magnetars are magnetically powered, rotating neutron stars

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, residual surface heat or accretion

Live tens of millions of years

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

Radio pulsars

Magnetars

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

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)

How were SGRs discovered?

ApJ 1987

ApJ 1995

AIP Conference Proceedings 366, 1995

~180000 lys

N49 and the March 5th error box

0.09 arcminsq

Chandra observation of SGR 1627-41

SGR burst time history

0 5000 10000 15000 Time (sec)

Outburst of AXP 1E 2259+586 in 2002

Kaspi et al 2003

Persistent Emission

Woods et al 2001

SGR 1806-20

Kaspi et al. 2001

AXP 1E 1048.1-5937

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

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

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

SGR 1900+141996 May 98 Sep-Oct 98 1999 2000Aug 98

Gogus et al. 2002

BURSTS

Typical SGR Bursts

• Brief

• Soft

• L ~ 10-2 – 103 LEdd

• E ~ 1036 – 1041 erg

Gogus et al. 1999

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

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

SGR 1900+14

Woods et al. 2001

Woods et al. 2001 Kouveliotou et al. 2003

SGR 1900+14

SGR 1627-41

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

SOC Systems

(Aschwanden et al. 2000)(Lay & Wallace 1995)

Earthquakes

Solar Flares

Earthquakes

Solar Flares

SOC Systems: Earthquakes

(adopted from Nadeau & McEvilly 1999)

Recurrence Times of Micro Earthquakes

Duration – Magnitude Correlation of Earthquakes

(adopted from Lay & Wallace 1995)

Burst Duration-Fluence Correlation

SGR 1806-20 SGR 1900+14

Gogus et al. 2001

SGR 1806-20DECEMBER 27, 2004 GIANT FLARE (SWIFT)

Palmer et al, Nature, 2005

SGR 1806-20 December 27, 2004 GIANT FLARE (RHESSI)

Hurley et al, Nature 2005

Palmer et al, 2005

Palmer et al, 2005

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

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.

Detection of an expanding RadioNebula associated with the December 27, 2004 Giant Flare

Frail et al Nature 1998

SGR 1900+14

Crystal Brogan, NRAO/UoHawaii

VLA image (330 MHz) of the area around SGR 1806-20

Gaensler et al Nature 2005

VLA J180839-202439

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)

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

SGR 1900+14

Frail et al Nature 1998

Gaensler et al Nature 2005

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]

Gaensler et al, Nature 2005

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

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