Kavli Affiliate: Erin Kara
| First 5 Authors: Oluwashina Adegoke, Javier Garcia, Riley Connors, Yuanze Ding, Guglielmo Mastroserio
| Summary:
MAXI J1803-298 is a transient black hole candidate discovered in May of 2021
during an outburst that lasted several months. Multiple X-ray observations
reveal recurring "dipping" intervals in several of its light curves,
particularly during the hard/intermediate states, with a typical recurrence
period of $sim7,mathrm{hours}$. We report analysis of four NuSTAR
observations of the source, supplemented with NICER data where available, over
the duration of the outburst evolution covering the hard, intermediate and the
soft states. Reflection spectroscopy reveals the black hole to be rapidly
spinning ($a_*=0.990pm{0.001}$) with a near edge-on viewing angle
($i=70pm{1}deg$). Additionally, we show that the light-curve dips are caused
by photo-electric absorption from a moderately ionized absorber whose origin is
not fully understood, although it is likely linked to material from the
companion star impacting the outer edges of the accretion disk. We further
detect absorption lines in some of the spectra, potentially associated with Fe
XXV and Fe XXVI, indicative of disk winds with moderate to extreme velocities.
During the intermediate state and just before transitioning into the soft
state, the source showed a sudden flux increase which we found to be dominated
by soft disk photons and consistent with the filling of the inner accretion
disk, at the onset of state transition. In the soft state, we show that models
of disk self-irradiation provide a better fit and a preferred explanation to
the broadband reflection spectrum, consistent with previous studies of other
accreting sources.
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