Interstellar Scattering of Sgr A D C Backer

Interstellar Scattering of Sgr A* D. C. Backer Astronomy Department & Radio Astronomy Laboratory UC Berkeley Credit: B 4, F. Lo, G. Bower, Y. Lithwick, et multi-alia Sgr A* 30 th Fest -- 2004 March 1

An Early View on Scatter Broadening Backer 1978 Ap. J, 222, L 9 b zb/Z Sgr A* 30 th Fest -- 2004 March 2

Origins of DCB 1978… Sgr A* 30 th Fest -- 2004 March 3

Demagnification of Angular Broadening • Scattering angle is property of screen • Observed source apparent size is result of magnification Sgr A* 30 th Fest -- 2004 March 4

1985 Nature, 315, 124 Sgr A* 30 th Fest -- 2004 March 5

OH Maser Scattering Frail et al. (1994) Ap. J 427, L 43 Sgr A* 30 th Fest -- 2004 March 6

Wide Field Source Scattering Bower et al. (2001) Ap. J, 558, L 27 Lazio & Cordes (1998) Ap. J, 505, 715 Sgr A* 30 th Fest -- 2004 March 7

Summary • Sgr A* has 2: 1 image size dependent on lambda 2. 0 & image shape on baseline 2. 0 • OH masers within ~0. 5 o (lat; 65 pc) have similar sizes & ellipticities. • Required scattering measure: few pc cm-6 on scales of 10’s km (from max b & z/Z estimate). Sgr A* 30 th Fest -- 2004 March 8

Location of Scattering Plasma-I • Mezger & Pauls, 1979 IAU Symposium 84, p. 357 • EI: 300 pc (l); 120 pc (b); 1. 4 x 104 pc cm-6; 7 cm-3 • EII: 130 pc (l); 80 pc (b); 3. 1 x 104 pc cm-6; 16 cm-3 Sgr A* 30 th Fest -- 2004 March 9

X-Ray Emitting Hot Plasma • Koyama et al. (1996) PASJ, 48, 249; Munro et al. (2003) Ap. J, 589, 225 -- 8. 5’ x 8. 5’ (20 pc x 20 pc) • Koyama et al. (1996): 3 x 10 -13 ergs cm-2 s-1 arcmin-2; Mereghetti et al. (1999) 5/3 larger; something like 2 -8 ke. V; point sources 10% Sgr A* 30 th Fest -- 2004 March 10

Bipolar Wind Bland-Hawthorne & Cohen (2003) Ap. J, 582, 246 At apex cylindrical shell: Sgr A* 30 th Fest -- 2004 March 11

Location of Scattering Plasma-II Sgr A* 30 th Fest -- 2004 March 12

IPS Survey of Backgrnd QSO/AGN Cohen & Gunderman (1968) Ap. J, 145, 165 Sgr A* 30 th Fest -- 2004 March 13