Ultraluminous X-ray sources are bright point sources shining at above the Eddington limit for a 10 solar moss black hole. The nature of this type of sources are still unclear leaving astronomer scratching their heads. Scientists from CAMK PAN in Warsaw: Samaresh Mondal, Agata Różańska and Alex Markowitz in collaboration with Barbara De Marco from the Catalan University of Technology in Barcelona discovered the presence of Fe K alpha line and soft X-ray lag in NGC 7456 ULX-1. Such features are very rare in ULXs, so far NGC 7456 ULX-1 is the second to detect the iron K alpha line and gift to have the soft X-ray lag. Therefore such discoveries can provide unique insight into the behavior of high accretion rate. Due to the low signal to noise above 6 keV we only obtained the upper limit on the width of the iron K alpha line which indicate the line must be originated beyond 85 rg. The large amplitude of the soft X-ray lag ~1300 s and absence of the soft excess in the covariance spectra suggest the scattering inside the wind outflowing for the origin of the soft X-ray lag.
For more details please check the original paper published in MNRAS Letters: “Evidence for Fe K alpha line and soft X-ray in NGC 7456 ULX-1”
Figure: The upper panel shows the presence of Fe K alpha line at 6.4 keV and the bottom panel shows detestation of ~1300 s soft X-ray lag at 0.1 mHz.
