CEA DSM Dapnia SAp Diego Gotz - Hard X-ray tails in Magnetars 15/05/2007 1 Hard X-ray Tails in...

Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 1

Hard X-ray Tails in Magnetars

A Case Study for Simbol-X

Diego GötzCEA Saclay


Introduction

•Magnetars are neutron stars whose main energy source is

neither rotation nor accretion, but the magnetic energy

•There are 12 members and 3 candidates

•Historically they are didvided in 2 classes: the Anomalous X-ray

Pulsars (AXPs) and the Soft Gamma-Ray Repeaters (SGRs)

•The AXPs have been originally identified as a « class » due to their

narrow period distribution and due to other X-ray properties

•No evidence for companion stars; 2 (or 3 ?) are in Supernova Remnants (very faint IR counterparts, no Doppler delays in pulses)

• Rotational period of a few seconds (5-12 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 (kT~0.5 keV)


Introduction

P dP/dt

(s) (10-11 s/s)

4U 0142+61 8.7 0.21E 2259+586 7 0.051E 1048-5937 6.4 2-31E 1841-045 11.8 4AX J1845-03 7 -RXS 1708-40 11 2CXO J0110-72 8 2XTE J1810-197 5.5 1.8 Tr.CXO J1647-45 10.6 0.1 Tr.

1E 1048 3 bursts in 8 yrs1E 2259: >80 bursts in few hoursXTE J1810: 4 bursts in 3 yrs4U 0142 1 burst in 8 yrs (+4 last week!)CXO J1647 1 burst

“SGR-like” short bursts seen from five AXPs


Introduction

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

NUMBER OF EVENTS

836 GAMMA-RAYBURSTS

0

4

8

12

16

20

NUMBER OF EVENTS42 SOFT GAMMA

REPEATERS

Durations

100 101 102 103 104 105 106 107

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

FLUX, photons/cm

2s keV

GAMMA-RAY BURST

SOFT GAMMA REPEATER

kT~30 keV

Spectra


Introduction 4 confirmed SGRs

3 are in the Galactic plane typical distance ~several kpc

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

Soft X-ray spectra and timing properties similar to AXPs

1806-201900+14

0526-66

1627-41

1801-23 ?


Introduction3 Giant Flares from 3 SGRs

1979 March 5 - SGR 0526-66

1998 August 27 - SGR 1900+14

2004 December 27 – SGR 1806-20


INTEGRAL/IBIS Discovery of Hard TailsAXPs SGRsKuiper et al. 2004 Mereghetti et al. 2005den Hartog et al. 2005 Molkov et al. 2005Kuiper et al. 2006 Götz et al. 2006

Clear evidence for non-thermal persistent emission.

Energetically important contribution: L(>10 keV) ~1036 erg/s

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

The AXPs tails are pulsated up to 100%

No clear physical model has yet been devloped for the broad-band spectra of Magnetars.

Persistent hard X-ray emission can be due to: 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 cyclotron scattering (Thompson et al. 2002). Cutoff at ~1 MeVGötz et al. 2006


2003 2004

- 20-100 keV power law spectrum

- both spectral hardness and intensity correlate with burst rate

- source “activity level” increased in 2003-2004… … leading to the Dec 27 Giant Flare

Mereghetti et al. 2005

SGR 1806-20: variability

PERSISTENT

BURSTS


GiantFlare

(Mereghetti et al. 2005, Tiengo et al 2005, Rea et al. 2005)


PULSE PERIOD

POWER LAW INDEX(2-10 keV)

2-10 keV FLUX XMM

20-40 keV FLUXINTEGRAL/IBIS

INFRARED FLUXIsrael et al. (2005)


Long term variability: SGR 1900+14

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Esposito et al. 2006 using SAX and INTEGRAL/IBIS data

2003-2004

1997


Simbol-X Simulations: 1708 10 ks

Working Hypothesis: « traditional » 2 components model Black Body + power law with the addition an « upward » break at 10 keV (from ~2.8 to ~1.5), to cope with INTEGRAL data.

The break is clearly detectable already with a 10 ks. The single power law gives an unacceptable fit 2

r~2


Simbol-X Simulations: 1806 100 ks

Input Model: Faint Blackbody component (discovered by XMM with a 50 ks observation) + a power law with a « downward » less stong break (from 1.2 to 1.8)

With 100 ks fitting a single power law yields a 2

r~1.2, while adding a broken one gets 2

r~1.03. No strong evidence for a break, black body component not required. (S-X is 4 to 5 times less sensitive than XMM @ 2 keV)

Single power law fit


Simbol-X Simulations: 1806 1 Ms

With a 1 Ms observation all spectral components are found: • fitting the data with a single yields a 2

r~3.3; • adding a break one gets a 2

r~1.6; • finally adding the black body component one gets 2

r~1.02.

Single power law fit


Conclusions

•Simbol-X will largely contribute to further unveiling the spectral porperties of Magnetars

– We will be able to monitor the spectral changes of the sources on the 10-100 ks time scale (Note that we used sharp breaks in our simulations!)

– A deep observation (100ks - 1Ms) will allow us to do a detailed spectral modeling on a very broad (1-80 keV) energy range

• Disentagle the differences between AXPs and SGRs

– Only simultaneous broad band observations will allow us to study and try to understand the nature of the long term variability of these sources (not feasible with the current instrumentation)

– The excellent sensitivity due to imaging will allow to • Detect for the first time pulsations from SGRs (2.5 sigma level with

INTEGRAL)

• Do broad band phase resoved spectroscopy

– Possibly detect proton (electron?)-cyclotron resonant scattering absorbtion lines in the hard X-ray range, currently not expected in the current Magnetar model, but…

Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007

Hystorical CAFS STUDies

(Iwasawa et al. 1992)

Absorption detected in 1990 (from GINGA data)around 10 keV. Never detected again. It lies close to the CCD high energy “edge”Ecyc around 6-15 keV (B15~0.8-2 G)

Such shape was observed only after the burst activitystate


Conclusions

•Simbol-X will largely contribute to further unveiling the spectral porperties of Magnetars

– We will be able to monitor the spectral changes of the sources on the 10-100 ks time scale (Note that we used sharp breaks in our simulations!)

– A deep observation (100ks - 1Ms) will allow us to do a detailed spectral modeling on a very broad (1-80 keV) energy range

• Disentagle the differences between AXPs and SGRs– Only simultaneous broad band observations will allow us to study and try to

understand the nature of the long term variability of these sources (not feasible with the current instrumentation)

– The excellent sensitivity due to imaging will allow to • Detect for the first time pulsations from SGRs (2.5 sigma level with INTEGRAL)

• Do broad band phase resoved spectroscopy – Possibly detect proton(electron)-cyclotron resonant scattering absorbtion

lines in the hard X-ray range (not expected in the current Magnetar model)– Sutdy the otburst mechanisms of the transient AXPs by observing them in

outburst and quiescence (2 orders of magnitude flux variations!) • XTE 1810 and CXO 1647 could not be studied during their outburst

with INTEGRAL, but only at energies below 10 keV. Nothing is known to date about these sources in the hard X-ray band

Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007

XTE J1810-197: the first TAXP

A 5.5s transient X-ray pulsar was dicovered in 2003 soon noticed to be an AXP

CEA DSM Dapnia SAp Diego Gotz - Hard X-ray tails in Magnetars 15/05/2007 1 Hard X-ray Tails in...

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