Loooking for Arcs in the Spectra of J1819 385

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Loooking for Arcs in the Spectra of J1819385

• Barney Rickett, Bill Coles
• (UCSD)
• J-P Macquart Ger de Bruyn
• (RUG, ASTRON)

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pulsar
minutes
S1(n,t)
S2(fn,ft)
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scattering screen
I E1 E22 if E1 and E2 are coherent
E12 E22 2E1E2cos(Df) where Df
2p(n1t1-n2t2) t1 tdt1 , n1 ndn1 Df
2pn(dt1- dt2)(dn1- dn2)t .. ..O(dn dt)
V
dt1 zq12/2c is the relative time delay dn1
n(V.q1)/c is the relative Doppler frequency
(ie fringe frequency)
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fn dt1- dt2 q12- q12 (z/2c) relative
delay ft dn1- dn2 (q1x- q2x)V/l fringe
frequency
With q2 0 we get q1x ft l/V and q12
2cfn/z so q1y (2cfn/z - (ft l/V)2 Then
S2(fn, ft) is bounded by a parabolic "arc" fn
ft2 zl2/2cV2
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quasar
D
qsrc
Coherence scale at the screen bsrc l/(pqsrc)
s
ISM
z
At spacing s, relative time delay fn
s2/(2cz) Fringe amplitude (S2) is decreased due
to loss of coherence at fn gt bsrc2/(2cz)
l2/(2p2zcq2src) ie fn gt (qFr/qsrc)2(1/2pn0) This
gives a cut-off in delay due to source diameter
observer
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Simulation of screen at 1.4 GHz with 160 MHz
total Bandwidth
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Simulation of screen at 1.4 GHz with 160 MHz
total Bandwidth
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Simulation of screen at 1.4 GHz with 160 MHz
total Bandwidth
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Simulation of screen at 1.4 GHz with 160 MHz
total Bandwidth
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Now look at 1.4 GHz observations of
J1819385 From Westerbork 22 Feb 2003 12 Apr
2003 19 Jun 2003 25 Dec 2003
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• Screen Model
• Distance Lpc
• Isotropic Kolmogorov spectrum (zero inner
  scale)
• qFr 25µas (LpcnGHz)-0.5
• ntrans 5 GHz to match large scintillation
  index at 5 GHz
• Source Model Two Gaussian components
• L 5 pc 50 pc
• Angular radius 0.03 qFr qa 4.7 1.5 µas
  (FWHM)
• Angular radius qFr qb 160 50 µas (FWHM)
• Ratio of flux densities is parameter in
  following simulations..

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0.03 qFr 10 Flux qFr 90 Flux
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0.03 qFr 5 Flux qFr 95 Flux
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0.03 qFr 1 Flux qFr 99 Flux
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5pc, 50pc at 50 km/s
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Preliminary Results (work in progress)

• No arc detected at 21 or 6 cm (need to set
  detection threshold)
• Screen model at 5-50 pc ultra-compact (1-5 µas)
  component has less than 1 mJy at 21 cm
• gt Tb lt 1.5x1013 K
• OR
• inner scale gt 200-500 km