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High-Energy Pulsars: Current Status and Future Prospects

This presentation outlines the current high-energy (≥10 keV) status of pulsars and discusses the need for a better understanding of the production of gamma-rays and other physical processes. It also highlights recent progress and discoveries in this field of research.

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High-Energy Pulsars: Current Status and Future Prospects

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  1. Pulsar research at soft g-rays s Lucien Kuiper, Wim Hermsen Hans Bloemen

  2. Outline of presentation • Introduction: pulsars in a nutshell • Overview current high-energy status (> 10 keV) • Concluding remarks

  3. Pulsars (rapidly spinning neutron stars with high B-fields) can be grouped into three sub-classes: I: spin-down powered pulsars a) normal pulsars b) millisecond 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

  4. Spin-down powered (energetic) pulsars(Class Ia) • CGRO (1991-2000; 20 keV-30 GeV) heritage: number of g-ray pulsars increased from 2 (Crab;Vela) to 7 (10) : all associated with young (≤ 100 ky) and energetic pulsars; exception ms-pulsar PSR J0218+4232 • The only established galactic source population emittingg-rays over a wide (0.5 keV – 10 GeV) energy band • Inspite ~30 year research we still do NOT know where the g-rays are produced in the magnetosphere (outer gap/polar cap) and whichphysical processes are acting (synchrotron, curvature, inverse Compton, photon splitting etc.)

  5. At soft/medium g-ray energies (20 keV – 30 MeV) only 4 pulsars were known (CGRO, RXTE, SAX; all with very different pulse profile morphologies and spectra):a) PSR B0531+21; PSR B1509-58; PSR B0540-69 (< 10 kyr; young) b) PSR B0833-45 (Vela pulsar) (middle aged; < 100 kyr) PSR B0531+21 (Crab) PSR B1509-58 PSR B0540-69 ↖3s IBIS ISGRI; 1 Ms Note: Vela very weak; near 3s IBIS ISGRI sensitivity limit

  6. Multi-wavelength profile collage of PSR B0833-45 incl. IBIS ISGRI (2 Ms) 15-150 keV profile (6.2s) RXTE PCA Comptel EGRET XMM RXTE PCA IBIS ISGRI RXTE PCA EGRET XMM OSSE HE-profile morphology very complex! Statistics still poor for 20 keV-10 MeV window ☹

  7. To understand the HE emission characteristics (pulse profile morphology changes vs. energy ↔ phaseresolved spectroscopy; double/triple peaked or asymmetric single peaked profiles) requires a significant increase of the number of g-ray pulsars • Recent post-CGRO progress (Chandra/XMM/RXTE/INTEGRAL): Targetted (very) deep searches at the cores of SN-remnants or error boxes of unid. EGRET sources yielded the detection of several radio dim/quiet energeticpulsars emitting hard X-rays (> 10 keV): e.g. - 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

  8. 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 These young energetic pulsars can be studied in great detail over the softg-ray band with instruments 10-50 x ISGRI sensitivity!

  9. 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 HE-spectra (>20 keV) below IBIS ISGRI 3s-limit…,butcan be studied with instrument 10-50x more sensitive than IBIS ISGRI!

  10. Spin-down powered millisecond pulsars(Class Ib) • Six (seven) systems show pulsed X-ray emission: 2 sub-classes • I – broad pulses; soft spectra II – small pulses; hard spectra up to ~20 keVg-rays from PSR J0218+4232! low X-ray luminosity high X-ray luminosity heated polar cap magnetospheric; high Blc systems (Crab like); giant radio pulses X-rays: 0.1-10 keV ↖3s IBIS ISGRI; 1 Ms ￪GLAST￪ The hard tails (>20 keV) can be studied in detailby instruments 10-50 x ISGRI sensitivity!

  11. Accretion powered millisecond pulsars (Class IIa; currently six members) • The case IGR J00291+5934: Discovered in outburst during INTEGRAL GP scan • Single symmetric pulse profile [2-150 keV]; pulsed emission detected up to ~150 keV • Total emission spectrum [5-200 keV]: thermal Comptonization spectrum on plasma with electron temperature of ~50 keV • Pulsed spectrum shows hardening towards higher energies: Doppler boosting on Comptonized spectrum? Need for high statistics measurements at energies ≥ 50 keV

  12. Anomalous X-ray pulsars (Class III) • Anomalous X-ray pulsars (status before early 2004)- Norotation powered pulsar! LX >> Lsd- No X-ray pulsar in LMXB/HMXB steady spin-down; no apparent (no accretion-powered pulsar) optical counterpart; no periodic Doppler delay in X-ray timing • Characteristics: • Pulse periods: 5 -12 s • “Steady” spin-down like rotation powered pulsars (glitches observed also) • X-ray luminosities: 1034-36 erg/s (steady, but outbursts also detected; transient AXPs) • (very) soft X-ray (0.5-10 keV) spectra: BB (0.35 – 0.6 keV) + PL (2 – 4) • Similar to Soft Gamma-Ray Repeaters Magnetars (neutron stars (glitches; (out)bursts) with B ~ 1014-15 Gauss powered by decay of B-field) • Young population concentrated along galactic plane; some embedded in Supernova remnants

  13. AXP Discovery P[s] B[1014 G] Persistent 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 Transients AX J1845-026 1998 6.97 ?XTE J1810-197 2003 5.54 2.6

  14. HE-Picture changed dramatically by the detection of point-sources at AXPlocations at energies above 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! HEXTE4.2s 3.1s 2.7s

  15. High-energy spectra Kes 73 andAXP 1E 1841-045(Kuiper, Hermsen & Mendez, 2004, ApJ 613, 1173) 4) Pulsed 1E 1841-045; RXTE/HEXTE g = 0.94±0.16 1) Kes 73 + 1E 1841-045; XMM-Newton ① ⑤ ⑥ 2) Total 1E 1841-045; Chandra (Morii et al. 2003) 5) Kes 73 (?) + 1E 1841-045; IBIS ISGRI ② ④ ③ 6) Kes 73 (?) + 1E 1841-045; CGRO COMPTEL 3) Pulsed 1E 1841-045; RXTE/PCA HE-spectrum of 1E 1841-045 must break above ~100 keV!This can be studied in detail with an instrument 10-50 x more sensitive than IBIS ISGRI

  16. 4U0142+614 4U0142+614 5.7s 3.4s 2.1s

  17. 4U0142+614 ① ChandraDC+Pulsed ④ IBIS ISGRIDC+Pulsed ④ ① ⑥ ② ASCA GIS Pulsed ⑤ RXTE HEXTEPulsed ⑤ ② ③ ③ RXTE PCAPulsed ⑥ CGRO COMPTELDC+Pulsed Very hard soft g-ray spectrum up to ~200 keV; beyond drastic break!The transition can be studied in detail with an instrument 10-50 x ISGRI/COMPTEL sensitivity!

  18. Conclusion • In the soft g-ray band drastic spectral changes/pulse morphologychanges (e.g. Vela/Crab) occur for any type of pulsar. Therefore: • Improving the instrument sensitivity by more than a factor of 10 in the soft g-ray band will boost our understanding of the physics acting in the various types of pulsars enormously! Young spin-downpowered pulsars AXPs Hopefully such a soft g-ray mission will be selected in near futureto significantly increase our knowledge of pulsars in general!

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