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Spectral Properties of Heavy Ions Associated with Interplanetary Shocks at 1 AU SHINE 2004 Big Sky, Montana M. I. Desai University of Maryland, College.

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Presentation on theme: "Spectral Properties of Heavy Ions Associated with Interplanetary Shocks at 1 AU SHINE 2004 Big Sky, Montana M. I. Desai University of Maryland, College."— Presentation transcript:

1 Spectral Properties of Heavy Ions Associated with Interplanetary Shocks at 1 AU SHINE 2004 Big Sky, Montana M. I. Desai University of Maryland, College Park, MD 20742, USA Co-Authors: G. M. Mason: University of Maryland C.M.S.Cohen & M. E. Wiedenbeck: SRL, Caltech, CA J. E. Mazur: Aerospace Corp J. R. Dwyer: Florida Institute of Technology R.E. Gold & S. M. Krimigis: JHU/APL C.W.Smith: University of New Hampshire Q. Hu: IGPP, UC Riverside, CA R. M. Skoug: Los Alamos National Laboratory

2 CME-driven Interplanetary Shocks

3 “Ambient” (Desai et al. 2001, ApJ 553, L89 & 2003, ApJ, 588, 1149). Surveyed 72 shocks between Oct. 1997-Oct. 2002 3 He ions accelerated in 45 IP shocks Pre-shock intervals provide a “proxy” for ambient particles in the IP medium Intensity-time profiles for an IP shock

4 Ambient and SEP Abundances Ambient material comprises ~30% from impulsive flares, and ~70% from large gradual SEPs (Desai et al. 2003 ApJ, 588, 1149).

5 IP Shock compared with solar wind abundances (Desai et al. 2003 ApJ, 588, 1149). Shock abundances are poorly correlated with solar wind abundances No clear dependence on M/Q Difficult to understand in terms of rigidity-dependent acceleration of solar wind ions

6 IP Shock compared with ambient suprathermal abundances (Desai et al. 2003 ApJ, 588, 1149). Shock abundances are well correlated with ambient suprathermal abundances Exhibit a M/Q-dependent depletion Consistent with rigidity- dependent shock acceleration of ambient suprathermals

7 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) Fe/O at IP shocks is depleted relative to ambient values Larger decrease at higher energy

8 Energy Spectra during an IP shock: All Spectra fitted by j = j 0 E -  exp(-E/E 0 ) ParameterCarbonOxygenIron No. of Points8108 j0j0 4.64  0.879.32  1.213.17  1.49  1.36  0.111.33  0.091.08  0.27 E0E0 0.69  0.090.72  0.060.35  0.06    0.870.910.88 however  and E 0 are coupled; Use only 0.1-0.5 MeV n -1 to obtain the power-law indices

9 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) Spectral indices of C, O, & Fe Differences in Fe and O indices are at odds with injection of a mono-energetic seed population

10 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) O e-folding energy vs. shock parameters E-folding energy is independent of local shock parameters

11 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) ACE/ULEIS 0.1-0.5 MeV n -1  Spectral index is poorly correlated with compression ratio, M  Results are at odds with predictions of simple steady-state models 2-hr. av. O spectral index vs. (M+2)/(2M-2)

12 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) IP shock event measured by ULEIS & SIS

13 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) Energy spectra measured by ULEIS & SIS

14 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) 3 Classes of Fe/O energy-dependence

15 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) Energy-dependence of Fe/O  Fe = Fe/O (0.62 MeV/n.) Fe/O (0.22 MeV/n.)

16 (Adapted from Desai et al. 2004, To appear in ApJ. Aug. 20, 2004)  Fe vs. 3 He/ 4 He ratio; 3 He/ 4 He ratio vs.  Bn Extreme Events Only

17 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue)  Fe vs. 3 He/ 4 He ratio; 3 He/ 4 He ratio vs.  Bn All events

18 3 He/ 4 He ratio vs. Injection Threshold Speed, V inj = V S *sec(  Bn ) Most IP shocks including the 3 with rising Fe/O ratios have V inj <2*V sw 3 He/ 4 He ratio and  Fe are poorly correlated with V inj V inj > 600 km s -1 3 He/ 4 He > 2% Conclusion: Injection threshold speeds do not appear to play a significant role in the energy-dependent behavior of Fe/O

19 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue)  Fe vs. O spectral index & O fluence

20 Fe/O at IP shocks vs. ambient (Desai et al. 2003 ApJ, 588, 1149). Fe/O ratios at IP shocks and ambient are well correlated

21 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) Shock C/O & Fe/O normalized to ambient values Fe/O ratios are depleted by ~30% relative to ambient values Energy-dependence of Fe/O is diminished when compared with ambient Fe/O - not expected from mono-energetic injection

22 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) O Spectral index & Fe/O dependence at IP shocks vs. Ambient

23 SummarySummary Spectral parameters and energy-dependence of Fe/O are independent of local shock parameters 5 out of 72 events (~7%) have rising Fe/O with energy; Fe/O in other events are constant or decrease with energy Fe/O at IP shocks are typically ~30% lower than in the ambient population The O spectra and energy-dependence of Fe/O are similar at IP shocks and in the ambient population

24 (Desai et al. To appear in ApJ.Aug. 20, 2004 issue) Sketch of Re-acceleration of Seed spectra at IP shocks

25 ConclusionConclusion IP shocks accelerate seed spectra composed of suprathermal ions from gradual and impulsive SEP events by a systematic rigidity-dependent mechanism where ions with higher M/Q are accelerated less efficiently than those with lower M/Q

26 Relevant Issues How common are IP shock events with rising Fe/O ratios?  ~7% of events have rising Fe/O with energy What are the key differences between IP shocks with rising and decreasing Fe/O ratios?  No appreciable differences in shock properties Does any particular local shock parameter play a role in determining the energy-dependent behavior of Fe/O?  Cannot rule this out completely, but no evidence that local shock properties are important The primary cause of rising Fe/O in IP shocks  Re-acceleration of energetic ion seed spectra that themselves have rising Fe/O with energy

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