IAUC 7265: C/1999 S3; GM Sgr, SAX J1819.3-2525 = XTE J1819-254 The following International Astronomical Union Circular may be linked-to from your own Web pages, but must not otherwise be redistributed (see these notes on the conditions under which circulars are made available on our WWW site). ------------------------------------------------------------------------ Read IAUC 7264 [ SEARCH ] Read IAUC 7266 View IAUC 7265 in .dvi or .ps format. IAUC number ------------------------------------------------------------------------ Circular No. 7265 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7244/7440/7444 (for emergency use only) COMET C/1999 S3 (LINEAR) Additional astrometry is published on MPEC 1999-S18, from whence the following preliminary parabolic orbital elements are taken: T = 1999 Nov. 6.073 TT Peri. = 42.810 Node = 12.476 2000.0 q = 1.92488 AU Incl. = 71.679 1999 TT R. A. (2000) Decl. Delta r Elong. Phase m1 Sept.19 1 41.16 +42 23.8 1.229 2.014 128.6 23.0 13.5 24 1 23.34 +46 19.7 1.194 1.997 130.5 22.4 13.4 29 1 01.17 +50 01.1 1.172 1.982 131.3 22.3 13.3 Oct. 4 0 34.49 +53 15.2 1.162 1.968 130.8 22.6 13.3 9 0 03.81 +55 50.1 1.166 1.956 129.1 23.4 13.2 GM SAGITTARII AND SAX J1819.3-2525 = XTE J1819-254 Further to their report on IAUC 7254, R. M. Hjellming et al. write: "Continued VLA observations of GM Sgr show that, since it became optically thin on Sept. 17.0 UT, the radio fluxes have decayed with a power law and spectrum approximated by 0.33[(JD-2451437)**-2.05](f**-0.66), where f is the frequency in GHz, reaching 3.9, 1.8, and 1.1 mJy at 1.49, 4.9, and 8.5 GHz on Sept. 22.0. VLA observations at 21 cm on Sept. 17.0 show strong H I absorption, identical within the noise to that seen against a nearby extragalactic calibrator (J1820-2528), suggesting that GM Sgr is at least a few hundred parsecs away; these data give no constraints on the maximum distance. The corresponding total H I column density is 1.8 x 10**21 (T_s/100 K) cm**-2, where T_s is the spin temperature. On Sept. 16.02 the 0.41-Jy source at 4.9 GHz was resolved into a 0.34-Jy source (at the position reported on IAUC 7254) and extensions roughly 0".25 north and south. On Sept. 17.93, a 14.9-GHz image obtained with 'fast-phase' referencing to J1820-2528 showed a about 4-mJy source at the IAUC 7254 radio position and a about 9-mJy source located about 0".25 south, at the same location as the southern extension on Sept. 16.02. Observations on Sept. 22.00 and 24.1 show only this southern source. Accurate optical astrometry is needed to show where GM Sgr lies with respect to the radio emission. This would determine whether the Sept. 22-24 radio source should be interpreted as unusually long-lived ejecta, perhaps interacting with some surrounding material (cf. XTE J1748-288), or simply residual emission from the central object." (C) Copyright 1999 CBAT 1999 September 26 (7265) Daniel W. E. Green ------------------------------------------------------------------------ Read IAUC 7264 [ SEARCH ] Read IAUC 7266 View IAUC 7265 in .dvi or .ps format. ------------------------------------------------------------------------ Our Web policy. Index to the CBAT/MPC/ICQ pages. CBAT