X-RAY MONITORING OF ULTRALUMINOUS X-RAY SOURCES
- Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242 (United States)
- Department of Engineering Physics and Center for Astrophysics, Tsinghua University, Beijing 100084 (China)
X-ray monitoring observations were performed with the Swift observatory of the ultraluminous X-ray sources Holmberg IX X-1, NGC 5408 X-1, and NGC 4395 X-2 and also of the nuclear X-ray source in NGC 4395. Holmberg IX X-1 remains in the hard X-ray spectral state as its flux varies by a factor of 7 up to a (isotropic) luminosity of 2.8 x 10{sup 40} erg s{sup -1}. This behavior may suggest an unusually massive compact object. We find excess power at periods near 60 days and 28 days in the X-ray emission from Holmberg IX X-1. Additional monitoring is required to test the significance of these signals. NGC 5408 X-1 and NGC 4395 X-2 appear to remain in the soft spectral state found by Chandra and XMM with little variation in spectral hardness even as the luminosity changes by a factor of 9. We found an outburst from the nuclear source in NGC 4395 reaching an X-ray luminosity of 9 x 10{sup 40} erg s{sup -1}, several times higher than any previously reported.
- OSTI ID:
- 21335987
- Journal Information:
- Astrophysical Journal, Vol. 702, Issue 2; Other Information: DOI: 10.1088/0004-637X/702/2/1679; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
X-RAY SPECTRAL CUTOFF AND THE LACK OF HARD X-RAY EMISSION FROM TWO ULTRALUMINOUS X-RAY SOURCES M81 X-6 AND HOLMBERG IX X-1
DISCOVERY OF A 115 DAY ORBITAL PERIOD IN THE ULTRALUMINOUS X-RAY SOURCE NGC 5408 X-1