The spin-down accretion regime of Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124

The relative high fluxes of the Galactic ultra-luminous X-ray pulsar Swift J0243 allow a detailed study of its spin-down regime in quiescence state, for a first time. After the 2017 giant outburst, its spin frequencies show a linear decreasing trend with some variations due to minor outbursts. The linear spin-down rate is $\sim-1.9\times10^{-12}$ Hz/s during the period of lowest luminosity, from which one can infer a dipole field $\sim1.75\times10^{13}$ G. The $\dot{\nu}-L$ relation during the spin-down regime is complex, and the $\dot{\nu}$ is close to 0 when the luminosity reaches both the high end ($L_{38}\sim0.3$) and the lowest value ($L_{38}\sim0.03$). The luminosity of zero-torque is different for the giant outburst and other minor outbursts. It is likely due to different accretion flows for different types of outburst, as evidenced by the differences of the spectra and pulse profiles at a similar luminosity for different types of outburst (giant or not). The pulse profile changes from double peaks in the spin-up state to a single broad peak in the low spin-down regime, indicating the emission beam/region is larger in the low spin-down regime. These results show that accretion is still ongoing in the low spin-down regime for which the neutron star is supposed to be in a propeller state.Comment: 7 pages, 7 figs, to appear in ApJ, comments welcom

Pulsar Glitches: A Review

$\sim 6\%$ of all known pulsars have been observed to exhibit sudden spin-up events, known as glitches. For more than fifty years, these phenomena have played an important role in helping to understand pulsar (astro)physics. Based on the review of pulsar glitches search method, the progress made in observations in recent years is summarized, including the achievements obtained by Chinese telescopes. Glitching pulsars demonstrate great diversity of behaviours, which can be broadly classified into four categories: normal glitches, slow glitches, glitches with delayed spin-ups, and anti-glitches. The main models of glitches that have been proposed are reviewed and their implications for neutron star structure are critically examined regarding our current understanding. Furthermore, the correlations between glitches and emission changes, which suggest that magnetospheric state-change is linked to the pulsar-intrinsic processes, are also described and discussed in some detail.Comment: Accepted for publication in Universe. 50 pages, 11 figures, contribution to special issue "Frontiers in Pulsars Astrophysics

1Cademy @ Causal News Corpus 2022: Leveraging Self-Training in Causality Classification of Socio-Political Event Data

This paper details our participation in the Challenges and Applications of Automated Extraction of Socio-political Events from Text (CASE) workshop @ EMNLP 2022, where we take part in Subtask 1 of Shared Task 3. We approach the given task of event causality detection by proposing a self-training pipeline that follows a teacher-student classifier method. More specifically, we initially train a teacher model on the true, original task data, and use that teacher model to self-label data to be used in the training of a separate student model for the final task prediction. We test how restricting the number of positive or negative self-labeled examples in the self-training process affects classification performance. Our final results show that using self-training produces a comprehensive performance improvement across all models and self-labeled training sets tested within the task of event causality sequence classification. On top of that, we find that self-training performance did not diminish even when restricting either positive/negative examples used in training. Our code is be publicly available at https://github.com/Gzhang-umich/1CademyTeamOfCASE.Comment: Paper from CASE workshop at EMNLP 202

Measurement of the vertical atmospheric density profile from the X-ray Earth occultation of the Crab Nebula with Insight-HXMT

In this paper, the X-ray Earth occultation (XEO) of the Crab Nebula is investigated by using the Hard X-ray Modulation Telescope (Insight-HXMT). The pointing observation data on the 30th September, 2018 recorded by the Low Energy X-ray telescope (LE) of Insight-HXMT are selected and analyzed. The extinction lightcurves and spectra during the X-ray Earth occultation process are extracted. A forward model for the XEO lightcurve is established and the theoretical observational signal for lightcurve is predicted. The atmospheric density model is built with a scale factor to the commonly used MSIS density profile within a certain altitude range. A Bayesian data analysis method is developed for the XEO lightcurve modeling and the atmospheric density retrieval. The posterior probability distribution of the model parameters is derived through the Markov Chain Monte Carlo (MCMC) algorithm with the NRLMSISE-00 model and the NRLMSIS 2.0 model as basis functions and the best-fit density profiles are retrieved respectively. It is found that in the altitude range of 105--200 km, the retrieved density profile is 88.8% of the density of NRLMSISE-00 and 109.7% of the density of NRLMSIS 2.0 by fitting the lightcurve in the energy range of 1.0--2.5 keV based on XEOS method. In the altitude range of 95--125 km, the retrieved density profile is 81.0% of the density of NRLMSISE-00 and 92.3% of the density of NRLMSIS 2.0 by fitting the lightcurve in the energy range of 2.5--6.0 keV based on XEOS method. In the altitude range of 85--110 km, the retrieved density profile is 87.7% of the density of NRLMSISE-00 and 101.4% of the density of NRLMSIS 2.0 by fitting the lightcurve in the energy range of 6.0--10.0 keV based on XEOS method. This study demonstrates that the XEOS from the X-ray astronomical satellite Insight-HXMT can provide an approach for the study of the upper atmosphere.Comment: 31 pages, 15 figures, 5 tables, accepted for publication in Atmospheric Measurement Technique

Cancer-targeted and intracellular delivery of Bcl-2-converting peptide with functional macroporous silica nanoparticles for biosafe treatment

Abstract(#br)Therapeutic peptide, NuBCP-9 (N9) as a Bcl-2 functional converter, has been demonstrated to have the remarkable anticancer efficiency in Bcl-2-abundant cancer. However, it faced technical challenges in clinical use, such as the low bioavailability, the easily-destroyed bio-stability, and the insusceptibility to cellular interior. With the potential of mesoporous silica nanoparticles (MSNs) as the promising delivery vehicle of therapeutic macromolecules, we developed a kind of MSNs with the surface coating of folic acid (FA) for cancer cell targeting and with the macropore loading of N9 peptide for cancer therapy. Our results showed that the functional MSNs had the relatively greater biosafety than the naked MSNs in zebrafish models, leading to less than 30% embryo of death at 200 μg/ml, which could further specifically target the folate receptor (FR)-overexpressed cervical cancer HeLa cells instead of FR-negative normal embryonic kidney HEK 293T cells in a FA-competitive manner. N9 peptide with the delivery of functional MSNs could be internalized by HeLa cells, and co-localized with mitochondria in a Bcl-2-dependent manner. Moreover, N9 peptide delivered by FA-modified MSNs displayed the excellent anticancer efficiency with great selectivity, inducing approximately 52% HeLa cells into apoptosis. In summary, our results illustrated the potential of functional MSNs with large pore size as an efficient nanocarrier for the intracellular delivery of peptide drugs with targeting proteins to realize cancer therapy