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

SLAC, May 18th 2006 1

Magnetars, SGRs, and QPOsMagnetars, SGRs, and QPOs

Marcus ZieglerSanta Cruz Institute for Particle Physics

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope


Talk based on: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, 2006http://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 HurleyUC Berkeley, Space Sciences Laboratory


-3 -2 -1 0 1 2

Log[Period (s)]

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Radio pulsarAXPSGRRadio quiet pulsarHE pulsar

• ~1500? radio pulsars

• 10 -ray pulsars

• ~30 X-ray pulsars

• 7 AXPs

• 5 SGRs

From Alice KFrom Alice K. Harding Harding


Basic FactsBasic Facts

• SGRs are sources of short (~100 ms), repeating bursts of soft -radiation (<100 keV)


Short Repeating BurstsShort Repeating Bursts

0 10 20 30 40 50 60TIME, SECONDS

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200

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ULYSSESSGR1900+1425-150 keV980530D


SGR ENERGY SPECTRA ARE TYPICALLY CHARACTERIZEDBY kT≈25 keV FOR THE SHORT BURSTS

Histogram from the data of Aptekar et al. 2001

Kouveliotou et al. 1993

BATSESGR1900+14

SH

OR

T B

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0 10 20 30 40 50 60 70 80 90 300 400 500keV

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• 4 are known

– 3 in our galaxy (SGR1806-20, 1900+14, 1627-41)

– 1 in the direction of the Large Magellanic Cloud (SGR0525-66)


Locations of the four known SGRsLocations of the four known SGRs

SGR 1806-20 SGR 1900+14

SGR0525-66

N49LMC

SGR1627-41




• 4 are known

– 3 in our galaxy (SGR1806-20, 1900+14, 1627-41)


• They are quiescent X-ray sources (2-150 keV)


QUIESCENT X-RAY SOURCE ASSOCIATED WITH QUIESCENT X-RAY SOURCE ASSOCIATED WITH SGR1806-20SGR1806-20

ASCA, 2-10 keV INTEGRAL-IBIS, 18-60 keV10-11 erg cm-2 s-1




• 4 are known

– 3 in our galaxy (SGR1806-20, 1900+14, 1627-41)



• They have rotation periods in the 5-8 s range, which are increasing with time


THE PERIOD OF SGR1806-20 AND ITS DERIVATIVE FROM THE PERIOD OF SGR1806-20 AND ITS DERIVATIVE FROM QUIESCENT SOFT X-RAYS (2-10 keV) 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

●




• 4 are known

– 3 in our galaxy (SGR1806-20, 1900+14, 1627-41)



• 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)


• Occur perhaps every 30 years on a given SGR

• Intense (3x1046 erg at the source, 1 erg/cm2 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 SpectacularGiant Flare are Spectacular


THE GIANT FLARE FROM SGR1806-20THE GIANT FLARE FROM SGR1806-20

• December 27 2004 21:30:26 UT

• SGR1806-20 was over longitude 146.2º W, latitude +20.4º (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/cm2

• X- and gamma-ray energy released at the source: 3x1046 erg

• This should be considered a lower limit to the energy released (saturation effects, limited energy ranges)


Two Giant FlaresTwo Giant Flares

5.16 s period 7.56 s period50.0 100.0 150.0 200.0 250.0 300.0 350.0

TIME, s.

103

104

105

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SGR1900+14

AUGUST 27 1998

ULYSSES

25-150 keV

0 100 200 300 400Tim e, s

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SGR1806-20DECEMBER 27, 2004

RHESSI20-100 keV


101 102 103

ENERGY, keV

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SMALL BURST

GIANT FLARE


Some Statistics:Some Statistics:DURATIONS OF SHORT BURSTS FOLLOW A LOGNORMAL DURATIONS OF SHORT BURSTS FOLLOW A LOGNORMAL

DISTRIBUTION (Gogus et al. 2001)DISTRIBUTION (Gogus et al. 2001)

LOGNORMAL LOGNORMAL


STATISTICSSTATISTICSWAITING TIME DISTRIBUTIONWAITING TIME DISTRIBUTION

RXTESGR1900

Gogus et al. 1999

LOGNORMAL


STATISTICSSTATISTICSNUMBER-INTENSITY DISTRIBUTIONNUMBER-INTENSITY DISTRIBUTION

Götz et al. 2006

POWER LAW

All bursts detected by integral (2003 to 2004)


STATISTICSSTATISTICSDISTRIBUTIONS OF SGR PROPERTIESDISTRIBUTIONS 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


SPINDOWN IS IRREGULAR, BUT NOT RELATED TO BURSTING SPINDOWN IS IRREGULAR, BUT NOT RELATED TO BURSTING ACTIVITY (Woods et al. 2002, 2006)ACTIVITY (Woods et al. 2002, 2006)

SGR1900+14Woods et al. 2006

GIANT FLARE

This argues against accretion as the cause of the bursts


QUIESCENT X-RAY FLUX LEVEL IS RELATED TO THE QUIESCENT X-RAY FLUX LEVEL IS RELATED TO THE BURSTING ACTIVITYBURSTING ACTIVITY

Reasons are probably complex, but related to magneticstresses on the surface of the neutron star

GIANT FLARE

SGR1806-20Woods et al. 2006


SGR1806-20 IS INVISIBLE IN THE OPTICAL (nSGR1806-20 IS INVISIBLE IN THE OPTICAL (nHH~6x10~6x102222 cm cm-2-2), ),

BUT JUST BARELY VISIBLE IN THE INFRAREDBUT 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


THE MAGNETAR MODELTHE MAGNETAR MODEL(R. Duncan & C. Thompson)(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 3x1017 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 Alfvèn waves, which accelerate electrons to ~100 keV; they radiate their energy in short (100 ms) bursts with energies 1040 – 1041 erg (magnitude 19.5 crustquake)



• 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 (>1014 G required to contain electrons)

• Periodic component comes from the surface of the neutron star


ARE SOME SHORT GRBs ACTUALLY ARE SOME SHORT GRBs ACTUALLY MAGNETAR FLARES IN NEARBY MAGNETAR FLARES IN NEARBY

GALAXIES?GALAXIES?

GIANT FLARE FROM SGR1806-20RHESSI DATA

•Giant flare begins with ~0.2 s long, hard spectrum spike

•The spike is followed by a pulsating tail with ~1/1000th 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

0 100 200 300 400Tim e, s

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View inside a Neutron-StarView inside a Neutron-Star


Inside ‘Extreme’ Neutron Stars Inside ‘Extreme’ Neutron Stars

???

~ 1 x 1015 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?


Torsional Modes, the Earth Analogy 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)


NASA’s Rossi X-ray Timing Explorer NASA’s Rossi X-ray Timing Explorer (RXTE)(RXTE)

Launched in December, 1995, 10th anniversary symposium and party was held at Goddard in January, 06.

http://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html

RXTE’s Unique Strengths

• Large collecting area

• High time resolution

• High telemetry capacity

• Flexible observing

SLAC, May 18th 2006 33Israel 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.


SGR 1806-20: RHESSI Confirmation of SGR 1806-20: RHESSI Confirmation of the Oscillations 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).


Conclusion and many more questionsConclusion 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?

Documents

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