[vsnet-alert 4502] (fwd) XTE J1118+480

[Taichi Kato <tkato>]

(fwd) XTE J1118+480

Date: Thu, 30 Mar 2000 11:21:41 -0500 (EST)
From: Ron Remillard <rr@space.mit.edu>

The RXTE All-Sky Monitor has detected X-ray emission from a new
source, XTE J1118+480. The ASM position (equinox 2000.0, with a 90%
confidence radius of 6') is centered at R.A. = 11h 18m 17s, 
Decl. = +48o 03'.0 The average X-ray intensity (2-12 keV) is 
39(8) mCrab on March 29. Retrospective ASM analysis indicates that the 
X-ray flux has been slowly rising since March 5. Another modest outburst
had previously occurred during Jan 2-29 2000, peaking at 37(3) mCrab on
Jan 6. The SIMBAD database lists only an unremarkable guide star (V~11)
near the X-ray position. The source was confirmed in an 800 s 
RXTE pointed observation beginning on 23:14 UT March 29. Rapid flares 
(e.g. 10 s) were seen, reaching a factor of 5 above the baseline flux 
near 25 mCrab and suggesting a Galactic X-ray source. No pulsations 
were detected. The X-ray spectrum does not vary appreciably during 
intense flares. Preliminary spectral analysis indicates a power-law
visible to 30 keV. The photon index is roughly 1.8, which is similar
to Cyg X-1 in its hard state. The high galactic latitude (62o) 
and X-ray properties present a puzzling combination, 
and observations at other wavelengths are urgently needed.

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