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Cyclotron resonant scattering features (CRSFs) are the absorption features in the X-ray spectra of strongly magnetized accretion neutron stars (NSs), which are probably the most reliable probe to the surface magnetic fields of NSs. The high-mass X-ray binary GX 301–2 exhibits a very wide, variable, and complicated CRSF in the average spectra, which should be two absorption lines based on Nuclear Spectroscopic Telescope Array (NuStar) and Hard X-ray Modulation Telescope (Insight - HXMT) observations. With the Insight - HXMT frequent observations, we performed the phase-resolved spectroscopy and confirmed two cyclotron absorption lines in the phase-resolved spectra, with their centroid energy ratio ∼1.6–1.7 in the supercritical luminosity case. A major hindrance in understanding those CRSFs is the very poorly constrained magnetic inclination angle, which is also a fundamental property of an NS and key to understanding the emission characteristics of a pulsar. Comparing the phase-resolved CRSF with simulated X-ray spectra, the magnetic inclination angle is found to be ≳70°, i.e. nearly orthogonal between the NS's spin and magnetic axis. The implications of an orthogonal rotator and magnetic structure evolution in the accreting X-ray binary are also discussed. [ABSTRACT FROM AUTHOR]

The Einstein Probe (EP) satellite is designed for X-ray time-domain astronomy. The Follow-up X-ray Telescope (FXT) is one of the scientific payloads onboard EP. It will mainly be used for the follow-up X-ray observation, and it will also be used for the sky survey and Target of Opportunity (ToO) observation. The focal plane detector of FXT provided by the Max Planck Institute for Extraterrestrial Physics (MPE) adopts a PNCCD sensor. For detector cooling, a helium pulse tube refrigerator is used, provided by the Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS), to keep the detector working at a temperature of −90 ± 0.5 °C. The PNCCD driving and data acquisition electronics are developed by the Institute of High Energy Physics (IHEP), CAS. To observe different celestial sources, we designed six filter wheel positions and three scientific operating modes for the PNCCD detector: the full-frame mode, the partial-window mode, and the timing mode. In the full-frame mode, the system frame rate is 20 frame/s and the energy resolution of the whole system reaches 92 eV @ 1.49 keV (FWHM). The frame rate of partial-window mode is 500 frame/s. In the timing mode, the time resolution is about 94 μs. This paper mainly introduces the design and test results of the focal plane camera. [ABSTRACT FROM AUTHOR]

The Follow-up X-ray Telescope (FXT) is one of the key payloads onboard EP. It is a Wolter-I type X-ray focusing telescope equipped with two telescope modules (focal length 1.6 m), with a total effective area of ~ 600 cm2 at 1.25 keV and an energy range of 0.3–10 keV. FXT is mainly composed of an X-ray focusing mirror assembly (MA) and a camera assembly with a PNCCD detector module. The two FXT modules are completely independent from each other, thus avoiding a single point failure. We completed the internal composites of FXT structural design, which meets the function and performance requirements of mechanical, thermal, contamination control and X-ray optics. The FXT passed successfully the mechanical, thermal qualification level tests on the spacecraft platform in the phase C. [ABSTRACT FROM AUTHOR]

An observation simulator is established, on an event-by-event basis, for the Polarimetry Focusing telescope Array (PFA) on board the planned enhanced X-ray Timing and Polarimetry observatory (eXTP). An event generator, based on XIMPOL, is used to sample the parameters of the X-rays reaching the aperture of the telescope. The trajectories and interactions of X-rays through the telescope and the corresponding secondaries are calculated using the optics and detector simulation model built in GEANT4, before being translated into signals in the pixelated readout electronics. It is shown that mirror deformation is required for the optics simulation model, and transportation of ionization electrons is required for the detector simulation model to reproduce the overall performance of the telescope. The developed tool is useful in different mission phases, such as payload optimization in the design phase, discrimination of new phenomena against known physics models in the calibration phases, and sensitivity studies of potential polarized X-ray sources in observation planning. The sensitivity of PFA to the Crab Nebula and Crab pulsar is investigated to demonstrate the application of the tool. Even with the dilution effect, space-resolved and phase-resolved polarimetry can reveal important aspects of the Crab Nebula and Crab pulsar and help break the degeneracy between different models. [ABSTRACT FROM AUTHOR]

The black hole candidate MAXI J1535-571 is a recently discovered X-ray transient. We report on the monitoring observations of Swift Gamma-Ray Burst Mission during outburst. The source transits from the hard state to the intermediate state, and reaches the soft state; near the end of the outburst, it returns to the hard state passing through the low intermediate state, following a typical Q-shaped loop in the hardness-intensity diagram. During the high intermediate state, detailed spectral analyses using a multitemperature disc model reveal that the disc luminosity is flatter than the inner disc temperature to the fourth power, and the disc temperature profile varies as the disc radius raised to the power of −0.5, consistent with the behavior of a slim disc, implying that the disc structure has been modified due to the high luminosity of ∼1039 erg s−1. Meanwhile, the column density increases with the Eddington ratio, suggesting that the outflow matters are driven by radiation pressure due to the high accretion rate. [ABSTRACT FROM AUTHOR]