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Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters Sandro MEREGHETTI IASF – INAF - Milano

Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters Sandro MEREGHETTI IASF – INAF - Milano. Brief introduction on Soft Gamma-ray Repeaters Recent results on SGR 1806-20 with XMM-Newton INTEGRAL Super Giant Flare of Dec 27 th.

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Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters Sandro MEREGHETTI IASF – INAF - Milano

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  1. Anomalous X-ray Pulsars and Soft Gamma-ray RepeatersSandro MEREGHETTI IASF – INAF - Milano S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  2. Brief introduction on Soft Gamma-ray Repeaters • Recent results on SGR 1806-20 with • XMM-Newton • INTEGRAL • Super Giant Flare of Dec 27th S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  3. The Soft Gamma-ray Repeaters were discovered through their recurrent emission of soft g-ray bursts • Initially considered a peculiar class of Gamma-Ray Bursts: • “soft” • “repeating” • Not always active (long “quiescent” periods) • Only 4 known to date (plus 1 candidate) S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  4. bursts from SGR 1806-20 observed with INTEGRAL 15-40 keV 40-100 keV S.Mereghetti - XXXX Rencontres de Moriond - La Thuile (Götz, Mereghetti, Mirabel & Hurley 2004, A&A 417, L45)

  5. 1900+14 1806-20 1627-41 0526-66 1801-23 ? SGRs are in the Galactic plane  typical distance ~several kpc one is in the N49 supernova remnant in the Large Magellanic Cloud (d=55 kpc) S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  6. SNR N49 in LMC Mazets et al. 1979 Giant flare of March 5, 1979 in SGR 0526-66 known d = 55 kpc  Released Energy >1044 ergs S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  7. Persistent X-ray emission from SGRs • Lx = 1035 -1036 erg /s (1-10 keV) • Pulsations with periods 5 - 10 s • secular spin-down at 10-11 - 10-10 s/s • power law + blackbody spectra  confirm that SGRs are neutron stars • if spin-down is due to dipole energy loss B~1014-15 Gauss • properties similar to those of Anomalous X-ray Pulsars S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  8. “Magnetar” model Duncan & Thompson 1992, ApJ 392, L9 Thompson & Duncan 1995, MNRAS 275, 255 Thompson et al. 2000, ApJ 543, 340 Thompson, Lyutikov and Kulkarni 2002, ApJ 574, 332. • Isolated neutron stars with B = 1014 - 1015 G • Cfr. the strongest man-made magnetic fields:~5 105 G (steady) ~107 G (for a few ms) S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  9. Requirements for a super strong magnetic field in the giant flare of March 5, 1979 • Spin-down to 8 sec in SNR lifetime • Enough magnetic energy to power the flare (>1044 ergs) • 0.2 s initial hard spike = time for large-scale magnetic readjustment (magnetic disturbances must travel through the star) • Drive magnetic dissipation quickly enough to explain SGR activity in a time of order 10,000 years, • Enough energy to power the persistent X-ray emission • Render the hot plasma which emitted soft tail (and normal SGR bursts) nearly transparent to X-rays. • Magnetic confinement of the hot plasma which emitted the soft tail (“trapped fireball”) S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  10. Summary of SGR energetics S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  11. XMM-Newton Results Work done with: A. Tiengo, P. Esposito, D. Gotz – IASF Milano L. Stella, G.L. Israel, N. Rea – Oss. Astron. Roma M. Feroci – IASF Roma R. Turolla – Univ. Padova S. Zane – MSSL London • Four observations of SGR 1806-20 • 2003 April • October • September • October Mereghetti et al. 2005, astro-ph/0502417, ApJ subm. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  12. April 2003 Oct. 2003 Sept. 2004 Oct. 2004 PULSE PROFILES at P = 7.5 s S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  13. 1993 1999 2004 S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  14. Correlation between spectral hardness and spin-down rate in SGRs and AXPs (Marsden & White 2001) Harder X-ray spectrum Larger Spin-down rate S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  15. Correlation between spectral hardness and spin-down rate in SGRs and AXPs (Marsden & White 2001) Harder X-ray spectrum Larger Spin-down rate S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  16. INTEGRAL Results • Discovery of persistent hard X-ray emission with D. Gotz – IASF Milano K. Hurley - Berkeley I.F. Mirabel – ESO Astron. & Astroph. Lett. in press, astro-ph/0411695 • The “Super” Giant Flare of 2004 Dec.27 with D. Gotz – IASF Milano • von Kienlin, A. Rau, G. Lichti – MPE Garching G. Weidespointner, P. Jean – CESR Toulouse Mereghetti et al. 2005, Ap.J.Lett. subm., astro-ph/0502577 S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  17. First detection of persistent emission above 10 keV from a SGR 20-60 keV 60-100 keV Exposure Time ~ 1 Msec Images obtained with the coded mask IBIS/ISGRI telescope S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  18. Autumn 2003 Spring 2004 Autumn 2004 Spring 2003 Long term variability of hard X-ray flux S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  19. Persistent Emission: Spectra F20-100 keV=(4.7±0.8)10-11 erg cm-2 s-1 F20-100 keV=(7.9±1.4)10-11 erg cm-2 s-1 G ~1.9 G ~1.5 Exp: 800 ksec Exp: 200 ksec S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  20. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  21. 21 Imager IBIS Spectrometer SPI Giant Flare INTEGRAL Satellite Imaging and spectroscopy in the 15 keV to 10 MeV band S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  22. INTEGRAL SPI Anti Coincidence Shield (ACS) (512 kg, 91 BGO blocks) • The ACS is also used as an • omni-directional GRB detector • ( E > 80 keV) • Provides: • 50 ms light curve • No direction information • No energy information S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  23. 7.56 s periodicity “signature” of SGR 1806-20 S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  24. Peak affected by instrument saturation S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  25. Initial hard spike • duration ~ 0.2 sec • Peak flux ~ 10 erg/cmq/s E>20 keV • E ~ 4x1046 ergs (for d = 15 kpc) Hurley et al. 2005 – RHESSI & IPN Mazets et al. 2005 – Konus/Wind & Helicon/Coronas F Palmer et al. 2005 – Swift Terasawa et al. 2005 - GEOTAIL S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  26. 2.8 light seconds flux from SGR 1806-20 S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  27. Initial giant pulse backscattered by the Moon S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  28. Initial giant pulse backscattered by the Moon S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  29. With reasonable spectral assumptions and based on Monte Carlo simulations to derive the ACS effective area for the SGR 1806-20 direction we obtain: • Fluence in Moon-backscattered peak ~2x10-6 erg/cmq at E>80 keV  ~ 2 erg/cmq in initial peak • Fluence in pulsating tail ~ 3 10-4 erg/cmq (>80 keV) These results are consistent with those from other satellites… …but we see also something else S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  30. Long lasting emission after the “pulsating tail” 400 s long pulsating tail ~1 hour long emission decaying as t -0.85 S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  31. ACS - Sensitive to photons and to particle background PSAC - Sensitive to particle background only 11 hours S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  32. What is this long lasting emission ? • No pulsations detected - unlikely to come from NS surface or magnetosphere • Synchrotron expanding nebula seen in radio band (Gaenlser et al. 2005, Cameron et al. 2005) • Interaction of relativistic ejections with ambient medium - analogous to GRB afterglow • INTEGRAL emission could be the afterglow S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  33. Eikenberry et al. 2001 Candidate B resolved into 3 fainter objects with adaptive optics observations at ESO VLT. One is variable and coincident with precise radio position Israel et al. 2005, AstroTel First IR counterpart of a SGR Chandra error circle 0.7” radius on K-band image S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  34. 3 Giant Flares from SGRs 1979 March 5 - SGR 0626-66 1998 August 27 - SGR 1900+14 2004 December 27 – SGR 1806-20 S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  35. 3 Giant Flares from SGRs Despite the x100 larger initial energy release, the energy in the tail is of the same order of the other SGRs !!  “magnetically trapped fireball” with similar B intensity S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  36. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  37. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  38. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  39. Summary of XMM-Newton Results • 1-10 keV luminosity doubled in 2004 • X-ray spectrum hardened • Spin-down rate increased by factor ~ 5 • Marsden-White correlation seen in the same source for the first time • For the first time a blackbody component seen in the spectrum (kT= 0.65 keV) Mereghetti et al. 2005, astro-ph/0502417, ApJ subm. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  40. Summary INTEGRAL Results 1/2 • Good Imaging in hard X-rays with IBIS instrument: • First discovery of persistent emission at E > 20 keV in a SGR - power law spectrum up to ~150 keV • Mereghetti et al. 2005 A&A in press, astro-ph/0411695 • Faintest bursts detected from this source • (fluence down to 10-8 erg/cmq) • Hardness – Intensity anti-correlation in short bursts • Gotz et al. 2004, A&A 417, L45 S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  41. Summary INTEGRAL Results 2/2 • High omni-directional sensitivity of SPI-ACS: • Continuous (non-interrupted) coverage of the first Giant Flare from SGR 1806-20 at E > 100 keV • First detection of backscatter from the Moon of an extra-solar astrophysical source !! • First observation of “afterglow” emission in the hard X-ray range • Mereghetti et al. 2005, Ap.J.Lett. subm., astro-ph/0502577 S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  42. Conclusions • The “Super” Giant Flare of December 27 was the culmination of a trend of increasing activity manifested through: • Rise in persistent luminosity at soft and hard X-rays • Hardening of the spectrum • Increase in the spin-down • Increase in the rate of burst S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  43. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  44. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  45. Magnetic energy can dominate over rotational energy after the NS has slowed down to periods of ~seconds EB ~ (1/12) B2 R3ER = ½ I W2 EB ~ 2 1046 (P/5 s) P-11ER = 8 1044 (P/5 s)-2 . (For R=10 km, I=1045 g cm2, and B~6.4 1019 (P dP/dt)1/2 Gauss ) S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  46. R.Duncan Magnetic energy powers SGR emission: • Hard X-ray bursts • Magnetic stresses in the NS crust • Giant flares • Large scale magnetic field rearrangements • Steady X-rays • Heating of NS interior by motion of material driven by magnetic field  surface heating • Shifts of magnetic field drive currents in the magnetosphere  hot spots, comptonization S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  47. Hardness-Intensity Anticorrelation with INTEGRAL (bursts with more than 200 net counts) Hardness Ratio Counts/s S.Mereghetti - XXXX Rencontres de Moriond - La Thuile Götz et al., 2004, A&A submitted

  48. S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  49. Dec 27 Giant Flare of SGR 1806-20 in XMM-Newton EPIC data S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

  50. Basic Models for SGRs FACTS:  Rotational Energy insufficient to power steady X-ray emission.  No binary companion observed so far. MODELS: Magnetar Model:  Magnetic Energy (B 1014-15G) as main energy source.  Diffusion of B powers persistent X-ray emission.  B-driven Starquakes power short bursts and giant flares.  Dipole braking for interpreting P, Pdot. Fossil Disk Model:  Accretion from fall-back disk powers persistent X-ray emission.  Accretion disk torque on NS for interpreting P, Pdot.  Pdot-driven starquakes or Solid-body accretion for short bursts.  Giant flares? S.Mereghetti - XXXX Rencontres de Moriond - La Thuile

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