1. X-rays from Magnetic Cataclysmic Variables and ASTROSAT
K.P Singh Tata Institute of Fundamental Research Mumbai, India 1

2. Talk Outline Introduction to CVs Types and classes of CVs
Non-magnetic systems
Magnetic systems: Polars and Intermediate Polars
X-ray Light Curves of Polars and IPs
Wide-Band, Low-Resolution X-ray spectra
ASTROSAT
Conclusions
18 Feb 2012
HEAP12- HRI (KP Singh) 2 2

3. CVs: what are they? Cataclysmic Variables are
semi-detached binaries accreting
from a red dwarf main-sequence-like secondary star
to a more massive white dwarf primary star
Binary: Roche potential: the gravitational potential around two orbiting point masses – resultant force on a test mass: 2
Centre of Mass
credit: csep10.phys.utk.edu
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4. Roche Lobe Overflow
Semi-detached  secondary star fills its Roche lobe so that it is distorted into a pear shape.
At Lagrangian 1 (L1) point, gravitational and centrifugal forces cancel and material is lost from the secondary star into the primary Roche lobe.
Material falls towards the white dwarf in a stream
The 4 other stationary points L2 – L5 are important for orbit theory 2
credit: csep10.phys.utk.edu
credit:
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5. The CV Zoo: subtypes Cataclysmic Variables (non-magnetic)
Novae large eruptions 6–9 magnitudes
Recurrent Novae previous novae seen to repeat
Dwarf Novae regular outbursts 2–5 magnitudes
SU UMa stars occasional Superoutbursts
Z Cam stars show protracted standstills
U Gem stars all other DN
Nova-like variables
VY Scl stars show occasional drops in brightness
UX UMa stars all other non-eruptive variables
Intermediate Polars/DQ Her stars
Polars/AM Her stars
magnetic systems
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6. (1) Non-Magnetic CVs
magnetic field on primary <106 G (100 T)  non-magnetic CV
accretion takes place through a disk
via boundary layer on white dwarf
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7. (2) Magnetic CVs: Polars
NO DISK: accretion takes place via a stream and accretion column directly onto white dwarf
Largest circular polarization varying with the orbital period: magnetic field > 107 G (1000 T)  polar/AM Her system
the magnetic field controls the flow from some threading region
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8. Polars: Synchronisation
All of the variability in Polars occurs at a single period: the orbital period
radial velocity curves of the secondary
X-ray light curves from the primary
polarisation variations
the white dwarf/red dwarf are locked into the same orientation: synchronised rotation
The mechanism for synchronisation is the dissipation due to the magnetic field of the primary being dragged through the secondary
As relative spin rate of primary decreases, locking can occur due to the dipole-dipole magnetostatic interaction between primary and (weaker) secondary magnetic field
Some Polars not quite in synchronism; in these systems it typically takes 5–50 days for white dwarf orientation to repeat itself
Very useful systems to study the effect of orientation of magnetic field on the accretion process
18 Feb 2012
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9. Polars: Radial Accretion
hard X-rays
white dwarf
shock
cold supersonic flow
hot postshock flow
soft X-rays/ extreme UV
optical/IR cyclotron radiation
Infalling material is forced to follow the magnetic field lines
Gas is initially in free-fall but then it encounters a shock front
Shock converts kinetic energy into thermal energy (bulk motion into random motion)  temperature increases to ~50 keV
Velocity drops by 1/4 and density increases by 4
Material radiates by cyclotron and bremsstrahlung and gradually settles on white dwarf
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10. X-ray Spectrum
Rothschild et al (1981)
Polars/AM Her stars were found to be strong soft X-ray emitters (~1033 erg/s) in early surveys
X-ray emission characterized by thermalized free-fall velocities from a white dwarf so emission is from a hot region close to the white dwarf surface: post-shock
Cyclotron emission must also be from a hot region (otherwise narrow cyclotron emission lines rather than continuum)
AM Her
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11. Polars: Spectral Energy Distribution
Most of the energy from these systems is a result of accretion
3 main components:
cyclotron radiation from accretion column
hard X-ray emission, also from accretion column
soft X-ray emission, from heated surface of primary
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Beuermann (1998) 11

12. XMM-Newton Spectrum of V1432 Aql
XMM: Rana, Singh et al. 2005, ApJ
Model Compenents:
Black body emission (88±2 eV)
Absorbers:1.7±0.3 x 1021 cm-2, fully covering the source & 1.3 ±0.2 x 1023 cm-2, covering 65%
Multi-temperature plasma model
Gaussian for 6.4 keV line emission
Absorption due to ISM = 4.5 x 1020 cm-2 (fixed from ROSAT Obs;
Staubert et al. 1994)
18 Feb 2012
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13. RXTE Spectrum of V1432 Aql
Bremsstrahlung model (temperature of >90 keV ;
highest in Polars and IPs)
Mass of the WD related to the shock temperature
Mass of the WD in V1432 Aql is 1.2±0.1 solar mass.
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Model = Absorption (Multi-temperature Plasma + Gaussian) 13

14. AM Her (Polar) Pspin (X-ray)=11139 s
Girish, Rana & Singh 2007
Two-pole accretion based on optical
Polarization
Inclination=52+-5 degrees
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15. UZ For (Eclipsing Polar): P=7591.8 s
Two accretion regions evident
Weak accretion stream
UZ For
Sky
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STJ photometry: Perryman et al (2001) 15

16. (3) Magnetic CVs: Intermediate Polars
magnetic field ~106 G  intermediate polar/DQ Her system
accretion takes place through a hollowed-out disk and then via accretion columns onto the white dwarf
magnetic field controls the flow in the final stages
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17. Intermediate Polars: models
Intermediate Polars spin variability can be explained in several ways
visibility of the accretion region on the white dwarf
visibility of the accretion “curtains”
reprocessing of flux on the disk (optical/UV)
From studies of the relative phasing in different wavelength bands and including the absorption effects now known to be a combination of the above models leading to the complex behavior in Intermediate Polar light curves
stream
Adapted from Hellier (2001)
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18. AO Psc (Intermediate Polar)
Cropper et al (2002)
AO Psc: Optical spectrum like that of Polars, but without any identifiable polarisation
Variability on three different timescales now known to be
the orbital h,
the spin period of the white dwarf s
the mixture of the two (beat/synodic period)
AO Psc
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19. AO Psc (IP) Power Spectra
Ginga:
Norton et al.
By performing a Fourier Transform of the previous data, the main periodicities can be identified
orbital period
white dwarf spin
beat (very faint in this system)
Also evident are harmonics when the variations are non-sinusoidal (2, 3, 2)
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20. TV Col (Intermediate Polar) =1909.7s =5.5 h
First clear detection of
Orbital modulation
Rana, Singh et al. 2004, AJ, 127, 489
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21. TV Col (IP): Spin and Orbital Phase LCs
Absorption Dips due to stream
18 Feb 2012
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Rana, Singh et al. 2004, AJ, 127, 489 21 21

22. INTEGRAL Discovered IP: IGR J17195-4100
New spin period: s
New Binary Orbital period: 3.5 hours
Girish & Singh, MNRAS, 2012
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23. Multi-temperature plasma, partial absorber and flourescence – sometimes
a weak soft X-ray component. Accretion Curtain but perhaps no disc in this IP !
Girish & Singh, MNRAS, 2012

24. X-ray Spectrum: EX Hya (IP)
X-ray spectra of Intermediate Polars generally show just the multi-temperature thermal bremsstrahlung component from the hot radial accretion flow – no soft reprocessed component from the white dwarf
Main explanation is likely to be the larger area over which accretion takes place, but also photoelectric absorption is important
Fujimoto & Ishida 1997
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25. ASTROSAT (1. 55 tons; 650 kms, 8 deg inclination orbit by PSLV
ASTROSAT (1.55 tons; 650 kms, 8 deg inclination orbit by PSLV. 3 gyros and 2 star trackers for attitude control by reaction wheel system with a Magnetic torquer ) Launch: end of 2012
2 UV(+Opt ) Imaging Telescopes
3 Large Area Xenon
Proportional Counters
Soft X-ray Telescope
CZTI
Radiator Plates
For SXT and CZT
Scanning Sky Monitor (SSM)
Folded Solar panels
SSM (2 – 10 keV)

26. UVIT: Two Telescopes f/12 RC Optics Focal Length: 4756mm
Diameter: 38 cm
Simultaneous Wide Angle ( ~ 28’) images in FUV ( nm) in one and NUV ( nm) & VIS ( nm) in the other
MCP based intensified CMOS detectors
Spatial Resolution : 1.8”
Sensitivity in FUV: mag. 20 in 1000 s
Temporal Resolution ~ 30 ms, full frame ( < 5 ms, small window )
Gratings for Slit-less spectroscopy in FUV & NUV
R ~ 100
K.P. Singh 26
Feb 13, 2012

27. Large Area Xenon Proportional Counter (LAXPC): Characteristics
Energy Range : 3-80 keV ( 50  Mylar window, 2 atm. of 90 % Xenon + 10 % Methane )
Effective Area : 6000 cm² 20 keV)
Energy Resolution : ~10% FWHM at 22 keV
Onboard purifier for the xenon gas
Field of View : 1° x 1° FWHM (Collimator : 50µ Sn + 25µ Cu + 100µ Al )
Blocking shield on sides and bottom : 1mm Sn mm Cu
Timing Accuracy : 10 μsec in time tagged mode
(oven-controlled oscillator). 27

28. LAXPC: Effective Area
Feb 13, 2012
K.P. Singh 28

29. Sensitivity 0.5 mCrab (5 sigma; 10 4 s) CZT Imager characteristics
Area
1024 cm 2
Pixels
16384
Pixel size
2.4 mm X 2.4 mm (5 mm thick)
Read-out
ASIC based (128 chips of 128 channels)
Imaging method
Coded Aperture Mask (CAM)
Field of View
17 X 17 deg2 (uncollimated)
6 X 6 (10 – 100 keV) – CAM
Angular resolution
8 arcmin
Energy resolution
100 keV
Energy range
10 – 100 keV - Up to 1 MeV (Photometric)
Sensitivity
0.5 mCrab (5 sigma; s) 29

30. SXT Characteristics
Telescope Length: mm (Telescope + camera + baffle + door)
Top Envelope Diameter: 386 mm
Focal Length: mm
Epoxy Replicated Gold Mirrors on Al substrates in conical Approximation to Wolter I geometry.
Radius of mirrors: mm; Reflector Length: 100 mm
Reflector thickness: 0.2 mm (Al) + Epoxy (~50 microns) + gold (1400 Angstroms)
Reflector Smoothness: 8 – 10 Angstroms
Minimum reflector spacing: 0.5 mm
No. of reflectors: 320 (40 per quadrant)
Detector : E2V CCD-22 (Frame-Store) 600 x 600
Field of view : x 41.3 arcmin
PSF: ~ 4 arcmins
Sensitivity (expected): 15 Crab (1 cps/mCrab)
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K.P. Singh 30

31. SXT Effective Area vs. Energy (after subtraction of shadowing effects due to holding structure)
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32. Scanning Sky Monitor (SSM)
Detector : Proportional counters with resistive anodes
Ratio of signals on either ends of anode gives position.
Energy Range : keV
Position resolution : mm
Field of View : 10 x 90 (degs) (FWHM)
Sensitivity : 30 mCrab (5 min integration)
Time resolution : 1 ms
Angular resolution : ~ 10 arc min
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K.P. Singh 32 32

33. ASTROSAT – Key Strengths
Simultaneous UV to hard X-ray continuum (pure continuum) measurements
Large X-ray bandwidth, better hard X-ray sensitivity with low background
UV imaging capability better than GALEX

34. Simultaneous UV to hard X-ray spectral measurements with ASTROSAT : MCVs
Objectives
Resolving all the spectral components (continuum): UV and soft X-rays (thermal) from accretion disk, hard X-ray reflection component, intrinsic power-law comp
Variability:
WD Rotation Period
Binary Periods
Eclipses
Absorption Dips
Shock Temperatures and Mass of the WD

35. Cataclysmic Variables with Astrosat
SXT
LAXPC C 35 35

36. CVs: Open Issues
Many aspects deserve further investigation: here are some
boundary layer in non-magnetics
the base of the post-shock accretion flow in magnetics and the way this diffuses into the white dwarf
heating of the atmosphere around the accretion region in magnetics, and effect on overall energy distribution
low accretion rate regimes in magnetics, whether this results in a bombardment solution (no shock)
disk-magnetosphere interaction in IPs: important in a number of contexts
disk-stream interactions in non-magnetics
magnetosphere-stream interactions in Polars
irradiation of the stream and secondary by X-ray flux
more astrophysics in the post-shock flow models (such as the separation of electron and ion fluids)
Combinations of high quality data (e.g. eclipse mapping of spectra) and new astrophysical fluid computations will transform the field and allow ever more intricate understandings of accretion phenomena to be achieved
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37. CVs in the grander scheme of things
Cataclysmic variables are fairly common systems.
CVs produce the low-level background of discrete sources in galactic X-ray emission – fainter but much more numerous than neutron-star or Black hole X-ray binaries
They are highly important laboratories for studies of accretion
disk behaviour
instabilities,
stream impacts,
warps,
tidal resonances,
spiral waves etc.
magnetically dominated accretion
accretion columns,
emission from post-shock flow,
shocks, instabilities etc.
Multi-wavelength emission (polarized in many cases) allows a multi-wavelength approach, providing very strong observational constraints on the interpretation of data
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38. CVs in the grander scheme of things (contd.)
Important for investigations on how material interacts with a magnetic field:
threading region in Polars,
inner region of disk in Intermediate Polars,
Dwarf Nova oscillations in non-magnetic CVs
In general, the balance of:
visibility of underlying system &
the emission (X-ray, optical) has been fundamental to making enormous progress in understanding a wide range of astrophysics
It is a field which incorporates fluid dynamics, MHD, a full range of emission processes, stellar evolution, gravitational radiation etc.
A large number of important observational techniques have been developed in the context of CVs and then used elsewhere:
Doppler tomography,
eclipse mapping of disks and streams,
Stokes imaging,
timing analyses
Progenitors of Type I Supernovae – Cosmological Distance Ladder
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39. Thank you !
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K.P. Singh 39 39 39

40. V1432 Aql: Asynch. Polar
XMM: Rana, Singh et al. 2005, ApJ
Triple hump profile: 2-pole or 3-pole accretor ?
A strict recurrence of X- ray features at ~12150 s
1st dip: Sharp and narrow at spin phase 0.6 -> rapid uncovering of the hard X- ray source due to an absorber
No significant X-ray emission during the 2nd dip -> eclipse
3rd Dip: Absorption
HEAP12- HRI (KP Singh)
18 Feb 2012 40 40

41. V1432 Aql: Asynchronous Polar
XMM keV light curve with 1s time resolution.
No aliasing problem
Shorter base line several components are merged.
Dominant peak at 2nd harmonic of the fundamental periods
Several higher harmonics of the spin and orbital periods are detected
along with other side band frequencies.
18 Feb 2012
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Rana, Singh et al. 2005, ApJ 41

42. Galactic centre with SXT
Feb 13, 2012
K.P. Singh 42 42

43. SXT Simulations: 3 APEC Models; 1E-11 ergs/cm2/s; 20ksec
Hot Thermal Plasma Emission
kT=0.7 keV -> 0.77 cts/s (black) kT= 1.8 keV ->0.62 cts/s  (green) kT= 5 keV  -> 0.42 cts/s (light green)
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K.P. Singh 43 43

44. Binary X-ray Pulsars with Astrosat
Simulated 10 ks observations of hard X-ray spectrum of Accreting Pulsar 4U The cyclotron lines are nicely resolved by ASTROSAT, but not by RXTE or Beppo-SAX. 44

45. Non-thermal component in Clusters of galaxies?
SXT
LAXPC
CZTI H
Spectral model from
Rephaeli et al. (1999)
Feb 13, 2012
K.P. Singh
02/17/09
K.P. Singh (TIFR, Mumbai) 45 45 45 45

46. (Pbeat)-1 = (Pspin)-1 - (Porb)-1
Properties of Asynchronous Polars
Mouchet et al. 1999
(Pbeat)-1 = (Pspin)-1 - (Porb)-1
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47. V1432 Aql: Optical Polarization
Linear polarization is almost constant except for a small change during spin phase.
The position angle shows a small change near 0.9 spin phase.
Spin modulated circular polarization with double hump profile.
+ve (+2%) and –ve (- 1%) both values for circular pol. are observed.
18 Feb 2012
HEAP12- HRI (KP Singh)
Rana, Singh et al. 2005, ApJ 47 47

48. V1432 Aql: Power Density Spectra
ROSAT Soft X-ray ( keV)
Spin frequency - 
Orbital frequency – 
 and  are clearly resolved
Dominant peak at first harmonic of the spin period
187 day aliases of the spin period and other frequency component are detected
Rapid oscillations with a period of ±0.0012s
18 Feb 2012
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Rana, Singh et al. 2005, ApJ 48

49. V1432 Aql: Circular Polarization
Prominent peak at 187 day positive alias of first harmonic of the spin period (i.e. 2 component).
Spin frequency  has relatively less power
Several higher harmonics of the spin period are also detected.
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Rana, Singh et al. 2005, ApJ 49

50. V1432 Aql: Photo-ionized Plasma Model
Kinkhabwala et al. 2004
Low density, steady state photo-ionized plasma.
Simple geometry of cone of ions with the source located at the tip of the cone.
Ionic column densities for different ions are incorporated to account for line emission; Fe I-XVI = 8E18;Fe XVII-XIX = 3E18; Fe XX-XXIV = 3E17; Fe XXV = 2E18;
Fe XXVI = 3E18 cm-2
18 Feb 2012
HEAP12- HRI (KP Singh)
Rana, Singh et al. 2005, ApJ 50 50

51. Spectral Models for X-ray emission from Polars
A good spectral model should account for:
The multi-temperature nature of post shock plasma.
Reflection of hard X-rays from the WD surface.
For high magnetic field systems, the cyclotron cooling effects along with the bremsstrahlung cooling.
The temperature and density profile of the post shock plasma.
Line emission from various elements.
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52. Multi-temperature Plasma Model
Plasma emissivity is taken from MEKAL or APEC plasma codes for the continuum and the line emission from a collisionally ionized hot plasma containing all the abundant elements.
Other effects included are:
Cyclotron cooling effects.
Reflection of hard X-rays from the surface of the WD.
Effects of gravitational potential on the stratified accretion column.
Spectral fitting leads to Mass estimation of the WD using mass- radius relationship of Nauenberg (1972).
18 Feb 2012
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Cropper et al. 1999 52 52

53. Multi-temperature Plasma Model
Temperature and density profile of magnetically confined plasma in post shock region given by Aizu (1973) assuming a negligible shock height and hence neglecting the effects due to gravity.
Cropper et al. (1999) used 1D steady state conservation
equations including the gravitational potential of white
dwarf.
x= spatial coordinate
= density
v = flow velocity
P = pressure
 = adiabatic index
T = temperature
 = mean molecular weight
mH= mass of hydrogen atom
G = gravitational constant
M = white dwarf mass
 = cooling term, including both
bremsstrahlung and cyclotron
cooling (br + cyc)
With ideal gas law;
P/ = kT/mH
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54. Polars: accretion region hydrodynamics
Solutions to equations produce run of hydrodynamic variables (Temperature, Pressure etc) from which emissivity as a function of height can be calculated…
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55. UVIT: filters
Feb 13, 2012
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