1. X-ray Spectroscopy of Accreting White Dwarf Binaries Koji Mukai (NASA/GSFC/CRESST & UMBC)

2. High Resolution Alone is Insufficient 2015 August 19Chandra Workshop 20152  Plasma is shock-heated when accretion flow hits the white dwarf surface  Shock temperature can exceed 50 keV kT>10 keV plasma primarily emits Bremsstrahlung continuum  Plasma models must handle such high kT  Pre-shock accretion flow further modifies the spectral shape via absorption  Understanding of the broad-band continuum is essential for both measurements using, and interpretation of, high-resolution X-ray spectroscopy  Also, broad-band, moderate resolution data have their uses: WD mass can ben inferred from kTmax Reflection amplitude provides an extra handle on geometry

3. Shock Temperature and Mass 2015 August 19Chandra Workshop 20153

4. Two Types of Intermediate Polars 2015 August 19Chandra Workshop 20154  Non-magnetic CVs and low luminosity IPs exhibit Cooling Flow like X-ray spectra  Normal IPs were characterized by Mukai et al. (2003) as having photoionized X-ray spectra

5. Aizu Model 2015 August 19Chandra Workshop 20155 X-ray emission region in magnetic CVs are better understood – Aizu Model  Isobaric cooling flow is a decent (but not perfect) approximation  Analytical solutions (inc. those used in CV-specific models) often approximates plasma cooling using Bremsstrahlung cooling only  Additional cooling channels can be present (cyclotron, Compton) Accretion disk boundary layer (non-magnetic case) is a far trickier problem

6. Global Fit for EX Hya 2015 August 19Chandra Workshop 20156  Luna et al. (2015) used ½ M sec HETG data on EX Hya.  A cooling flow model does a decent job fitting the entire HETG data  In detail, however, there are indications that the emission measure distribution deviates from that predicted by the isobaric cooling flow  Pandel et al. (2005) analyzed XMM-Newton (EPIC+RGS) data for a sample of dwarf noave (i.e., non-magnetic) and found cooling flow-like solutions but with the EM distributions were not always the same.  Pandel et al. and Byckling et al. (2010) found kTmax consistent with strong shocks from Keplerian flow in non-magnetic CVs.

7. EX Hya: Selected Results 2015 August 19Chandra Workshop 20157  Orbital motion of the white dwarf detected in X-rays (Hoogerwerf et al. 2004); but not the spin modulation  Broad component detected in several lines, notably OVIII (Luna et al. 2010), presumably from photoionized pre-shock flow  Use of Fe L lines (Fe XVII and Fe XXII) as potential density diagnostics  Fluorescent 6.4 keV Fe line seen, but weak

8. V1223 Sgr: a Normal IP 2015 August 19Chandra Workshop 20158  At high accretion rate, the shock is close to the white dwarf surface  Most X-ray photons cannot escape throught the sides of the post-shock region – complex absorption ensues  This causes the energy- dependent spin modulation of X-ray intensity, a defining characteristic of IPs  Done & Magdziarz (1998) developed a complex absorption model  Complex absorption x cooling flow can explain the X-ray spectra of normal IPs Spin modulation of EX Hya is probably mostly purely geometrical (both post-shock regions are simultaneously visible much of the time)

9. Normal IPs at CCD resolution 2015 August 19Chandra Workshop 20159  High S/N EPIC data can be modeled, above 1 keV, using pwab(mkcflow+ga)  V709 Cas appears to have discrete features (photoionized lines of Ne IX and O VII?)  NY Lup appears to have a soft, blacbody-like component from the heated surface of the secondary  The most notable feature in V1223 Sgr is neither...

10. Photoionized Absorber 2015 August 19Chandra Workshop 201510  The OVII edge has now been detected in V1223 Sgr with HETG (Mukai et al. 2001), EPIC, and with RGS  Also seen in several other IPs  The same, pre-shock flow has the physical characteristics ripe for both OVII edge in absorption and resonant lines in emission  Can this be the reason why the detection of RRC has proved elusive?  An ionized version of the pwab model is in the works

11. Potential Science with ASTRO-H 2015 August 19Chandra Workshop 201511  Density diagnostics using He-like Kalpha for V1223 Sgr  Probing the origin of hard X-rays in SS Cyg during outburst

12. Prospects for Dynamical Studies 0.8 Mo1.0 Mo1.2 Mo1.4Mo Free-fall Velocity5500 km/s6900 km/s8700 km/s13800 km/s ¼ Vff1375 km/s1725 km/s2175 km/s3450 km/s Keplerian Velocity3900 km/s4900 km/s6200 km/s9800 km/s ¼ Vkep975 km/s1225 km/s1550 km/s2450 km/s Gravitational Redshift50 km/s80 km/s130 km/s320 km/s 2015 August 19Chandra Workshop 201512  At 6 keV, 300 km/s is 6 eV: these velocities are within reach of the SXS  In the post-shock region, plasma decelerates further as it cools: lower energy lines are not expected to have anywhere near ¼ Vff or ¼ Vkep (studying Fe lines an advantage)  A fraction of the 6.4 keV line is from the white dwarf surface: gravitational redshift may well be measurable The steep mass dependence makes it a great tool for near Chandrasekhar- mass white dwarfs

13. Gravitational Redshift 2015 August 19Chandra Workshop 201513 One exciting possibility is to use the gravitational redshift of the white dwarf mass in symbiotic stars such as T CrB – for near- Chandrasekhar mass, this may be the best and most accurate method for WD mass determination If indeed T CrB harbors a near-Chandrasekhar mass white dwarf, which is suggested using less direct method, then we will ask: how did the white dwarf become so massive, and what is its ultimate fate?

14. Summary  Accreting white dwarfs all have the same central engine – a cooling flow like, multi-temperature, optically thin(-ish) emission region High quality data can probe the deviation from the isobaric cooling flow model Complex absorbers can create an illusion of dichotomy  The best grating data available so far is on EX Hya, an atypical (low luminosity) IP  Most other X-ray data on accreting white dwarf binaries lack the S/N and/or the spectral resolution to enable similarly detailed studies  ASTRO-H is going to change this, with high S/N, high resolution (with SXS) and broad-band (with HXI) data The calorimeter brings dynamical studies into the realm of possibility As a special case, gravitational redshift is potentially within reach of the SXS if the white dwarf is massive  Also, chemical abundances of CVs and symbiotic stars may yield unexpected insights 2015 August 19Chandra Workshop 201514