Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-09-16
Astrophys.J. 582 (2003) 654-658
Astronomy and Astrophysics
Astrophysics
7 pages, 3 figures, emulateapj5 style, accepted version, scheduled for ApJ v582 n2 January 10, 2003 issue
Scientific paper
10.1086/344711
We report the discovery of a new ultraluminous X-ray source (ULX) in the nearby galaxy NGC 4244 from Chandra archival data. The source, 1WGAJ1216.9+3743, is one of the least luminous and softest ULXs discovered so far. Its X-ray spectrum is the best available for a representative of the soft ULXs, a class of sources recently discovered by Chandra and XMM-Newton. 1WGAJ1216.9+3742 appears point-like in the Chandra image and has a complex spectral shape: a multicolor disk model, suitable for brighter ULXs, is inadequate for this source. 1WGAJ1216.9+3743 spectrum is heavily absorbed (NH ~ (1-4)E21 cm^-2),and very soft. The best-fit power-law model gives a photon index ~ 5 and implies a luminosity L(0.5-10 keV) ~ 1E39 erg/s. A comparison with previous detections shows that, despite the variability displayed by the source during the Chandra observation, 1WGAJ1216.9+3743 count rate, spectral shape and absorption are practically unchange over a 9-year period. We performed also deep optical imaging of the field containing the X-ray source, and found a possible R ~ 23.7 counterpart.
Cagnoni Ilaria
Celotti Annalisa
Elvis Martin
Huang Sheng-Jun
Kim Dae Wook
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