Pulse phase resolved Pulse phase resolved spectroscopy of spectroscopy of

accreting HMXB pulsarsaccreting HMXB pulsars1A 1118-61 and Vela X-1 1A 1118-61 and Vela X-1

with Suzakuwith Suzaku

Chandreyee Maitra Chandreyee Maitra

HEAP 2012HEAP 2012

Plan of the talkPlan of the talk

Accreting HMXB pulsarsAccreting HMXB pulsars Pulse profiles & energy dependencePulse profiles & energy dependence X-ray spectra: Continuum modelX-ray spectra: Continuum model X-ray spectra: Line model (CRSFs)X-ray spectra: Line model (CRSFs) The case of two HMXBs: 1A 1118-61 & Vela X-1The case of two HMXBs: 1A 1118-61 & Vela X-1 Discussion & ConclusionDiscussion & Conclusion Future prospects: Studies with ASTROSAT & X-Future prospects: Studies with ASTROSAT & X-

rayray

polarimetric studies.polarimetric studies.

Accreting HMXB Accreting HMXB pulsarspulsars

Wind accretion (Dips & Flares) Be & Supergiant companions L

x ~ 1033-1038 ergs s-1

Pulsation period in the range 0.1<P<104 s

(Negueruela based on Davidson & Ostriker 1973

Strong magnetic field ~ 1012 GFlow couples to the magnetic field at Alfven radius. Chanelling of matter along the magnetic field linesFormation of accretion column above polar caps & pulsationsSource of X-ray radiation → Thermal Bremsstrahlung & Comptonization

Pulse Profiles & Energy Pulse Profiles & Energy dependencedependence

Shape of the pulse profile depends on the anisotropic Shape of the pulse profile depends on the anisotropic emission of radiation from the polar caps and modified emission of radiation from the polar caps and modified by absorption & scattering & light bending.by absorption & scattering & light bending.

General trend of high energy pulses to have simpler General trend of high energy pulses to have simpler shapes and for modulation of the pulse profiles to shapes and for modulation of the pulse profiles to increase with energies (White, Swank & Holt 1983; increase with energies (White, Swank & Holt 1983; Bildsten et al. 1997)Bildsten et al. 1997)

Multi peaked profile at lower energies and and a single Multi peaked profile at lower energies and and a single asymmetric peak at higher energies ( > 10 keV) have asymmetric peak at higher energies ( > 10 keV) have been found in many pulsars:been found in many pulsars: Her X-1 Her X-1 (Nagase 1989) (Nagase 1989) 4U 4U 0115+630115+63( Tsygankov et al. 2007) ,and more recently in ( Tsygankov et al. 2007) ,and more recently in GRO J1008-57 GRO J1008-57 (Naik et al. 2011), (Naik et al. 2011), GX 304-1GX 304-1 (Devasia et (Devasia et al. 2011) and al. 2011) and 1A 1118-611A 1118-61 (Doroshenko et al. 2011; (Doroshenko et al. 2011; Devasia et al. 2011; Nespoli et al. 2011)Devasia et al. 2011; Nespoli et al. 2011)

Energy dependent pulse profiles of GRO J1008-57 (Naik et al. 2011)

Energy dependent pulse profiles of GX 301-4 (Devasia et al. 2011)

X-ray X-ray spectra :Continuum spectra :Continuum

modelmodel

Continuum modelling: Continuum modelling: phenomenological modelsphenomenological models mostly mostly

Exhibits pulse phase dependenceExhibits pulse phase dependence

Becker & Wolff (2005, 2007) Becker & Wolff (2005, 2007) → modelled spectra arising from a pulsar accretion column including bulk motion & thermal comptonization :

X-ray spectra LineX-ray spectra Line model:model:cyclotron resonance scattering cyclotron resonance scattering

features (CRSF)features (CRSF)Continuum X-ray photons produced resonantly scattered with the quantized plasma electrons producing the CRSF .

Classically : spiralling motion of an electron in the magnetic field

Quantization of electron energy + to the B-field lines into Landau Levels

r~ΛB =ħ/mev

Bcrit

= (m2c3/ħe ) = 44.14 x 1012 G

Line modeling: Emperical: Gaussian or Lorenzian profiles: F(E)= CONT(E).exp(-Ƭ(E))Physical models: (depends on KTe, Ƭ, B, μ) (Araya & Harding 1999,2000; Schonherr et. al 2007; Nishimura 2011, Mukherjee & Bhattacharya 2011)

Observations of CRSF: & results obtained Observations of CRSF: & results obtained

EEcyccyc=11.6 keVB=11.6 keVB12 12 --> -->

effected due to gravitational redshift.effected due to gravitational redshift.

CRSF observed: CRSF observed: E Ecyccyc=(1+Z)E=(1+Z)Eobs obs --> a methord to --> a methord to

estimate the magnetic fields of X-ray pulsarsestimate the magnetic fields of X-ray pulsars Magnetic field of ~ 17 XRP's measured. ( Wilms Magnetic field of ~ 17 XRP's measured. ( Wilms

2010;Heindl et al. 2004; Staubert et al. 2003; Coburn et al. 2010;Heindl et al. 2004; Staubert et al. 2003; Coburn et al. 2002; Santangelo at al. 2000) by 2002; Santangelo at al. 2000) by RXTE, Integral, Beppo RXTE, Integral, Beppo SAXSAX & recently & recently SuzakuSuzaku

Mainly HMXB pulsars --> 50 % transient --> Mainly HMXB pulsars --> 50 % transient --> B ~ 1-5 * 10B ~ 1-5 * 1012 12

G.G. Nearly harmonic spacing --> deviations found can be Nearly harmonic spacing --> deviations found can be

explained by relativistic corrections (explained by relativistic corrections (4U 0115+63 4U 0115+63 Santangelo et al. 1999)Santangelo et al. 1999) Vela X-1 ( kreykenbohm 2002) and Vela X-1 ( kreykenbohm 2002) and A0535+26 (Caballero 2009) A0535+26 (Caballero 2009)

Variation of the parameters observed with pulse phase . Variation of the parameters observed with pulse phase . ((4u 1538-52 , Cen X-3, GX 301-24u 1538-52 , Cen X-3, GX 301-2; Robba et al. 2001; Naik ; Robba et al. 2001; Naik 2011;Suchy et al. 2011) 2011;Suchy et al. 2011)

4U 0115+63 RXTE Heindl et al. 1999

GX301-2 Suzaku Suchy et al. 2011

41 keV

Variation of the cyclotron parameters with pulse phase --> Variation of the cyclotron parameters with pulse phase --> cross section & depth of the CRSF is thought to depend cross section & depth of the CRSF is thought to depend significantly on the viewing angle of the accretion column significantly on the viewing angle of the accretion column

Variation of the CRSF parameters with phase used to Variation of the CRSF parameters with phase used to model the structure of magnetic field around neutron stars model the structure of magnetic field around neutron stars can probe magnetic field distortions & deviations from a can probe magnetic field distortions & deviations from a dipole geometry. Can be used to infer the properties of the dipole geometry. Can be used to infer the properties of the plasma & constraints between parameters plasma & constraints between parameters

To perform phase resolved spectroscopy: need to separate To perform phase resolved spectroscopy: need to separate the effect of variation of accretion rate (Lthe effect of variation of accretion rate (L

xx) from that due ) from that due

to field structure alone. to field structure alone. Pulse phase resolved spectroscopy requires high sensitivity Pulse phase resolved spectroscopy requires high sensitivity

( ( SuzakuSuzaku ; in future ; in future ASTROSATASTROSAT)) Also requires good continuum modelling : Broad-band Also requires good continuum modelling : Broad-band

spectroscopy useful : spectroscopy useful : Suzaku, ASTROSATSuzaku, ASTROSAT

Essential Requirements to probe these features in detail→ Broad-Band Energy Coverage & High sensitivity ....

Suzaku launched in 2005 covers 0.2-600 KeV and good sensitivity → This would allow reliable broad-band continuum modelingspecially required for the study to CRSFs.

The Case of 2 HMXBs- 1A 1118-61 The Case of 2 HMXBs- 1A 1118-61 & Vela X-1& Vela X-1

1A 1118-61: 1A 1118-61: Hard X-ray transient pulsar; optical Hard X-ray transient pulsar; optical counterpart Be star; 3counterpart Be star; 3rdrd Giant Outburst in 2009 by Swift Giant Outburst in 2009 by Swift (Mangano et al. 2009). Pulsations detected at (Mangano et al. 2009). Pulsations detected at 407.68407.68±± 0.02 0.02 ss ; Observations by ; Observations by SuzakuSuzaku twice: during the peak of the outburst and ~20 twice: during the peak of the outburst and ~20 days laterdays later

Vela X-1Vela X-1: Wind fed HMXB containing a supergiant companion and a : Wind fed HMXB containing a supergiant companion and a massive neutron star. Pulsations detected at massive neutron star. Pulsations detected at 283.23 283.23 ± 0.15 s± 0.15 s; ; Observations with Observations with Suzaku Suzaku on June 2008. Long observations ~ 103 kson June 2008. Long observations ~ 103 ks

Pulse profiles: 1A 1118-61 Pulse profiles: 1A 1118-61 Peak of the outburstPeak of the outburst

Double peaked structure Double peaked structure with secondary peak with secondary peak decreasing with energy. → decreasing with energy. → disappears at ~ 12 keVdisappears at ~ 12 keV

At high energies profile At high energies profile shows a single peak with a shows a single peak with a large pulse fraction.large pulse fraction.

A narrow low energy peak A narrow low energy peak (< 2 keV) is seen (< 2 keV) is seen coincident with the pulse coincident with the pulse minima at higher energies. minima at higher energies. → phase dependent soft-→ phase dependent soft-excess originating from the excess originating from the reprocessing in the reprocessing in the accretion mound /column ?accretion mound /column ?

Pulse profiles: Declining phase Pulse profiles: Declining phase

Pulse profile similar to the Pulse profile similar to the peak of the outburst peak of the outburst ( secondary peak merges ( secondary peak merges with the rising part of the with the rising part of the main peak & soft excess main peak & soft excess peak detected)peak detected)

Additional pulse component Additional pulse component seen after main peak < 2 seen after main peak < 2 keV & between 6-7 keVkeV & between 6-7 keV

5 peaked structure at lower 5 peaked structure at lower energies (< 12 keV) strength energies (< 12 keV) strength of peaks and dips varying of peaks and dips varying with energywith energy

Double peaked structure at Double peaked structure at higher energies.higher energies.

Explained due to energy Explained due to energy dependent anisotropic dependent anisotropic emission from the polar caps emission from the polar caps and the accretion and the accretion mound/column & a phase mound/column & a phase locked absorption in the locked absorption in the accretion streamaccretion stream

Pulse phase resolved Pulse phase resolved spectroscopy carried out → spectroscopy carried out → probes the accretion column probes the accretion column at different viewing angles at different viewing angles w.r.t. our L.O.S.w.r.t. our L.O.S.

Pulse profiles: Vela X-1Pulse profiles: Vela X-1

Light curve along with hardness ratio for theentire duration of observation of Vela X-1. Stretchwith constant hardness ratio is chosen to ensure results are free from systematic phase averagedspectral variability.

Intensity dependentPulse profiles of velaX-1. To avoid intensityDependence averagedData over intensity band< 50 c s-1

Spectral analysis: Phase Spectral analysis: Phase averaged averaged

Fitted with a partial covering cutoff-powerlaw model with Fitted with a partial covering cutoff-powerlaw model with interstellar absorption and a narrow gaussian Fe kinterstellar absorption and a narrow gaussian Fe kαα line at 6.4 keV line at 6.4 keV for both sourcesfor both sources

For Vela X-1 additionally a Thermal comptonization model is used which give For Vela X-1 additionally a Thermal comptonization model is used which give similar statistics to the more phenomenological model.similar statistics to the more phenomenological model.

For For 1A 1118-61 1A 1118-61 :A broad cyclotron absorption feature found in the spectra at ~ :A broad cyclotron absorption feature found in the spectra at ~ 49 keV49 keV during the peak & ~ during the peak & ~ 52 keV52 keV declining the declining phase respectively . declining the declining phase respectively . For For Vela X-1Vela X-1 fundamental and harmonic at ~ fundamental and harmonic at ~ 25 & 52 KeV25 & 52 KeV. . Line Ratios Line Ratios !!==2 !!!2 !!!

Fitted with a lorenzian profile ”cyclabs” in Xspec. Fitted with a lorenzian profile ”cyclabs” in Xspec. 1A 1118-61 → Result may imply slight increase in the centroid of the line 1A 1118-61 → Result may imply slight increase in the centroid of the line

energy with decreasing Lenergy with decreasing Lxx in agreement with variation in cyclotron line energy in agreement with variation in cyclotron line energy

with the height of the accretion column. (Mihara et al. 2004; Nakajima et al. with the height of the accretion column. (Mihara et al. 2004; Nakajima et al. 2006). CRSF feature is also broader during the peak (More later...)2006). CRSF feature is also broader during the peak (More later...)

Phase averaged spectra during the peak o the outburst : 1A 1118-61

Phase averaged spectra during the declining phase of the outburst : 1A 1118-61

Phase average spectra of Vela X-1

Phase averaged parameters of spectral fitting

1A 1118-61 Vela X-1

Phase resolved parameters duringthe peak of the outburst

Phase resolved parameters duringthe declining phase

1A 1118-611A 1118-61

Spectral analysis: phase resolved continuumSpectral analysis: phase resolved continuum

Vela X-1Vela X-1

Spectral analysis: phase resolved continuumSpectral analysis: phase resolved continuum

Energy dependence of the pulse profiles → dependence of Energy dependence of the pulse profiles → dependence of the spectrum with pulse phasethe spectrum with pulse phase

Abrupt increase in absorption column density and/or Abrupt increase in absorption column density and/or covering fraction during the dips in the pulse profile. → covering fraction during the dips in the pulse profile. → aadditional absorption component at that pulse phase dditional absorption component at that pulse phase which obscures radiation → phase locked accretion which obscures radiation → phase locked accretion stream??stream??

Spectral hardening during the pulse peaks observed Spectral hardening during the pulse peaks observed for Vela X-1 and during the peak of the outburst for for Vela X-1 and during the peak of the outburst for 1A 1118-61 → 1A 1118-61 → deep and more direct view into the deep and more direct view into the emission region ??emission region ??

For the comptonization model → At the dips in the pulse For the comptonization model → At the dips in the pulse profiles optical depth increases and KT minimum. KT profiles optical depth increases and KT minimum. KT highest at ascending and descending edges of peaks; Efold highest at ascending and descending edges of peaks; Efold of ”Highecut” and KT of ”CompTT” show similar trend.of ”Highecut” and KT of ”CompTT” show similar trend.

Spectral analysis: Spectral analysis: phase resolved CRSFphase resolved CRSF

Cyclotron energy follows the pulse profile and the value maximum at the peaks of the profile.Indication of anti-correlation and hysterisis betweenthe energy and width of the profile.

Two models give consistent results for the variationof the CRSF parameters. Deepest and widest linesat the ascending and descending edges of the peak

Two models give consistent results for the variationof the CRSF parameters. Deepest and widest linesat the ascending and descending edges of the peak

Two models give consistent results for the variationof the CRSF parameters. Deepest and widest linesat the ascending and descending edges of the peak

Ratio of the line energies in Vela X-1 as obtained by fitting with ‘Highecut’ and ‘CompTT’ model. “Circle” denotes the parameters obtained with the‘Highecut’ model and “star” denotes the same obtained with the ‘CompTT’ model.

Discussion & Conclusion Discussion & Conclusion

Owing to the broad-band capability and high sensitivity of Owing to the broad-band capability and high sensitivity of Suzaku we have been able to investigate the complex energy Suzaku we have been able to investigate the complex energy dependence of the pulse profiles in detail.dependence of the pulse profiles in detail.Dips in the pulse profile can be explained due to additional Dips in the pulse profile can be explained due to additional absorption component at that phase absorption component at that phase accretion stream phase accretion stream phase locked to neutron star.locked to neutron star.Pulse phase resolved spectroscopy of the CRSFs of 1A 1118-61 Pulse phase resolved spectroscopy of the CRSFs of 1A 1118-61 and Vela X-1 and Vela X-1 most detailed results obtained so far. most detailed results obtained so far.Variation of both fundamental and harmonic CRSF of Vela X-1 Variation of both fundamental and harmonic CRSF of Vela X-1 with phase line ratios deviate from 2.with phase line ratios deviate from 2.Detailed theoretical modeling required Detailed theoretical modeling required for interpretation of for interpretation of radiation in these systems which can fit pulse phase resolved radiation in these systems which can fit pulse phase resolved spectra.spectra.

Studies with ASTROSATStudies with ASTROSAT

Spectra of five accretion poweredpulsars as would be detected byLAXPC. The lines are model spectrawithout the CRSFs, and the datashow the simulated spectra for LAXPC.

Polarimetric studiesPolarimetric studies Thomson scattering polarimeter (5-30 keV) : Thomson scattering polarimeter (5-30 keV) :

pulse phase resolved polarimetric studies pulse phase resolved polarimetric studies probing the structure & geometry of the magnetic probing the structure & geometry of the magnetic fields of neutron stars; beaming mechanism, its fields of neutron stars; beaming mechanism, its relation with luminosity mass accretion rate etc. relation with luminosity mass accretion rate etc.

Thank you Thank you