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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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 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 >> Rotational Energy Loss
• Very soft X-ray spectrum (kT~0.5 keV)
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 3
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 4
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 5
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 ?
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 6
Introduction3 Giant Flares from 3 SGRs
1979 March 5 - SGR 0526-66
1998 August 27 - SGR 1900+14
2004 December 27 – SGR 1806-20
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 7
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 8
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 9
GiantFlare
(Mereghetti et al. 2005, Tiengo et al 2005, Rea et al. 2005)
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 10
PULSE PERIOD
POWER LAW INDEX(2-10 keV)
2-10 keV FLUX XMM
20-40 keV FLUXINTEGRAL/IBIS
INFRARED FLUXIsrael et al. (2005)
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 11
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 12
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 13
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 14
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 15
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
Diego Gotz - Hard X-ray tails in MagnetarsCEA DSM Dapnia SAp15/05/2007 17
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