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Status pulsar studies in soft gamma-rays. Lucien Kuiper, Wim Hermsen, [Hans Bloemen]. Three classes of pulsars seen in g rays. I: spin-down powered pulsars a) normal pulsars b) millisec pulsars (old recycled systems)

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status pulsar studies in soft gamma rays

Status pulsar studiesin soft gamma-rays

Lucien Kuiper, Wim Hermsen, [Hans Bloemen]

Toulouse June 2005


Three classes of pulsars seen in g rays

I: spin-down powered pulsars a) normal pulsars b) millisec pulsars (old recycled systems)

II: accretion powered pulsars a) LMXB (incl. transient ms-pulsars) b) HMXB (Be-binaries, [sub-]giant binaries) III: magnetically powered pulsars (=magnetars) AXPs/SGRs

Toulouse June 2005

class ia spin down powered normal pulsars
Class Ia: Spin-down powered [normal] pulsars
  • CGRO (20 keV-30 GeV) heritage: number of g-ray pulsars increased from 2 (Crab, Vela) to 7 (10), all young (≤ 100 ky) and energetic
  • This is the only established Galactic g-ray source population, emitting over a wide energy range (0.5 keV – 10 GeV)
  • We still do not know where the g-rays are produced in the magnetosphere (outer gap/polar cap) and which physical processes are acting (synchrotron, curvature radiation, inverse Compton, photon splitting, …)

Toulouse June 2005


Normal pulsars continued…

At soft/medium g-ray energies (20 keV – 30 MeV) only 4 pulsars are known from CGRO/RXTE/BeppoSAX, with very different pulse profiles and spectra.

PSR B0531+21

(Crab)PSR B1509-58PSR B0540-69

↖3s IBIS ISGRI; 1 Ms

Detections near ISGRI sensitivity limit – we see just the top of the iceberg it seems

Toulouse June 2005


Normal pulsars continued…

Pulse profile vs energy

PSR B0833-45 (Vela) incl. ISGRI (2 Ms) 15-150 keV (6.2s)














Understanding the HE characteristics (energy-dependent single/double/triple peaked profiles) will profit from detailed light curves for more pulsars

Toulouse June 2005


Normal pulsars continued…

Promising recent progress (Chandra/XMM/RXTE/INTEGRAL)

Deep searches at the cores of SN-remnants and in the error boxes of unidentified EGRET sources yielded detections of several radio dim/quiet energetic pulsars emitting hard X-rays (> 10 keV)


- PSR J1930+1852 (in G54.1+0.3; radio dim)- PSR J1811-1925 (in G11.2-0.3; radio quiet)- PSR J1846-0258 (in Kes 75; radio quiet)- PSR J1617-5055 (near RCW 103)

PSR J1930+1852 in G54.1+0.3Chandra

PSR J1846-0258

in Kes 75

Toulouse June 2005


Normal pulsars continued…

- Pulsed emission has been detected up to ~100 keV (RXTE HEXTE) from these 4 pulsars (Kuiper et al. 2005)

- HE-pulse profile: asymmetric single pulse similar to PSR B1509-58

- Pulsed spectra hard, similar to PSR B1509-58; very likely reaching maximum luminosity at MeV energies

PSR J1846-0258 (Kes 75)RXTE HEXTE 20-100 keV

↖3s IBIS ISGRI; 1 Ms

Top of the iceberg seems seen indeed… the pulsars can be studied in great detail with instruments 10-50 x ISGRI sensitivity

Toulouse June 2005


Normal pulsars continued…

Weaker hard X-ray emitting pulsars (all with hard X-ray spectra)

  • - PSR J0537-6910 (LMC; N157B; radio quiet)- PSR J0205+64 (in 3C58)- PSR J2229+6114 in 3EG J2229+6122- PSR J1747-2958 (“Mouse”, G359.23-0.82)- PSR J2021+3651 in 3EG J2021+3716

X-ray Pulse profiles

↖3s IBIS ISGRI; 1 Ms

Below ISGRI limit, but good potentials with 10-50 x more sensitivity

Toulouse June 2005

class ib spin down powered millisec pulsars
Class Ib: Spin-down powered millisec pulsars

- 6-7 systems show pulsed X-ray emission

- 2 sub-classes: I – broad pulses; soft spectra

II – narrow pulses; hard spectra up to ~20 keV seen

0.1-10 keV

↖3s IBIS ISGRI; 1 Ms


Hard tails of ms pulsars can be studied in detail with 10-50x ISGRI sensitivity

Toulouse June 2005


Class II: accretion powered pulsars

Currently 6 members, e.g. IGR J00291+5934, discovered in outburst during INTEGRAL GP scan:

- Single symmetric pulse [2-150 keV]; pulsed emission seen up to ~150 keV

- Total emission [5-200 keV]: thermal Comptonization on plasma with Te ~50 keV

- Pulsed spectrum shows hardening: Doppler boosting on Comptonized spectrum?

Accretion powered pulsars need high-statistics measurements above 50 keV

Toulouse June 2005


Class III: Anomalous X-ray pulsars (AXPs)

Status before early 2004:

- Not rotation powered pulsars (LX >> Lsd)

- Not accretion powered pulsars [i.e. not X-ray pulsars in LMXBs/HMXBs] (steady spin-down; no apparent optical counterpart; no periodic Doppler delay in X-ray timing)

- Characteristics:

  • Pulse periods 5 -12 s
  • “Steady” spin-down like rotation powered pulsars (incl. glitches)
  • X-ray luminosities 1034-36 erg/s (steady, but outbursts; transient AXPs)
  • [Very] soft X-ray (0.5-10 keV) spectra: BB (0.35–0.6 keV) and PL (2–4)
  • Similar to SGRs (glitches; (out)bursts), suggesting magnetars (NSs with B ~ 1014-15 G powered by decay of the B-field)
  • Young population concentrated along Galactic plane, some in SNRs

Toulouse June 2005


AXPs continued…

AXP Discovery P[s] B[1014 G]


1E2259+586 (SNR) 1981 6.98 0.61E1048-594 1985 6.45 5.04U 0142+614 1993 8.69 1.31RXS J1708-4009 1997 11.00 4.61E1841-045 (SNR) 1997 11.77 7.1CXOU J0100-721 (SMC) 2002 8.02 3.9


AX J1845-026 1998 6.97 ?XTE J1810-197 2003 5.54 2.6

Toulouse June 2005


AXPs continued…

HE-picture changed dramatically with the detection of AXPs at energies >20 keV in IBIS ISGRI skymaps: 1E 1841-045

1RXS J1708-4009

4U 0142+614

- Pulsed nature of >20 keV emission

- Pulsed fraction ➙ 100%

- Emission is very hard


4.2s 3.1s 2.7s

Toulouse June 2005

axp 1e 1841 045 kes 73 kuiper hermsen mendez 2004 apj 613 1173

AXPs continued…

AXP 1E 1841-045 (+ Kes 73) (Kuiper, Hermsen & Mendez, 2004, ApJ 613, 1173)

④AXP pulsed


g = 0.94±0.16

①AXP + Kes 73


②AXP total


⑤AXP total

[+ Kes 73 ?]


③AXP pulsed


⑥AXP total

[+ Kes 73 ?]


AXP spectrum must break above ~100 keV

Toulouse June 2005


AXPs continued…

AXP 4U0142+614

①DC+Pulsed (Chandra)


②Pulsed (ASCA GIS)

⑤Pulsed (RXTE HEXTE)





AXPs have very hard spectra in the 10-100 keV regime, followed by a drastic break… this can be studied in detail with 10-50 x ISGRI/COMPTEL sensitivity

Toulouse June 2005

axp 1e2259 586 ctb 109

AXPs continued…

AXP 1E2259+586 (+ CTB 109)

Screened PCU-2 exposure of747 ks



Onset hard tail


Toulouse June 2005

  • For any type of pulsar,in the soft g-ray band drastic spectral changes & pulse morphology changes occur
  • HE pulsar emission is
  • largely a puzzle
  • Requirements:
  • - maximum sensitivity in
  • the 50 keV – MeV regime
  • - accurate timing
  • - polarization measurement of distinct interest

Toulouse June 2005