Broadband Spectroscopy of Xray Binary Pulsars Sachindra Naik

Broad-band Spectroscopy of X-ray Binary Pulsars Sachindra Naik Physical Research Laboratory, Ahmedabad

X-ray Binaries v Most brightest X-ray sources in the sky v Two stars in the system rotate around the common center of mass v The compact object is either a White Dwarf, Black Hole or a Neutron star v Most of the neutron stars are rapidly rotating and highly magnetic. v Misalignment of the spin and magnetic axis of rotating neutron star causes pulsation in the emitted radiation (Pulsars). 11/3/2020 Sachindra Naik, PRL

Types of X-Ray Pulsars v Rotation Powered X-ray Pulsars: Isolated rotating neutron stars Radiate energy via slowing down Pulse period usually ≤ 1 sec, d. P/dt > 0 Ex : Crab pulsar (33 ms) in Crab Nebula, Vela pulsar (89 ms) in Vela SNR etc…. v Accretion Powered X-ray Pulsars: Compact objects in binary systems Accrete matter from normal companion star P ~ sub-seconds to hundreds of seconds , d. P/dt <0 Wind fed X-ray pulsars (HMXBs), Disk fed X-ray pulsars (LMXBs) v Young, (Anomalous highly magnetized, neutron stars. Magnetars X-ray Pulsarsisolated ): 13 15 11/3/2020 Magnetic field ~10 13 -1015 Gauss, 10 known & 1 candidate Spin Period ~ 5 - 12 s Sachindra Naik, PRL

Accretion Powered X-Ray Pulsars Ø Flux of matter falling from stellar wind or/and Roche lobe overflow Ø Interaction with the magnetic field at the magnetospheric radius Ø Formation of accreting slabs or columns of matter at the polar caps : Source of X-ray radiation Ø Transport of X-ray radiation through a strongly magnetized plasma 11/3/2020 Sachindra Naik, PRL

Broad-band Spectra in XRBPs can be characterized by following components n Continuum Spectrum n Line of sight absorption n Soft excess n Emission line features n Cyclotron resonance features n Orbital phase dependent n Pulse phase dependent Endo et al. 2000 All these components vary with respect to pulse phase and orbital phase! 11/3/2020 Sachindra Naik, PRL

Broad-band Spectra in XRBPs Dal Fiume et al. 1998 11/3/2020 Sachindra Naik, PRL

Soft Excess in XRBPs 11/3/2020 Sachindra Naik, PRL

Soft Excess in XRBPs n Detectable only in low absorption systems n Pulsating? ? n Emission region EXO 053109 -6609. 2, PP = 13. 7 s, NH ~ 1021 atoms cm-2 11/3/2020 Sachindra Naik, PRL

Pulsation in soft component LMC X-4: PP = 13. 5 s Naik & Paul 2004 SMC X-1: PP = 0. 71 s Paul et al. 2002 11/3/2020 Sachindra Naik, PRL

Soft Excess in XRBPs 11/3/2020 Sachindra Naik, PRL

Soft Excess Emission Region 11/3/2020 Hickox et al. 2004. Sachindra Naik, PRL

Broad-band Spectra of XRBPs (GX 1+4) GX 1+4 : One of the Brightest and hard X-ray source…. . Pulse Period ~ 2 mins, single peaked pulse profile, M 5 giant companion star 11/3/2020 Sachindra Naik, PRL

Partial covering absorption model for transient Be-X-ray Binary Pulsars (GROJ 1008 -57) Pulse Period ~ 93. 74 s, Orbital Period ~ 260 days Naik et al. 2011 11/3/2020 Sachindra Naik, PRL

Partial covering absorption model for transient Be-X-ray Binary Pulsars 1 A 1118 -61 : Maitra et al. 2012 GX 304 -1 : Devasia et al. 2011 11/3/2020 Sachindra Naik, PRL

Broad-band Spectra of XRBPs (LMC X-4) Pulse period = 13. 5 s, Orbital period = 1. 4 d Super-orbital period = 30. 3 d Phases of obs. = 0. 39 (2008 -01 -18), 0. 27 (2008 -02 -11), 0. 07 (2008 -04 -05) 11/3/2020 Hung et al. 2010 Sachindra Naik, PRL

Broad-band Spectra of XRBPs (LMC X-4) Hung et al. 2010 11/3/2020 Sachindra Naik, PRL

Orbital Phase Resolved Spectroscopy : Cen X-3: PP ~ 4. 8 s, OP = 2. 1 d, O-type supergiant companion Ebisawa et al. 1996 11/3/2020 Sachindra Naik, PRL

Cen X-3: Orbital Phase Resolved Spectrum Most probable emitting region of 6. 4 ke. V fluorescent line is close to the neutron star where as the other two lines are produced in a region far from the neutron star i. e. in highly photoionized wind of the companion star or in the accretion disk corona. 11/3/2020 Sachindra Naik, PRL

Cen X-3: Orbital Phase Resolved Spectrum 11/3/2020 Sachindra Naik, PRL

Cen X-3: Orbital Phase Resolved Spectrum Eclipse egress Normal Dip Eclipse Dip Naik, Paul, Ali 2011 11/3/2020 Sachindra Naik, PRL

Change in Iron Line Parameters at Different Orbital Phase Decrease in the intensity and increase in equivalent width of 6. 4 ke. V, 6. 7 ke. V and 6. 97 ke. V lines during the dips 11/3/2020 Sachindra Naik, PRL

Cyclotron lines in accretion powered X-ray pulsars Cyclotron resonance features (CRFs) in X-ray pulsars are due to resonant scattering of the line of sight X-ray photons against electrons (and protons) embedded in magnetic fields (1011 – 1013 Gauss). A method to estimate the magnetic field of X-ray pulsars [Ea = 11. 6 x B 12 (1+z)-1 ke. V] (where B 12 is in the units of 1012 Gauss) 11/3/2020

Cyclotron lines with Suzaku (Gx 301 -2, 1 A 111861) CRSF at ~ 58 ke. V CRSF at ~ 35 ke. V Pottschmidt et al. 2011 11/3/2020 Sachindra Naik, PRL

Cyclotron lines with Suzaku (A 0535+262 & Her X 1) Ea ~ 45 ke. V Terada et al. (2006); Naik et al. (2008) 11/3/2020 Ea ~ 36 ke. V, Enoto et al. (2008) Sachindra Naik, PRL

Luminosity Dependent Change of Ea (Ginga Obs. Of 4 U 0115+63) Recurrent transient pulsar, sp=3. 6 s, op=24. 3 d, D ~ 7 kpc 1991 Obs. L = 2× 1037 erg/s 1990 Obs. L = 14× 1037 erg/s 11. 3 & 22 ke. V 17 ke. V Mihara et al. 2004 11/3/2020 Sachindra Naik, PRL

Luminosity Dependent Change of Ea A 0535+262 : Caballero et al. 2007 4 U 0115+63 : Nakajima et al. 2006 11/3/2020 Sachindra Naik, PRL

Luminosity Dependence of Cyclotron lines INTEGRAL 11/3/2020 RXTE Sachindra Naik, PRL

Luminosity Dependence of Cyclotron lines Her X-1 : Staubert et al. 2007 11/3/2020 Sachindra Naik, PRL

Phase-resolved spectroscopy of Cyclotron lines (Her X-1) Occtober 2000 observation of Her X-1. Beppo. SAX observed the first “main on” state after an extended low state that lasted almost two years Search for features in the rising and falling edge of the main peak pulse… 11/3/2020 Sachindra Naik, PRL

Phase-resolved spectroscopy of Cyclotron lines (Her X-1) Deep fundament al Shallow fundament al Nothing exciting here 11/3/2020 Second Harmonic! Sachindra Naik, PRL

Phase-resolved spectroscopy of Cyclotron lines (1 A 1118 -61) Maitra, Paul, Naik 2012 11/3/2020 Sachindra Naik, PRL

Phase-resolved spectroscopy of Cyclotron lines (GX 301 -2) 19 -60 ke. V pulse profle 60 ks of Suzaku observation 200 ks of RXTE observation Change in CRSF with pulse phase shows the signature of a magnetic dipole field. Using dipole model, the expected field values for different pulse phases can be calculated along with a set of geometrical angles, constraining the dipole geometry in the neutron star. 11/3/2020 Sachindra Naik, PRL

Summery v Continuum spectrum in X-ray pulsars v Soft excess in X-ray pulsars and its origin v Iron line emission in X-ray pulsars, change in the line properties over pulse/orbital phases v Cyclotron line features in X-ray pulsars and estimation of neutron star magnetic field , luminosity dependence of the cyclotron line. 11/3/2020 Sachindra Naik, PRL