ABSTRACT
The megajansky radio burst, FRB 20200428, and other bright radio bursts detected from the Galactic source SGR J1935+2154 suggest that magnetars can make fast radio bursts (FRBs), but the emission site and mechanism of FRB-like bursts are still unidentified. Here, we report the emergence of a radio pulsar phase of the magnetar 5 months after FRB 20200428. Pulses were detected in 16.5 hours over 13 days using the Five-hundred-meter Aperture Spherical radio Telescope, with luminosities of about eight decades fainter than FRB 20200428. The pulses were emitted in a narrow phase window anti-aligned with the x-ray pulsation profile observed using the x-ray telescopes. The bursts, conversely, appear in random phases. This dichotomy suggests that radio pulses originate from a fixed region within the magnetosphere, but bursts occur in random locations and are possibly associated with explosive events in a dynamically evolving magnetosphere. This picture reconciles the lack of periodicity in cosmological repeating FRBs within the magnetar engine model.
ABSTRACT
A black hole X-ray binary produces hard X-ray radiation from its corona and disk when the accreting matter heats up. During an outburst, the disk and corona co-evolves with each other. However, such an evolution is still unclear in both its geometry and dynamics. Here we report the unusual decrease of the reflection fraction in MAXI J1820+070, which is the ratio of the coronal intensity illuminating the disk to the coronal intensity reaching the observer, as the corona is observed to contrast during the decay phase. We postulate a jet-like corona model, in which the corona can be understood as a standing shock where the material flowing through. In this dynamical scenario, the decrease of the reflection fraction is a signature of the corona's bulk velocity. Our findings suggest that as the corona is observed to get closer to the black hole, the coronal material might be outflowing faster.
ABSTRACT
The detection of cancer cells in clinical samples is of great interest for a range of diagnostic applications, and separation and enrichment of cancer cells in low concentrations from complex sample matrices is necessary for efficient cancer diagnostics. In the present study, new surface-modified iron oxide nanoparticles were synthesized for the separation of lung cancer cells by simple precipitation of Fe(II) and Fe(III) salts in an aqueous ammonia solution, followed by the addition of polyethylenimine (PEI). The modified nanoparticles were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). XRD and TEM revealed that the particles were ~10 nm in diameter, while FTIR and XPS showed that their surfaces were well coated with PEI. VSM results confirmed the superparamagnetic nature of PEI-coated Fe3O4 nanoparticles. The separation and enrichment of lung cancer cells from sputum samples was demonstrated using the synthesized developed PEI-coated Fe3O4 magnetic nanoparticles. Exfoliative cytopathology showed that the percentage of positive cells increased from 6.3% (38/600) in untreated sputum samples to 38.5% (231/600) in sputum samples treated with PEI-coated Fe3O4 magnetic nanocomposites. This finding indicated that PEI-coated Fe3O4 magnetic nanocomposites can be used to efficiently enrich lung cancer cells from sputum for subsequent cytopathological analysis.
