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Considering the spatially separated polarization radiation and Faraday rotation regions to simulate complex interstellar media, we study synchrotron polarization gradient techniques' measurement capabilities. We explore how to trace the direction of projected magnetic field of emitting-source region at the multifrequency bands, using the gradient technique compared with the traditional polarization vector method. Furthermore, we study how Faraday rotation density in the foreground region, i.e. a product of electron number density and parallel component of magnetic fields along the line of sight, affects the measurement of projected magnetic field. Numerical results show that synchrotron polarization gradient technique could successfully trace projected magnetic field within emitting-source region independent of radio frequency. Accordingly, the gradient technique can measure the magnetic field properties for a complex astrophysical environment. [ABSTRACT FROM AUTHOR]

Based on high-resolution 3D data cubes from a magnetohydrodynamic (MHD) turbulence simulation, we study how to reveal the direction of the magnetic field within the optically thick interstellar medium by using the velocity gradient technique (VGT), correlation function anisotropy (CFA), and principal component analysis of anisotropies (PCAA). Considering the CO molecular tracers as a tracing method for radiative transfer processes, we find that the VGT and CFA can successfully trace the orientation of mean magnetic fields, which is in good agreement with the low-resolution numerical results obtained in the case of an optically thin medium. Similar to the simulation of an optically thin ISM, our simulations show that PCCA is still unusable in optically thick media. The synergetic application of the VGT and CFA to high-resolution spectroscopic observations is expected to yield valuable information on the interstellar magnetic field. [ABSTRACT FROM AUTHOR]

We analysed an XMM–Newton plus a simultaneous Rossi X-ray Timing Explorer observation and a separate Suzaku observation of the neutron star low-mass X-ray binary 4U 1728–34. We fitted the X-ray spectra with the self-consistent reflection model relxill. We found that the inclination angle of 4U 1728–34 is 49 ± 5 degree, consistent with the upper limit of 60 degree deduced from the absence of eclipses or dips in this source. The inclination angle in the fit of the XMM–Newton /RXTE observation is larger than 85 degree, which may be due to the possible calibration issues of the PN instrument in timing mode. We also found that the thermal emission from the accretion disc is not significant. This could be explained either by the relatively high column density of the interstellar medium along the line of sight to the source, which decreases the number of soft disc photons, or if most of the soft thermal photons from the disc are reprocessed in the corona. The ionization parameter derived from the fits is larger than the value predicted in the framework of the standard reflection model, wherein the disc is irradiated by an X-ray source above the compact object. This inconsistency suggests that irradiation from the neutron star and its boundary layer may play an important role in the ionization of the accretion disc, and hence in the reflection component in this source. [ABSTRACT FROM AUTHOR]