Interstellar Scattering of Sgr A

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Interstellar Scattering of Sgr A

• D. C. Backer
• Astronomy Department Radio Astronomy Laboratory
• UC Berkeley

Credit B4, F. Lo, G. Bower, Y. Lithwick, et
multi-alia
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An Early View on Scatter Broadening

• Backer 1978 ApJ, 222, L9

b
zb/Z
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Origins of DCB 1978
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Demagnification of Angular Broadening

• Scattering angle is property of screen
• Observed source apparent size is result of
  magnification

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1985 Nature, 315, 124
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OH Maser Scattering

• Frail et al. (1994) ApJ 427, L43

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Wide Field Source Scattering

• Bower et al. (2001) ApJ, 558, L27

Lazio Cordes (1998) ApJ, 505, 715
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Summary

• Sgr A has 21 image size dependent on lambda2.0
  image shape on baseline2.0
• OH masers within 0.5o (lat 65 pc) have similar
  sizes ellipticities.
• Required scattering measure few pc cm-6 on
  scales of 10s km (from max b z/Z estimate).

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Location of Scattering Plasma-I

• Mezger Pauls, 1979 IAU Symposium 84, p.357
• EI 300 pc (l) 120 pc (b) 1.4x104 pc cm-6 7
  cm-3
• EII 130 pc (l) 80 pc (b) 3.1x104 pc cm-6 16
  cm-3

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X-Ray Emitting Hot Plasma

• Koyama et al. (1996) PASJ, 48, 249 Munro et al.
  (2003) ApJ, 589, 225 -- 8.5 x 8.5 (20 pc x 20
  pc)
• Koyama et al. (1996) 3x10-13 ergs cm-2 s-1
  arcmin-2 Mereghetti et al. (1999) 5/3 larger
  something like 2-8 keV point sources 10

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Bipolar Wind

• Bland-Hawthorne Cohen (2003) ApJ, 582, 246
• At apex cylindrical shell

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Location of Scattering Plasma-II
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IPS Survey of Backgrnd QSO/AGN

• Cohen Gunderman (1968) ApJ, 145, 165