2002/09/16 by I. Cagnoni, R. Turolla, A. Treves +6 · 1 citation
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/344711
published as Astrophys.J. 582 (2003) 654-658 · 7 pages, 3 figures, emulateapj5 style, accepted version, scheduled for ApJ v582 n2 January 10, 2003 issue
arxiv created 2002/09/16 · openalex publication_date 2003/01/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We report the discovery of a new ultraluminous X-ray source (ULX) in the nearby galaxy NGC 4244 from Chandra archival data. The source, 1WGA J1216.9+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 . 1WGA J1216.9+3743 appears pointlike in the Chandra image and has a complex spectral shape; a multicolor disk model, suitable for brighter ULXs, is inadequate for this source. The 1WGA J1216.9+3743 spectrum is heavily absorbed ( N H ~ 1-4 × 10 21 cm -2 ) and very soft. The best-fit power-law model gives Γ ~ 5 and implies a luminosity L (0.5-10 keV) ~ 10 39 ergs s -1 . A comparison with previous detections shows that, despite the variability displayed by the source during the Chandra observation, the 1WGA J1216.9+3743 count rate, spectral shape, and absorption are practically unchanged over a 9 yr period. We also performed deep optical imaging of the field containing the X-ray source and found a possible R ~ 23.7 counterpart.