1. SLAC, May 18 th 2006 1 Magnetars, SGRs, and QPOs Marcus Ziegler Santa Cruz Institute for Particle Physics Gamma-ray Large Area Space Telescope

2. SLAC, May 18 th 2006 2 Talk based on: Talk at APS meeting from Tod Strohmayer, NASA’s Goddard Space Flight Center Anna L Watts, Tod E Strohmayer, Detection with RHESSI of high frequency X-ray oscillations in the tail of the 2004 hyperflare from SGR 1806-20, 2006 http://arxiv.org/abs/astro-ph/0512630 P.M. Woods and C. Thompson, Soft Gamma Repeaters and Anomalous X-ray Pulsars: Magnetar Candidates, 2004 http://arxiv.org/abs/astro-ph/0406133 Talk at APS meeting from Kevin Hurley UC Berkeley, Space Sciences Laboratory

3. SLAC, May 18 th 2006 3 ~1500? radio pulsars 10  -ray pulsars ~30 X-ray pulsars 7 AXPs 5 SGRs From Alice K Harding From Alice K. Harding

4. SLAC, May 18 th 2006 4 Basic Facts SGRs are sources of short (~100 ms), repeating bursts of soft  -radiation (<100 keV)

5. SLAC, May 18 th 2006 5 Short Repeating Bursts

6. SLAC, May 18 th 2006 6 SGR ENERGY SPECTRA ARE TYPICALLY CHARACTERIZED BY kT≈25 keV FOR THE SHORT BURSTS Histogram from the data of Aptekar et al. 2001 Kouveliotou et al. 1993 BATSE SGR1900+14 SHORT BURSTS 0102030405060708090300400500 keV 0 10 20 30 40 50 60 70 NUMBER OF BURSTS

7. SLAC, May 18 th 2006 7 Basic Facts SGRs are sources of short (~100 ms), repeating bursts of soft  - radiation (<100 keV) 4 are known –3 in our galaxy (SGR1806-20, 1900+14, 1627-41) –1 in the direction of the Large Magellanic Cloud (SGR0525-66)

8. SLAC, May 18 th 2006 8 Locations of the four known SGRs SGR 1806-20 SGR 1900+14 SGR0525-66 N49 LMC SGR1627-41

9. SLAC, May 18 th 2006 9 Basic Facts SGRs are sources of short (~100 ms), repeating bursts of soft  - radiation (<100 keV) 4 are known –3 in our galaxy (SGR1806-20, 1900+14, 1627-41) –1 in the direction of the Large Magellanic Cloud (SGR0525-66) They are quiescent X-ray sources (2-150 keV)

10. SLAC, May 18 th 2006 10 QUIESCENT X-RAY SOURCE ASSOCIATED WITH SGR1806-20 ASCA, 2-10 keV INTEGRAL-IBIS, 18-60 keV 10 -11 erg cm -2 s -1

11. SLAC, May 18 th 2006 11 Basic Facts SGRs are sources of short (~100 ms), repeating bursts of soft  - radiation (<100 keV) 4 are known –3 in our galaxy (SGR1806-20, 1900+14, 1627-41) –1 in the direction of the Large Magellanic Cloud (SGR0525-66) They are quiescent X-ray sources (2-150 keV) They have rotation periods in the 5-8 s range, which are increasing with time

12. SLAC, May 18 th 2006 12 THE PERIOD OF SGR1806-20 AND ITS DERIVATIVE FROM QUIESCENT SOFT X-RAYS (2-10 keV) Kouveliotou et al. 1998 P=7.47 s Woods et al. 2000 P~10 -10 s/s High spindown rate 6.8 years ●

13. SLAC, May 18 th 2006 13 Basic Facts SGRs are sources of short (~100 ms), repeating bursts of soft  - radiation (<100 keV) 4 are known –3 in our galaxy (SGR1806-20, 1900+14, 1627-41) –1 in the direction of the Large Magellanic Cloud (SGR0525-66) They are quiescent X-ray sources (2-150 keV) They have rotation periods in the 5-8 s range, which are increasing with time Occasionally they emit long giant flares, which produce the most intense cosmic gamma-ray fluxes ever measured at Earth (3 observed so far)

14. SLAC, May 18 th 2006 14 Occur perhaps every 30 years on a given SGR Intense (3x10 46 erg at the source, 1 erg/cm 2 at Earth), ~5 minute long bursts of X- and gamma-rays with very hard energy spectra (up to several MeV at least) Are modulated with the neutron star periodicity Display fast oscillations which provide a clue to the structure of the neutron star Giant Flare are Spectacular

15. SLAC, May 18 th 2006 15 THE GIANT FLARE FROM SGR1806-20 December 27 2004 21:30:26 UT SGR1806-20 was over longitude 146.2 º W, latitude +20.4 º (near Hawaii) Detected by at least 24 spacecraft (and probably numerous military spacecraft) – most of which had no X- or gamma-ray detectors! The most intense solar or cosmic transient ever observed Measured X- and gamma-ray flux at the top of the atmosphere: 1.4 erg/cm 2 X- and gamma-ray energy released at the source: 3x10 46 erg This should be considered a lower limit to the energy released (saturation effects, limited energy ranges)

16. SLAC, May 18 th 2006 16 Two Giant Flares 5.16 s period 7.56 s period

17. SLAC, May 18 th 2006 17

18. SLAC, May 18 th 2006 18 Some Statistics: DURATIONS OF SHORT BURSTS FOLLOW A LOGNORMAL DISTRIBUTION (Gogus et al. 2001) LOGNORMAL

19. SLAC, May 18 th 2006 19 STATISTICS WAITING TIME DISTRIBUTION RXTE SGR1900 Gogus et al. 1999 LOGNORMAL

20. SLAC, May 18 th 2006 20 STATISTICS NUMBER-INTENSITY DISTRIBUTION Götz et al. 2006 POWER LAW All bursts detected by integral (2003 to 2004)

21. SLAC, May 18 th 2006 21 STATISTICS DISTRIBUTIONS OF SGR PROPERTIES Lognormal duration and waiting time distributions, and power law number- intensity distribution, are consistent with: –Self-organized criticality (Gogus et al. 2000; Maxim Lyutikov’s talk) system (neutron star crust) evolves to a critical state due to a driving force (magnetic stress) slight perturbation can cause a chain reaction of any size, leading to a short burst of arbitrary size (but not a giant flare) –A set of independent relaxation systems (Palmer 1999) Multiple, independent sites on the neutron star accumulate energy Sudden releases of accumulated energy

22. SLAC, May 18 th 2006 22 SPINDOWN IS IRREGULAR, BUT NOT RELATED TO BURSTING ACTIVITY (Woods et al. 2002, 2006) SGR1900+14 Woods et al. 2006 GIANT FLARE This argues against accretion as the cause of the bursts

23. SLAC, May 18 th 2006 23 QUIESCENT X-RAY FLUX LEVEL IS RELATED TO THE BURSTING ACTIVITY Reasons are probably complex, but related to magnetic stresses on the surface of the neutron star GIANT FLARE SGR1806-20 Woods et al. 2006

24. SLAC, May 18 th 2006 24 SGR1806-20 IS INVISIBLE IN THE OPTICAL (n H ~6x10 22 cm -2 ), BUT JUST BARELY VISIBLE IN THE INFRARED m K’ = 22 Kosugi et al. 2005 This is the only optical or IR counterpart to an SGR so far

25. SLAC, May 18 th 2006 25 THE MAGNETAR MODEL (R. Duncan & C. Thompson) In some rare supernova explosions, a neutron star is born with a fast rotation period (~ ms) and a dynamo which creates a strong magnetic field (up to 3x10 17 G theoretically possible) Differential rotation and magnetic braking quickly slow the period down to the 5-10 s range Magnetic diffusion and dissipation create hot spots on the neutron star surface, which cause the star to be a quiescent, periodic X-ray source The strong magnetic field stresses the iron surface of the star, to which it is anchored The surface undergoes localized cracking, shaking the field lines and creating Alfv è n waves, which accelerate electrons to ~100 keV; they radiate their energy in short (100 ms) bursts with energies 10 40 – 10 41 erg (magnitude 19.5 crustquake)

26. SLAC, May 18 th 2006 26

27. SLAC, May 18 th 2006 27 Localized cracking can’t relieve all the stress, which continues to build Over decades, the built-up stress ruptures the surface of the star profoundly – a magnitude 23.2 starquake Magnetic field lines annihilate, filling the magnetosphere with MeV electrons Initial spike in the giant flare is radiation from the entire magnetosphere (>10 14 G required to contain electrons) Periodic component comes from the surface of the neutron star

28. SLAC, May 18 th 2006 28 ARE SOME SHORT GRBs ACTUALLY MAGNETAR FLARES IN NEARBY GALAXIES? GIANT FLARE FROM SGR1806-20 RHESSI DATA Giant flare begins with ~0.2 s long, hard spectrum spike The spike is followed by a pulsating tail with ~1/1000 th of the energy Viewed from a large distance, only the initial spike would be visible It would resemble a short GRB It could be detected out to 100 Mpc Some short GRBs are almost certainly giant magnetar flares

29. SLAC, May 18 th 2006 29 View inside a Neutron-Star

30. SLAC, May 18 th 2006 30 Inside ‘Extreme’ Neutron Stars ???  ~ 1 x 10 15 g cm -3 Superfluid neutrons The physical constituents of neutron star interiors still largely remain a mystery after 35 years. Pions, kaons, hyperons, quark-gluon plasma?

31. SLAC, May 18 th 2006 31 Torsional Modes, the Earth Analogy Crust fractures in general will excite global modes. Many such modes observed in the days after the 2004 Sumatra – Andaman great earthquake. Spectrum of modes excited depends on fracture geometry, but non-trivial patterns possible. Park et al. (2005)

32. SLAC, May 18 th 2006 32 NASA’s Rossi X-ray Timing Explorer (RXTE) Launched in December, 1995, 10 th anniversary symposium and party was held at Goddard in January, 06. ://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html http://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html RXTE’s Unique Strengths Large collecting area High time resolution High telemetry capacity Flexible observing

33. SLAC, May 18 th 2006 33 Israel et al. 2005 Oscillations in the Dec. 2004 SGR 1806-20 Flare RXTE recorded the intense flux through detector shielding. Israel et al. (2005) reported a 92 Hz quasi-periodic oscillation (QPO) during a portion of the flare. Oscillation is transient, or at least, the amplitude time dependent, associated with particular rotational phase, and increased unpulsed emission. Also evidence presented for lower frequency signals; 18 and  30 Hz. Suggested torsional vibrations of the neutron star crust; following on work by Duncan (1998), and others.

34. SLAC, May 18 th 2006 34 SGR 1806-20: RHESSI Confirmation of the Oscillations Timing study by Watts & Strohmayer (2006, astro-ph/0512630) confirms 92 Hz oscillation, and evidence for higher frequency (626 Hz) modulation. Ramaty High Energy Solar Spectroscopic Imager (RHESSI) also detected the December, 2004 flare from SGR 1806-20 (Hurley et al. 2005).

35. SLAC, May 18 th 2006 35 Conclusion and many more questions Detection of multiple frequencies with consistent scaling is highly suggestive of crustal modes, but need more data! Further understanding and detections could help constrain neutron star properties (EOS, and crust properties, magnetic fields). Unfortunately, giant flares are rare. How are modes excited and damped? How do the mechanical motions modulate the X-ray flux?