Pulsars: The radio/gamma-ray Connection

Alice K. Harding NASA Goddard Space Flight Center

• Prospects for pulsar studies with AGILE and GLAST • Synergy with radio telescopes – Timing and follow-up – Radio vs. g -ray beams – Polarimetry

Radio versus

g

-ray beams

Rotation axis Open magnetic field lines Radio beam Slot gap Gamma rays Outer gap Magnetic axis

Compton Gamma-Ray Observatory (CGRO)

• 7 (+3) gamma-ray pulsars detected

Unresolved questions

• How are particles accelerated so efficiently to 10 TeV?

• Where does this acceleration take place?

• Do all pulsars emit g -rays?

• How are radio and g -ray emission beams related?

• How many radio-quiet g -ray pulsars (Gemingas) are there?

What do we need from radio telescopes?

• Find more g -ray pulsars • Sensitive surveys • Pulse timing • Follow-up observations • Study the brightest ones in more detail • Better pulse profiles • Full-phase polarimetry

AGILE (Astro-rivelatore Gamma a Immagini LEggero)

• Italian collaboration • Launched on 23 April 2007!!

• Operational 2007-2008 • Pair production telescope (30 MeV – 30 GeV) • Somewhat more sensitive than EGRET • Should discover > 15-20 new g -ray pulsars

Gamma-Ray Large Area Space Telescope (GLAST)

2 instruments: Large Area Telescope (LAT) Gamma-ray Burst Monitor (GBM) LAT characteristics • Very large FOV (~20% of sky), factor 4 greater than EGRET Launch in early 2008 g • Broadband (4 decades in energy, 20 MeV – 300 GeV) ACD [surrounds 4x4 array of TKR towers] Tracker • Unprecedented PSF for gamma rays (factor > 3 better than EGRET for E>1 GeV)

e + e –

Calorimeter • Factor > 30 improvement in sensitivity • Much smaller deadtime per event (25 microsec, factor >4,000 better than EGRET) • No expendables => long mission without degradation

Pulsars detected by CGRO

 Only the youngest and/or nearest pulsars were detectable  5 of the 7 radio pulsars with the highest L SD /d 2 detected -9 -10 -11 -12 Princeton Pulsar Catalog c. 1995 10 15 G 10 14 G 10 3 yr 10 13 G -13 B 0 = 10 12 G -14 -15 -16 -17 10 11 G 10 5 yr 10 7 yr 10 9 yr Radio pulsar g -ray pulsar -18 -19 -20 -3 -2 10 10 G 10 9 G -1 0 Log[Period (s)] 1 2

More pulsars detectable with AGILE and GLAST

 ~53 radio pulsars in error circles of EGRET unidentified sources (18 20 plausible counterparts)  AGILE will discover new sources g -ray pulsars associated with EGRET  GLAST will detect sources 25 times fainter or 5 times further away – possibly 50 – 200 new g ray pulsars  Will be able to detect to the Galactic Center g -ray pulsars further than the distance  Middle-aged and older pulsars, including millisecond pulsars should be detected in g -rays -15 -16 -17 -18 -19 -20 -9 -10 -11 10 13 G ATNF catalog c. 2007 10 15 G 10 14 G 10 3 yr -12 -13 B 0 = 10 12 G -14 -3 10 11 G AGILE -2 10 10 G 10 9 G -1 0 Log[Period (s)] Radio pulsar AXP SGR g -ray pulsar 1 GLAST 10 5 yr 10 7 yr 10 9 yr 2

Radio pulsar properties

8 6 4 2 0 0.00

10.0

8.0

6.0

1.00

EGRETsources Total Period 2.00

Period (s) 3.00

Age 4.00

4.0

2.0

0.0

3.0

4.0

5.0

6.0

7.0

LOG(Age) 8.0

9.0

10.0

12.0

120.0

10.0

80.0

8.0

6.0

Surface B 40.0

4.0

2.0

0.0

5.00

250.0

0.0

8.0

9.0

10.0

11.0

12.0

LOG (B) 13.0

14.0

L sd 8.0

200.0

6.0

150.0

4.0

100.0

2.0

50.0

0.0

150 100 50 0.0

28 29 30 31 32 33 34 35 LOG(L sd ) 36 37 38 39 40 0 400.0

300.0

200.0

100.0

0.0

Young radio pulsars and EGRET sources

PSR J2021+3651 in 3EG J2021+3716

P = 104 ms, t = 17 kyr (Roberts et al 2002)

PSR J1928+1746, 3EG J1928+1733 P = 68 ms,

t

= 82 kyr Ė = 1.6 10 36 erg/s

(Cordes et al. 2006)

Predicted GLAST pulsar populations

49 95 (Recycled) 1680 Slot gap 116 30

Radio timing needs

 Collecting enough g -ray photons requires years  Young, energetic pulsars are weak and/or noisy  225 pulsars above L g erg/s ~ 3 x 10 34  g -ray observations would like 1-10 milli-period accuracy on photon arrival times  Large campaigns planned or underway at major radio telescopes (Parkes, Jodrell, Nancay) Need Arecibo to time the faint young pulsars below 1 mJy for GLAST) ( Approved timing proposal of 22 pulsars with flux

Faint young pulsars

• Young, energetic pulsars with very low fluxes can be timed only with Arecibo Pulsar name Radio flux (mJy) J1930+1852 0.06

J1928+1746 0.25

J2021+3651 0.1

B1853+01 0.19

Puzzling gamma-ray vs. radio profiles Vela Core beam?

Cone beam?

Crab Cone beam?

+ core beam?

430 MHz radio >100 MeV g -ray

Relative

g

-ray and radio emission altitude

a =70 o , z =55 o Crab and Vela Slot gap g -rays Crab High-altitude (0.2-0.6 R LC ) radio cone Vela Low-altitude (0.08 R LC ) radio cone

Rotating Vector Model

W a

B

b b = 3 0 -3.0

0 9.0

0 3.0

0 -0.1

0 b = -3 0 b = -0.1

0 Line of sight b = 9 0

Full-phase polarimetry – only at Arecibo

Everett & Weisberg 2001 a = 117 0 b = -1.5

0 Only way to determine viewing and inclination angle a = 162 0 b = 0.96

0

Follow-up radio observations

Pulsar “suspects” g -ray sources with hard spectra with cutoffs, low variability, located in pulsar wind nebulae Unknown millisecond pulsars?

Follow-up radio observations of GLAST sources Radio period g -ray period

Summary

• Expect 50 – 100 (?) g -ray pulsars in next 5 – 10 years • 100 – 300 (?) more g -ray sources that might be pulsars • Simultaneous radio timing needed to detect g -ray pulsars • Sensitivity needed • To detect unknown faint radio pulsars counterparts • To study radio vs. g -ray beams • To measure polarization at all pulse phases