“New Views on Accreting X-ray Pulsars, a brief review of recent results”

Andrea Santangelo,IAAT KC-Tü

Tokyo 01.12.2010 MAXI International Symposium

“New Views on Accreting X-ray Pulsars,a brief review of recent results”

Andrea Santangelo (…and the Magnet Collaboration)

Institut für Astronomie und AstrophysikKepler Center for Astro and Particle Physics

Karls-Eberhard-Universität Tübingen


A. Santangelo, D. Klochkov, V. Doroshenko, D. Müller, R. Doroshenko, R. Staubert, M. Sasaki (IAAT), J. Wilms, L. Barragán, T. Dauser, I. Kreykenbohm, J. Schmid, F. Schwarm (ECAP), G. Schönherr (AIP), I. Caballero (Saclay), C. Ferrigno, N. Mowlawi (ISDC), P. Kretschmar (ESAC), V. McBride (Soton), U. Kraus (Uni Hildesheim), O. Nishimura (Nagano), K. Postnov, N. Shakura (SAI), K. Pottschmidt (CRESST/UMBC/GSFC), R. Rothschild, S. Suchy (UCSD), L. Sidoli (INAF Milano) …

Magnet Collaboration …

Partial list …


Wako 10.12.2009 Seminar at RIKEN

Courtesy of Scientific American

X-ray Binaries with a NS: Pulsars?

Liu et al. A&A, 2000, 2005

G10B 12Most of them are in HMXRB

A few LMXRB (Her X-1, 4U1626-67,

GX1+4)

Mass Transfer from the Normal to the compact star


AccretionRoche Lobe Overflow Wind Accretion

2

2

2

1

1 r2

1

rr

GM

rr

GM)r(

const)r(

Davidson & Ostriker, 1973Lubov & Shu, 1975 €

˙ M =10 −5( )− −7( ) MSun yr−1

€

v ≈103 km s−1


SG/X-ray Binaries Wind Accretion

Kreykenbhom, 2004

2NS

2w vvm

2

1

r

GMm

2NS

2w

acc vv

GM2r

Bozzo+, 2008 SFXT

Interaction between the inflow wind matter and the NS magnetosphere: different regimes at different luminosities


Interaction disk/wind magnetosphere

Details of matter transfer are not understood


r A

Ghosh & Lamb, 1978, 79

Kuster, 2003

At the Boundary Layer disk is disrupted. The plasma is forced to follow the field lines and matter is funnelled in accretion column onto the Neutron Star Magnetic Poles

r H6

22

Magn r88

BP

In the Boundary Layer disk is not longer keplerian

21

3k r

GM)r(


What is the Corotation Radius ? At the Corotation Radius the angular velocity of the magnetosphere equals the keplerian velocity of the Disk.

r H

€

rH ≈ 3×103Km

€

rH

Disk = 5.2 ×108 ˙ M 16−2 7μ30

4 7 M

MSun

⎛

⎝ ⎜

⎞

⎠ ⎟

− 17

cm

€

rH < rco


Not so simple: Open Field lines

Lovelace et al. 1995


Outflows and conical windsMHD simulations Romanova et al., 2009


Do we have evidence of these outflows?


Continuous Monitoring of Pulse Period, Pdot, Lx

Based on Swift/BAT data

Klochkov +, 2009

Her X-1

P

Time

P.


Strong Spin-down episodes

Outflow episodes!


Other evidence: decay of Porb

Klochkov +, 2008; Staubert+, 2009 A decay of the Orbital Period has been

measured

€

˙ P Orb = −4.85 ×10−11dd−1

Lx ≈ 2 ×1037erg s−1

Matter is ejected!

It cannot be reconciled with a conservative scenario

In strong spin-down episodes the spin-down power is used to expel matter from the inner disk radius

Ji et al., 2009 (Chandra)


Surprises from wind/magnetosphere interactions?


The strange case of an old friendGX 301-2


Why is GX 301-2 so slow?Why is GX 301-2 so slow?

Doroshenko+, 2010


Torque Balance

€

Idω

dt= K+ + K−

The Spin frequency of the source is determined by accelerating and braking torques

Decelerating Torques

Davidson & Ostriker, 1973 Turbolent Viscosity

Ilarionov & Kompaneets, 1990 Compton Heated Outflows

€

K+ = ˙ M kwRA2Ωorb

Accelerating Torque depends on accretion rate, wind velocity through kw

Davies +, 1979


Assuming equilibrium…

kw~0.25-1



Doroshenko et al., 2009CGRO-BATSE


GX 301-2 a hidden “magnetar”? Not an unique case…


Vela X-1 (Ps ~283.5 s)_

Other evidence from: QPOs, Noise Power Spectrum

€

B ≈1013−14 G

Doroshenko 2010a, (submitted)Kreykenbohm+, 2008, Inoue+ 1984

Gogus+, 2010 in GX 301-2

OFF states (Suzaku obs.)

Flux drops dramatically

Propeller regime due to wind density fluctuations of clumpy winds?


Peculiar hard emission at lower luminosity

€

20 − 40 keV(Doroshenko +, 2010b, in prep.)

The source still pulsates

OFF state

Accretion though at much lower luminosity is there! Pulse profile changes at hard energies

We possibly observe the inhibition of the column at lower luminosities: radiation comes from the polar cap

In “the gated accretion” scenario of Bozzo+ (2008), we might see here the transition to KH Instab.

€

B > 2 ×1013G


Emission from the accretion column


Accretion ColumnsBasko & Sunyaev, 1976

Kuster, 2003 G10B 1312

€

v ≈ 0.6 − 0.8 c

EddLL Solid Column Hallow Cylinder

€

˙ M ≈10−9...−11 MSun yr−1



Kretschmar, 1996 Harding, 1994

€

L ≈1037 erg/sec

Transition between two accretion regime depending on the luminosity: Eddington vs. Sub-Eddington

Right) High accretion rate: shock is formed, plasma is decelerated to subsonic speed and heated. The Plasma then sinks to the NS surface. Emitted photons can only escape perpendicularly to the column forming a wide Fan beam.

Left) Lower accretion rate No shock is formed, plasma is decelerated onto the neutron star surface by Coulomb collisons; photons are generated by Bremsstrahlung and Compton Cooling. They can escape along the accretion column, generating a pencil beam


Cyclotron LinesElectrons in the magnetosphere plasma move helicodally along the B field lines: their motion perpendicularly to the B field is quantized in the Landau levels

G1014.4e

cmB 13

32

cr

z1

1

θsin

1θsinBBn2mc

mcω 2

2

crit

2

2n

γmc

eBωc

cn ωnω For B<< Bcr

Gauss 12

10 of unitsin B keVB6.11E 12c,e

Equispaced



Cyclotron lines as absorption lines

Electron is excited to the n Landau level

Lifetime is short

De-excitation to ground state via single or multiple photon emission

Mean free path is short, quasi instantaneous re-capturing of the photon


Can we probe these two regimes Using Cyclotron lines…

Wilms+, 2010 + GX 304-1 ~54 keV P13


Do cyclotron lines trace the B field of the Neutron Star?

• Do cyclotron lines trace the B field of the NS?

• How the energy of the line is related to the luminosity ? Do we observe a change of regime around 1037 ergs/sec ?

? MH Anticorrelation ?

€

H ∝Mcol

˙ M ?

Correlation ?

Andrea Santangelo,IAAT KC-TüMihara+ 2007, Nakajima 2008


Wako 10.12.2009

Correlation or Anti-correlation?

Tsygankov et al., 2006; 2010 Mowlavi et al., 2006 V0332+53, Outburst 2005 Anti-correlation is clearly observed

Staubert et al., 2007 Her X-1, 5 years of data Correlation is clearly observed; sub-Eddington!

Caballero et al., 2007, 2009 A0535+26


New Studies using pulse to pulse variability…


PC

A c

ts/s

/PC

U (

~3-3

0 ke

V)

Time in days

light curverepeated pulse profile

V0332+53

Pulse to pulse variability…(Klochkov+, P23)


PC

A c

ts/s

/PC

U (

~3-3

0 ke

V)

puls

e fl

ux b

ins

Strong spectral variability

Time in days


Example: X0115+63Spectral variability with the single pulse amplitude

With increasing pulse amplitude, the power-law becomes steeper, the cyclotron line shifts towards lower energies

Klochkov+ 2010 (in prep.)


Dependence of spectral parameters on pulse height: summary

V0332+V0332+5353

X0115+X0115+6363 Her X-1Her X-1 A0535+A0535+

2626

- flux- flux

- flux- flux ?

-flux-flux ? ? ?

“negative pulsars” “positive pulsars”

We found two types of spectral dependencies on the single pulse flux. We interpret them as an indication of two distinct accretion regimes (poster by D. Klochkov et al.)


Again instabilities…


A0535+26 (2005 Outburst)

Wako 10.12.2009 Seminar at RIKEN Caballero + 2007, 2008


A question remains… is the cyclotron line tracing the B field of the NS (in

systems like GX 301-2 and Vela X-1)?


Basko & Sunyaev,1976 high columns can be predicted

Solution of the contradiction?Doroshenko et al., 2009

The Cyclotron lines traces the field of the production site and this could be located at the top of the column

€

L ~ 2σ SBTEDD4 2πRsinθH ⇒ H ~ 10 − 30 km


Formation of the spectra is very complex…


POHEI (E) =E E<Ecut

E>EcutEexp(-(E-Ecut)/Ef))

)EEE

exp(1

1)E(FDCO

cut

kTE

22kTE

21 e))E(oE(e)EAEA(NPEX 21

White+, 1983

Tanaka, 1986

Mihara+, 1995 Approximates thermal comptonization Sunyaev and Titarchuk, 1980

The continuum?

Segreto, 2001


Physical Models (high luminosity)Becker & Wolff, 2005a,b and 2007

A Radiative shock dominates the formation of the emitted continuum

• Accretion mound produces soft X-rays via bremsstrahlung

• X-rays are up-scattered via bulk motion comptonization and diffuse through the walls of the columns

• Cyclotron emission occurs together with bbody emission from a thermal mound

Limited to COLUMN!


A quantitative attempt: 4U 0115+634

Ferrigno et al., 2009: Model in XSPEC!

Thermal and bulk Comptonization of Cyclotron emission.

Thermal and bulk Comptonization of Cyclotron emission.

Thermal Comptonization of 0.5 keV BB

Thermal Comptonization of 0.5 keV BB

Gaussian to correct the rough modelling

Gaussian to correct the rough modelling

Cyclotron emission is concentrated around the peak. Thermal comptonization is almost constant

Cyclotron emission is concentrated around the peak. Thermal comptonization is almost constant


4U 0115+634 Emission Geometry

Ferrigno et al., 2009

Low Energy Diffused Halo producing a fan componentLow Energy Diffused Halo producing a fan component

Beamed High Energy emission from the column (Fan beam)

Beamed High Energy emission from the column (Fan beam)

Magnetic field of Cyclotron emission and of absorption line forming region are different!Magnetic field of Cyclotron emission and of absorption line forming region are different!

Analysis is being extended to other sources like 4U1907+67, Cen X-3, …(Ferrigno et al. 2010)

Andrea Santangelo,IAAT KC-TüKraus, 2003, 2010; Sasaki 2010; Caballero 2010

Light Bending and Geometry


Beam Pattern: three components Kraus et al., 2010

Reprocessed radiation in the accretion stream

Reprocessed radiation in the accretion stream

Low Energy Diffuse Halo ComponentLow Energy Diffuse Halo Component

• Isotropic column emission

• Beamed emission

Column componentColumn component

Emission components?Emission components?



Conclusions

Emission processes of spectral formation …spectral reprocessing

Geometry of the pulsed components …of the line forming region

Plasma Parameters …B, T, tau, etc…

• Progresses on Accreting Pulsars study have been dramatic in the last few years

• Discovery of outflows (in Her X-1)• Pre-outburst flares and magnetospheric instabilities in A0535+26 • Evidence of magnetar-like sources in Binary systems (?)• A “new” technique: Pulse to pulse variability• Modelling of the physics of the emission of continuum and of cyclotron line

profiles (Not discussed here!)• Modelling of Pulse Profiles (Not discussed here!)• Eventually all this greatly improved our understanding on:


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“New Views on Accreting X-ray Pulsars, a brief review of recent results”

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