The High Energy X-ray telescope (HE) on-board the Hard X-ray Modulation Telescope (Insight-HXMT) can serve as a wide Field of View (FOV) gamma-ray monitor with high time resolution (μs) and large effective area (up to thousands cm2). We developed a pipeline to search for Gamma-Ray Bursts (GRBs), using the traditional signal-to-noise ratio (SNR) method for blind search and the coherent search method for targeted search. By taking into account the location and spectrum of the burst and the detector response, the targeted coherent search is more powerful to unveil weak and sub-threshold bursts, especially those in temporal coincidence with Gravitational Wave (GW) events. Based on the original method in literature, we further improved the coherent search to filter out false triggers caused by spikes in light curves, which are commonly seen in gamma-ray instruments (e.g. Fermi/GBM, POLAR). We show that our improved targeted coherent search method could eliminate almost all false triggers caused by spikes. Based on the first two years of Insight-HXMT/HE data, our targeted search recovered 40 GRBs, which were detected by either Swift/BAT or Fermi/GBM but too weak to be found in our blind search. With this coherent search pipeline, the GRB detection sensitivity of Insight-HXMT/HE is increased to about 1.5E-08 erg cm−2 (200 keV–3 MeV). We also used this targeted coherent method to search Insight-HXMT/HE data for electromagnetic (EM) counterparts of LIGO-Virgo GW events (including O2 and O3a runs). However, we did not find any significant burst associated with GW events.
We report on the Insight-HXMT observations of the new black hole X-ray binary MAXI J1820+070 during its 2018 outburst. Detailed spectral analysis via the continuum fitting method shows an evolution of the inferred spin during its high soft sate. Moreover, the hardness ratio, the non-thermal luminosity and the reflection fraction also undergo an evolution, exactly coincident to the period when the inferred spin transition takes place. The unphysical evolution of the spin is attributed to the evolution of the inner disc, which is caused by the collapse of a hot corona due to condensation mechanism or may be related to the deceleration of a jet-like corona. The studies of the inner disc radius and the relation between the disc luminosity and the inner disc radius suggest that, only at a particular epoch, did the inner edge of the disc reach the innermost stable circular orbit and the spin measurement is reliable. We then constrain the spin of MAXI J1820+070 to be $a_*=0.2^{+0.2}_{-0.3}$. Such a slowly spinning black hole possessing a strong jet suggests that its jet activity is driven mainly by the accretion disc rather than by the black hole spin.
We studied the 2018 outburst of the black hole transient H 1743−322 with a series of Insight-HXMT, NICER and NuSTAR observations, covering the 1–120 keV band. With our broad-band X-ray spectral modelling, we confirm that the source remained in the low/hard state throughout the month-long outburst, although it became marginally softer at peak flux. We detected Type-C Quasi-periodic Oscillations (QPOs) and followed the evolution of their properties. The QPO frequency increased from ∼0.1 to ∼0.4 Hz during the rising phase of the outburst and decreased again in the decline. Continuum X-ray flux, power-law photon index, QPO frequency, and QPO root-mean-square amplitude were positively correlated. The QPO amplitude was slightly higher in the soft X-ray band (typical values of 12–16 per cent, compared with 8–10 per cent in the hard band). Our spectral-timing results shed light on the initial rising phase in the low/hard state, which has rarely been monitored with such high cadence, time resolution and broad-band coverage. Combining spectral and timing properties, we find that “failed” (hard state only) and “successful” outbursts follow the same initial evolutionary track, although the former class of outburst never reaches the threshold for a transition to softer (thermally dominated) accretion regimes.
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.
BackgroundRecessive SZT2 variants are reported to be associated with developmental and epileptic encephalopathy 18 (DEE-18) and occasionally neurodevelopment abnormalities (NDD) without seizures. This study aims to explore the phenotypic spectrum of SZT2 and the genotype-phenotype correlation.MethodsTrios-based whole-exome sequencing was performed in patients with epilepsy. Previously reported SZT2 mutations were systematically reviewed to analyze the genotype-phenotype correlations.ResultsSZT2 variants were identified in six unrelated cases with heterogeneous epilepsy, including one de novo null variant and five pairs of biallelic variants. These variants had no or low frequencies in controls. All missense variants were predicted to alter the hydrogen bonds with surrounding residues and/or protein stability. The three patients with null variants exhibited DEE. The patients with biallelic null mutations presented severe DEE featured by frequent spasms/tonic seizures and diffuse cortical dysplasia/periventricular nodular heterotopia. The three patients with biallelic missense variants presented mild partial epilepsy with favorable outcomes. Analysis of previously reported cases revealed that patients with biallelic null mutations presented significantly higher frequency of refractory seizures and earlier onset age of seizure than those with biallelic non-null mutations or with biallelic mutations containing one null variant.SignificanceThis study suggested that SZT2 variants were potentially associated with partial epilepsy with favorable outcomes without NDD, expanding the phenotypic spectrum of SZT2. The genotype-phenotype correlation helps in understanding the underlying mechanism of phenotypic variation.
We report the evolution of the X-ray pulsations of EXO 2030+375 during its 2021 outburst using the observations from Insight-HXMT. Based on the accretion torque model, we study the correlation between the spin frequency derivatives and the luminosity. Pulsations can be detected in the energy band of 1–160 keV. The pulse profile evolves significantly with luminosity during the outburst, leading to that the whole outburst can be divided into several parts with different characteristics. The evolution of the pulse profile reveals the transition between the super-critical (fan-beam dominated) and the sub-critical accretion (pencil-beam dominated) mode. From the accretion torque model and the critical luminosity model, based on a distance of 7.1 kpc, the inferred magnetic fields are (0.41 − 0.74) × 1012 G and (3.48 − 3.96) × 1012 G, respectively, or based on a distance of 3.6 kpc, the estimated magnetic fields are (2.4 − 4.3) × 1013 G and (0.98 − 1.11) × 1012 G, respectively. Two different sets of magnetic fields both support the presence of multipole magnetic fields of the NS.
MAXI J1816–195 is a newly discovered accreting millisecond X-ray pulsar that went outburst in June 2022. Through timing analysis with NICER and NuSTAR observations, we find a transient modulation at ~2.5 Hz during the decay period of MAXI J1816–195. The modulation is strongly correlated with a spectral hardening, and its fractional rms amplitude increases with energy. These results suggest that the modulation is likely to be produced in an unstable corona. In addition, the presence of the modulation during thermonuclear bursts indicates that it may originate from a disk-corona where the optical depth is likely the main factor affecting the modulation, rather than temperature. Moreover, we find significant reflection features in the spectra observed simultaneously by NICER and NuSTAR, including a relativistically broadened Fe-K line around 6–7 keV, and a Compton hump in the 10–30 keV energy band. The radius of the inner disc is constrained to be Rin = (1.04–1.23) RISCO based on reflection modeling of the broadband spectra. Assuming that the inner disc is truncated at the magnetosphere radius, we estimate that the magnetic field strength is $\le 4.67 \times 10^{8}\, \rm G$.
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