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MAGNETARS

MAGNETARS. Soft gamma-ray repeaters Anomalous x-ray Pulsars. A few slides on strong b fields. Table of Too Much Information. http:// solomon.as.utexas.edu / magnetar.html.

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MAGNETARS

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  1. MAGNETARS Soft gamma-ray repeaters Anomalous x-ray Pulsars

  2. A few slides on strong b fields

  3. Table of Too Much Information http://solomon.as.utexas.edu/magnetar.html

  4. Above the quantum electrodynamic field strength, atoms become atomic needles, the quantum vacuum becomes birefringent, and x-ray photons can merge or split. Good ‘ol wiki

  5. A quantum field limit of 10^49 – 10^53 G: monopoles!

  6. Soft Gamma Ray repeaters

  7. 1979: the year of SGR discovery, if we were looking for them. Jan 7: SGR 1806-20 Mar 14: SGR 1900+14 -3 events 3 days Mar 5: SGR 0526−66 -2 events 2 days

  8. March 5, 1979: a day that will live in infamy Venera 11 Helios 2 Venera 12 Pioneer Earth ISEE Light curve of the March 5th event, as recorded by gamma-ray detectors aboard the Venera 12 space probe. (From E.P. Mazets et al., 1979, Nature 282, p. 587.) 

  9. 7 data points, a little geometry, and the location was identified: LMC, SNR N49 X-ray point source: coincidence? Core phase changes? And thus began the the theorist mad scramble for the most-awesome-theory award. Quark nuggets?

  10. Anomalous x-ray Pulsars

  11. AXPs have softer x-ray spectrum compared to an x-ray binary and pulse between 5-9s. Magnetar? Fossil Disk? Pulsing optical emission, near infrared emission help distinguish the two theories.

  12. And then they burst in the x-ray…

  13. The magnetar Model

  14. Neutron stars form their magnetic fields in the first 20s of formation by dynamo action. Pulsars have failed dynamos: Crab pulsar with birth speed of 20ms was much to slow.

  15. Magnetars lose angular momentum quickly through efficient magnetic waves, thus they don’t pulse radio. Expect: Thermal X-ray! SGR Bursts! The magnetic field is so strong material is pushed around in the crust and interior. Release of magnetic energy comes from shifts in the crust.

  16. Magnetic field of 10^14 G? tell me more about those quark nuggets…

  17. By 1995, Thompson and Duncan had the theoretical ground work laid down for observation to follow. (1) Spin down the star to an 8.0 s period in the age of the SNR. (2) Provide enough energy for the March 5th event, a putative magnetic flare. (3) Account for the short, 0.2-second duration of the March 5th event's hard spike. This is the time needed to make a large-scale magnetic readjustment, since magnetic disturbances must travel through the star. (4) Drive magnetic dissipation quickly enough to explain SGR activity in a time of order 10,000 years, the ages of SGRs (as inferred from their associated SNRs). (5) Provide enough energy to power the steady X-ray glow of SGRs. ("the X-ray point sources"). (6) Render the hot gas of particles which emitted the March 5th event's soft tail (and normal SGR bursts) nearly transparent to X-rays. This is necessary to explain why SGR bursts are so extraordinarily bright. (7) Hold down, with magnetic forces, the hot gas of particles which emitted the March 5th event's soft tail.

  18. After initial burst, magnetic field lines hold in plasma for a few second/minutes depending on the scale of the burst. Robert Duncan’s Color pencil drawings!

  19. 1998: the year of Magnetar discovery, now that we are looking for them. May 21: SGR 1806-20 P and Pdot measured: 10^14 G again. Jun: NEW! SGR 1627-41 -100 bursts Aug 27: SGR 1900+14 -GIANT FLARE May-June: SGR 1900+14 -50 outbursts Aug: SGR 1900+14 -P Pdotmeasured: 10^14 G

  20. Aug 27, 1998: Flare so strong disrupts naval communications (well sort of).

  21. The tail ended abruptly, predicted by magnetar model, as fireball evaporates. Lets see you do that strange star! M. Feroci, K. Hurley, R.C. Duncan & C. Thompson 2001, Astrophysical Journal , 549, p.1021.)

  22. Observable Properties

  23. Short bursts: last about .1s, concentrated in time, spaced log-normal, with energy distributions of E^(-5/3) (for some). Log mean ~ 10^4 s L=10^41 erg/s (above L_edd) Except for length, these characteristics also happen to describe: earthquakes, Solar flares, and avalanches.

  24. Burst spectra: as it turns out they are different. Combined with timing information, they are easy to distinguish. Well modeled as optically thin thermal bremsstrahlung

  25. Giant Flares: only two so far with lower bound of 10^44 erg/s E^(-1.5) distribution.

  26. Intermediate bursts appear to be aftershocks of the giant flares. 10^41 – 10^43 erg More bursts are filling in the gaps of energy distribution, so most likely a continuum. Spectrally the same as short, and giant except for two.

  27. Persistent x-ray emission is variable fit to two component blackbody with no spectral features. Sit normally at 10^35 – 10^36 ergs /s but suddenly drop to 10^33 for extended periods of time.

  28. Pulse timing gives all the normal stats for a neutron stars.

  29. Magnetars also have larges glitches which was previously predicted by theory.

  30. Further magnetar evidence can be seen as the pulse shape changes after bursts. -Timing changes as well indicating an increase in magnetic torque.

  31. Magnetars simplify their fields, die and become dim x-ray sources as they cool off… <!!!BUT THE FIELDS ARE STILL THERE!!!>

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