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 luminosities ranging between to 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 (~ 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 crust inducing 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) Newborn Neutron star

Several neutron star populations may belong to 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

~ lys

N49 and the March 5 th error box 0.09 arcminsq

Chandra observation of SGR

SGR burst time history

Time (sec) Outburst of AXP 1E in 2002 Kaspi et al 2003

Persistent Emission

Woods et al 2001 SGR Kaspi et al AXP 1E

SGR Timing Properties SGR 1806–20: P = 7.48 s = 8.3 x 10 –11 s s –1 B = 3.2 x (P ) 1/2 G B ~ 8 x G (Kouveliotou et al. 1998) SGR : 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 G

ObjectB-field (Gauss) Galactic nuclei Our Galaxy 2x10 -6 Planets: Jupiter 4 Earth 0.6 Sun (general field) 1 (sunspots) 4,000 Common iron magnet 100 Common MRI field 10,000 Strongest SUSTAINED Lab fields 4.5x10 5 Strongest man-made B 10 7 Radio Pulsars Magnetars

What is the magnetar energy source? L X = erg/s Ė rot = erg/s Accretion: several arguments why it does not work i) No companions detected ii) Bursts cannot be explained iii) ISM:extremely dense and cold medium + extremely slow SGR iv) 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 May 98Sep-Oct Aug 98 Gogus et al. 2002

BURSTS

Typical SGR Bursts Brief Soft L ~ – 10 3 L Edd E ~ – erg Gogus et al. 1999

Intermediate SGR Bursts E ~ 6 x erg Two more events August 29, 1998 & April 28, 2001 had E ~ 10 41–42 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) Rate (c/s) August 27, 1998 L ~ 10 6 – 10 7 L Edd E ~ – erg Hard initial spike + spin modulated soft tail

SGR Woods et al. 2001

Kouveliotou et al SGR SGR

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 SGR Gogus et al. 2001

SGR DECEMBER 27, 2004 GIANT FLARE (SWIFT) Palmer et al, Nature, 2005

SGR December 27, 2004 GIANT FLARE (RHESSI) Hurley et al, Nature 2005

Palmer et al, 2005

X-ray Flare Properties Main Peak duration ~ 0. 5 s Rise time ~ 1.5 msec Tail Duration ~ 380 s ( s) Peak Flux >5 ergs/cm 2 s Total (isotropic) energy release>10 46 erg (Peak) and 5x10 43 erg (tail) Some comparisons: GRB prompt emission peak fluxes: ergs/cm 2 s X-ray afterglows of long bursts: ~ – ergs/cm 2 s Previous giant flares: ~10 -3 ergs/cm 2 s Typical SGR bursts: – ergs/cm 2 s

Giant Flares and short GRBs The two previous giant flares could have been detected Up 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 the 150 BATSE detected The isotropic distribution of short GRBs, the lack of excess from Virgo cluster indicates that at most 5% of short GRBs are SGR GFs or The distance to SGR is less than 15 kpc The SGR GF rate is less than assumed, the GF rate is less than 1/30-40 years, or there are more luminous GFs.

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

Frail et al Nature 1998 SGR

Crystal Brogan, NRAO/UoHawaii VLA image (330 MHz) of the area around SGR

Gaensler et al Nature 2005 VLA J

At a distance of D = 15 d 15, the 1.4 GHz flux of VLA J , at first detection, implies an isotropic spectral luminosity of 5D 2 x10 15 W/Hz, which is ~ 700 times larger than the radio afterglow seen from SGR ! International campaign monitoring over 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 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 ( 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 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) E min > 4x10 43 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 are the magnetar progenitors? What is the magnetar formation Rate? OPEN QUESTIONS