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X-ray spectral state is not correlated with luminosity in Holmberg II X-1
Fabien Grisé, Philip Kaaret, Hua Feng +2
The ultraluminous X-ray source (ULX) Holmberg II X-1 has been observed over 4 months in 2009/2010 by the Swift observatory. The source luminosity varied by a factor of up to 14, re…
Detection of Strong Short-Term Variability in NGC 6946 X-1
Fengyun Rao, Hua Feng, Philip Kaaret
Using two archival XMM-Newton observations, we identify strong X-ray flux variations in NGC 6946 X-1 indicating it is the most variable ultraluminous X-ray source (ULX) on mHz time…
Transition to the disk dominant state of a new ultraluminous X-ray source in M82
Jing Jin, Hua Feng, Philip Kaaret
We report on the identification of a third, new ultraluminous X-ray source (ULX) in the starburst galaxy M82. Previously, the source was observed at fluxes consistent with the high…
VLBI observations of SN 2008iz: I. Expansion velocity and limits on anisotropic expansion
A. Brunthaler, I. Marti-Vidal, K. M. Menten +9
We present observations of the recently discovered supernova 2008iz in M82 with the VLBI High Sensitivity Array at 22 GHz, the Very Large Array at frequencies of 1.4, 4.8, 8.4, 22…
Direct Detection of an Ultraluminous Ultraviolet Source
Philip Kaaret, Hua Feng, Diane S. Wong +1
We present Hubble Space Telescope observations in the far UV of the ultraluminous X-ray source in NGC 6946 associated with the optical nebula MF 16. Both a point-like source coinci…
Identification of the X-Ray Thermal Dominant State in an Ultraluminous X-Ray Source in M82
Hua Feng, Philip Kaaret
The thermal dominant state in black hole binaries (BHBs) is well understood but rarely seen in ultraluminous X-ray sources (ULXs). Using simultaneous observations of M82 with Chand…