70 research outputs found
Black holes: accretion processes in X-ray binaries
Accretion onto black holes is one of the most efficient energy source in the
Universe. Black hole accretion powers some of the most luminous objects in the
universe, including quasars, active galactic nuclei, tidal disruption events,
gamma-ray bursts, and black hole X-ray transients. In the present review, we
give an astrophysical overview of black hole accretion processes, with a
particular focus on black hole X-ray binary systems. In Section 1, we briefly
introduce the basic paradigms of black hole accretion. Physics related to
accretion onto black holes are introduced in Section 2. Models proposed for
black hole accretion are discussed in this section, from the Shakura-Sunyaev
thin disk accretion to the advective-dominated accretion flow. Observational
signatures that make contact to stellar-mass black hole accretion are
introduced in Section 3, including the spectral and fast variability
properties. A short conclusion is given in Section 4.Comment: invited chapter for the 'Handbook of X-ray and Gamma-ray Astrophysics
(Eds C.Bambini and A Santangelo, Springer, Singapore, 2023
X-ray performance of a customized large-format scientifc CMOS detector
In recent years, the performance of Scientifc Complementary Metal Oxide
Semiconductor (sCMOS) sensors has been improved signifcantly. Compared with CCD
sensors, sCMOS sensors have various advantages, making them potentially better
devices for optical and X-ray detection, especially in time-domain astronomy.
After a series of tests of sCMOS sensors, we proposed a new dedicated
high-speed, large-format X-ray detector in 2016 cooperating with Gpixel Inc.
This new sCMOS sensor has a physical size of 6 cm by 6 cm, with an array of
4096 by 4096 pixels and a pixel size of 15 um. The frame rate is 20.1 fps under
current condition and can be boosted to a maximum value around 100 fps. The
epitaxial thickness is increased to 10 um compared to the previous sCMOS
product. We show the results of its frst taped-out product in this work. The
dark current of this sCMOS is lower than 10 e/pixel/s at 20C, and lower than
0.02 e/pixel/s at -30C. The Fixed Pattern Noise (FPN) and the readout noise are
lower than 5 e in high-gain situation and show a small increase at low
temperature. The energy resolution reaches 180.1 eV (3.1%) at 5.90 keV for
single-pixel events and 212.3 eV (3.6%) for all split events. The continuous
X-ray spectrum measurement shows that this sensor is able to response to X-ray
photons from 500 eV to 37 keV. The excellent performance, as demonstrated from
these test results, makes sCMOS sensor an ideal detector for X-ray imaging and
spectroscopic application.Comment: 20 pages. published in PAS
Evolution of QPOs in GX 339-4 and EXO 1846-031 with Insight-HXMT and NICER
We conduct a spectral and timing analysis of GX 339-4 and EXO 1846-031 with
the aim of studying the evolution of Type-C QPOs with spectral parameters. The
high cadence data from Insight-HXMT and NICER allow us to track them. Type-C
QPOs appear at the end of low-hard state and/or hard-intermediate state. The
results reveal that the QPO frequency is closely related to the inner disk
radius and mass accretion rate in the two sources. Such a correlation is nicely
consistent with the dynamic frequency model.Comment: 14 pages, 13 figures, comments welcom
Fast On-orbit Pulse Phase Estimation of X-ray Crab Pulsar for XNAV Flight Experiments
The recent flight experiments with Neutron Star Interior Composition Explorer
(\textit{NICER}) and \textit{Insight}-Hard X-ray Modulation Telescope
(\textit{Insight}-HXMT) have demonstrated the feasibility of X-ray pulsar-based
navigation (XNAV) in the space. However, the current pulse phase estimation and
navigation methods employed in the above flight experiments are computationally
too expensive for handling the Crab pulsar data. To solve this problem, this
paper proposes a fast algorithm of on-orbit estimating the pulse phase of Crab
pulsar called X-ray pulsar navigaTion usIng on-orbiT pulsAr timiNg (XTITAN).
The pulse phase propagation model for Crab pulsar data from
\textit{Insight}-HXMT and \textit{NICER} are derived. When an exposure on the
Crab pulsar is divided into several sub-exposures, we derive an on-orbit timing
method to estimate the hyperparameters of the pulse phase propagation model.
Moreover, XTITAN is improved by iteratively estimating the pulse phase and the
position and velocity of satellite. When applied to the Crab pulsar data from
\textit{NICER}, XTITAN is 58 times faster than the grid search method employed
by \textit{NICER} experiment. When applied to the Crab pulsar data from
\textit{Insight}-HXMT, XTITAN is 180 times faster than the Significance
Enhancement of Pulse-profile with Orbit-dynamics (SEPO) which was employed in
the flight experiments with \textit{Insight}-HXMT. Thus, XTITAN is
computationally much efficient and has the potential to be employed for onboard
computation
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