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

2. 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

3. 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 ~ Gauss, 10 known & 1 candidate
Spin Period ~ s
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Sachindra Naik, PRL

4. 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
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Sachindra Naik, PRL

5. 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!
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Sachindra Naik, PRL

6. Broad-band Spectra in XRBPs
Dal Fiume et al. 1998
Sachindra Naik, PRL
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7. Soft Excess in XRBPs
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Sachindra Naik, PRL

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

9. 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
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Sachindra Naik, PRL

10. Soft Excess in XRBPs
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Sachindra Naik, PRL

11. Soft Excess Emission Region
Hickox et al
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Sachindra Naik, PRL

12. 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

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

14. Partial covering absorption model for transient Be-X-ray Binary Pulsars
1A : Maitra et al. 2012
GX : Devasia et al. 2011
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Sachindra Naik, PRL

15. 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 ( ), 0.27 ( ), 0.07 ( )
Hung et al. 2010
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Sachindra Naik, PRL

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

17. Orbital Phase Resolved Spectroscopy : Cen X-3:
PP ~ 4.8 s, OP = 2.1 d, O-type supergiant companion
Ebisawa et al. 1996
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Sachindra Naik, PRL

18. 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.
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Sachindra Naik, PRL

19. Cen X-3: Orbital Phase Resolved Spectrum
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Sachindra Naik, PRL

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

21. 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
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Sachindra Naik, PRL

22. 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)
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23. Cyclotron lines with Suzaku (Gx 301-2, 1A1118-61)
CRSF at ~ 58 keV
CRSF at ~ 35 keV
Pottschmidt et al. 2011
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Sachindra Naik, PRL

24. 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)
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Sachindra Naik, PRL

25. 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
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Sachindra Naik, PRL

26. Luminosity Dependent Change of Ea
Caballero et al. 2007
4U : Nakajima et al. 2006
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Sachindra Naik, PRL

27. Luminosity Dependence of Cyclotron lines
RXTE
INTEGRAL
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Sachindra Naik, PRL

28. Luminosity Dependence of Cyclotron lines
Her X-1 : Staubert et al. 2007
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Sachindra Naik, PRL

29. 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

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

31. Phase-resolved spectroscopy of Cyclotron lines (1A1118-61)
Maitra, Paul, Naik 2012
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Sachindra Naik, PRL

32. 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.
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Sachindra Naik, PRL

33. 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