Columbia University Astronomy and Astrophysics

IGR J18450-0435 = AX J18450-0433
ATel #692; J. P. Halpern, E. V. Gotthelf

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. = -04° 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. = -04° 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 - 1993 October 19
Cross at Optical Counterpart
1&sigma Error Circle of IGR J18450-0435
Light Curve

UPDATE: The Swift XRT observed this source on 2006 March 5 and found it flaring again, and consistent in position with the ASCA source and its supergiant companion. The Swift XRT quicklook position is R.A. = 18h 45m 01.3s, Decl. = -04° 33' 59" (J2000).

Swift XRT - 2006 March 5
1&sigma INTEGRAL Error Circle
Swift XRT
Light Curve


New Transient X-Ray Source in the Scutum Region Discovered with ASCA, S. Yamauchi, et al., PASJ, 47, 189-194 (1995)

Discovery of the optical counterpart to the ASCA transient AX 1845.0-0433, M. J. Coe, J. Fabregat, I. Negueruela, P. Roche, & I. A. Steele, MNRAS, 281, 333-338 (1996)

Restoration of the ASCA Source Position Accuracy, E.V. Gotthelf, Y. Ueda, R. Fujimoto, T. Kii, & K. Yamaoka, Ap.J., 543, 417-424 (2000)

A Hard X-ray Survey of the Sagittarius Arm Tangent with the IBIS Telescope of the INTEGRAL Observatory: A Catalog of Sources, S.V. Molkov, A.M. Cherepashchuk, A.A. Lutovinov, M.G. Revnivtsev, K.A. Postnov, & R.A. Sunyaev, Astronomy Letters, 30, 534-539 (2004)

Supergiant Fast X-ray Transients: A New Class of High Mass X-ray Binaries Unveiled by INTEGRAL, I. Negueruela, D.M. Smith, P. Rieg, S. Chaty, & J. M. Torrejon, in Proceedings of "The X-ray Universe 2005" (astro-ph/0511088)

The Second IBIS/ISGRI Soft Gamma-ray Source Catalog, A.J. Bird, et al., Ap.J., 636, 765-776 (2006)

IGR J18450-0435 = AX J18450-0433, J. P. Halpern & E. V. Gotthelf, ATEL #692 (2006)


Last modified: March 6, 2006