arXiv subjects

Y. Huang

Publications and source records attributed to Y. Huang.

At least 145 records · Page 8Linked to original sources

arXiv2021

Broadband variability study of MAXI J1631-479 in its Hard-Intermediate State observed with Insight-HXMT

We report the energy-resolved broadband timing analysis of the black hole X-ray transient MAXI J1631-479 during its 2019 outburst from February 11 to April 9, using data from the Insight-Hard X-ray Modulation Telescope (Insight-HXMT), which caught the source from its hard intermediate state to the soft state. Thanks to the large effective area of Insight-HXMT at high energies, we are able to present the energy dependence of fast variability up to ~100 keV. Type-C quasi-periodic oscillations (QPOs) with frequency varying between 4.9 Hz and 6.5 Hz are observed in the 1-100 keV energy band. While the QPO fractional rms increases with photon energy from 1 keV to ~10 keV and remains more or less constant from ~10 keV to ~100 keV, the rms of the flat-top noise first increases from 1 keV to ~8 keV then drops to less than 0.1% above ~30 keV. We suggest that the disappearance of the broadband variability above 30 keV could be caused by the non-thermal acceleration in the Comptonizing plasma. At the same time, the QPOs could be produced by the precession of either a small-scale jet or a hot inner flow model.

astro-ph.HE↗

arXiv2021

Study on the energy limits of kHz QPOs in Sco X-1 with $RXTE$ and $Insight$-HXMT observations

We present a detailed spectral-timing analysis of the Kilohertz quasi-periodic oscillations (kHz QPOs) in Sco X-1 using the data of Rossi X-ray Timing Explorer ($RXTE$) and the Hard X-ray Modulation Telescope ($Insight$-HXMT). The energy band with detectable kHz QPOs is studied for the first time: on the horizontal branch, it is $\sim$ 6.89--24.01 keV and $\sim$ 8.68--21.78 keV for the upper and lower kHz QPOs detected by $RXTE$, and $\sim$ 9--27.5 keV for the upper kHz QPOs by $Insight$-HXMT; on the lower normal branch, the energy band is narrower. The fractional root mean square (rms) of the kHz QPOs increases with energy at lower energy, reaches a plateau at about 16 keV and 20 keV for the lower and upper peaks, and then levels off though with a large uncertainty. The simulation of the deadtime effect of $RXTE$/PCA shows that the deadtime does not affect much the search of the kHz QPOs but makes the rms amplitude underestimated. No significant QPO is detected below $\sim$ 6 keV as shown by the $RXTE$ data, implying that the kHz QPOs do not originate from the black body emission of the accretion disk and neutron star surface. In addition, with the combined analysis of the energy spectra and the absolute rms spectra of kHz QPOs, we suggest that the kHz QPOs in Sco X-1 originate from the Comptonization of the inner part of the transition layer, where the rotation sets the frequency and the inward bulk motion makes the spectrum harder.

astro-ph.HE↗

arXiv2021

HXMT Identification of a non-thermal X-ray burst from SGR J1935+2154 and with FRB 200428

Fast radio bursts (FRBs) are short pulses observed in radio band from cosmological distances. One class of models invoke soft gamma-ray repeaters (SGRs), or magnetars, as the sources of FRBs. Some radio pulses have been observed from some magnetars, however, no FRB-like events had been detected in association any magnetar burst, including one giant flare. Recently, a pair of FRB-like bursts (FRB 200428 hereafter) separated by milliseconds (ms) were detected from the general direction of the Galactic magnetar SGR J1935+2154. Here we report the detection of a non-thermal X-ray burst in the 1-250 keV energy band with the Insight-HXMT satellite, which we identify as emitted from SGR J1935+2154. The burst showed two hard peaks with a separation of 34 ms, broadly consistent with that of the two bursts in FRB 200428. The delay time between the double radio and X-ray peaks is about 8.57 s, fully consistent with the dispersion delay of FRB 200428. We thus identify the non-thermal X-ray burst is associated with FRB 200428 whose high energy counterpart is the two hard peaks in X-ray. Our results suggest that the non-thermal X-ray burst and FRB 200428 share the same physical origin in an explosive event from SGR J1935+2154.

astro-ph.HE↗

arXiv2021

Physical origin of the nonphysical spin evolution of MAXI J1820+070

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.

astro-ph.HE↗

arXiv2021

Local Stellar Kinematics and Oort Constants from the LAMOST A-type Stars

We estimate the solar peculiar velocities and Oort constants using a sample of 5,627 A-type stars with $d<0.6\,\rm kpc$ and $|z|<0.1\,\rm kpc$, selected from the LAMOST surveys. The radial and tangential velocities of these A-type stars are fitted by using a non-axisymmetric model. The best-fitting result yields the solar peculiar velocities $(U_\odot,V_\odot,W_\odot)=(11.69\pm0.68, 10.16\pm0.51, 7.67\pm0.10)\,\rm km\,s^{-1}$ and Oort constants $A=16.31\pm0.89\,\rm km\,s^{-1}\,kpc^{-1}$, $B=-11.99\pm0.79\,\rm km\,s^{-1}\,kpc^{-1}$, $C=-3.10\pm0.48\,\rm km\,s^{-1}\,kpc^{-1}$, $K=-1.25\pm1.04\,\rm km\,s^{-1}\,kpc^{-1}$, respectively. $|K+C|>4\,\rm km\,s^{-1}\,kpc^{-1}$ means that there is a radial velocity gradient in the extended local disk, implying the local disk is in a non-asymmetric potential. Using the derived Oort constants, we derive the local angular velocity $Ω\,{\approx}\,A-B=28.30\pm1.19\,\rm km\,s^{-1}\,kpc^{-1}$. By using A-type star sample of different volumes, we further try to evaluate the impacts of the ridge pattern in $R$-$V_ϕ$ plane on constraining the solar motions and Oort constants. As the volume becomes larger toward the anti-center direction, the values of $A$ and $B$ become larger (implying a steeper slope of the local rotation curve) and the value of $V_\odot$ becomes smaller probably caused by the ridge structure and its signal increasing with distance.

astro-ph.GA↗

arXiv2021

Broad-band X-ray spectra and timing of the accretion-powered millisecond pulsar Swift J1756.9$-$2508 during its 2018 and 2019 outbursts

The accreting millisecond X-ray pulsar Swift J1756.9$-$2508 went into outburst in April 2018 and June 2019, 8.7 yr after the previous activity period. We investigated the temporal, timing and spectral properties of these two outbursts using data from NICER, XMM-Newton, NuSTAR, INTEGRAL, Swift and Insight-HXMT. The two outbursts exhibited similar broad-band spectra and X-ray pulse profiles. For the first time, we report the detection of the pulsed emission up to $\sim100$ keV observed by Insight-HXMT during the 2018 outburst. We also found the pulsation up to $\sim60$ keV observed by NICER and NuSTAR during the 2019 outburst. We performed a coherent timing analysis combining the data from two outbursts. The binary system is well described by a constant orbital period over a time span of $\sim12$ years. The time-averaged broad-band spectra are well fitted by an absorbed thermal Comptonization model in a slab geometry with the electron temperature $kT_{\rm e}=40$-50 keV, Thomson optical depth $τ\sim 1.3$, blackbody seed photon temperature $kT_{\rm bb,seed}\sim $0.7-0.8 keV and hydrogen column density of $N_{\rm H}\sim 4.2\times10^{22}$ cm$^{-2}$. We searched the available data for type-I (thermonuclear) X-ray bursts, but found none, which is unsurprising given the estimated low peak accretion rate ($\approx0.05$ of the Eddington rate) and generally low expected burst rates for hydrogen-poor fuel. Based on the history of four outbursts to date, we estimate the long-term average accretion rate at roughly $5\times10^{-12}\ M_\odot\,{\rm yr}^{-1}$ for an assumed distance of 8 kpc. The expected mass transfer rate driven by gravitational radiation in the binary implies the source can be no closer than 4 kpc.

astro-ph.HE↗

arXiv2021

Accretion Torque Reversals in GRO J1008-57 Revealed by Insight-HXMT

GRO J1008-57, as a Be/X-ray transient pulsar, is considered to have the highest magnetic field in known neutron star X-ray binary systems. Observational data of the X-ray outbursts in GRO J1008-57 from 2017 to 2020 were collected by the Insight-HXMT satellite. In this work, the spin period of the neutron star in GRO J1008-57 was determined to be about 93.28 seconds in August 2017, 93.22 seconds in February 2018, 93.25 seconds in June 2019 and 93.14 seconds in June 2020. GRO J1008-57 evolved in the spin-up process with a mean rate of $-(2.10\pm 0.05)\times$10$^{-4}$ s/d from 2009 -- 2018, and turned into a spin down process with a rate of $(6.7\pm 0.6)\times$10$^{-5}$ s/d from Feb 2018 to June 2019. During the type II outburst of 2020, GRO J1008-57 had the spin-up torque again. During the torque reversals, the pulse profiles and continuum X-ray spectra did not change significantly, and the cyclotron resonant scattering feature around 80 keV was only detected during the outbursts in 2017 and 2020. Based on the observed mean spin-up rate, we estimated the inner accretion disk radius in GRO J1008-57 (about 1 - 2 times of the Alfvén radius) by comparing different accretion torque models of magnetic neutron stars. During the spin-down process, the magnetic torque should dominate over the matter accreting inflow torque, and we constrained the surface dipole magnetic field $B\geq 6\times 10^{12}$ G for the neutron star in GRO J1008-57, which is consistent with the magnetic field strength obtained by cyclotron line centroid energy.

astro-ph.HE↗

arXiv2021

QPOs and Orbital elements of X-ray binary 4U 0115+63 during the 2017 outburst observed by Insight-HXMT

In this paper, we presented a detailed timing analysis of a prominent outburst of 4U 0115+63 detected by \textit{Insight}-HXMT in 2017 August. The spin period of the neutron star was determined to be $3.61398\pm 0.00002$ s at MJD 57978. We measured the period variability and extract the orbital elements of the binary system. The angle of periastron evolved with a rate of $0.048\pm0.003$ $yr^{-1}$. The light curves are folded to sketch the pulse profiles in different energy ranges. A multi-peak structure in 1-10 keV is clearly illustrated. We introduced wavelet analysis into our data analysis procedures to study QPO signals and perform a detailed wavelet analysis in many different energy ranges. Through the wavelet spectra, we report the discovery of a QPO at the frequency $\sim 10$ mHz. In addition, the X-ray light curves showed multiple QPOs in the period of $\sim 16-32 $ s and $\sim 67- 200 $ s. We found that the $\sim100$ s QPO was significant in most of the observations and energies. There exist positive relations between X-ray luminosity and their Q-factors and S-factors, while the QPO periods have no correlation with X-ray luminosity. In wavelet phase maps, we found that the pulse phase of $\sim 67- 200 $ s QPO drifting frequently while the $\sim 16-32 $ s QPO scarcely drifting. The dissipation of oscillations from high energy to low energy was also observed. These features of QPOs in 4U 0115+63 provide new challenge to our understanding of their physical origins.

astro-ph.HE↗

arXiv2021

Overview of KAGRA: Calibration, detector characterization, physical environmental monitors, and the geophysics interferometer

KAGRA is a newly built gravitational wave observatory, a laser interferometer with a 3 km arm length, located in Kamioka, Gifu, Japan. In this series of articles, we present an overview of the baseline KAGRA, for which we finished installing the designed configuration in 2019. This article describes the method of calibration (CAL) used for reconstructing gravitational wave signals from the detector outputs, as well as the characterization of the detector (DET). We also review the physical environmental monitors (PEM) system and the geophysics interferometer (GIF). Both are used for characterizing and evaluating the data quality of the gravitational wave channel. They play important roles in utilizing the detector output for gravitational wave searches. These characterization investigations will be even more important in the near future, once gravitational wave detection has been achieved, and in using KAGRA in the gravitational wave astronomy era.

gr-qc↗

arXiv2020

A variable ionized disk wind in the black-hole candidate EXO 1846-031

After 34 years, the black-hole candidate EXO 1846-031 went into outburst again in 2019. We investigate its spectral properties in the hard intermediate and the soft states with NuSTAR and Insight-HXMT. A reflection component has been detected in the two spectral states but possibly originating from different illumination spectra: in the intermediate state, the illuminating source is attributed to a hard coronal component, which has been commonly observed in other X-ray binaries, whereas in the soft state the reflection is probably produced by the disk self-irradiation. Both cases support EXO 1846-031 as a low inclination system of ~40 degrees. An absorption line is clearly detected at ~7.2 keV in the hard intermediate state, corresponding to a highly ionized disk wind (log ξ > 6.1) with a velocity up to 0.06c. Meanwhile, quasi-simultaneous radio emissions have been detected before and after the X-rays, implying the co-existence of disk winds and jets in this system. Additionally, the observed wind in this source is potentially driven by magnetic forces. The absorption line disappeared in the soft state and a narrow emission line appeared at ~6.7 keV on top of the reflection component, which may be evidence for disk winds, but data with the higher spectral resolution are required to examine this.

astro-ph.HE↗

arXiv2020

Insight-HXMT observations of Swift J0243.6+6124: the evolution of RMS pulse fractions at super-Eddington luminosity

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 $7.71\times10^{38}$~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.

astro-ph.HE↗

arXiv2020

X-ray reprocessing in accreting pulsar GX 301-2 observed with Insight-HXMT

We investigate the absorption and emission features in observations of GX 301-2 detected with Insight-HXMT/LE in 2017-2019. At different orbital phases, we found prominent Fe Kalpha, Kbeta and Ni Kalpha lines, as well as Compton shoulders and Fe K-shell absorption edges. These features are due to the X-ray reprocessing caused by the interaction between the radiation from the source and surrounding accretion material. According to the ratio of iron lines Kalpha and Kbeta, we infer the accretion material is in a low ionisation state. We find an orbital-dependent local absorption column density, which has a large value and strong variability around the periastron. We explain its variability as a result of inhomogeneities of the accretion environment and/or instabilities of accretion processes. In addition, the variable local column density is correlated with the equivalent width of the iron Kalpha lines throughout the orbit, which suggests that the accretion material near the neutron star is spherically distributed.

astro-ph.HE↗

arXiv2020

Insight-HXMT observations of a possible fast transition from jet to wind dominated state during a huge flare of GRS~1915+105

We present the analysis of the brightest flare that was recorded in the \emph{Insight}-HMXT data set, in a broad energy range (2$-$200 keV) from the microquasar GRS~1915+105 during an unusual low-luminosity state. This flare was detected by \emph{Insight}-HXMT among a series of flares during 2 June 2019 UTC 16:37:06 to 20:11:36, with a 2-200 keV luminosity of 3.4$-$7.27$\times10^{38}$ erg s$^{-1}$. Basing on the broad-band spectral analysis, we find that the flare spectrum shows different behaviors during bright and faint epochs. The spectrum of the flare can be fitted with a model dominated by a power-law component. Additional components show up in the bright epoch with a hard tail and in the faint epoch with an absorption line $\sim$ 6.78 keV. The reflection component of the latter is consistent with an inner disk radius $\sim$ 5 times larger than that of the former. These results on the giant flare during the "unusual" low-luminosity state of GRS~1915+105 may suggest that the source experiences a possible fast transition from a jet-dominated state to a wind-dominated state. We speculate that the evolving accretion disk and the large-scale magnetic field may play important roles in this peculiar huge flare.

astro-ph.HE↗

arXiv2020

The distances of 61 PGCCs in the Second Galactic Quadrant

Determining the distances to the Planck Galactic cold clumps (PGCCs) is crucial for the measurement of their physical parameters and the study of their Galactic distribution. Based on two large catalogues of stars with robust distances and reddening estimates from the literature, we have estimated accurate distances to 61 PGCCs in the second Galactic quadrant. For this purpose, we have selected stars along the sightlines overlapping with the cores of the sample clumps and fitted the reddening profiles with a simple reddening model. The typical uncertainties of the resultant distances of these PGCCs are less than 8 per cent. The new estimates differ significantly from the kinematic values, well known to suffer from large errors. With the new distances, we have updated the physical properties including the radii, masses and virial parameters of the cores of the PGCCs.

astro-ph.GA↗

arXiv2020

Three-Dimensional Distribution of the Interstellar Dust in the Milky Way

We present a three-dimensional (3D) extinction map of the southern sky. The map covers the SkyMapper Southern Survey (SMSS) area of $\sim$ 14,000 ${\rm deg^{2}}$ and has spatial resolutions between 6.9 and 27 arcmin. Based on the multi-band photometry of SMSS, the Two Micron All Sky Survey, the Wide-Field Infrared Survey Explorer Survey and the Gaia mission, we have estimated values of the $r$-band extinction for $\sim$ 19 million stars with the spectral energy distribution (SED) analysis. Together with the distances calculated from the Gaia data release 2 (DR2) parallaxes, we have constructed a three-dimensional extinction map of the southern sky. By combining our 3D extinction map with those from the literature, we present an all-sky 3D extinction map, and use it to explore the 3D distribution of the Galactic dust grains. We use two different models, one consisting a single disk and another of two disks, to fit the 3D distribution of the Galactic dust grains. The data is better fitted by a two-disk model, yielding smaller values of the Bayesian Information Criterion (BIC). The best fit model has scale heights of 73 and 225 pc for the "thin" and "thick" dust disks, respectively.

astro-ph.GA↗

arXiv2020

Prediction and understanding of soft proton contamination in XMM-Newton: a machine learning approach

One of the major and unfortunately unforeseen sources of background for the current generation of X-ray telescopes are few tens to hundreds of keV (soft) protons concentrated by the mirrors. One such telescope is the European Space Agency's (ESA) X-ray Multi-Mirror Mission (XMM-Newton). Its observing time lost due to background contamination is about 40\%. This loss of observing time affects all the major broad science goals of this observatory, ranging from cosmology to astrophysics of neutron stars and black holes. The soft proton background could dramatically impact future large X-ray missions such as the ESA planned Athena mission (http://www.the-athena-x-ray-observatory.eu/). Physical processes that trigger this background are still poorly understood. We use a Machine Learning (ML) approach to delineate related important parameters and to develop a model to predict the background contamination using 12 years of XMM observations. As predictors we use the location of satellite, solar and geomagnetic activity parameters. We revealed that the contamination is most strongly related to the distance in southern direction, $Z$, (XMM observations were in the southern hemisphere), the solar wind radial velocity and the location on the magnetospheric magnetic field lines. We derived simple empirical models for the first two individual predictors and an ML model which utilizes an ensemble of the predictors (Extra Trees Regressor) and gives better performance. Based on our analysis, future missions should minimize observations during times associated with high solar wind speed and avoid closed magnetic field lines, especially at the dusk flank region in the southern hemisphere.

astro-ph.IM↗

arXiv2020

Constraining the transient high-energy activity of FRB180916.J0158+65 with Insight-HXMT followup observations

A link between magnetars and fast radio burst (FRB) sources has finally been established. In this context, one of the open issues is whether/which sources of extra galactic FRBs exhibit X/gamma-ray outbursts and whether it is correlated with radio activity. We aim to constrain possible X/gamma-ray burst activity from one of the nearest extragalactic FRB sources currently known over a broad energy range, by looking for bursts over a range of timescales and energies that are compatible with being powerful flares from extragalactic magnetars. We followed up the as-yet nearest extragalactic FRB source at a mere 149 Mpc distance, the periodic repeater FRB180916.J0158+65, during the active phase on February 4-7, 2020, with the Insight-Hard X-ray Modulation Telescope (HXMT). Taking advantage of the combination of broad band, large effective area, and several independent detectors available, we searched for bursts over a set of timescales from 1 ms to 1.024 s with a sensitive algorithm, that had previously been characterised and optimised. Moreover, through simulations we studied the sensitivity of our technique in the released energy-duration phase space for a set of synthetic flares and assuming different energy spectra. We constrain the possible occurrence of flares in the 1-100 keV energy band to E<10^46 erg for durations <0.1 s over several tens of ks exposure. We can rule out the occurrence of giant flares similar to the ones that were observed in the few cases of Galactic magnetars. The absence of reported radio activity during our observations does not allow us to make any statements on the possible simultaneous high-energy emission.

astro-ph.HE↗

arXiv2020

Diagonal Ridge pattern of different age populations found in Gaia DR2 with LAMOST Main-Sequence-Turn-Off and OB type Stars

We revisit the diagonal ridge feature (diagonal distributions in the $R, v_ϕ$ plane) found in $Gaia$ and present timing analysis for it between Galactocentric distances of $R=7.5$ and 12 \,kpc, using Main-Sequence-Turn-Off and OB stars selected from the LAMOST Galactic spectroscopic surveys. We recover the ridge pattern in the $R$--$v_ϕ$ plane color coded by mean radial velocity and find this feature is presented from very young (OB stars, few hundred \,Myr) to very old populations ($τ$ = 9$-$14 \,Gyr). Meanwhile, some ridge features are also revealed in the metallicity [Fe/H], [$α$/Fe] and $v_{z}$ distributions. In the $L_{Z}, v_ϕ$ plane, one of the ridge patterns, with constant angular momentum per unit mass, shows variations with different age populations compared. However, the remaining two ones are relatively stable, implying there might have two kinds of ridge patterns with different dynamical origins and evolution.

astro-ph.GA↗