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A statistical hardness classification of ultraluminous X-ray sources using long-term Swift/XRT monitoring
Sinan Allak, Wei Yu, Menglei Zhou +2
We characterize long-term hardness behavior in 29 ultraluminous X-ray sources (ULXs) using over 3500 archival Swift/XRT observations. We classify observations as soft-band dominate…
EXPO: a quantum leap in fast, wide-band X-ray polarimetry for astrophysics
Paolo Soffitta, Sebastien Guillot, Ian Hutchinson +137
The Enhanced X-ray Polarimetry Observatory (EXPO) is a mission concept proposed to ESA as an M8 candidate, with a prospective launch in 2041. Building on the scientific success of…
Stable X-ray reverberation lags in the black hole X-ray binary Swift J1727.8-1613
Wei Yu, Sinan Allak, Zi-Xu Yang +3
Aims. We investigate the evolution of X-ray reverberation lags in the black hole X-ray binary Swift J1727.8-1613 during its 2023 outburst, with the aim of probing the inner accreti…
Testing Black Holes with Interstellar Missions: II. Flyby Probes
Yi Fan, Cosimo Bambi, Leda Gao +2
Recently, we demonstrated that while an interstellar mission to the nearest black hole remains highly speculative and extraordinarily challenging, it is not entirely implausible wi…
Spectral and timing variability of the transient ultraluminous X-ray source NGC 4631 X-4
Sinan Allak, Wei Yu, Lorenzo Ducci +4
Ultraluminous X-ray sources (ULXs) are among the best laboratories for studying super-Eddington accretion onto compact objects. We present a detailed spectral and timing analysis o…
A candidate cyclotron line at 1.89 keV in the ultraluminous X-ray source NGC 4861 X-2
Sinan Allak, Lorenzo Ducci, Valery F. Suleimanov +6
In this Letter, we report the detection of an absorption-like feature at ~1.89 keV in Chandra/ACIS spectra of the ultraluminous X-ray source NGC 4861 X-2, based on the deepest obse…