1. The Nature of the Doppler Lines in the Ultra-compact Binary

2. Doppler Lines and Fe Fluorescence in the Ultra-compact Binary
Previous HETG GTO observations:
- Schulz et al. 2001: Double Peaked X-ray Lines from the
O/Ne-rich Accretion Disk in 4U : OBSIDs 104, 39 ksec
- Krauss et al. 2007: High Resolution X-ray Spectroscopy of the
Ultra-compact LMXB Pulsar 4U : OBSIDs 104, 39 ksec
3504, 97 ksec

3. Doppler Lines and Fe Fluorescence in the Ultra-compact Binary
New HETG GTO observations:
Chakrabarty & Schulz 2009 Cycle 11 GO time: OBSIDs 11058, 80 ksec, Jan

4. Doppler Lines and Fe Fluorescence in the Ultra-compact Binary
Tbnew (Powerlaw + Bbodyrad):
NH = 1.2x1021 cm-1
AG = ph cm-2 s-1
= 0.80
Abb = 593 (R2km / D2kpc)
kTbb = 0.20 keV
Tbnew (Powerlaw + Bbodyrad):
NH = 1.2x1021 cm-1
AG = ph cm-2 s-1
= 1.19
Abb = 83 (R2km / D2kpc)
kTbb = 0.48 keV

5. Flares and Dips in the New Light Curve of 4U1626-67
Obsid 11058:
Obsid 3504:

6. Doppler Lines in the Ultra-compact Binary 4U1626-67

7. Doppler Lines in the Ultra-compact Binary 4U1626-67

8. Ionization Model Fits to the X-ray Spectrum of 4U1626-67
Photo-ionized modeling:
Collisional-ionized modeling:

9. Collisional Ionization Model Fits to the X-ray Spectrum of 4U1626-67
Aped_density = 13:

10. Doppler Lines and Fe Fluorescence in the Ultra-compact Binary
Pure C/O/Ne disk?:
Cannot maintain C I/Ne I/O I :
log x > r~109 cm
Pure C/O disk model predicts
T = km
(Werner et al. 2006)

11. Magnetospheric Accretion Shocks in the Ultra-compact Binary
Emission Volumes:

12. Doppler Lines in the Ultra-compact Binary 4U1626-67
In conclusion we propose the following:
Rco = 8.5x108 cm
Rco = Rmag
Vshift ~ 2000 km/s
~ Vco
Vco ~ Vshock
Tjump < 60 MK
CO plasma
< 20 deg impact
Vshift = Vion
Tshock < 10 K
Magnetospheric Accretion Shocks

13. Doppler Lines in the Ultra-compact Binary 4U1626-67
In conclusion we propose the following:
• The light curve before torque reversal is featureless. The light curve after torque reversal shows enhance variability which includes type II flaring, intensity dips, and periods of quiescence.
• The X-ray flux at the time of the observation in 2009 is at about the same level as it was in 1994.
• The X-ray continuum after torque reversal is fit by the same spectrum as before, however with a higher blackbody temperature and a smaller emission radius .
• The spectrum shows a narrow Fe K fluorescence line, which was not observed before torque reversal.
• A photo-ionized plasma cannot fit the Ne and O Doppler
line emissions.
• The large ratio between the Ne X Lα line and the upper
limit to the Ne X Lβ line rules out significant contributions
due to resonance scattering
• A collisions ionized plasma fits both Ne and O line
ratios very well with enhanced plasma densities and
plasma temperature between 1 MK and 10 MK.
Magnetospheric Accretion Shocks