arXiv subjects

Y. G. Li

Publications and source records attributed to Y. G. Li.

32 records · Page 2Linked to original sources

arXiv2020

Joint Analysis of Energy and RMS Spectra from MAXI J1535-571 with Insight-HXMT

A new black hole X-ray binary (BHXRB) MAXI J1535-571 was discovered by MAXI during its outburst in 2017. Using observations taken by the first Chinese X-ray satellite, the Hard X-ray Modulation Telescope (dubbed as Insight-HXMT), we perform a joint spectral analysis (2-150 keV) in both energy and time domains. The energy spectra provide the essential input for probing the intrinsic Quasi-Periodic Oscillation (QPO) fractional rms spectra (FRS). Our results show that during the intermediate state, the energy spectra are in general consistent with those reported by Swift/XRT and NuSTAR. However, the QPO FRS become harder and the FRS residuals may suggest the presence of either an additional power-law component in the energy spectrum or a turn-over in the intrinsic QPO FRS at high energies.

astro-ph.HE↗

arXiv2019

Diagnostic of the spectral properties of Aquila X-1 by Insight-HXMT snapshots during the early propeller phase

We study the 2018 outburst of Aql X-1 via the monitor of all sky X-ray image (MAXI) data. We show that the outburst starting in February 2018 is a member of short-low class in the frame of outburst duration and the peak count rate although the outburst morphology is slightly different from the other fast-rise-exponential-decay (FRED) type outbursts with a milder rising stage. We study the partial accretion in the weak propeller stage of Aql X-1 via the MAXI data of the 2018 outburst. We report on the spectral analysis of 3 observations of Aquila X-1 obtained by Insight - hard X-ray modulation telescope (Insight-HXMT) during the late decay stage of the 2018 outburst. We discuss that the data taken by Insight-HXMT is just after the transition to the weak propeller stage. Our analysis shows the necessity of a comptonization component to take into account the existence of an electron cloud resulting photons partly up-scattered.

astro-ph.HE↗

arXiv2019

Insight-HXMT observation on 4U~1608--52: evolving spectral properties of a bright type-I X-ray burst

The evidences for the influence of thermonuclear (type-I) X-ray bursts upon the surrounding environments in neutron star low-mass X-ray binaries (LMXB) were detected previously via spectral and timing analyses. Benefitting from a broad energy coverage of Insight-HXMT, we analyze one photospheric radius expansion (PRE) burst, and find an emission excess at soft X-rays. Our spectral analysis shows that, such an excess is not likely relevant to the disk reflection induced by the burst emission and can be attributed to an enhanced pre-burst/persistent emission. We find that the burst and enhanced persistent emissions sum up to exceed Eddington luminosity by $\sim$ 40 percentages. We speculate that the enhanced emission is from a region beyond the PRE radius, or through the Comptonization of the corona.

astro-ph.HE↗

arXiv2019

$Insight$-HXMT study of the timing properties of Sco X-1

We present a detailed timing study of the brightest persistent X-ray source Sco X-1 using the data collected by the Hard X-ray Modulation Telescope ($Insight$-HXMT) from July 2017 to August 2018. A complete $Z$-track hardness-intensity diagram (HID) is obtained. The normal branch oscillations (NBOs) at $\sim$ 6 Hz in the lower part of the normal branch (NB) and the flare branch oscillations (FBOs) at $\sim$ 16 Hz in the beginning part of the flaring branch (FB) are found in observations with the Low Energy X-ray Telescope (LE) and the Medium Energy X-ray Telescope (ME) of $Insight$-HXMT, while the horizontal branch oscillations (HBOs) at $\sim$ 40 Hz and the kilohertz quasi-periodic oscillations (kHz QPOs) at $\sim$ 800 Hz are found simultaneously up to 60 keV for the first time on the horizontal branch (HB) by the High Energy X-ray Telescope (HE) and ME. We find that for all types of the observed QPOs, the centroid frequencies are independent of energy, while the root mean square (rms) increases with energy; the centroid frequencies of both the HBOs and kHz QPOs increase along the $Z$-track from the top to the bottom of the HB; and the NBOs show soft phase lags increasing with energy. A continuous QPO transition from the FB to NB in $\sim$ 200 s are also detected. Our results indicate that the non-thermal emission is the origin of all types of QPOs, the innermost region of the accretion disk is non-thermal in nature, and the corona is nonhomogeneous geometrically.

astro-ph.HE↗

arXiv2019

Insight-HXMT observations of 4U~1636-536: Corona cooling revealed with single short type-I X-ray burst

Corona cooling was detected previously from stacking a series of short type-I bursts occurred during the low/had state of atoll outburst. Type-I bursts are hence regarded as sharp probe to our better understanding on the basic property of the corona. The launch of the first Chinese X-ray satellite Insight-HXMT has large detection area at hard X-rays which provide almost unique chance to move further in this research field. We report the first detection of the corona cooling by Insight-HXMT from single short type-I burst showing up during {\bf flare} of 4U 1636-536. This type-I X-ray burst has a duration of $\sim$13 seconds and hard X-ray shortage is detected with significance 6.2~$σ$ in 40-70 keV. A cross-correlation analysis between the lightcurves of soft and hard X-ray band, shows that the corona shortage lag the burst emission by 1.6 $\pm$1.2~s. These results are consistent with those derived previously from stacking a large amount of bursts detected by RXTE/PCA within a series of {\bf flares} of 4U 1636-536. Moreover, the broad bandwidth of Insight-HXMT allows as well for the first time to infer the burst influence upon the continuum spectrum via performing the spectral fitting of the burst, which ends up with the finding that hard X-ray shortage appears at around 40 keV in the continuum spectrum. These results suggest that the evolution of the corona along with the outburst{\bf /flare} of NS XRB may be traced via looking into a series of embedded type-I bursts by using Insight-HXMT.

astro-ph.HE↗

arXiv2019

The High Energy X-ray telescope (HE) onboard the Insight-HXMT astronomy satellite

The Insight-Hard X-ray Modulation Telescope (Insight-HXMT) is a broad band X-ray and gamma-ray (1-3000 keV) astronomy satellite. The High Energy X-ray telescope (HE) is one of its three main telescopes. The main detector plane of HE is composed of 18 NaI(Tl)/CsI(Na) phoswich detectors, where NaI(Tl) serves as primary detector to measure ~ 20-250 keV photons incident from the field of view (FOV) defined by the collimators, and CsI(Na) is used as an active shield detector to NaI(Tl) by pulse shape discrimination. CsI(Na) is also used as an omnidirectional gamma-ray monitor. The HE collimators have a diverse FOV: 1.1°x 5.7° (15 units), 5.7°x 5.7° (2 units) and blocked (1 unit), thus the combined FOV of HE is about 5.7°x 5.7°. Each HE detector has a diameter of 190 mm, resulting in the total geometrical area of about 5100 cm_2. The energy resolution is ~15% at 60 keV. The timing accuracy is better than 10 μs and dead-time for each detector is less than 10 μs. HE is devoted to observe the spectra and temporal variability of X-ray sources in the 20-250 keV band either by pointing observations for known sources or scanning observations to unveil new sources, and to monitor the gamma-ray sky in 0.2-3 MeV. This paper presents the design and performance of the HE instruments. Results of the on-ground calibration experiments are also reported.

astro-ph.IM↗

arXiv2019

Timing analysis of 2S 1417-624 observed with NICER and Insight-HXMT

We present a study of timing properties of the accreting pulsar 2S 1417-624 observed during its 2018 outburst, based on Swift/BAT, Fermi/GBM, Insight-HXMT and NICER observations. We report a dramatic change of the pulse profiles with luminosity. The morphology of the profile in the range 0.2-10.0keV switches from double to triple peaks at $\sim2.5$ $\rm \times 10^{37}{\it D}_{10}^2\ erg\ s^{-1}$ and from triple to quadruple peaks at $\sim7$ $\rm \times 10^{37}{\it D}_{10}^2\ erg\ s^{-1}$. The profile at high energies (25-100keV) shows significant evolutions as well. We explain this phenomenon according to existing theoretical models. We argue that the first change is related to the transition from the sub to the super-critical accretion regime, while the second to the transition of the accretion disc from the gas-dominated to the radiation pressure-dominated state. Considering the spin-up as well due to the accretion torque, this interpretation allows to estimate the magnetic field self-consistently at $\sim7\times 10^{12}$G.

astro-ph.HE↗

arXiv2019

Constant cyclotron line energy in Hercules X-1 -- Joint Insight-HXMT and NuSTAR observations

The long-term evolution of the centroid energy of the CRSF in Her X-1 is still a mystery. We report a new measurement from a campaign between {\sl Insight}-HXMT and {\sl NuSTAR} performed in February 2018. Generally, the two satellites show well consistent results of timing and spectral properties. The joint spectral analysis confirms that the previously observed long decay phase has ended, and that the line energy instead keeps constant around 37.5 keV after flux correction.

astro-ph.HE↗

arXiv2019

Hot disk of the Swift J0243.6+6124 revealed by Insight-HXMT

We report on analysis of observations of the bright transient X-ray pulsar \src obtained during its 2017-2018 giant outburst with Insight-HXMT, \emph{NuSTAR}, and \textit{Swift} observatories. We focus on the discovery of a sharp state transition of the timing and spectral properties of the source at super-Eddington accretion rates, which we associate with the transition of the accretion disk to a radiation pressure dominated (RPD) state, the first ever directly observed for magnetized neutron star. This transition occurs at slightly higher luminosity compared to already reported transition of the source from sub- to super-critical accretion regime associate with onset of an accretion column. We argue that this scenario can only be realized for comparatively weakly magnetized neutron star, not dissimilar to other ultra-luminous X-ray pulsars (ULPs), which accrete at similar rates. Further evidence for this conclusion is provided by the non-detection of the transition to the propeller state in quiescence which strongly implies compact magnetosphere and thus rules out magnetar-like fields.

astro-ph.HE↗

arXiv2019

In-orbit demonstration of X-ray pulsar navigation with the Insight-HXMT satellite

In this work, we report the in-orbit demonstration of X-ray pulsar navigation with Insight-Hard X-ray Modulation Telescope (Insight-HXMT), which was launched on Jun. 15th, 2017. The new pulsar navigation method 'Significance Enhancement of Pulse-profile with Orbit-dynamics' (SEPO) is adopted to determine the orbit with observations of only one pulsar. In this test, the Crab pulsar is chosen and observed by Insight-HXMT from Aug. 31th to Sept. 5th in 2017. Using the 5-day-long observation data, the orbit of Insight-HXMT is determined successfully with the three telescopes onboard - High Energy X-ray Telescope (HE), Medium Energy X-ray Telescope (ME) and Low Energy X-ray Telescope (LE) - respectively. Combining all the data, the position and velocity of the Insight-HXMT are pinpointed to within 10 km (3 sigma) and 10 m/s (3 sigma), respectively.

astro-ph.IM↗

arXiv2018

A low-energy sensitive compact gamma-ray detector based on LaBr3 and SiPM for GECAM

The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) project is the planned Chinese space telescope for detecting the X and gamma-ray counterpart. It consists of two micro-satellites in low earth orbit with the advantages of instantaneous full-sky coverage, low energy threshold down to 6 keV and can be achieved within a short period and small budget. Due to the limitation of size, weight and power consumption of micro-satellites, silicon photomultipliers (SiPMs) are used to replace the photomultiplier tubes (PMTs) to assemble a novel gamma-ray detector. A prototype of a SiPM array with LaBr3 crystal is built and tested, and it shows a high detection efficiency (70% at 5.9 keV) and an acceptable uniformity. The low-energy X-ray of 5.9 keV can be detected by a simply readout circuit, and the energy resolution is 6.5% (FWHM) at 662 keV. The design and performance of the detector are discussed in detail in this paper.

astro-ph.IM↗

arXiv2018

Insight-HXMT observations of the New Black Hole Candidate MAXI J1535-571: timing analysis

We present the X-ray timing results of the new black hole candidate (BHC) MAXI J1535-571 during its 2017 outburst from Hard X-ray Modulation Telescope (\emph{Insight}-HXMT) observations taken from 2017 September 6 to 23. Following the definitions given by \citet{Belloni2010}, we find that the source exhibits state transitions from Low/Hard state (LHS) to Hard Intermediate state (HIMS) and eventually to Soft Intermediate state (SIMS). Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of \emph{Insight}-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV which is rarely explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lags) and strongly correlated with the centroid frequency. By assuming a geometrical origin of type-C QPOs, the source is consistent with being a high inclination system.

astro-ph.HE↗

arXiv2016

Alfvenic Ion Temperature Gradient Activities in a Weak Magnetic Shear Plasma

We report the first experimental evidence of Alfvenic ion temperature gradient (AITG) modes in HL-2A Ohmic plasmas. A group of oscillations with $f=15-40$ kHz and $n=3-6$ is detected by various diagnostics in high-density Ohmic regimes. They appear in the plasmas with peaked density profiles and weak magnetic shear, which indicates that corresponding instabilities are excited by pressure gradients. The time trace of the fluctuation spectrogram can be either a frequency staircase, with different modes excited at different times or multiple modes may simultaneously coexist. Theoretical analyses by the extended generalized fishbone-like dispersion relation (GFLDR-E) reveal that mode frequencies scale with ion diamagnetic drift frequency and $η_i$, and they lie in KBM-AITG-BAE frequency ranges. AITG modes are most unstable when the magnetic shear is small in low pressure gradient regions. Numerical solutions of the AITG/KBM equation also illuminate why AITG modes can be unstable for weak shear and low pressure gradients. It is worth emphasizing that these instabilities may be linked to the internal transport barrier (ITB) and H-mode pedestal physics for weak magnetic shear.

physics.plasm-ph↗

arXiv2010

Ab initio simulations of the kinetic properties of the hydrogen monomer on graphene

The understanding of the kinetic properties of hydrogen (isotopes) adatoms on graphene is important in many fields. The kinetic properties of hydrogen-isotope (H, D and T) monomers were simulated using a composite method consisting of density functional theory, density functional perturbation theory and harmonic transition state theory. The kinetic changes of the magnetic property and the aromatic $π$ bond of the hydrogenated graphene during the desorption and diffusion of the hydrogen monomer was discussed. The vibrational zero-point energy corrections in the activation energies were found to be significant, ranging from 0.072 to 0.205 eV. The results obtained from quantum-mechanically modified harmonic transition state theory were compared with the ones obtained from classical-limit harmonic transition state theory over a wide temperature range. The phonon spectra of hydrogenated graphene were used to closely explain the (reversed) isotope effects in the prefactor, activation energy and jump frequency of the hydrogen monomer. The kinetic properties of the hydrogen-isotope monomers were simulated under conditions of annealing for 10 minutes and of heating at a constant rate (1.0 K/s). The isotope effect was observed; that is, a hydrogen monomer of lower mass is desorbed and diffuses more easily (with lower activation energies). The results presented herein are very similar to other reported experimental observations. This study of the kinetic properties of the hydrogen monomer and many other involved implicit mechanisms provides a better understanding of the interaction between hydrogen and graphene.

cond-mat.mtrl-sci↗