2. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters Sandro Mereghetti INAF - IASF Milano

3. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Short review of AXP and SGR properties AXP / SGR relationship 2 recent results XMM-Newton > Variability in AXP 1E1048 INTEGRAL > Spectral evolution in bursts from SGR 1806 OUTLINE

4. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti NORMAL x-ray pulsars are rotating magnetized neutron stars 1) In binary systems powered by accretion from a companion star e.g. Vela X-1, Cen X-3 Periods from 60 ms to a few 1000 s 2) rotation powered radio pulsars e.g. Crab, Geminga, PSR 1957+20 Periods from 1.5 ms - a few seconds

5. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Spin Period (s) Maximum X-ray Luminosity (erg/s) Most accreting pulsars are in massive binaries AXP are only found in the narrow period range 5-12 s AXP in the context: Accreting pulsars

6. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti

7. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti No evidence for massive companion stars limits on a x sin i from timing limits on F x /F opt from optical/IR observations Period of a few seconds (6-12 s) Almost steady spin down Very soft X-ray spectrum kT BB 3-4 AXP PROPERTIES

8. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti AXP AXP have very soft X-ray spectra

9. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti 2 ( or 3 ? ) are in SNRs X-ray luminosity L x = 10 34 - 10 36 erg s -1 L x > rotational energy loss for a neutron star AXP PROPERTIES

10. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti SPIN - DOWN ENERGY LOSS X-RAY LUMINOSITY ROTATION-POWERED PULSARS (Possenti et al. 2002) L x = E rot.

11. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti a spinning down pulsar, with a soft X-ray spectrum, apparently not powered by accretion from a (massive) companion star, and with luminosity larger than the rotational energy loss (assuming a neutron star) Operational definition of AXP

12. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti AXP census PdP/dt (s)(10 -11 s/s) 4U 0142+618.70.2- 1E 2259+58670.05CTB 109 1E 1048-59376.42-3- 1E 1841-04511.84Kes 73 AX J1845-037-G296+0.1, Var. RXS 1708-40112- CXO J0110-7282in SMC XTE J1810-1975.51.8- Var.

13. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti MAGNETIC ENERGY - field decay - enhanced thermal emission ACCRETION - very low mass companion - ISM / molecular clouds - disk around isolated NS ROTATIONAL ENERGY - isolated NS - isolated WD MODELS ? ?

14. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Isolated NS + accretion disk Thorne-Zytkow object (Van Paradijs et al. 1995, Ghosh et al. 1997) fall back after SN explosion (Chatterjiee et al. 2000, Alpar 2001) capture of SNR ejecta by fast moving NS (Marsden et al. 2000, 2001)

15. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Magnetar model (Thompson and Duncan) Emission powered by magnetic field decay and/or enhanced cooling Originally developed for SGRs where evidence for high B is stronger due to large flares and bursts Extended to AXP due to similar P and dP/dt values Isolated NS with B > 10 14 Gauss

16. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Soft Gamma-ray Repeaters Initially discovered as a peculiar class of Gamma- Ray Bursts soft repeating About 5 currently known (1 in the LMC) Not always active (long quiescent periods)

17. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti SGRs vs. GRBs DurationsSpectra Courtesy K. Hurley

18. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Energetics of SGRs Short Bursts: Peak Luminosity~10 38 -10 42 erg s -1 Total Energy~10 39 -10 42 erg Giant Flares: Peak Luminosity~4 x 10 44 erg s -1 Total Energy~0.7-2 x 10 44 erg

19. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Giant Flares Mazets et al. 1979, Cline et al. 1980 1998 August 27 from SGR 1900+14 1979 March 5 from SGR 0526-66 Feroci et al. 1999

20. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Persistent X-ray emission from SGRs Lx = 10 35 -10 36 erg /s (1-10 keV) Pulsations with periods 5 - 10 s secular spin-down at 10 -11 s/s power law (+ blackbody) spectra VERY SIMILAR TO AXPs !!

21. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti AXP

22. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti (Kaspi et al. 2003) SGR-like activity in the AXP 1E2259+586

23. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti bursts have L peak : 10 36 -4 10 38 erg/s Change in pulse morphology Glitch = 4 10 -6 (Kaspi et al. 2003)

24. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti AXP=SGR ? Only observational selection effects introduced a distinction between these sources belonging to the same class of objects: in AXP the quiescent, pulsating emission was discovered first SGR were discovered through their bursts

25. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Short review of AXP and SGR properties AXP / SGR relationship 2 recent results XMM-Newton > Variability in AXP 1E1048 INTEGRAL > Spectral evolution in bursts from SGR 1806 OUTLINE

26. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti (Mereghetti et al. 2004) First evidence for significant variability in 1E 1048-59 2 EPIC XMM-Newton observation

27. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti 2000 89 % 2003 53 % The pulsed fraction decreased while the flux increased Spectrum did not vary BB+PL kT=0.6 keV = 3

28. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti 4U 0142+61 SAX (Israel et al 1999) Power law photon index = 3.9 + Blackbody kT = 0.4 keV

29. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Most AXP require 2 component model PL + BB Phot.index kT BB R BB N H 10 22 1E 1048-59 2.9 0.63 keV0.4 d 3 km 1.0 4U0142+61 3.9 0.40 keV1.8 d 1 km 1.1 1E 2259+583.6 0.41 keV2.6 d 4 km 0.9 RXS1708-40 2.6 0.46 keV7.9 d 8 km 1.4 AXJ1845-00 - 0.64 keV3.9 d 15 km 6 1E 1841-00453.0 - - 2

30. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Are the two spectral components related to distinct emitting regions and/or physical processes ?

31. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti (Oezel, Psaltis, Kaspi 2001) small energy dependence of pulsed fraction requires ad hoc tuning of the BB and PL components

32. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Despite the large flux variation the spectral shape did not vary BB+PL in both observations kT = 0.6 keV phot. Index = 3... these are the typical parameters seen in this source

33. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti 2000 89 % 2003 53 % The pulsed fraction decreased while the flux increased BB and PL are not physically distinct components

34. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Short review of AXP and SGR properties AXP / SGR relationship 2 recent results XMM-Newton > Variability in AXP 1E1048 INTEGRAL > Spectral evolution in bursts from SGR 1806 OUTLINE

35. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti SGR1806-20 entered a new period of activity in July 2003 An INTEGRAL ToO observation started on 3 September 2003, while the source was still active INTEGRAL continued to observe SGR 1806-20 (l = 9.99 deg, b = -0.24 deg) during the Galactic Center Deep Exposre (GCDE) until mid October 24 bursts were detected by IBIS in real time by the INTEGRAL Burst Alert System (IBAS) and confirmed later by off-line analysis

36. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti 24 bursts from SGR 1806-20 have been detected with the INTEGRAL Burst Alert System. ToO GCDE INTEGRAL Julian Day Number of bursts/day

37. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti GCDE Bursts

38. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti JEM-X IBIS/ISGRI Fluence (15-100 keV) 2.5×10 -8 erg cm -2 Yoff = -0.97º Zoff = -2.22º 3-20 keV 100-200 keV 15-40 keV 40-100 keV

39. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti 15-100 keV IBIS/ISGRI spectra of the bursts with more than 500 net counts Optically Thin Thermal Bremsstrahlung model provides good fits (power-law, blackbody, Band GRB model are ruled out) kT ÷ 32-42 keV Conversion factor (15-100 keV, = 38 keV) 1 count s -1 = 1.5x10 -10 erg cm -2 s -1 Spectral Analysis

40. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti INTEGRAL Log N- Log S (Fluence distribution) INTEGRAL Log N- Log P (Peak Flux distribution)

41. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti THE SGR BURSTS OBSERVED BY IBIS ARE NORMAL IN MOST RESPECTS Durations, energy spectra are typical However, the fluences are very low,~1.5x10 - 8 erg/cm 2, 25-100 keV These are the among the weakest bursts seen from this SGR; thanks to imaging, we are certain that the source is indeed SGR1806-20

42. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti IBIS (20-40 keV) (INTEGRAL CP data ~ 1 Msec, courtesy Ada Paizis) 2-3 mCrab source 6 sigma detection

43. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Thompson & Duncan (1995) e + e - plasma Highly magnetized (B~10 15 G), slowly rotating (P~ 5-8 s) neutron stars Bursts are triggered by a sudden shift in the magnetospheric footpoints driven by a fracture in the neutron star crust The radiation originates from the cooling of an optically thick pair-photon plasma The MAGNETAR model predictions

44. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Woods et al. (1999) SGR 1900+14: an exception Two peculiar bursts of intermediate duration (~1 s) and and with hard (kT~100 keV) spectra Soft-to-hard evolution For typical (~0.1 s long) bursts: No signifcant spectral evolution predicted and in general NOT observed up to now (e.g. Fenimore et al. 1994, Kouveliotou et al. 1987) Time (seconds since trigger) Photon Index

45. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Spectral Evolution of weak bursts with INTEGRAL Götz et al., 2004, A&A submitted 15-40 keV 40-100 keV

46. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Götz et al., 2004, A&A submitted Hardness-Intensity Anticorrelation with INTEGRAL (bursts with more than 200 net counts) Counts/s Hardness Ratio

47. Topics in X-ray astronomy - Tuebingen February 2004 S.Mereghetti Conclusions 1) XMM / EPIC detected the first significant variation in the flux and pulsed fraction of the AXP 1048 the spectral invariance is a further evidence that the PL+BB spectral decomposition does not have a physical meaning 2) INTEGRAL / IBIS detected the first evidence for spectral evolution of fain SGR bursts as well as a hardness intensity anticorrelation these properties are not (yet) foreseen in the magnetar model