1. Recent Suzaku Results on Strongly Magnetized Neutron Stars
Kazuo Makishima
(University of Tokyo and RIKEN)
T. Enoto, T. Mihara, M. Nakajima, K. Nakazawa, & Y. Terada
2008/5/29
X-ray Universe 2008

2. 1. Strongly Magnetized NSs
Measurements of surface m.f. using electron cyclotron resonances;
　Ea = 11.6 (B/1012G) keV
Measured m.f. strengths clustered in (1~5)x1012 G (Makishima + 99).
“Field decay” hypothesis unlikely.
Resonance photosphere height depends on Lx (Nakajima Poster D.7). 2 4 6 8 10
Resonance Energy (keV)
Number
100 20 5 50
Log B
(Gauss) 12 13
BeppoSAX
Ginga
RXTE
Suzaku
ASCA
Is m.f. due to nuclear ferromagnetism (Makishima + 99)?
Magnetars really have G?
Any objects in between ordinary pulsars and magnetars?
Origin of the resonance width?
2008/5/29
X-ray Universe 2008

3. 2. Suzaku Observations [Accreting Binary Pulsars]
A Terada+ ApJL (2006); Naik+ ApJ (2008)
Her X Enoto+ PASJ (2008); Terada+ AdSpRes (2007) 4U
GRO J (TOO)
[Rotation-Powered Pulsars]
The Crab pulsar
PSR Terada+ PASJ (2008)
[Magnetars]
4U Enoto+. in prep.
1E Morii+ AIPC (2008)
AXP CXOU J (TOO) Naik+ PASJ (2008)
SGR (TOO)
SGR (TOO; burst+persistent) Esposito+ A&A (2008)
PSR 1509 On-Off, 45 ks
HXD-PIN
HXD-GSO
2008/5/29
X-ray Universe 2008

4. 3. Crab Ratios Continuum and absorption couple strongly.
0.05
0.02
0.01
.002
42 keV
2005
36 keV
HXD-GSO
2006
0.1
.01
Lx=4x1035 erg/s
A (Suzku,Terada+06）
HXD-PIN
Her X-1 on-off (Suzaku, Enoto + 08) Lx=3x1037 erg/s
23 keV 1 .1
.01
Energy (keV)
Continuum and absorption couple strongly.
Using regions near Ea1/2 and >3Ea1, define the continuum as
f(E)=AEα exp(-E/Ecut)
X (RXTE ; Nakjima + 08)
Lx=3x1038 erg/s
2008/5/29
X-ray Universe 2008

5. 4. Extraction of Absorption Profiles
Assuming spectrum = f(E)xexp[-S(E)], exp[-S] is plotted logarithmically. The vertical scale thus becomes -S itself.
The energy axis is normalized to Ea1, and ordinatge is adjusted by ~20%
The three objects exhibt very similar profiles. A
Her X-1 On-Off
X0331 RXTE 1
0.5
0.2
0.1
pivot
2008/5/29
X-ray Universe 2008

6. 5. Joint Fitting of the 3 Pulsars
F(E)=(aE-α+bEβ) exp(-E/Ecut) exp{-S1(E/Ea1)-S2(E/Ea2)}
・“NPEX” continuum : independent among the three.
・S1: Lorentzian xE2, common to the three as a function of E/Ea.
・S2 : likewise, but X0331 is allowed to have separate Ea2 and W2.
Count Spectra
X0331 (PCA)
X0331 (HEXTE)
Deconvolved νFν
keV
Her X-1
A0535 (PIN)
A0535 (GSO)
χ2/ν=1.08
D1=1.61 ± 0.06
W1/Ea1=0.36 ±0.02
D2=1.51 ± 0.13
keV
2008/5/29
X-ray Universe 2008

7. 6. Implications
The 3 objects are in common physical conditions, despite the luminosity differences by ~3 orders of magnitude.
cf. Not claiming that this applies to all accreting pulsars.
The NPEX continuum is justified; the1st and 2nd resonances heavily affect the continuum even in between Ea1 and Ea2.
Gaussian absorption cross section gives significantly worse joint fits than the Lorentzian x E2 cross section (Enoto et al. 2008); chi^2= vs for the same d.o.f=287.
The resonance width may not be explained by the thermal Doppler effects. Unexpectedly short lifetimes of the excited Landau levels (Enoto et al. 2008)?
2008/5/29
X-ray Universe 2008

8. 7. AXP 4U (Enoto et al.)
Observed with Suaku on 2007 Aug. 13 for 93 ksec.
Soft pulsations are stable.
Hard pulses vary on ~30 ks.
Very hard component with Gamma~1.
Improves INTEGRAL results (Kuiper+06).
GSO
XIS
PIN
P= sec
1st 30 ks 2nd 30 ks 3rd 30 ks
0.06
0.04
0.02
e+e- creation --> rush onto mag.poles --> non-thermal Bremss --> Compton back scatt. (Kotoku+07 PASJ) A
BGD-subtracted keV folded pulse profile
2008/5/29
X-ray Universe 2008

9. 8. Summary
Spectra of accreting X-ray pulsars are strongly affected by electron cyclotron resonances, but the effects may be rather common among different objects. The continuum must be carefully determined using wide-band data.
The spectrum of an AXP, 4U is clearly distinct from those of any accreting/rotating X-ray pulsars. A ultra-strong MF provides the most likely explanation.
Existence of intermediate objects between magnetars and normal strong-field NSs is open (cf. Dr. Haberl’s talk).
Further Suzaku observations are of great value.
2008/5/29
X-ray Universe 2008