Cyclotron Line Science with LAXPC. Dipankar Bhattacharya IUCAA, Pune

Transcription

1 Cyclotron Line Science with LAXPC Dipankar Bhattacharya IUCAA, Pune Workshop on Science with LAXPC/Astrosat, Hyderabad, 16 December 2014

2 A High Mass X-ray Binary Cyclotron Resonant Scattering Features (CRSF) arise in the accretion column of X-ray binary systems containing high-field Neutron Stars

3 Cyclotron Line in HMXB Shock Column Mound Romanova, Kulkarni and Lovelace 2008 Polar accretion geometry

4 Heindl 2001

5 Cyclotron resonance Gyration of electrons in a magnetic field B Landau quantum levels e - p?n m e c = p 2n(B/B crit ) E n = For q m 2 ec 4 + c 2 (p 2 + p 2?n ) p = 0 and B << B crit ; n = 0, 1, 2,... ; B crit = m2 ec 3! ce = eb m e c e~ G Classical Cyclotron Frequency (2 ) 3 B (G) MHz ~! ce 12 B 12 kev E n m e c 2 = n~! ce Relativistic gyration frequency:! ce /

6 Cyclotron resonance Resonant interaction between electromagnetic wave and charged particle in a magnetic field Absorption, Scattering, Stimulated Emission ~! res n m e c 2 = q 1 + 2n(B/B crit ) sin 2 1 sin 2 for QED: p = 0 In X-ray binary systems, scattering is the most dominant process Absorption, Emission : First order process Magneto-Compton scattering: Second order process. Involves resonant intermediate states

7 Resonant scattering cross section Resonances are very sharply peaked, profoundly affect electronphoton interaction near them Cross section lower than Thompson at low energy Affects Eddington Luminosity Sandeep Kumar 2013

8 Resonant cross sections Scattering Absorption Harding & Daugherty 1991

9 Cyclotron Resonance General resonance condition for a moving electron cp 0 = cp + ~! cos E n = E 0 + ~! For arbitrary (!,, B, n) there could be 0, 1 or 2 solutions of p These are the electrons the resonant scattering will occur from. Scattering probability will depend on the electron distribution at these momenta f(p ) kte=5 kev 0.2 cp S. Kumar 2013

10 Scattering line profiles B = 0.03 kte = 5 kev Sandeep Kumar 2013

11 Gruber et al 2001 Cyclotron line sources known (24) Ecyc (kev) Energy (kev) RXJ NuSTAR Tendulkar et al 2014 Swift J KS U IGR J U IGR J U Vela X-1 V Cep X-4 Cen X-3 X Per IGR J RX J MXB U XTE J U GX Her X-1 1A GX A GRO J ,24,36,48, , ? 22,47 24,52 27,51, , ? 79? Ginga, BeppoSAX, CGRO, RXTE, INTEGRAL,Suzaku, NuSTAR,...

12 Cyclotron Lines (CRSF) in HMXB Estimate magnetic field from: E c 12 B 12 kev (fundamental) Key unknowns: Location of line formation, field geometry Source and nature of the continuum Distribution and dynamics of plasma Short-term and secular evolution Important observational indicators E c vs L X and pulse phase, line shape, harmonic spacing Energy-resolved timing Continuum shape, phase dependence

13 Astrosat advantage: More effective area in cyclotron line bands (LAXPC) than any other previous mission. Simultaneous broad-band coverage provides characterisation of underlying continuum, which is crucial for the study of cyclotron lines Key objective: Sensitive study of cyclotron line behaviour as a function of pulse phase and luminosity Paul 2004

14 Time evolution of cyclotron spectrum 1 JEM X V ISGRI /Crab 1 10 Rev. 273 Rev. 278 Rev. 284 Rev. 287 V03 erg dam clo cha out Energy (kev) 30 Mowlavi et al 2006 (Mow

15 4U Phase resolved spectroscopy Ferrigno et al 2009

16 Cyclotron line Energy vs Lx V Her X-1 Ecyc (kev) Tsygankov et al 2010 Vasco et al 2011 Lbol (10 37 erg/s) Ecyc (kev) RXTE INTEGRAL Suzaku A Caballero et al MJD BAT Counts Three types of behaviour seen: Positive Correlation Negative Correlation No Correlation

17 Cyclotron line Energy vs Lx COULOMB BRAKING RADIATION BRAKING Ecyc kev GAS SHOCK L X L coul L X L crit GX V A Her X 1 4U L X ergs sec 1 Becker et al 2012

18 E c -L x correlation depends on continuum model 15 4U NPEX E0 [kev] time (MJD-54500) 10 CutoffPL kev LX [10 37 erg s 1 ] Müller et al 2013

19 Mass : M Field distortion caused by mound of accreted matter Mass : M Mass : M Mass : M Mukherjee & DB 2012

20 Filled parabolic mound, Z c =50 m B GS /B dip for filled parabolic mound, Z c =50m Height in km Height in km Height in km Radius in km Hollow mound, Z c =38 m 0.2 Height in km Radius in km B GS /B dip for hollow mound, h c =38m Magnetic field distortion in accretion column due to the presence of a filled / hollow mound Radius in km Radius in km Mukherjee, DB, Mignone 2014

21 Hotspot emission viewing geometry Shadow effect in a Hollow mound Light bending: cos α u + (1 - u) cos ψ ; u = 2GM/c 2 r df cos α (d cos α/d cos ψ) ds (Beloborodov 2002) Gravita?onal redshi@: E = (1- u) 1/2 E 0 Mukherjee & DB 2012, 2013

22 Degeneracy pressure dominated structures 10% energy resol CRSF profile l Multi-peaked structure due to large variation of surface field strength. l Broader and more complex profiles for hollow mounds. Filled mound l High resolution and sensitivity required to probe line shapes Hollow mound Mukherjee, DB, Mignone 2012, 2013 Profiles of fundamental features only; computed using basic CRSF shapes from Schonherr et al (2007)

23 CRSF profiles from accretion mounds Distinction between thermal and magnetic pressure dominated structures = Thermal Magnetic Priymak et al 2014

24 Cyclotron line: Spin Phase Dependence Vela X C. Maitra & B. Paul E (kev)

25 Monte Carlo Spectra i=10 o Accretion Column z t r t r tt z b θ h z c r c r b r bb Sandeep Kumar & DB 2013

26 Interchange mode instability observed in 3D MHD simulation of mounds with PLUTO code The more massive the mound, the quicker is the growth of the instability Mukherjee, DB & Mignone 2013

27 1.e-05 1D toroidal PSD of density for r ~ 700 m, z ~ 25 m 1.e-06 1.e-07 Normalised power spectra 1.e-08 1.e-09 1.e-10 1.e-11 1.e-02 1.e-03 1.e-04 t = 0.25 t A Density fluctuation spectrum in MHD instabilities 1.e-05 1.e-06 t = 0.60 t A 1.e-07 1.e Mode number Mukherjee, DB & Mignone 2013

28 Timing signature of MHD instabilities Intensity vs time Power spectral density for hollow mound Normalised intensity Power spectra Time in seconds Frequency in Hz Mukherjee, DB & Mignone 2013

29 Proton Cyclotron Feature in Magnetars? SGR E Ibrahim et al 2002 An et al 2014 If proton cyclotron resonance, then the features imply B ~ G

30 LAXPC cyclotron line targets Persistent HMXB pulsars spin-phase resolved spectroscopy luminosity dependent variation fast timing in resonance band Transient HMXB pulsars time resolved spectroscopy near outbursts Magnetar outbursts hunt for proton cyclotron signature Simultaneous fitting of pulse profile and cyclotron spectra using radiative transfer models, to probe the emission region

31 120 Average Fluxes of persistent cyclotron line sources 90 Average kev flux (mcrab) Vela X- 1 GX301-2 Cen X- 3 4U1626 Her X- 1 4U1538 4U1907 IGR16493

32 Vela X-1 50 ks SXT: 3 c/s CZTI: 185 c/s LAXPC: 3219 c/s

33 Determining the continuum CompTT vs HighEcut Vela X ks

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35 50 ks SXT 39 c/s CZTI 98 c/s LAXPC 3000 c/s

36 Summary LAXPC, along with CZTI, has the capability to seriously push to the envelope of cyclotron line science. Should be a key science programme Better estimate of continuum to better define the line Systematic study of dependence of line on pulse phase, luminosity changes, orbital phase and time in accreting NS systems of a dozen sources. Campaign for discovery of new cyclotron line sources - Be transients at outbursts, magnetar bursts Devoting a couple of megaseconds on this study over the mission lifetime would be well worth the effort