Hard Xray Tails in Magnetars

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Hard X-ray Tails in Magnetars

• A Case Study for Simbol-X
• Diego Götz
• CEA Saclay

2
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 gtgt Rotational
  Energy Loss
• Very soft X-ray spectrum (kT0.5 keV)

3
Introduction
P dP/dt (s) (10-11 s/s) 4U
014261 8.7 0.2 1E 2259586 7 0.05 1E
1048-5937 6.4 2-3 1E 1841-045 11.8 4 AX
J1845-03 7 - RXS 1708-40 11 2 CXO
J0110-72 8 2 XTE J1810-197 5.5 1.8
Tr. CXO J1647-45 10.6 0.1 Tr.
SGR-like short bursts seen from five AXPs
1E 1048 3 bursts in 8 yrs 1E 2259 gt80
bursts in few hours XTE J1810 4 bursts in 3
yrs 4U 0142 1 burst in 8 yrs (4 last
week!) CXO J1647 1 burst
4
Introduction
SGRs Initially considered a peculiar class of
Gamma-Ray Bursts short, soft,
repeating , Lpeakgtgtgt LEddington
Spectra
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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 (d55 kpc)
• Soft X-ray spectra and timing properties similar
  to AXPs

6
Introduction
3 Giant Flares from 3 SGRs
1979 March 5 - SGR 0526-66 1998
August 27 - SGR 190014 2004 December
27 SGR 1806-20
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INTEGRAL/IBIS Discovery of Hard Tails
AXPs SGRs Kuiper et al. 2004 Mereghetti et al.
2005 den Hartog et al. 2005 Molkov et al.
2005 Kuiper et al. 2006 Götz et al. 2006
Clear evidence for non-thermal persistent
emission. Energetically important contribution
L(gt10 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 MeV

Götz et al. 2006
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SGR 1806-20 variability
PERSISTENT
BURSTS
Mereghetti et al. 2005

• 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

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Long term variability SGR 190014
1997
2003-2004
Esposito et al. 2006 using SAX and INTEGRAL/IBIS
data
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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 ?2r2
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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
?2r1.2, while adding a broken one gets
?2r1.03. No strong evidence for a break, black
body component not required. (S-X is 4 to 5 times
less sensitive than XMM _at_ 2 keV)
Single power law fit
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Simbol-X Simulations 1806 1 Ms

• With a 1 Ms observation all spectral components
  are found
• fitting the data with a single yields a ?2r3.3
  
• adding a break one gets a ?2r1.6
• finally adding the black body component one gets
  ?2r1.02.

Single power law fit
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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

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Hystorical CAFS STUDies
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 (B150.8-2 G)
Such shape was observed only after the burst
activity state
(Iwasawa et al. 1992)
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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

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XTE J1810-197 the first TAXP
A 5.5s transient X-ray pulsar was dicovered in
2003 soon noticed to be an AXP