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
Andrea Santangelo,IAAT KC-Tü
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 …
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
Interaction disk/wind magnetosphere
Details of matter transfer are not understood
Andrea Santangelo,IAAT KC-Tü
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(
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
Not so simple: Open Field lines
Lovelace et al. 1995
Andrea Santangelo,IAAT KC-Tü
Outflows and conical windsMHD simulations Romanova et al., 2009
Andrea Santangelo,IAAT KC-Tü
Do we have evidence of these outflows?
Andrea Santangelo,IAAT KC-Tü
Continuous Monitoring of Pulse Period, Pdot, Lx
Based on Swift/BAT data
Klochkov +, 2009
Her X-1
P
Time
P.
Andrea Santangelo,IAAT KC-Tü
Strong Spin-down episodes
Outflow episodes!
Andrea Santangelo,IAAT KC-Tü
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)
Andrea Santangelo,IAAT KC-Tü
Surprises from wind/magnetosphere interactions?
Andrea Santangelo,IAAT KC-Tü
The strange case of an old friendGX 301-2
Wako 10.12.2009 Seminar at RIKEN
Why is GX 301-2 so slow?Why is GX 301-2 so slow?
Doroshenko+, 2010
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
Assuming equilibrium…
kw~0.25-1
Andrea Santangelo,IAAT KC-Tü
Wako 10.12.2009 Seminar at RIKEN
Doroshenko et al., 2009CGRO-BATSE
Andrea Santangelo,IAAT KC-Tü
Wako 10.12.2009 Seminar at RIKEN
Andrea Santangelo,IAAT KC-Tü
GX 301-2 a hidden “magnetar”? Not an unique case…
Andrea Santangelo,IAAT KC-Tü
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?
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
Emission from the accretion column
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
Wako 10.12.2009 Seminar at RIKEN
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
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
Wako 10.12.2009 Seminar at RIKEN
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
Andrea Santangelo,IAAT KC-Tü
Can we probe these two regimes Using Cyclotron lines…
Wilms+, 2010 + GX 304-1 ~54 keV P13
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
New Studies using pulse to pulse variability…
Andrea Santangelo,IAAT KC-Tü
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)
Andrea Santangelo,IAAT KC-Tü
PC
A c
ts/s
/PC
U (
~3-3
0 ke
V)
puls
e fl
ux b
ins
Strong spectral variability
Time in days
Andrea Santangelo,IAAT KC-Tü
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.)
Andrea Santangelo,IAAT KC-Tü
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.)
Andrea Santangelo,IAAT KC-Tü
Again instabilities…
Andrea Santangelo,IAAT KC-Tü
A0535+26 (2005 Outburst)
Wako 10.12.2009 Seminar at RIKEN Caballero + 2007, 2008
Andrea Santangelo,IAAT KC-Tü
Wako 10.12.2009 Seminar at RIKEN
Andrea Santangelo,IAAT KC-Tü
Wako 10.12.2009 Seminar at RIKEN
Andrea Santangelo,IAAT KC-Tü
A question remains… is the cyclotron line tracing the B field of the NS (in
systems like GX 301-2 and Vela X-1)?
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
Formation of the spectra is very complex…
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
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!
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
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
Andrea Santangelo,IAAT KC-Tü
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?
Andrea Santangelo,IAAT KC-Tü
Wako 10.12.2009 Seminar at RIKEN
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:
Andrea Santangelo,IAAT KC-Tü
Thanks for listening