INTEGRAL & Magnetars: a high energy approach to extreme neutron starslpc2e.cnrs-orleans.fr/~pulsar/PSRworkshop/workshop2008/... · 2008. 11. 25. · 25/11/2008 CEA DSM Irfu/SApDiego

INTEGRAL & Magnetars: a high energyapproach to extreme neutron stars

Diego GötzCEA - Saclay - Irfu/Service d’Astrophysique

N. Rea (UvA), S. Zane (MSSL), R. Turolla (Uni Padova), M. Lyutikov (Purdue Univ.)P. Esposito, S. Mereghetti, A. Tiengo, G.L. Israel (INAF), K. Hurley (UCB), E.V.Gotthelf (Columbia Univ.)

Diego Götz - Pulsars Workshop - IAP ParisCEA DSM Irfu/SAp25/11/2008 2

Main manifestations of Neutron Stars:

• (Radio) Pulsars - Rotational energy

>1500 pulsars observed in radio (+ several Pulsar Wind Nebulae)the youngest seen also at higher energiesmostly isolatedtypical rotation periods: 1.5 ms – 5 s

• Accreting X-ray binaries - Gravitational energy

several hundreds in High Mass and Low Mass X-ray binariesmany are transientstypical rotation periods 0.1-1000 s

Magnetars do not fit in these two categories !


Originally identified as a“class” based on:

Periods in a narrow range

and other properties thatdistinguished them from the“classical” X-ray pulsars inHigh Mass X-ray Binaries

AXPs


• No evidence for companion stars (very faint IR counterparts, no Doppler delays in pulses) • Rotational period of a few seconds (2-12 s)

• Secular spin-down (0.05-4)x10-11 s/s

• Lx ˜ 1034 - 1036 erg s-1 >> Rotational Energy Loss

• Very soft X-ray spectrum below 10 keV (kT~0.5 keV)

• 3 (or 4 ?) are in Supernova Remnants

• 3 (or 4?) are transients

Summary of AXP properties


P dP/dt(s) (10-11 s/s)

4U 0142+61 8.7 0.2 -1E 2259+586 7 0.05 CTB 1091E 1048-5937 6.4 2-3 -1E 1841-045 11.8 4 Kes 73AX J1845-03 7 - G296+0.1 Tr.RXS 1708-40 11 2 -CXO J0110-72 8 2 in SMCXTE J1810-197 5.5 1.8 - Tr./RCXO J1647-45 10.6 0.1 in Wes 1 Tr.1E 1547.0-5408 2.07 2.3 - Tr./RPSR J1846 (Kes 75) 0.326 2 PWN

AXP Census - 10 confirmed 2 candidates


Durations Spectra

SGRs: Initially considered a peculiar class of Gamma-Ray Bursts

short, “soft”, “repeating” , Lpeak>>> LEddington

0.00 0.01 0.10 1.00 10.00 100.00 1000.00DURATION, SECONDS

0

25

50

75

100

125

150

NU

MB

ER

OF E

VE

NTS

836 GAMMA-RAY

BURSTS

0

4

8

12

16

20

NU

MB

ER

OF E

VE

NTS

42 SOFT GAMMA

REPEATERS

100

101 10

210

310

410

510

610

7

ENERGY, keV

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

FLU

X, p

hoto

ns/

cm2 s

keV

GAMMA-RAY BURST

SOFT GAMMA REPEATER

kT~30 keV


SGRs “bursting activity” is not continuous


Bursts from SGR 1806-20 observed with INTEGRAL

Götz, et al. (2004), A&A 417, L45

15-40 keV

40-100 keV


3 Giant Flares from 3 SGRs

1979 March 5 - SGR 0526-66

1998 August 27 - SGR 1900+14

2004 December 27 – SGR 1806-20


5 confirmed SGRs

4 are in the Galactic plane typical distance ~several kpc

one is in the N49 supernova remnant in the Large MagellanicCloud (d=55 kpc)

1806-201900+14

0526-66

1627-41

1801-23 ?

0501+4516

Soft Gamma Repeaters


“SGR-like” bursts seen from six AXPs

1E2259+586

Kaspi et al. 2003

1E 1048 3 bursts in 8 yrs1E 2259 >80 bursts in few hoursXTE J1810 4 bursts in 3 yrs4U 0142 5 burst in 8 yrs CXO J1647 1 burstPSR J1846 5 bursts in 10 years

Gavriil et al. 20061E 1048


Israel et al. (2007) CXO inWes 1

Transient Phenomena in AXPs

Gotthelf & Helfand (2007)

Swift/BAT

XTE 1810

Gavriil at al. (2008)PSR J1846


Esposito et al. 2008, MNRAS, in press, arXiv:0807.1658

SGR 1627-41 cooling

Γ ~3.3

Γ ~1.5

The persistent spectrum is much brighterand harder

Burst active phase

2 components flux decay


“Magnetar” modelDuncan & Thompson 1992, ApJ 392, L9 Thompson & Duncan 1995, MNRAS 275, 255Thompson et al. 2000, ApJ 543, 340 Thompson, Lyutikov & Kulkarni 2002, ApJ 574, 332.

• If the “proto-NS” isinitially spinning at~few ms an efficientdynamo can produceB~1015 G

• Magnetars spin-downquickly to P>10 s in104/B215 yrs


MAGNETIC ENERGY ROTATIONAL ENERGY

EB ~ (1/12) B2 R3 ER = ½ I Ω2

EB ~ 2 1046 (P/5 s) P-11 ER = 8 1044 (P/5 s)-2.

Magnetic energy dominates over rotational energy after the NS hasslowed down to periods of a few seconds

B = 3.2 x 10 19 (PP)1/2.


Known manifestations of Neutron Stars:

• (Radio) Pulsars - Rotational energy>1500 pulsars observed in radio (+ several Pulsar Wind Nebulae)the youngest seen also at higher energiesmostly isolated - typical periods 0.002 – 5 s

• Accreting X-ray binaries - Gravitational energyseveral hundreds in High Mass and Low Mass X-ray binariesmany are transients - typical periods 0.1-1000 s

• Magnetars – Magnetic energy - B~1015 Gauss4 Soft Gamma-ray Repeaters + ~10 Anomalous X-ray Pulsars

• “middle aged” isolated NS - Thermal energya few nearby NS – T~105-106 K

• Type I X-ray bursts - Nuclear energya subclass of Low Mass X-ray binaries


Götz et al. (2006)

SGRs

AXPs

Clear evidence for non-thermalpersistent emission.Energetically important contribution: L(>10 keV) ~1036 erg/s

Spectrum above 10 keV hardens forAXPs, while for SGRs it softens

No clear physical model has yetbeen developed for the broad-bandspectra of Magnetars.

Persistent hard X-ray emission can be dueto: Bremsstrahlung photons produced in a

thin layer close to the neutron star (Thompson& Belobodorov 2005). Cutoff at ~100 keV. at 100 km altitude in the magnetosphere

through multiple resonant cyclotronscattering (Thompson et al. 2002). Cutoff at ~1MeV A third scenario involving resonant

magnetic Compton up-scattering of soft X-ray photons by a non-thermal population ofhighly relativistic electrons has beenproposed by Baring et al. (2007)

Magnetars’ hard tails discovered by INTEGRAL


0.5 – 10 keV emission well represented by a blackbodyplus a power law: WHY?? Correlation in spectral hardening, luminosity, spin downrate - as in SGR 1806, during the pre (and post)-giant flare(24 Dec 2005) evolution Evolution of “transient” AXPs Model the hard tails

Our “immediate” goal:

Modelling Magnetars’ High Energy Emission


A key feature of twisted MSs is that they support current flows (inexcess of the Goldreich-Julian current).

Thermal seed photons (i.e. emitted from the star surface) travellingthrough the magnetosphere experience efficient resonant cyclotronscattering onto charged magnetospheric particles (e- and ions)

⇒ the thermal surface spectrum get distorted !

Twisted Magnetospheres

Thompson, Lyutikov and Kulkarni(2002):

Magnetars (AXPs and SGRs) differfrom radiopulsars since their internalmagnetic field is twisted up to 10times the external dipole.

At intervals, it can twist up theexternal field


While the twist grows, charged particles (e- and ions) produces both :

an extra heating of the star surface (by returning currents)-> X-ray luminosity increases

and a large resonant cyclotron scattering depth-> spectral hardening increases

The B-field flares out slightly -> open field flux > then in a dipole-> spin down torque increases

a) Crustal cracks occur when the crust cannot bear the stressanymore or b) a global rearrangement of the field lines. -> a forcedopening of the field outwards -> launch of an hot fireball

And everything is reversed during the aftermath (simplification of theexternal B-field and by a partial magnetospheric untwisting -> rapiddrop in the flux, spectral softening, period derivative decrease, etc..)

Qualitatively ok, and quantitatively?

Twisted Magnetospheres


PULSE PERIOD

POWER LAW INDEX(2-10 keV)

2-10 keV FLUX XMM

20-70 keV FLUXINTEGRAL

IPN BURST RATE

SGR 1806-20


Twisted magnetospheres are filled with plasma which may modify radiation properties.

Main point: closed field lines in NS magnetospheres are not dead.Populated by hot, highly over-dense plasma, n >> nGJ

(e.g. Thompson, Lyutikov & Kulkarni 2002; Liutykov & Gavriil 2006)

!

"RCS~

RL

re

#

$ %

&

' ( "T ~ 10

5"T

at 1 keV

!

RL~ 8R

NS

BNS

Bcrit

"

# $

%

& '

1/ 3

1keV

h(B

"

# $

%

& '

1/ 3

with

Resonant Cyclotron Scattering in Magnetars


Lyutikov & Gravriil, 2006: A simplified, 1D semi-analytical treatment of resonant cyclotronup-scattering of soft thermal photons

Resonant Thomson scattering occurs in a thin, plane parallel slab. Photons can onlypropagate along the slab normal, i.e. either towards or away from the star.

Static, non-relativistic, warm medium; ne constant. No electron recoil (hν mimics a thermal, 1D, motion (βT » mean e- energy » temperature ofthe 1D electron plasma). No bulk motion.

The e- velocity distribution averages to zero:-> a photon has the same probability to undergo up or downscattering-> no frequency shift due to the thermal motion of e-

Photon boosting by particle thermal motion in Thomson limit occurs only due to the spatial variation of the magnetic field.

For a photon propagating from high to low magnetic fields, multiple resonantcyclotron scattering will, on average, up-scatter the transmitted radiation-> hard tail.

Preliminary investigations (1D)


Same number of free parameters, same as for the empirical as theblackbody+power law model; same statistical significance

!

"RCS

= #RCSn$edzOptical depth (1-10)

!

"T

Electron thermal velocity (0.1-0.5)

Surface Temperature (keV)

!

kT (0.1-1.3)

Resonant Cyclotron Scattering in Magnetars

Rea, Zane, Turolla, Lyutikov & Götz (2008)

Distorsion of a seed blackbodyspectrum through resonantcyclotron scattering ontomagnetospheric electrons, for twovalues of the blackbodytemperature, 0.2 keV and 0.8 keV.Black lines: the RCS model for βT= 0.2 and τres = 2, 4, 8 (frombottom to top). Grey lines: βT = 0.4and τres = 2, 4, 8 (from bottom totop). The normalizations of thevarious curves are arbitrary. FromRea et al. 2008

Flux

1 - Energy (keV) - 10

Diego Götz - Pulsars Workshop - IAP ParisCEA DSM Irfu25/11/2008 26

4U 0142+61

RXS J1708-4009

1E 1841-045

BB+PL+PL

BB+PL+PL


BB+PL

4U 0142+61

RXS J1708-4009

1E 1841-045

RCS+PL

RCS+PL

RCS+PL

Flu

xRCS: AXPs with hard X-ray emission

KT consistent for all sources (0.33 keV) while β ∈ (1-2) and τ ∈ (0.2-0.4)


RCS

RCS

BB+PL

BB+PL

BB+PL

BB+PL

RCS

RCS

1E 1048-5937

1E 1547-5408

CXO 1647-4552

XTE 1810-197

Flu

x


RCS: Transient AXPs

Much softer spectra; β increases as flux decreases

Diego Götz - Pulsars Workshop - IAP ParisCEA DSM Irfu25/11/2008 28

BB+PL

SGR 1900+14

BB+PL

Fl

ux


RCS+PL

SGR 1900+14

SGR 1806-20

RCS+PL

SGR 1806-20

F

lux


RCS: SGRs with hard X-ray emission

Rea, Zane, Turolla, Lyutikov & Götz (2008))

Harder spectra below 10 keV. Additional PL needed at lowenergies, which extends up to 200 keV

BB+PL


Magnetospheric e- density of n~1.5x1013 cm-3 = 103 nGJ

τ res

L1-10keV (1034 erg/s)


• Twisted magnetosphere model, within magnetar scenario, in generalagreement with observations below 10 keV• Resonant scattering of thermal, surface photons produces spectra withright properties

– ESA press release “XMM-Newton and INTEGRAL clues on magneticpowerhouses” 14/10/2008

• More accurate treatment of cross section including QED effects andelectron recoil (Nobili, Turolla & SZ MNRAS in press)

• Many issues need to be investigated further

Use the model archive to fit model spectra to observations,investigate what causes the long term variability in AXPS andTAXPS

Phase resolved spectroscopy 10-100 keV tails: up-scattering by (ultra)relativistic (e±)

particles ?Necessity of more sensitive broad band observations (Simbol-X, NuStar)

Detailed models for magnetospheric currents

Conclusions & Future Developments

Documents

INTEGRAL & Magnetars: a high energy approach to extreme neutron starslpc2e.cnrs-orleans.fr/~pulsar/PSRworkshop/workshop2008/... · 2008. 11. 25. · 25/11/2008 CEA DSM Irfu/SApDiego