magnetars are magnetically powered, rotating neutron stars
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Magnetars are magnetically powered, rotating neutron stars. RADIO PULSARS 2000 discovered to date Radiate covering most of the electromagnetic spectrum Rotate with periods that span five decades (ms to a few hours). Are powered by their own rotational energy, - PowerPoint PPT PresentationTRANSCRIPT
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Magnetars are
magnetically powered,
rotating neutron stars
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RADIO PULSARS
2000 discovered to date
Radiate covering most of the electromagnetic spectrum
Rotate with periods that span five decades (ms to a few hours).
Are powered by their own rotational energy, residual surface heat or accretion
Live tens of millions of years
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MAGNETARS (11 discovered to date)
Radiate almost entirely in X-rays, with luminositiesranging between 1033 to 1036 erg/s
Emit typically brief (1-100 ms) bursts that may exceed Eddington Luminosities and very rarely, Giant Flares
Rotate in a very narrow period interval (5-11 s) and slow down faster than any other object (~10-10-10-11 s/s)
Are powered by magnetic field energy, which heats the neutron star interior so that the surface glows persistently in X-rays, and fractures the crustinducing short, repeated bursts at random intervals.
Die rather young; typical ages are ~10000 yrs
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Radio pulsars
Magnetars
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MAGNETARS
AGE: 0-10 s 0-10,000 years above 10,000 years
AGE: 0-10 s 0-10 million years above 10 million yrs
RADIO PULSARS
Ordinary Star (8-10 Msun)
NewbornNeutronstar
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Several neutron star populations may belongto the Magnetar class:
Soft Gamma Repeaters (SGRs)
Anomalous X-ray Pulsars (AXPs)
Dim Isolated Neutron Stars (DINs)
Compact Central X-ray Objects (CCOs)
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How were SGRs discovered?
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ApJ 1987
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ApJ 1995
AIP Conference Proceedings 366, 1995
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~180000 lys
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N49 and the March 5th error box
0.09 arcminsq
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Chandra observation of SGR 1627-41
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SGR burst time history
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0 5000 10000 15000 Time (sec)
Outburst of AXP 1E 2259+586 in 2002
Kaspi et al 2003
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Persistent Emission
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Woods et al 2001
SGR 1806-20
Kaspi et al. 2001
AXP 1E 1048.1-5937
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SGR Timing Properties
• SGR 1806–20: P = 7.48 s
= 8.3 x 10–11 s s–1
B = 3.2 x 1019 (P )1/2 G
B ~ 8 x 1014 G (Kouveliotou et al. 1998)
• SGR 1900+14:P = 5.16 s
= 6.1 x 10–11 s s–1 (Hurley et al. 1999; Kouveliotou et al. 1999)
.P .
P
.P B ~ 5.6 x 1014 G
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Object B-field (Gauss)
Galactic nuclei 10-2-10-3
Our Galaxy 2x10-6
Planets: Jupiter 4 Earth 0.6Sun (general field) 1 (sunspots) 4,000Common iron magnet 100Common MRI field 10,000Strongest SUSTAINEDLab fields 4.5x105
Strongest man-made B 107
Radio Pulsars 1012-1013
Magnetars Magnetars 10101414-10-101515
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What is the magnetar energy source?LX = 1035 erg/s
Ė rot = 1033 erg/s
Accretion: several arguments why it does not worki) No companions detectedii) Bursts cannot be explainediii) ISM:extremely dense and cold medium + extremely slow SGRiv) fossil disc: detection of persistent emission immediately after giant flare argues against it
Magnetar model (Duncan and Thompson 92)Decay of a super-strong magnetic field
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SGR 1900+141996 May 98 Sep-Oct 98 1999 2000Aug 98
Gogus et al. 2002
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BURSTS
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Typical SGR Bursts
• Brief
• Soft
• L ~ 10-2 – 103 LEdd
• E ~ 1036 – 1041 erg
Gogus et al. 1999
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Intermediate SGR Bursts
E ~ 6 x 1042 erg
Two more eventsAugust 29, 1998 &April 28, 2001 had E ~ 1041–42 erg
Continuum of
burst energies
Kouveliotou et al 2001
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Giant SGR Flares
(Mazets et al. 1979)
March 5, 1979
(Feroci et al. 1999)
Time (s)
Rat
e (c
/s)
August 27, 1998
• L ~ 106 – 107 LEdd
• E ~ 1044 – 1045erg
• Hard initial spike + spin modulated soft tail
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SGR 1900+14
Woods et al. 2001
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Woods et al. 2001 Kouveliotou et al. 2003
SGR 1900+14
SGR 1627-41
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Self-Organized Criticality• It states that composite systems self-organize to a
CRITICAL STATE where a slight perturbation can cause a chain reaction of any size.
• SOC is the evolution of a system into an organized form in the absence of any external constraints.
• Systems evolve from non- or slight correlation to a high degree of correlation (critical state)
Simple models: Sand piles, Earthquakes, stock market
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SOC Systems
(Aschwanden et al. 2000)(Lay & Wallace 1995)
Earthquakes
Solar Flares
Earthquakes
Solar Flares
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SOC Systems: Earthquakes
(adopted from Nadeau & McEvilly 1999)
Recurrence Times of Micro Earthquakes
Duration – Magnitude Correlation of Earthquakes
(adopted from Lay & Wallace 1995)
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Burst Duration-Fluence Correlation
SGR 1806-20 SGR 1900+14
Gogus et al. 2001
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SGR 1806-20DECEMBER 27, 2004 GIANT FLARE (SWIFT)
Palmer et al, Nature, 2005
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SGR 1806-20 December 27, 2004 GIANT FLARE (RHESSI)
Hurley et al, Nature 2005
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Palmer et al, 2005
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Palmer et al, 2005
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X-ray Flare Properties
• Main Peak duration ~ 0. 5 s• Rise time ~ 1.5 msec• Tail Duration ~ 380 s (50 cycles@ 7.56s)• Peak Flux >5 ergs/cm2 s• Total (isotropic) energy release>1046 erg (Peak)and 5x1043 erg (tail)
Some comparisons:
GRB prompt emission peak fluxes: 10-8-10-3 ergs/cm2 sX-ray afterglows of long bursts: ~10-11 – 10-13 ergs/cm2 s
Previous giant flares: ~10-3 ergs/cm2 sTypical SGR bursts: 10-9 – 10-6 ergs/cm2 s
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Giant Flares and short GRBs
The two previous giant flares could have been detectedUp to 8 Mpc; the recent one up to 40 Mpc
Taking into account the SFR in our Galaxy, we would expect 80 such events per year to be compared with the150 BATSE detected
The isotropic distribution of short GRBs, the lack ofexcess from Virgo cluster indicates that at most 5% of short GRBs are SGR GFs or
The distance to SGR 1806-20 is less than 15 kpcThe SGR GF rate is less than assumed, the GF rate isless than 1/30-40 years, or there are more luminous GFs.
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Detection of an expanding RadioNebula associated with the December 27, 2004 Giant Flare
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Frail et al Nature 1998
SGR 1900+14
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Crystal Brogan, NRAO/UoHawaii
VLA image (330 MHz) of the area around SGR 1806-20
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Gaensler et al Nature 2005
VLA J180839-202439
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At a distance of D = 15 d15, the 1.4 GHz flux of VLA J180839-202439, at first detection, implies an isotropic spectral luminosity of 5D2x1015 W/Hz, which is ~ 700 times larger than the radio afterglow seen from SGR 1900+14 !
International campaign monitoring over 0.35-16 GHz the AG from days 6-19 after the GF: VLA, ATCA, WSRT, MOST here (MERLIN, VLBA, GBT pending)
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The nebula shape is resolved at 8.5 GHz: except for day 16.8, the source is elliptical with axial ratio ~0.6 and major axis oriented ~60º W to N
Constant isotropic expansion at 0.27(10)c until day 19.7
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SGR 1900+14
Frail et al Nature 1998
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Gaensler et al Nature 2005
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The light curve exhibits an achromatic break at 8.8 days: e.g. at 4.8 GHz the decay index transitioning from 1.5 to 2.84
Significant linear polarization indicating synchrotron radiation. The early PA indicated B field alignment with the nebular axis
Spectral steepening at high freg. From day 11.2 single PL (0.84-8.5 GHz) with index -0.75(2)-> electron index p= 2.50(4) [p=1-2a]
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Gaensler et al, Nature 2005
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RADIO Flare Properties
• the radio emission was 500 times more luminous than the 1900+14 flare (at 15 kpc)
• the radio emission lasted over 45 days and counting
• the light curve exhibits a VERY STEEP achromatic break
• the spectrum is consistent with a power law index of –0.75(2) from 0.84 – 8.5 GHz
•VARIABLE linear polarization
• the radio nebula expands with 0.3c (~ 4mas per day)
• Emin > 4x1043 ergs
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What is the association between bursts and spin changes?
Is there a thermal component in the persistent emission in all magnetars? When does it emerge?
Are there lines in the X-ray spectra of magnetars?
Is there an association of magnetars with Supernovae Remnants and clusters of very massive stars? Which arethe magnetar progenitors? What is the magnetar formationRate?
OPEN QUESTIONS
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