We report on our analysis of the 2019 outburst of the X-ray accreting pulsar 4U 1901+03 observed with Insight-HXMT and NICER. Both spectra and pulse profiles evolve significantly in the decaying phase of the outburst. Dozens of flares are observed throughout the outburst. They are more frequent and brighter at the outburst peak. We find that the flares, which have a duration from tens to hundreds of seconds, are generally brighter than the persistent emission by a factor of ∼1.5. The pulse-profile shape during the flares can be significantly different from that of the persistent emission. In particular, a phase shift is clearly observed in many cases. We interpret these findings as direct evidence of changes of the pulsed beam pattern, due to transitions between the sub- and supercritical accretion regimes on a short time-scale. We also observe that at comparable luminosities the flares’ pulse profiles are rather similar to those of the persistent emission. This indicates that the accretion on the polar cap of the neutron star is mainly determined by the luminosity, i.e. the mass accretion rate.

Based on Insight-HXMT data, we report on the pulse fraction evolution during the 2017-2018 outburst of the newly discovered first Galactic ultraluminous X-ray source (ULX) Swift J0243.6+6124. The pulse fractions of 19 observation pairs selected in the rising and fading phases with similar luminosity are investigated. The results show a general trend of the pulse fraction increasing with luminosity and energy at super-critical luminosity. However, the relative strength of the pulsation between each pair evolves strongly with luminosity. The pulse fraction in the rising phase is larger at luminosity below 7.71 × 1038 erg s−1, but smaller at above. A transition luminosity is found to be energy independent. Such a phenomena is firstly confirmed by Insight-HXMT observations and we speculate it may have relation with the radiation pressure dominated accretion disk.

This paper reports on the growth and spectral properties of NaNd(MoO 4 ) 2 crystal. NaNd(MoO 4 ) 2 crystal with dimensions of 23615615 mm was grown from a flux of Na 2 Mo 2 O 7 by top seed solution growth method. The absorption and emission spectra of NaNd(MoO 4 ) 2 crystal were investigated. The results show that NaNd(MoO 4 ) 2 crystal has large absorption cross-section of 3?74610 -20 cm 2 with broad full width at half maximum of 15 nm at 806 nm for p-polarisation and 2?49610 -20 cm 2 with full width at half maximum of 16 nm at 807 nm for s-polarisation respectively. The emission cross-sections are 6?0610 -19 cm 2 at 1058 nm for p-polarisation and 3?93610 -19 cm 2 at 1065 nm for s-polarisation respectively. The above results indicated that NaNd(MoO 4 ) 2 crystal may be regarded as potential self-active laser materials.