arXiv subjects

L. M. Song

Publications and source records attributed to L. M. Song.

At least 73 records · Page 4Linked to original sources

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.

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arXiv2019

$Insight$-HXMT Science Operations

The Hard X-ray Modulation Telescope ($Insight$-HXMT) was successfully launched on June 15th, 2017. It performs broad band X-ray scan survey of the Galactic Plane to detect new black holes and other objects in active states. It also observes X-ray binaries to study their X-ray variabilities. Here we will introduce the Science Operations of $Insight$-HXMT, which is responsible for collecting and evaluating observation proposals, scheduling observations, and monitoring the working status of the payloads.

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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.

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arXiv2019

The Insight-HXMT mission and its recent progresses

The Hard X-ray Modulation Telescope HXMT or also dubbed as Insight HXMT is China s first astronomical satellite . It was launched on 15 th June 2017 in JiuQuan, China and is currently in service smoothly. It was designed to perform point ing , scan ning and gamma ray burst (GRB) observations and , based on the Direct Demodulation Method (DDM), the image of the scanned sky region can be reconstructed. Here we introduce the mission and its progresses in aspects of payload, core sciences, ground calibration/facility , ground segment, data archive, software, in orbit performance, calibration, background model, observations and preliminary results .

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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.

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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.

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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.

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arXiv2019

Broad-lined type Ic supernova iPTF16asu: A challenge to all popular models

It is well-known that ordinary supernovae (SNe) are powered by 56Ni cascade decay. Broad-lined type Ic SNe (SNe Ic-BL) are a subclass of SNe that are not all exclusively powered by 56Ni decay. It was suggested that some SNe Ic-BL are powered by magnetar spin-down. iPTF16asu is a peculiar broad-lined type Ic supernova discovered by the intermediate Palomar Transient Factory. With a rest-frame rise time of only 4 days, iPTF16asu challenges the existing popular models, for example, the radioactive heating (56Ni-only) and the magnetar+56Ni models. Here we show that this rapid rise could be attributed to interaction between the SN ejecta and a pre-existing circumstellar medium ejected by the progenitor during its final stages of evolution, while the late-time light curve can be better explained by energy input from a rapidly spinning magnetar. This model is a natural extension to the previous magnetar model. The mass-loss rate of the progenitor and ejecta mass are consistent with a progenitor that experienced a common envelope evolution in a binary. An alternative model for the early rapid rise of the light curve is the cooling of a shock propagating into an extended envelope of the progenitor. It is difficult at this stage to tell which model (interaction+magnetar+56Ni or cooling+magnetar+56Ni) is better for iPTF16asu. However, it is worth noting that the inferred envelope mass in the cooling+magnetar+56Ni is very high.

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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.

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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.

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arXiv2018

Time evolution of the X-ray and gamma-ray fluxes of the Crab pulsar

We studied the evolution of the X-ray and gamma-ray spectra of the Crab pulsar utilizing the 11-year observations from the Rossi X-ray Timing Explorer (RXTE) and 9-year observations from the Fermi Gamma-ray Space Telescope (FGST). By fitting the spectrum of each observation, we obtained the corresponding flux, and then analysed the long term evolution of the X-ray (or gamma-ray) luminosities as well as their correlations with the spin down power of the pulsar. The X-ray flux in 5-60 keV obtained by the Proportional Counter Array (PCA) of RXTE decreases with a rate of (-2.4+/-0.4)*10^(-14) erg cm^(-2) s^(-1) per day. The X-ray flux in 15-250 keV obtained by the High Energy X-ray Timing Experiment (HEXTE) of RXTE and the gamma-ray flux in 0.1-300 GeV by the Large Area Telescope (LAT) onboard FGST show similar decreasing trend, but are unsignificant statistically. The 5--60 keV X-ray luminosity L_(X) is correlated with the spin down power L_(sd) by L_(X) propto L_(sd)^(1.6+/-0.3), which is similar to the statistical results for young pulsars.

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arXiv2018

The minimum magnetic field of millisecond pulsars calculated according to accretion: application to the X-ray neutron star SAX J1808.4-3658 in a low-mass X-ray binary

Based on the model of the accretion-induced magnetic field decay of a neutron star (NS), millisecond pulsars (MSPs) will obtain their minimum magnetic field when the NS magnetosphere radius shrinks to the stellar surface during the binary accretion phase. We find that this minimummagnetic field is related to the accretion rate Mdot as Bmin ~2.0*10^7 G( Mdot/Mdot_min)^1/2, where Mdot_min = 4.6*10^15 g/s is the average minimum accretion rate required for MSP formation and is constrained by the long-term accretion time, which corresponds to the companion lifetime, being less than the Hubble time. The value of Bmin is consistent with that of observed radio MSPs and accreting MSPs in low-mass X-ray binaries, which can be found the illustrated case of the minimum and present field strength of SAX J1808.4-3658. The prediction of the minimum magnetic field of MSPs would be the lowest field strength of NSs in the Universe, which could constrain the evolution mechanism of the magnetic field of accreting NSs.

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arXiv2018

Modeling the Multi-band Afterglow of GRB 060908 with the Double Power-Law Hard Electron Energy Spectrum Model

Electrons accelerated in relativistic collisionless shocks are usually assumed to follow a power-law energy distribution with an index of $p$. Observationally, although most gamma-ray bursts (GRBs) have afterglows that are consistent with $p>2$, there are still a few GRBs suggestive of a hard ($p<2$) electron energy spectrum. Our previous works found strong evidence for the exist of a double power-law hard electron energy (DPLH) spectrum with $1 2$ and an injection break assumed as $γ_{\rm b}\propto γ^{q}$ in the relativistic regime. Moreover, these works suggested a possibly universal value of $q\sim0.5$. GRB~060908 is another case that shows a flat spectrum in the optical/near-infrared band and requires a hard electron energy distribution, which, along with the rich multi-band afterglow data, provides us an opportunity to test this conjecture. Based on the model of \citet{Resmi08}, we explain the multi-band afterglow of GRB~060908 in a wind medium and take also the synchrotron self-Compton effect. We show that though the DPLH spectrum is favored by the afterglow data, the value of $q$ is badly constrained due to the relatively large uncertainties of the spectral indices. However, the afterglow can be well reproduced if we adopt $q=0.5$, implying the compatibility of the above conjecture with the data.

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arXiv2018

Modeling the Multi-band Afterglows of GRB 060614 and GRB 060908: Further Evidence for a Double Power-Law Hard Electron Energy Spectrum

Electrons accelerated in relativistic collisionless shocks are usually assumed to follow a power-law energy distribution with an index of $p$. Observationally, although most gamma-ray bursts (GRBs) have afterglows that are consistent with $p>2$, there are still a few GRBs suggestive of a hard ($p<2$) electron energy spectrum. Our previous work showed that GRB 091127 gave strong evidence for a double power-law hard electron energy (DPLH) spectrum with $1 2$ and an "injection break" assumed as $γ_{\rm b}\propto γ^q$ in the highly relativistic regime, where $γ$ is the bulk Lorentz factor of the jet. In this paper, we show that GRB 060614 and GRB 060908 provide further evidence for such a DPLH spectrum. We interpret the multi-band afterglow of GRB 060614 with the DPLH model in an homogeneous interstellar medium by taking into account a continuous energy injection process, while for GRB 060908, a wind-like circumburst density profile is used. The two bursts, along with GRB 091127, suggest a similar behavior in the evolution of the injection break, with $q\sim0.5$. Whether this represents a universal law of the injection break remains uncertain and more such afterglow observations are needed to test this conjecture.

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arXiv2017

A Monte Carlo approach to magnetar-powered transients: II. Broad-lined type Ic supernovae not associated with GRBs

Broad-lined type Ic supernovae (SNe Ic-BL) are a subclass of rare core collapse SNe whose energy source is debated in the literature. Recently a series of investigations on SNe Ic-BL with the magnetar (plus 56Ni) model were carried out. Evidence for magnetar formation was found for the well-observed SNe Ic-BL 1998bw and 2002ap. In this paper we systematically study a large sample of SNe Ic-BL not associated with gamma-ray bursts. We use photospheric velocity data determined in a homogeneous way. We find that the magnetar+56Ni model provides a good description of the light curves and velocity evolution of our sample of SNe Ic-BL, although some SNe (not all) can also be described by the pure-magnetar model or by the two-component pure-56Ni model (3 out of 12 are unlikely explained by two-component model). In the magnetar+56Ni model, the amount of 56Ni required to explain their luminosity is significantly reduced, and the derived initial explosion energy is, in general, in accordance with neutrino heating. Some correlations between different physical parameters are evaluated and their implications regarding magnetic field amplification and the total energy reservoir are discussed.

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arXiv2017

Search for the Signatures of a New-Born Black Hole from the Collapse of a Supra-massive Millisecond Magnetar in Short GRB Light Curves

`Internal plateau' followed by a sharp decay is commonly seen in short gamma-ray burst (GRB) light curves. The plateau component is usually interpreted as the dipole emission from a supra-massive magnetar, and the sharp decay may imply the collapse of the magnetar to a black hole (BH). Fall-back accretion onto the new-born BH could produce long-lasting activities via the Blandford-Znajek (BZ) process. The magnetic flux accumulated near the BH would be confined by the accretion disks for a period of time. As the accretion rate decreases, the magnetic flux is strong enough to obstruct gas infall, leading to a magnetically-arrested disk (MAD). Within this scenario, we show that the BZ process could produce two types of typical X-ray light curves: type I exhibits a long-lasting plateau, followed by a power-law decay with slopes ranging from 5/3 to 40/9; type II shows roughly a single power-law decay with slope of 5/3. The former requires low magnetic filed strength, while the latter corresponds to relatively high values. We search for such signatures of the new-born BH from a sample of short GRBs with an internal plateau, and find two candidates: GRB 101219A and GRB 160821B, corresponding to type II and type I light curve, respectively. It is shown that our model can explain the data very well.

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arXiv2017

Design and construction of the POLAR detector

The POLAR detector is a space based Gamma Ray Burst (GRB) polarimeter with a wide field of view, which covers almost half the sky. The instrument uses Compton scattering of gamma rays on a plastic scintillator hodoscope to measure the polarization of the incoming photons. The instrument has been successfully launched on board of the Chinese space laboratory Tiangong~2 on September 15, 2016. The construction of the instrument components is described in this article. Details are provided on problems encountered during the construction phase and their solutions. Initial performance of the instrument in orbit is as expected from ground tests and Monte Carlo simulation.

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arXiv2017

Instrument Performance and Simulation Verification of the POLAR Detector

POLAR is a new satellite-born detector aiming to measure the polarization of an unprecedented number of Gamma-Ray Bursts in the 50-500 keV energy range. The instrument, launched on-board the Tiangong-2 Chinese Space lab on the 15th of September 2016, is designed to measure the polarization of the hard X-ray flux by measuring the distribution of the azimuthal scattering angles of the incoming photons. A detailed understanding of the polarimeter and specifically of the systematic effects induced by the instrument's non-uniformity are required for this purpose. In order to study the instrument's response to polarization, POLAR underwent a beam test at the European Synchrotron Radiation Facility in France. In this paper both the beam test and the instrument performance will be described. This is followed by an overview of the Monte Carlo simulation tools developed for the instrument. Finally a comparison of the measured and simulated instrument performance will be provided and the instrument response to polarization will be presented.

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