SALT & ASTROSAT Observations of Magnetic Cataclysmic Variables David Buckley SALT Science Director & C.V. Raman Senior Fellow

Observing cataclysmic variables with SALT & ASTROSAT Multiwaveband observations at high time resolution  X-rays, UV, and polarised optical cyclotron emission  accretion-driven flaring and eclipses on time scales of seconds Science/questions: size and location of impacting material and impact region size of the two stars heating mechanism  gives (T,) of plasma in impact region polarisation gives B

Model of a Polar (AM Herculis system)

Accretion column analogy on the Sun

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 6 Beuermann (1998) 6

Example: XMM-Newton Spectrum of V1432 Aql Rana, Singh, Buckley & Barrett 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 7 7

Determining Magnetic Field Strength & Geometry in Polars: Fitting cyclotron model fits to All-Stokes broadband polarimetry Single pole system Fit cyclotron parameters (plasma temp & density, cyclotron opacity, B & ) using Potter’s Stokes imaging technique fits model to data using a genetic algorithm Extend to spectropolarimetry Example: V834 Cen, Porb= 101 min SAAO 1.9-m photopolarimetry

Spectropolarimetric possibilities for mCVs Time resolved, all-Stokes mode (simultaneous circular + linear): Polars + Intermediate Polars e.g. MN Hya: a ~3.4h Polar Circ. Pol. Cyclotron emission harmonics Intensity

V834 Cen spectropolarimetry 20 keV,  = 0 AAT 3.9m Results indicate Multi-T shocks 20 keV,  = 0.7 Wickramasinghe Tuohy & Visvanathan ApJ 318, 326

Intermediate Polars magnetic field ~106 G  intermediate polar/DQ Her system accretion takes place through a truncated disk and then via accretion “curtains” onto the white dwarf magnetic field controls the flow in the final stages 18 Feb 2012 HEAP12- HRI (KP Singh) 11 11

Intermediate Polar example: AO Psc 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 3.591 h, the spin period of the white dwarf 805.4 s the mixture of the two (beat/synodic period) AO Psc 12 12

SALT Capabilities for Magnetic CV Observations Instrument modes are well suited to CVs High time resolution (sub-sec) observations photometry & spectroscopy UV (λ > 320 nm) sensitivity Polarimetric capability (e.g. magnetic CVs) All-Stokes imaging polarimetry Spectropolarimetry Low Res (R~50) imaging spectropolarimetry Advantages of SALT design and modus operandii 100% queue scheduled service observing Easy to schedule Targets of Opportunity Easy to schedule phase or time critical observations Easy to conduct regular long-term observations

SALT Design Principle New paradigm in cost effective design pioneered by the HET in Texas. fixed altitude (37 ± 6º zenith distance) track objects at prime focus optical analogue of Arecibo radio tel.

SALT: 91 x 1m mirrors

SALT Visibility Window Annulus of visibility for SALT: Annulus represents 12.5% of visible sky Declination range: +10º to -75º (70% of full sky coverage) Observation time available = time taken to cross annulus (east & west at mid Decs) Observation times from ~1h to 6h

SALT’s Instruments: 1. SALTICAM: UV-Vis CCD Camera (built at SAAO: Darragh O’Donoghue, PI) Cryostat & detector An efficient “video” (~10 Hz) camera over entire science FoV (8 arcmin). Efficient in the UV/blue (capable down to atmospheric cutoff at 320nm). Capable of broad and intermediate-band imaging (Johnson-Cousins; SLOAN & Strömgren filters, plus UV and H) High time-resolution (to ~90 ms) photometry. Fulfills role as both an acquisition camera and science imager/photometer. Filter jukebox Optics Optics SALTICAM in the lab

Resolving eclipses of Polars

SALT’s First-Science An example: a light curve of an eclipsing magnetic CV (Polar) taken with SALTICAM Each data point a 0.1 sec exposure Ingress/Egress = 1.2 to 1.5 sec

Model fit: locating hot-spot positions

SALTICAM Observations of Intermediate Polars SALT commissioning program primarily aimed to look for wavelength dependencies in the spin and beat modulations of IPs Also looking at the flickering & aperiodic behaviour of IPs (with Alexei Kniazev & Mikhail Revnivtsev) Power spectra clues to missing inner disk? Disrupted power law

INTEGRAL/SWIFT source 1GRJ 14536-5522 (Steve Potter, Martin Still, Koji Mukai, DB) Flickering and QPOs seen in SALTICAM photometry Polarimetry revealed system to be a Polar Discovery of short period (2 – 5 min) circular polarimetry QPO variations

New INTEGRAL/SWIFT source 1GRJ 14536-5522 HIPPO (SAAO 1.9m instrument) All-Stokes photopolarimetry Intensity Circ Pol Trailed periodograms Intensity Circ. Pol. DFTs

The Robert Stobie Spectrograph (RSS) (built at Wisconsin, Rutgers & SAAO) An efficient and versatile Imaging Spectrograph capable of UV-Vis spectroscopy from 310 – 900nm using VPHGs (red extension to 1.7μm, using a dichroic, is under construction. Completion in 2014?) high time resolution ablility (~0.1 s) specto- and imaging polarimetric capability Fabry Perot imaging (incl. with pol.) Multiple Object Spectroscopy Can observe ~50 objects at once Named in memory of Bob Stobie, previous SAAO Director & one the instigators of SALT. RSS reinstalled on SALT (Apr 2011)

RSS Polarimetry Imaging polarimetry Spectropolarimetry

Probing accretion columns polarimetrically with SALT

Phase resolved QS Tel spectra ESO/MPI 2.2m example Two poles accreting Cyclotron humps move in position and shape and size as a function of phase Schwope et al. 1995 A&A 293, 764

Stratified accretion shock models Allow testing of more realistic shock models(e.g. Potter et al.) with stratified temperature and density profiles dependent on parameters like: White dwarf mass, accretion rate magnetic field strength..

Recent SALT experiments with a photon counting camera The Berkeley Visible Image Tube (BVIT) installed at SALT Auxiliary Focus A very high time resolution imaging photometer. Enables a new time domain for astronomical observations with full imaging capability Time resolution to ~μsec BVIT is a simple instrument with minimal observational setup requirements and a high degree of post acquisition data flexibility. Based on Microchannel Plate & strip anode detector Prototype built with low QE S20 photocathode (peak of ~10% QE peaking at ~400nm) Now upgraded to Super GenII, with ~20x improvement in count rate UZ For (Polar)

ASTROSAT: India’s first astronomy satellite An ideal complement of instrumentsfor mCVs 2 UV(+Opt ) Imaging Telescopes 3 Large Area Xenon Proportional Counters (hard X-rays) Soft X-ray Telescope CZTI (hard X-rays) Radiator Plates For SXT and CZT Scanning Sky Monitor (SSM) Folded Solar panels SSM (2 – 10 keV)

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 Transient detector via SSM Satellite: 1.55 tons; 650 kms, 8 deg inclination. 3 gyros and 2 star trackers for attitude control by reaction wheel system with a magnetic torquer. Launch in ~mid 2013.

UVIT: Two Telescopes f/12 RC Optics Focal Length: 4756mm Diameter: 38 cm Simultaneous Wide Angle ( ~ 28’) images in FUV (130-180 nm) in one and NUV (180-300 nm) & VIS (320-530 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 33

UVIT: filters Feb 13, 2012 K.P. Singh 34

LAXPC: Effective Area Feb 13, 2012 K.P. Singh 35

SALT-ASTROSAT Program Simultaneous Optical, UV to hard X-ray spectral measurements with ASTROSAT & SALT 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, plasma diagnostics and masses of the WD Magnetic field strengths Plan to coordinate SALT & ASTROSAT observations of mCVs during GTO phase (6 months) Also aim to attempt contemporaneous observations during initial PV phase of ASTROSAT (e.g. AGN, XRBs, flare stars)

FINAL REMARKS Magnetic CVs offer multi-wavelength opportunities Emission from near IR to X-rays (even radio, if sufficient sensitivity) SALT has ideal instruments and capabilities for studying objects at high time resolution and polarimetrically ASTROSAT will have excellent capabilities to study the accretion physics by virtue of X-ray observation Simultaneous SALT-ASTROSAT observations of mCVs (& other similar multiwavelength emitters) provides excellent opportunities to extend our knowledge. Time is ripe for new India-South African bilateral program to exploit these possibilities