Arc Morphology Barney Rickett University of California San Diego - - PowerPoint PPT Presentation
Arc Morphology Barney Rickett University of California San Diego Generic Features observed in Secondary Spectra Smooth symmetric shapes Parabola (arc) Forward Narrow Forward Broad Forward arc, sharp outer boundary, filled interior Reverse
Barney Rickett University of California San Diego
Smooth symmetric shapes Parabola (arc) Forward Narrow Forward Broad Forward arc, sharp outer boundary, filled interior Reverse narrow (multiple arclets) Multiple forward arcs Asymmetry in Doppler Arc structure is often variable over time
Arecibo Observation at 1450 MHz from Stinebring et al. (2019) See his talk this afternoon For view at two frequencies
(Putney & Stinebring 2006)
Forward Narrow Forward Broad Forward filled interior Multiple narrow forward
Forward Broad Asymmetric Forward filled interior. Sharp outer boundary - characteristic
Note how the arc is narrower at 825 than at 340 MHz where scattering is stronger See talk by Dan Stinebring
B0834+06 Stinebring 2003, Arecibo
See Hill, et al. (2005) for detailed analysis of such arclets in B0834+06 Note reverse arclets with apexes along forward Parabola Note same arclets in Independent bands at 323 & 329 MHz Note deep “valley”
323 MHz 329 MHz
Modulation index = 0.56 => weak scint ? But note narrow DnISS (How to define width DnISS ?) Forward Narrow See Stinebring et al. 2019, where we modelled the secondary spectrum by 1-dim brightness distribution B(q) as follows:
dB
1-dim model fitted
B1133+16 1450 MHz MJD 57179 Arecibo (Stinebring et al. 2019)
+ is the fitted model Dashed red line is an isotropic Kolmogorov model (+ delta fn) Dashed black line is a 1-dim Kolmogorov model (+ delta fn)
max/min 10-15dB Black line is 1D model fitted to secondary spectrum Note deficit in model in center at lowest delay
1-dim model imperfect …… Remedy requires width perpendicular to velocity ie 2-dim
Note the observed power law drop as S2 ∝ t-2.5 Similar to weak Kolmogorov scint isotropic: S2 ∝ t-2.33 1-dim: : S2 ∝ t-1.83
Delay
0.01 0.1 1 µsec
Note also scattered pulse tail ∝ t-2.33
Consider the effects of: Strength of Scintillation mB2 <1 weak mB2 >1 strong Axial Ratio AR Orientation angle y relative to psr velocity More details were in talk by Bill Coles
Kolmogorov Screen simulation
ArcSim/mb2=0.2,ar=3,ph=0.mat θx (θF units)mB2 0.2 0.2 1.0 1.0 AR 3:1 10:1 3:1 10:1 Scattering strength axial ratio
0 30 60 Characterize the shapes by depth of valley in Doppler freq = dB difference between peak and valley
1 2 3 4 5 6 7 8 9 10
Axial Ratio
5 10 15 20 25 30 35 40
Depth of cross-cut valley (dB)
mb2=0.2 mb2=1 mb2=5 mb2=0.2, =30
Asymptotic strong scint
1 2 3 4 5 6 7 8 9 10
Scattering strength m B
2
1 2 3 4 5 6 7 8 9 10
Depth of cross-cut valley (dB) Isotropic Kolmogorov spectrum
10 20 30 40 50 60 70 80 90 100 axial ratio 10 20 30 40 50 60 max/min (dB) Depth of valley in strong Kolmogorov scattering = .15 s = .3 = .45
1508+55,53632.55,scan20,340MHz
20 40
Doppler Frequency (mHz)
20 40 60 80 100
Delay (microsec)
10 20
(sec3)
0.2 0.4 0.6 0.8 1 1.2 10-3
Forward Broad
1) Arcs are seen in a wide range of pulsars. But only few show deep valleys. 2) Arcs with deep valleys imply el elong ngated ed image e at angles y < 45 deg => 3) Arcs with sharp outer boundaries and filled interior are due to interference between an undeflected feature and outlying waves. Such as the un-scattered core in we weak statistical scattering. 4) Absence of deep valleys imply isotropic image => phase is isotropic 2-D => Isotropic fine structure OR superposition of randomly oriented 2-D fine structures 5) Asymmetry in Doppler is due to deflection by a plasma structure offset from the pulsar line of sight - OR due to refractive phase gradient covering pulsar 6) Reverse Arclets => deflection by plasma structures aligned parallel to the psr velocity. So Fine structure in plasma 7) Time variability in arcs imply very inhomogeneous fine structure in ISM