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Magnetars

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Magnetars

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  1. Magnetars SandroMereghetti INAF, IASF-Milano 44thRencontres de Moriond La Thuile – February 1-8, 2009

  2. Outline • Introduction • Soft Gamma-ray Repeaters • Anomalous X-ray Pulsars • Magnetars and GRBs • Recent results • SGR 1627-41: the reactivation • AXP 1547-48: a new Giant Flare ? S.Mereghetti - La Thuile - Feb.2009

  3. What is a “Magnetar” ? (Isolated) neutron stars where the main source of energy is the magnetic field most observed NS have B = 109 - 1012 G and are powered by accretion, rotational energy, residual internal heat In Magnetars B = 1014 - 1015 G cfr. the strongest man-made magnetic fields:~5 105 G (steady) ~107 G (for a few ms) S.Mereghetti - La Thuile - Feb.2009

  4. Main manifestations of Neutron Stars: • (Radio) Pulsars - • Powered by rotational energy>1700 pulsars observed in radio (+ several Pulsar Wind Nebulae)the youngest seen also at higher energiesmostly isolated typical rotation periods: 1.5 ms – 5 s • Accreting X-ray binaries - Powered by gravitational energyseveral hundreds in High Mass and Low Mass X-ray binariesmany are transientstypical rotation periods 0.1-1000 s Magnetars do not fit in these two categories ! S.Mereghetti - La Thuile - Feb.2009

  5. Two classes (?) of Magnetars: • Soft Gamma-ray Repeaters • Discovered in 1979 as transient sources of hard X-ray bursts and giant flares (GF) • 5 confirmed SGRs (3 emitted a GF ) • Anomalous X-ray Pulsars • Identified in the 90’s as a peculiar class of persistent X-ray pulsar with no signs of binary companions • 9 confirmed AXPs (3 in SNRs, 3 transients) [ see Mereghetti 2008, Astr. & Astroph. Reviews 15, 225 ] S.Mereghetti - La Thuile - Feb.2009

  6. SGRsSoft Gamma-ray Repeaters S.Mereghetti - La Thuile - Feb.2009

  7. SGRs emit short ( < 1 s ) repeating bursts of hard X / soft gamma- rays with soft spectrum (compared to GRBs) Hurley et al. 1999 Bursts Lx ~ 1040 – 1041 erg/s  Super Eddington for a NS spectra at E>10 keV well fit by thermal brem. with kT~30 keV S.Mereghetti - La Thuile - Feb.2009

  8. Location and discovery date of the 5 SGRs 1979 SGR 1900+14 1979 SGR 1806-20 1998 SGR 1627-41 NEW 2008 SGR 0501+45 1979 SGR 0526-66 S.Mereghetti - La Thuile - Feb.2009

  9. Besides the bursts, SGRs have “persistent” X-ray emission Lx ~ 1035 – 1036erg/s [extends up to ~ 200 keV] Pulsations 2.6 – 8 sec  Rotating Neutron stars Long term spin down 10-11 – 10-10 s/s small long term variability in 3 SGRs large variations in 2 “transient” SGRs S.Mereghetti - La Thuile - Feb.2009

  10. … and sometimes emit “Giant Flares” Only three observed 1979 March 5 - SGR 0526-66 L peak ~ 4 1044 erg/s ETOT ~ 5 1044 erg 1998 August 27 - SGR 1900+14 L peak > 8 1044 erg/s ETOT > 3 1044 erg 2004 December 27 – SGR 1806-20 L peak ~ 2-5 1047 erg/s ETOT ~ 2-5 1046 erg S.Mereghetti - La Thuile - Feb.2009

  11. AXPsAnomalous X-ray Pulsars Recognized in 1995 as a new class of pulsars with properties different from those of the other known classes of neutron stars Mereghetti & Stella 1995, ApJ 442, L17 van Paradijs, Taam & van den Heuvel 1995, A&A 299, L41 S.Mereghetti - La Thuile - Feb.2009

  12. Main properties of the AXPs • No evidence for companion stars (very faint IR ctps, no Doppler delays in pulses) • Rotational period of a few seconds (5-12 s) • Secular spin-down (0.05-4) x 10-11 s/s • Lx ˜ 1034 - 1036 erg s-1 >> Rotational Energy Loss • soft X-ray spectrum (kT~0.5 keV) + hard tail up to 200 keV • 3 are in Supernova Remnants • 3 are transients S.Mereghetti - La Thuile - Feb.2009

  13. The AXPs have properties very similar to those of the “quiescent” counterparts of SGRs  Bursts from AXPs were expected …. S.Mereghetti - La Thuile - Feb.2009

  14. 1E2259+586, Kaspi et al. 2003, ApJ 588, L93 1E1048-59 Gavriil et al. 2005, …and indeed short bursts from AXPs were finally discovered with RXTE S.Mereghetti - La Thuile - Feb.2009

  15. Summary • Both SGRs and AXPs are well explained by the Magnetar model • Steady dissipation of magnetic field  surface heating  persistent X-ray emission • NS crust fractures  short bursts • Large scale magnetic dissipation  Giant flares 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. S.Mereghetti - La Thuile - Feb.2009

  16. Outline • Introduction • Soft Gamma-ray Repeaters • Anomalous X-ray Pulsars • Magnetars and GRBs • afterglows from Giant Flares • SGRs and short GRBs • newly born magnetars as GRBs central engine • ……. • Recent results • SGR 1627-41 reactivation • A new Giant Flare ? S.Mereghetti - La Thuile - Feb.2009

  17. SGR – GRB connection: it is not a recent idea…. Mazets et al 1982, Ap&SS 84, 173 “Pre-BATSE era” S.Mereghetti - La Thuile - Feb.2009

  18. 1979 March 5 - SGR 0526-66 L peak ~4 1044 erg/s 1998 August 27 - SGR 1900+14 L peak > 8 1044 erg/s 2004 December 27 – SGR 1806-20 L peak ~ 2-5 1047 erg/s S.Mereghetti - La Thuile - Feb.2009

  19. Initial pulse saturated the instrument Mereghetti et al. 2005, ApJ 624, L105 2.8 light seconds Initial pulse backscattered by the Moon SGR 1806-20 Giant Flare 2004 Dec 2004 S.Mereghetti - La Thuile - Feb.2009

  20. A large fraction of the SHORT GRBs could be Giant Flares from SGRs in external galaxies Giant Flares with the luminosity of the 2004 Dec 27 event at few tens of Mpc would appear as short bursts if only the initial pulse is detected. S.Mereghetti - La Thuile - Feb.2009

  21. Distance of SGR 1806-20 Corbel & Eikenberry 2004 ~ 15 kpc (based on associations with other objects) S.Mereghetti - La Thuile - Feb.2009

  22. How many short GRBs are GF ? but large uncertainty on rate of GF: Nakar et al. 2005  from 10% to 100% of short GRBs could be GF S.Mereghetti - La Thuile - Feb.2009

  23. Outline S.Mereghetti, A.Tiengo, P. Esposito, G.Vianello at IASF MILANO D. Gotz, G.L.Israel, N.Rea, R.Turolla, S.Zane, L.Stella, K. Hurley, & al…. • Introduction • Magnetars and GRBs • Recent results (…of our group) • SGR 1627-41: reactivation • AXP 1547-48: a new Giant Flare ? S.Mereghetti - La Thuile - Feb.2009

  24. SGR 1627-41 S.Mereghetti - La Thuile - Feb.2009

  25. SGR 1627-41: the Transient SGR • Discovered in 1998 (Woods et al. 1999); active only a few weeks and quiescent since then • Spin Period could not be found • No identified optical/NIR counterparts (Wachter et al 2004) • Long term decrease in X-ray luminosity interpreted as cooling after crust heating by the bursts (Kouveliotou et al. 2003) S.Mereghetti - La Thuile - Feb.2009

  26. (Kouveliotou et al. 2003) SAX, ASCA and Chandra data spanning 4 years Model of cooling after the deep crustal heating occurred during the active period (Lyubarsky, Eichler & Thompson 2002) S.Mereghetti - La Thuile - Feb.2009

  27. SGR 1627-41: New outburst in May 2008 Esposito et al. 2008a, MNRAS S.Mereghetti - La Thuile - Feb.2009

  28. Comparison of X-ray flux decays after strong bursting episodes in different magnetars (Esposito et al. 2008, MNRAS, 390, L34) S.Mereghetti - La Thuile - Feb.2009

  29. XMM Target of Opportunity performed as soon as visibility constraints allowed it (Esposito et al. 2009, ApJ 690, L105) Discovery of the long-sought pulsations... … and diffuse soft X-ray emission from SNR P = 2.6 s S.Mereghetti - La Thuile - Feb.2009

  30. AXP 1E1547-5408 S.Mereghetti - La Thuile - Feb.2009

  31. 1E 1547-5408 (Gelfand & Gaensler 2007) X-rays - Chandra RADIO SNR G327.24-0.13 NIR S.Mereghetti - La Thuile - Feb.2009

  32. 1E 1547-5408 Halpern et al 2007) Pulsations and spin-down [discovered in radio] confirm that 1E1547 is an AXP (Camilo et al 2007) S.Mereghetti - La Thuile - Feb.2009

  33. on Jan 22 many bursts were detected from 1E 1547-5408 by ~all satellites Swift - Gronwall et al. GCN 8833 Fermi - Connaughton GCN 8835, von Kienlin & Connaughton GCN 8838, INTEGRAL - Savchenko et al. GCN 8837, Mereghetti et al. GCN 8841 Suzaku - Terada et al. GCN 8845, Konus-WIND - Golenetskii et al. GCN 8851, RHESSI - Bellm et al. GCN 8857 S.Mereghetti - La Thuile - Feb.2009

  34. 1E 1547-5408 - “SGR-like” bursts on Jan 22 INTEGRAL SPI-ACS E>80 keV S.Mereghetti - La Thuile - Feb.2009

  35. 1E 1547-5408 - a new Giant Flare ?? Mereghetti et al. GCN 8841 INTEGRAL SPI-ACS E>80 keV S.Mereghetti - La Thuile - Feb.2009

  36. 1E 1547-5408 - Swift/XRT follow-up 2-10 keV SUPER - PRELIMINARY !!! S.Mereghetti - La Thuile - Feb.2009

  37. Tiengo, SM, et al. GCN 8848 Expanding X-ray rings S.Mereghetti - La Thuile - Feb.2009

  38. X-ray halos from interstellar dust scattering s OBSERVER X-RAY SOURCE  DUST D = x Ds Ds S.Mereghetti - La Thuile - Feb.2009

  39. S.Mereghetti - La Thuile - Feb.2009

  40. Earth ionosphere disturbance caused by 1E1547 flare Chackrabarti et al. GCN 8881 S.Mereghetti - La Thuile - Feb.2009

  41. Summary of results • SGR 1627-41 • discovery of P=2.6 s (2nd fastest magnetar) • X-ray emission shows that SNR is more extended than desumed from radio data  the SGR is at the center • AXP 1547-58 • strong burst with pulsed tail (P=2.1 s) might be a Giant Flare (1st from an AXP) • Expanding dust scattering rings  properties of GF in X-ray (never observed before), distance S.Mereghetti - La Thuile - Feb.2009

  42. CONCLUSIONS • AXPs and SGRs  single class of objects (MAGNETARS) containing the highest magnetic fields observed in the Universe (~1015 G) • Physics of High B fields • Astrophysics of Neutron Stars and endpoints of massive stars • MAGNETAR – GRBs connections: • some of the Short GRBs are GF • central engines of long GRBs • “afterglows” in GFs • Many new results in the last few months… • cooperation from the sources + fast reaction of observations • …and more to come • Gravit. waves, UHE CR, neutrinos,… S.Mereghetti - La Thuile - Feb.2009

  43. S.Mereghetti - La Thuile - Feb.2009

  44. EXTRA SLIDES S.Mereghetti - La Thuile - Feb.2009

  45. 3 Giant Flares from SGRs Despite the x100 stronger initial spike of the 2004 GF, the energy in the tail is of the same order of the other SGRs !!  “magnetically trapped fireball” with similar B intensity S.Mereghetti - La Thuile - Feb.2009

  46. Mereghetti, Esposito, Tiengo 2006, astro-ph/0608364 S.Mereghetti - La Thuile - Feb.2009

  47. SGR 1806-20 X-RAY FLUX PHOTON INDEX PERIOD TIME (years) S.Mereghetti - La Thuile - Feb.2009

  48. Magnetar formation(a rare event…?) Standard Scenario - Duncan & Thompson 1992, ApJ 392, L9 Requires a “proto-NS” spinning very rapidly 0.6-3 ms Convection + differential rotations  efficientdynamo  can produce B~1015 G Dipole energy losses cause a rapid spin-down to P>10 s in 104/B215 yrs S.Mereghetti - La Thuile - Feb.2009

  49. The “standard” formation scenario predicted high recoil velocities ~1000 km/s Seemed consistent with offset from SNR centers However the claimed associations of three SGRs with SNRs are no more considered reliable (and the AXPs with SNRs are at the center) S.Mereghetti - La Thuile - Feb.2009

  50. Helfand et al 2007, ApJ – astro-ph/0703336 Proper motion of AXP XTE J1810 measured with VLBA 13.5 +/- 1 mas / yr D ~ 3.5 kpc  VT ~ 200 km/s S.Mereghetti - La Thuile - Feb.2009