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IAUC 7253: GM Sgr, SAX J1819.3-2525 = XTE J1819-254; P/1999 RO_28

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                                                  Circular No. 7253
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)
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Phone 617-495-7244/7440/7444 (for emergency use only)


GM SAGITTARII AND SAX J1819.3-2525 = XTE J1819-254
     R. Stubbings, Drouin, Vic., Australia, reports that GM Sgr is
undergoing a very bright outburst after showing recent rapid
variations, his visual magnitude estimates being:  Aug. 11.488 UT,
12.3; 14.436, 12.5; 29.424, 12.7; 31.496, 13.0; Sept. 9.462, 11.2;
11.599, 11.9; 12.409, 11.1; 13.397, 11.9; 14.491, 11.4; 15.395,
8.8; 15.408, 8.8.  Additional m_v estimates by A. Pearce, Nedlands,
W. Australia: Sept. 15.550, 9.5; 15.571, 9.6.
     D. A. Smith, A. M. Levine, and E. H. Morgan, Massachusetts
Institute of Technology (MIT), on behalf of the RXTE All-Sky
Monitor (ASM) team at MIT and Goddard Space Flight Center, report
that, in response to the visual observations of GM Sgr, SAX
J1819.3-2525 (an x-ray transient likely to be associated with GM
Sgr; cf. IAUC 7119, 7120) was measured by the ASM on Sept. 15.420
UT to have an intensity of 1.55 +/- 0.04 Crab (2-12 keV; estimated
error based solely on counting statistics).  Subsequent
measurements showed a rapid increase in x-ray intensity:  Sept.
15.422, 1.32 +/- 0.04 Crab; 15.423, 1.43 +/- 0.04; 15.488, 2.41
+/- 0.04; 15.489, 3.74 +/- 0.05; 15.701, 10.0 +/- 0.2; 15.703,
12.2 +/- 0.2.  The spectrum is harder than that of the Crab
nebula.
     The star attributed by Goranskij (1990, IBVS 3464) to GM Sgr
has been measured on the Digital Sky Survey by G. V. Williams,
Smithsonian Astrophysical Observatory, to be at R.A. =
18h19m21s.61, Decl. = -25o24'26".3 (equinox 2000.0; uncertainty +/-
1".0 in both coordinates); this is 1' north of the GCVS position
from Luyten (1927, HCO Bull. No. 852).


COMET P/1999 RO_28 (LONEOS)
     C. Hergenrother, Lunar and Planetary Laboratory, reports that
a co-added 600-s CCD exposure with the Steward Observatory 2.3-m
reflector on Sept. 13 of 1999 RO_28 (discovered by LONEOS; cf. MPEC
1999-R23; discovery position given below) shows a stellar
condensation with a faint 20" tail in p.a. 310 deg.  M. Tichy and
J. Ticha, Klet, later reported a faint coma of diameter 8" and 7"
on images taken on Sept. 8.93 and 10.02 UT, respectively.
Observations by J. V. Scotti with the Spacewatch telescope at Kitt
Peak on Sept. 15.4 show a coma diameter of 9" (m_1 = 18.6-18.7, m_2
= 20.6-21.0) and a 0'.72 tail in p.a. 308 deg.  New orbital
elements on MPEC 1999-R47 include T = 1999 Oct. 2.35 TT, q = 1.2302
AU, P = 6.46 yr.

     1999 UT             R.A. (2000) Decl.        m2
     Sept. 7.32994   23 41 39.78   -14 32 00.5   18.4

                      (C) Copyright 1999 CBAT
1999 September 15              (7253)            Daniel W. E. Green

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