emission

De De Jager Jager et al. 2000et al. 2000( )exp / b

n

g

o

dN Ek EdE

EE

γ−

⎛ ⎞ ⎡ ⎤= −⎜ ⎟ ⎣ ⎦⎝ ⎠b ~ 2

PSR B1951+32: How sharp is the cutoff?PSR B1951+32: How sharp is the cutoff?

10-4 10-3 10-2 10-1 100 101 102 103 104 105

Energy (GeV)

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

GeV

/(cm

2 s)

PSR1951+32

VERITAS

GLAST

EGRET

MAGIC

PSR B1706PSR B1706--44: Where is the cutoff?44: Where is the cutoff?

10-4 10-3 10-2 10-1 100 101 102 103 104 105

Energy (GeV)

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5G

eV/(c

m2

s)PSR1706-44

H.E.S.S.GLAST

EGRET

MAGIC

10-2 10-1 100 101 102 103 104 105 106 107

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Energy (MeV)

MeV

cm

-2 s

-1

EGRETCOMPTELOSSERXTE CANGAROOOPTICALROSAT

VELA PULSAR

101 102 103 104 105 106 107

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Energy (MeV)

MeV

cm

-2 s

-1

CRAB PULSAR

The mystery of the missing The mystery of the missing TeVTeV emissionemission

Potchefstrom 1990

CANGAROO 1997

Hirotani et al. 2003Outer gap model Cheng, Ho & Ruderman 1986

Outer gap model Cheng, Ho & Ruderman 1986

Whipple 1990

Outer gap model Romani 1996

Hirotani et al. 2003

CANGAROO 1998

Whipple 2000

HEGRA 1999

W

Smaller outer gap size

less TeV emission

But what will happen to predicted pulse shapes??MAGIC VERITAS

H.E.S.S.MAGIC

Detections of Detections of MSPs MSPs at high energyat high energy

1206>100Millisecond pulsars

812161400Normal pulsars

γ-raysteady

X-raypulsed

Radio

Why are so few seen at γ-ray energy?

Hard emission from millisecond pulsarsHard emission from millisecond pulsars

2 4

|| 2

1/ 42|| 7 1/ 4 1/ 4 3/ 4

8

3/ 4 5/ 4 3/ 4 11/ 48 0.15

4536

23

3 102

10 GeV

0.15

CRc

cCRR ms

CRpeak ms

eeE

EB P

e

B P

IR

γγρ

ργ η

ε κ η

κ

− −

− −

= =

⎛ ⎞= ≈⎜ ⎟⎜ ⎟

⎝ ⎠

≈

≈

&

Radiation reaction-limited acceleration

Curvature radiation peak energy:

PSR P (ms) B (G) d (kpc) ε CRpeak (GeV)

J0437-4715 5.75 6.95E+08 0.18 4.8B1821-24 3.05 4.47E+09 5.5 42.9J0218-4232 2.32 8.44E+08 5.85 17.3B1937+21 1.60 8.10E+08 3.60 26.7J0030+0451 4.86 4.46E+08 0.23 4.3J2124-3358 4.93 1.47E+09 0.25 10.2B1957+20 1.61 3.33E+08 1.6 13.6

Dependent on NS equation-of-state

Dependent on emission radius r/R

Usov 1983

Bulik, Rudak & Dyks 2000

Luo, Shibata & Melrose 2000

Harding, Muslimov & Zhang 2002

Harding, Usov & Muslimov 2004

1/ 2c Pρ ∝

108 109 1010 1011

B0 (Gauss)

100

101

102

103

104

105

106H

igh

Ene

rgy

Cut

off (

GeV

)

P = 1 - 10 ms

20 GeV

2R0

R0

100 GeV

Pair attenuation cutoff for ms pulsarsPair attenuation cutoff for ms pulsars

CR

Peak E

nergy (GeV

)

Maximum peak energy < 100 GeV

Curvature radiation from J0437Curvature radiation from J0437--4715 4715 ––can we constrain the NS equationcan we constrain the NS equation--ofof--state?state?

10-4 10-3 10-2 10-1 100 101 102 103 104 105

Energy (GeV)

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4G

eV/(c

m2

s)J0437-4715

H.E.S.S.

BPS: R6=0.8, I45=0.6FP: R6=1.0, I45=1.0PS: R6=1.6, I45=2.2

ICS

MAGIC

GLAST

EGRET

CR

Venter & De Jager 2004

But effect of altitude/viewing angle is strongerBut effect of altitude/viewing angle is stronger……

10-4 10-3 10-2 10-1 100 101 102 103 104 105

Energy (GeV)

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

GeV

/(cm

2 s)

J0437-4715

H.E.S.S.

R3R1R2R5

GLAST

EGRET

MAGIC

B1821-24: acceleration limited to low altitude

10-4 10-2 100 102 104 106

Energy (MeV)

10-10

10-8

10-6

10-4

MeV

/(cm

2 s)

B0 = 4.4 x 109 GP = 3 msχ = 1.0

PCAHRIEGRETHEXTEOSSE

GLAST

PSR B1821-24

H.E.S.S.

MAGIC

SR

ICS

CR

J0218+4232: unscreened acceleration

10-4 10-2 100 102 104 106

Energy (MeV)

10-9

10-7

10-5

10-3

MeV

/(cm

2 s)

MECSPCAHRIHEXTECOMPTELEGRET

GLAST

VERITASSR

CR

PSR J0218+4232

MAGIC

Predicted CR flux from millisecond pulsarsPredicted CR flux from millisecond pulsars

B182

1-24

B193

7+21

B195

7+20

J003

0+04

51

J021

8-42

32

J043

7-47

15

J212

4-33

58

47Tu

c10-1

100

101

102

103

Flux

(>10

0 M

eV) (

10-8

cm-2

s-1)

GLAST

EGRET

Outer gap model predictions for ms pulsarsOuter gap model predictions for ms pulsarsZhang & Cheng 2003Zhang & Cheng 2003

Hidden population of millisecond pulsars?Hidden population of millisecond pulsars?

10-3 10-2 10-1 100 101

Pdo

t (s

s-1)

10-22

10-20

10-18

10-16

10-14

10-12

P (s)

B1821-24

radiogamma-rayX-ray

Pair death lineJ0218+4232 J0437-4715

???

?

•• No pairsNo pairs•• No radio No radio •• No XNo X--raysrays•• Detectable Detectable

only in highonly in high--energy energy γγ--raysrays

•• At d = 100 pc:At d = 100 pc:

32 33 -14 10 erg sSDE −≈ ×&

8 2 -1

( 1 GeV)2 10 ph cm sF

−

> ≈×

8 2 -1

( 100 MeV)5 10 ph cm sF

−

> ≈×

10-4 10-3 10-2 10-1 100 101 102 103 104 105

Energy (GeV)

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

GeV

/(cm

2 s)

Vela

J0437-4715 VERITAS

MAGICGLAST

Radio-quiet MSP with P=3 ms, d=100 pc

Harding, Usov & Muslimov 2004

Detecting hidden millisecond pulsarsDetecting hidden millisecond pulsars

Number of Number of radioradio--quiet quiet MSPsMSPs::

MSP BirthrateMSP Birthrate

( )2

MSP MSPgal

dN d NR

τ⎛ ⎞

≤ = ⎜ ⎟⎜ ⎟⎝ ⎠

&

6 14 1040,000

MSPN yrtotal

− −≈ ×&

( ) 2400MSP kpcN d d≤ ≈

Chandra Detection of Millisecond Pulsars in 47 Tuc

Grindlay et al. 2001

15 millisecond radio pulsars in 47 15 millisecond radio pulsars in 47 TucTuc

•• Total predicted flux > 100 Total predicted flux > 100 MeVMeV

EGRET limit ( )EGRET limit ( )

•• This and other globular clusters should This and other globular clusters should be detectable by GLASTbe detectable by GLAST

8 2 -16.5 10 ph cm s−×8 2 -15 10 ph cm s−×

Hard Emission from Kes 73 and AXP 1E 1841-045

11

22

33

44

55

66

1) Total1) TotalXMMXMM--NewtonNewton

2) Total 2) Total 1E 18411E 1841--045;045;

ChandraChandra((MoriiMorii et al. 2003)et al. 2003)

3) Pulsed 3) Pulsed RXTE/PCARXTE/PCAγγ 1.931.93±±0.010.01

4) Pulsed 4) Pulsed RXTE/HEXTERXTE/HEXTEγγ 0.940.94±±0.160.16

5) Total 5) Total RXTE/HEXTERXTE/HEXTEγγ 1.471.47±±0.050.05

6) Total6) TotalINTEGRALINTEGRAL

((MolkovMolkov et al 2004)et al 2004)

KuiperKuiper,, HermsenHermsen, Mendez 2004, Mendez 2004

Resonant Compton Resonant Compton UpscatteringUpscattering??

Baring 2004Baring 2004

Polarization signature of photon splitting in Polarization signature of photon splitting in AXPsAXPs

10-3 10-2 10-1 100 101 102 103

E (MeV)

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

⊥II

MeV

/(cm

2 s)

Bo = 10 Bcr

EGRET

GLAST

Full polar cap

⊥ →Only permitted splitting mode

Photon splitting cutoff

Pair attenuation cutoff

Outer gap model predictions for Outer gap model predictions for SGRsSGRsZhang & Cheng 2002Zhang & Cheng 2002

What we can learn from coordinated What we can learn from coordinated observations with GLAST and observations with GLAST and ACTsACTs

• Where and how sharp are high-energy cutoffs?

• Is there an ICS TeV component from the outer gap ?

• CR component (1-50 GeV) from millisecond pulsars

• Radio (and X-ray) quiet MSPs

• Hard emission from AXPs

Which pulsars have slot gaps?Which pulsars have slot gaps?

10-3 10-2 10-1 100 101

Pdot

(s s

-1)

10-22

10-20

10-18

10-16

10-14

10-12

P (s)

CR

ICS

Only the younger pulsars above the death line for production of curvature radiation pairs will have

SLOT GAPS

Harding, Muslimov & Zhang 2002

Older pulsars belowthe death line for production of curvature radiation pairs will have unscreened E|| and

NO SLOT GAPS

B1821-24

radiogamma-rayX-ray

J0437-4715

J0218+4232

Slot gap modelSlot gap model

• Pair-free zone near last open field-lineSlower accelerationPair formation front at

higher altitudeSlot gap forms

between conducting walls

• E|| acceleration is not screened

e+e-

Pair plasma

µ

slot

gap

Pairformation

front

∆ ξSG

Closed field region

|| 0E =

(Muslimov & Harding 2003, 2004)

Slot gap width:∆ξ SG P B≈ −015 0 1 12

4 7. ./

Solid angle:2

SG o SGrθ ξΩ ∝ ∆Slot gap pair

cascade

Primary CR, IC

Closed fieldregion

Crab NebulaCrab Nebula

From Rowell 2003