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

X-ray Binaries Most brightest X-ray sources in the sky Two stars in the system rotate around the common center of mass The compact object is either a White Dwarf, Black Hole or a Neutron star Most of the neutron stars are rapidly rotating and highly magnetic. Misalignment of the spin and magnetic axis of rotating neutron star causes pulsation in the emitted radiation (Pulsars). 5/6/2019 Sachindra Naik, PRL

Types of X-Ray Pulsars Rotation Powered X-ray Pulsars: Isolated rotating neutron stars Radiate energy via slowing down Pulse period usually ≤ 1sec, dP/dt > 0 Ex : Crab pulsar (33 ms) in Crab Nebula, Vela pulsar (89 ms) in Vela SNR etc…. Accretion Powered X-ray Pulsars: Compact objects in binary systems Accrete matter from normal companion star P ~ sub-seconds to hundreds of seconds , dP/dt < 0 Wind fed X-ray pulsars (HMXBs), Disk fed X-ray pulsars (LMXBs) Magnetars (Anomalous X-ray Pulsars): Young, highly magnetized, isolated neutron stars. Magnetic field ~1013-1015 Gauss, 10 known & 1 candidate Spin Period ~ 5 - 12 s 5/6/2019 Sachindra Naik, PRL

Accretion Powered X-Ray Pulsars Flux of matter falling from stellar wind or/and Roche lobe overflow Interaction with the magnetic field at the magnetospheric radius Formation of accreting slabs or columns of matter at the polar caps : Source of X-ray radiation Transport of X-ray radiation through a strongly magnetized plasma 5/6/2019 Sachindra Naik, PRL

Broad-band Spectra in XRBPs can be characterized by following components Continuum Spectrum Line of sight absorption Soft excess Emission line features Cyclotron resonance features Orbital phase dependent Pulse phase dependent Endo et al. 2000 All these components vary with respect to pulse phase and orbital phase! 5/6/2019 Sachindra Naik, PRL

Broad-band Spectra in XRBPs Dal Fiume et al. 1998 Sachindra Naik, PRL 5/6/2019

Soft Excess in XRBPs 5/6/2019 Sachindra Naik, PRL

Soft Excess in XRBPs Detectable only in low absorption systems Pulsating?? Emission region EXO 053109-6609.2, PP = 13.7 s, NH ~ 1021 atoms cm-2 Sachindra Naik, PRL 5/6/2019

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 5/6/2019 Sachindra Naik, PRL

Soft Excess in XRBPs 5/6/2019 Sachindra Naik, PRL

Soft Excess Emission Region Hickox et al. 2004. 5/6/2019 Sachindra Naik, PRL

Broad-band Spectra of XRBPs (GX 1+4) One of the Brightest and hard X-ray source….. Pulse Period ~ 2 mins, single peaked pulse profile, M5 giant companion star 5/6/2019 Sachindra Naik, PRL

Partial covering absorption model for transient Be-X-ray Binary Pulsars (GROJ1008-57) Pulse Period ~ 93.74 s, Orbital Period ~ 260 days Naik et al. 2011 5/6/2019 Sachindra Naik, PRL

Partial covering absorption model for transient Be-X-ray Binary Pulsars 1A 1118-61 : Maitra et al. 2012 GX 304-1 : Devasia et al. 2011 5/6/2019 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) Hung et al. 2010 5/6/2019 Sachindra Naik, PRL

Broad-band Spectra of XRBPs (LMC X-4) Hung et al. 2010 5/6/2019 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 5/6/2019 Sachindra Naik, PRL

Cen X-3: Orbital Phase Resolved Spectrum Most probable emitting region of 6.4 keV 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 photo-ionized wind of the companion star or in the accretion disk corona. 5/6/2019 Sachindra Naik, PRL

Cen X-3: Orbital Phase Resolved Spectrum 5/6/2019 Sachindra Naik, PRL

Cen X-3: Orbital Phase Resolved Spectrum Eclipse Dip Normal Eclipse egress Naik, Paul, Ali 2011 5/6/2019 Sachindra Naik, PRL

Change in Iron Line Parameters at Different Orbital Phase Decrease in the intensity and increase in equivalent width of 6.4 keV, 6.7 keV and 6.97 keV lines during the dips 5/6/2019 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 B12 (1+z)-1 keV] (where B12 is in the units of 1012 Gauss) 5/6/2019

Cyclotron lines with Suzaku (Gx 301-2, 1A1118-61) CRSF at ~ 58 keV CRSF at ~ 35 keV Pottschmidt et al. 2011 5/6/2019 Sachindra Naik, PRL

Cyclotron lines with Suzaku (A0535+262 & Her X-1) Ea ~ 45 keV Terada et al. (2006); Naik et al. (2008) Ea ~ 36 keV, Enoto et al. (2008) 5/6/2019 Sachindra Naik, PRL

Luminosity Dependent Change of Ea (Ginga Obs. Of 4U0115+63) Recurrent transient pulsar, sp=3.6 s, op=24.3 d, D ~ 7 kpc 1990 Obs. L = 14×1037 erg/s 1991 Obs. L = 2×1037 erg/s 11.3 & 22 keV 17 keV Mihara et al. 2004 5/6/2019 Sachindra Naik, PRL

Luminosity Dependent Change of Ea Caballero et al. 2007 4U0115+63 : Nakajima et al. 2006 5/6/2019 Sachindra Naik, PRL

Luminosity Dependence of Cyclotron lines RXTE INTEGRAL 5/6/2019 Sachindra Naik, PRL

Luminosity Dependence of Cyclotron lines Her X-1 : Staubert et al. 2007 5/6/2019 Sachindra Naik, PRL

Phase-resolved spectroscopy of Cyclotron lines (Her X-1) Occtober 2000 observation of Her X-1. BeppoSAX 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… Sachindra Naik, PRL 5/6/2019

Phase-resolved spectroscopy of Cyclotron lines (Her X-1) Deep fundamental Second Harmonic! Shallow fundamental Nothing exciting here 5/6/2019 Sachindra Naik, PRL

Phase-resolved spectroscopy of Cyclotron lines (1A1118-61) Maitra, Paul, Naik 2012 5/6/2019 Sachindra Naik, PRL

Phase-resolved spectroscopy of Cyclotron lines (GX 301-2) 19-60 keV 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. 5/6/2019 Sachindra Naik, PRL

Summery Continuum spectrum in X-ray pulsars Soft excess in X-ray pulsars and its origin Iron line emission in X-ray pulsars, change in the line properties over pulse/orbital phases Cyclotron line features in X-ray pulsars and estimation of neutron star magnetic field , luminosity dependence of the cyclotron line. Thanks for your attention….. 5/6/2019 Sachindra Naik, PRL