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Voyager 1 CRS Update

SSG MeetingJHU/APL

9 September 2013

V1 H, He, C, and O spectra for 2012/342-2013/161.

Spectra flattten below few hundred MeV/nuc due to ionization energy losses.

Believe we are observing GCRs down to ~3 MeV/nuc for H and He;C & O down to ~5 MeV/nuc.

GCR H, He spectra peak at ~10-40 MeV/nuc with H/He ratio =13 at 7.8-57 MeV/nuc.

GCR C/O ratio ~1. ACRs not contributing to low-energy GCR spectrum, contrary to Scherer et al 2008.

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Moskalenko et al.2002 – DC

GALPROPtuned to ACEby Lave et al 2013

Fisk & Gloeckler2012 -- pump

Webber & Higbie2009 -- LB

Preliminary V1 spectra for 2012/342-2013/161 for 8 elements (red).

Also shown are spectra from a reference period (blue, 2011/1-365),dominated by ACRs below ~50 MeV/nuc.

So, for first time at low energies V1 is observing GCRs in LISM at true energies – no adiabatic energy loss effects.

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Preliminary V1 spectra for 2012/342-2013/161 for 8 elements together with two GALPROP unmodulated spectra propagated to near Sun with parameters tuned by Lave et al. 2013 to match ACE observations at 1 AU. Conventional model with reacceleration matches ACE and Voyager data better than plain diffusion model.

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GCR abundance comparison

The GALPROP conventional model with reacceleration is shown and matches Voyager data quite well

Systematic trends in 1 AU data is due to modulation.

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Gradients?

100 MeV H vs time from Strauss et al. 2013.

Gradient ~0.5%/AU for ~60 AU after heliopause.

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Gradients negligible so far

CRS HET 2 Guard singles rate10

Krimigis et al., 2013

Other singles rates show statistically significant variations that presumably are due to varying anisotropy

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Preliminary GCR electron spectra.

Two spectra due to use of two different sets of response functions:

Open: pre-flight accelerator calibration

Solid: Geant4 simulation

Difference indicates level of systematic uncertainty.

Parameters of power-law fits:Open: dJ/dE = 276*(E/10)-1.55

Solid: dJ/dE = 284*(E/10)-1.37

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Preliminary

Working on adding electron points from HET B end of telescopes.

Parameters of power-law fit:dJ/dE = 270*(E/10)-1.69

Voyager 1 Cosmic Ray Telescopes

HET 2

HET 1

TET

HET 1 & 2willbe the focus for next part of talk. Nominal look directions in NT plane are shown.

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BmagA

A

V

Directionof rotationfor magrolsand LECPoffpoints

Voyager HET:PEN rate is defined by B1.B2.C1

~40 degree full opening angle(bi-directional)

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66

Krimigis et al., 2013

67 68 69 70 71 72Magrol #’s

Recent magrol times shown

Average of rolls 64-66 (left) shows no significant anisotropyAverage of rolls 68-72 (right) does show an anisotropy – two dips

180 degrees apart due to bi-directionality of telescopes for penetrating events

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Pitch angle distribution for rolls

68-72

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Minimum at 90o pitch angle.

40o Full angular width ~ same as opening angle of telescope -> could be a 100% dropout only a few degrees wide right at 90o.

Note: 70 degree LECP offpoint location shows a bigger effect in HET 1 than in HET 2 for rolls

71 and 72.

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And that is consistent with distance from 70 degree offpoint location to 90 degree pitch angle for rolls 71 and 72 (72 shown): smaller in HET 1 (~15o) than in HET 2 (~22o).Note: using average field direction from Science paper would flip this around and be inconsistent.

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HET 1

HET 2

Anisotropy is gone by roll 73 –

2013/214

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• Observing local interstellar GCR H and He spectra down to ~3 MeV/nuc and GCR C and O down to ~5 MeV/nuc.– 45-90 MeV/nuc: GCR B/C = 0.14 C/O = 1.1– 7.8-57 MeV/nuc: GCR H/He = 13.0– Good agreement with GALPROP conventional diffusive reacceleration

model tuned by Lave et al. 2013 to match ACE observations at 1 AU.– ACRs not contributing to low-energy GCR spectrum, contrary to Scherer et

al. 2008• GCR electron spectrum in LISM ~E-1.3 to ~E-1.7 from ~3-70 MeV.• No GCR gradients so far• Small time variability in some rates likely due to variation in anisotropy

of GCRs• GCR anisotropy likely due to drop out of particles within a few degrees

of 90o pitch angle– With more analysis of the angular efficiency of the HET telescopes and

more analysis of both the magrol and LECP offpoint data, it should be possible to better quantify the characteristics of the notch

Summary

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The End