University:
Boston University
Course:
CAS AS 311 | Planetary Physics
Academic year:

2024
Views:

462

Pages:

16
Author:

Jerome Eaton

Cross Sections (Ozak et al. 2010, Schultz et al. in prep) Peak X-ray emission efficiency for E ≈ 1.5 MeV/u  4I   P( z ( s))e  ( s ) ds z Initial Energies: 1.2 MeV/u - O 0.51 MeV/u - S S/O = 204 Fits to CXO observation ID 3726 Initial Energies: 2.0 MeV/u - O 1.86 MeV/u - S S/O = 0.94 Summary of X-Ray Model Comparisons    Sulfur and Oxygen lines are sufficient (no Carbon Hui et al. 2010a) -- magnetospheric ions and not solar wind ions. 1.5—2 MeV/u oxygen ions and 1-2 MeV/u sulfur ions are most efficient in producing X-rays Quenching and Opacity effects need to be included (and hence some details of the neutral atmosphere matter) (Ozak et al. 2010). Could explain some N-S spectral differences (more work needed). X-Ray Emission - Parallel Acceleration    Magnetospheric ion populations are not adequate in flux or energy (50 keV). One solution is to accelerate these ions parallel to the magnetic field - this not only energizes them but increases the flux to the atmosphere by filling the loss cone (Knight mechanism). Otherwise, most charged particles in the magnetosphere magnetically mirror before reaching the atmosphere. Is this “x-ray” current (Cravens et al. 2003) the main oval return current (Vasyliunas cycle) or is it linked to the magnetopause (Dungey cycle)(Bunce et al. 2004)? What about Saturn? No Auroral X-rays Observed!  There is x-ray emission, BUT it is concentrated at non-polar latitudes  Large temporal variability  Correlated to the solar x-ray flux    Saturn: Auroral x-ray emission are not observed (upper limit on luminosity: 2% of Jupiter, 1GW vs. 8 - 24 MW) Analysis of absence of Saturnian auroral x-rays (Branduardi-Raymont et al., 2009; Hui et al., 2010b). Estimates of possible x-ray luminosity are orders of magnitude below observational limit. Oct. 2002 Apr. 2005 Oct. 2005 Summary     Jovian X-ray emission is caused by precipitation of oxygen, sulfur and maybe (although not likely) carbon It is a diagnostic of downward Birkeland currents due to ions in the outer magnetosphere or magnetopause region, just as electron precipitation is a diagnostic of upward currents. The ion precipitation is probably powered by magnetic reconnection and can be a valuable tool in understanding M-I coupling at this planet. Saturn: lack of x-ray emission - inadequate fieldaligned potentials generated and/or cusp entry of solar wind ions Polar Emission vs. Disk Emission OVII 0.55 – 0.60 keV OVII 0.63 0.68 keV   FeXVII 0.70 and 0.80 keV (Branduardi-Raymont et al. 2007) XMM-Newton Nov. 2003 MgXI 1.30 – 1.40 keV Differences in Spectral Shape Between High Latitude Emissions and Disk • (BranduardiRaymont et al. 2007) • XMM-Newton Nov. 2003 Charge Exchange Mechanisms for Xray Emission •  • Magnetospheric or solar wind ion Mq + (O, S, C..) Charge state q = 6, 7, 8 for O or q = 8, 9, 10, 11, 12… for S produces x-ray emission Charge transfer excitation collisions: Mq + + H2 ---> H2+ + M (q-1) +* M (q-1) +* -----> M (q-1) + + hn Monte Carlo Model (MCM) • • • • • Takes into account the charge history of the precipitating ions. O2+ and S+ ions are chosen as initial charge states, since they are common in the outer magnetosphere. Each ion initially has an arbitrarily chosen energy and a randomly chosen pitch angle. Calculate the probability of a having a collision and with this the displacement of each ion into the atmosphere in terms of the column density: ΔN = -Ln(Prob)/ σtot Choose collision type from different processes: • • • p0 = σioniz /σtot , p+ = σstrip /σtot , p- = σcx /σtot Calculate energy loss using empirical power. Repeat until ion runs out of energy. Jovian X-Ray Emission Mechanism Magnetospheric Ion Precipitation    X-ray emission is from high charge state O and S ions, yet only low charge state ions are seen in the magnetosphere (O+, O++, S+, S++, S+++). High charge state ions (and x-rays) can be produced by collisions of high energy ions (E > 1 MeV/amu) with atmospheric targets. But the X-ray emission is from very high latitudes (that is, the outer magnetosphere - r > 50 RJ) and the energetic ion populations are not sufficient to give the observed x-ray power (or the energies) – (Mauk et al. 2004).