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IGR J18450-0435 = AX J18450-0433

ATel #692; J. P. Halpern, E. V. Gotthelf (Columbia U,)
on 14 Jan 2006; 22:13 UT
Credential Certification: Jules Halpern (jules@astro.columbia.edu)

Subjects: X-ray, Gamma Ray

Negueruela et al. (2005) noted that many fast X-ray transients with supergiant binary companions (SFXTs) are being found in INTEGRAL monitoring of the Galactic Plane. They mentioned that the flaring ASCA source AX J1845.0-0433, discovered on 1993 October 19, also exhibited such properties (Yamauchi et al. 1995; Coe et al. 1996), although no further X-ray activity has been reported from it. Here, we point out that AX J1845.0-0433, located at a refined position of R.A. = 18h 45m 02.1s, Decl. = -04d 33' 55" (J2000) using the calibration of Gotthelf et al. (2000), is very likely the same object as IGR J18450-0435, detected in 2003 (Molkov et al. 2004; Bird et al. 2006). Using the precise position of its optical counterpart, R.A. = 18h 45m 01.59s, Decl. = -04d 33' 56.5" (J2000), the ASCA source lies 2.3' from the Bird et al. INTEGRAL position. Although the latter is assigned a 1.8' (1 sigma) radius error circle, there is no other ASCA source near the INTEGRAL source (see link below), and the X-ray properties of AX J1845.0-0433 make a compelling case for the identification.

The mean flux of IGR J18450-0435 was 8x10(-12) erg/cm2/s in the 20-40 keV band (Bird et al.), corresponding to L(20-40 keV) = 1x10(34) erg/s at a distance of 3.6 kpc (Coe et al.). This is in between the quiescent and flaring luminosities measured by ASCA, which range over 5x10(33) < L(0.7-10 keV) < 5x10(35) erg/s (Yamauchi et al.). Even though the flaring duty cycle of this source is unknown, since activity was detected from it in an ASCA observation lasting only 16 hours, the INTEGRAL detection during its 10 days of effective exposure time on this region is not unexpected. INTEGRAL should therefore be able to compile a complete sample of such sources, with distance limited by luminosity.

ASCA Images and Light Curve