arXiv subjects

Da-Ming Wei

Publications and source records attributed to Da-Ming Wei.

At least 73 records · Page 4Linked to original sources

arXiv2020

Is GW190425 consistent with being a neutron star$-$black hole merger?

GW190425 is the second neutron star merger event detected by the Advanced LIGO/Virgo detectors. If interpreted as a double neutron star merger, the total gravitational mass is substantially larger than that of the binary systems identified in the Galaxy. In this work we analyze the gravitational-wave data within the neutron star$-$black hole merger scenario. For the black hole, we yield a mass of $2.40^{+0.36}_{-0.32}M_\odot$ and an aligned spin of $0.141^{+0.067}_{-0.064}$. As for the neutron star we find a mass of $1.15^{+0.15}_{-0.13}M_\odot$ and the dimensionless tidal deformability of $1.4^{+3.8}_{-1.2}\times 10^{3}$. These parameter ranges are for 90\% credibility. The inferred masses of the neutron star and the black hole are not in tension with current observations and we suggest that GW190425 is a viable candidate of a neutron star$-$black hole merger event. Benefitting from the continual enhancement of the sensitivities of the advanced gravitational detectors and the increase of the number of the observatories, similar events are anticipated to be much more precisely measured in the future and the presence of black holes below the so-called mass gap will be unambiguously clarified. If confirmed, the mergers of neutron stars with (quickly rotating) low-mass black holes are likely important production sites of the heaviest r-process elements.

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arXiv2020

The Masses of Isolated Neutron Stars Inferred from the Gravitational Redshift Measurements

For some neutron stars (NSs) in the binary systems, the masses have been accurately measured. While for the isolated neutron stars (INSs), no mass measurement has been reported yet. The situation will change soon thanks to the successful performance of the Neutron Star Interior Composition Explorer (NICER), with which the radius and mass of the isolated PSR J0030+0451 can be simultaneously measured. For most INSs, no mass measurements are possible for NICER because of observational limitations. Benefiting from recent significant progress made on constraining the equation of state of NSs, in this work we propose a way to estimate the masses of the INSs with the measured gravitational redshifts. We apply our method to RX J1856.5-3754, RX J0720.4-3125, and RBS 1223, three members of "The Magnificent Seven" (M7), and estimate their masses to be $1.24_{-0.29}^{+0.29}M_{\odot}$, $1.23_{-0.05}^{+0.10}M_{\odot}$, and $1.08_{-0.11}^{+0.20}M_{\odot}$, respectively. These masses are consistent with that of binary NS systems, suggesting no evidence for experiencing significant accretion of these isolated objects.

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arXiv2019

The equation of state and some key parameters of neutron stars: constraints from GW170817, the nuclear data and the low mass X-ray binary data

In this work we parameterize the Equation of State of dense neutron star (NS) matter with four pressure parameters of $\{\hat{p}_1, \hat{p}_2, \hat{p}_3, \hat{p}_4\}$ and then set the combined constraints with the data of GW 170817 and the data of 6 Low Mass X-ray Binaries (LMXBs) with thermonuclear burst or alternatively the symmetry energy of the nuclear interaction. We find that the nuclear data effectively narrow down the possible range of $\hat{p}_1$, the gravitational wave data plays the leading role in bounding $\hat{p}_2$, and the LMXB data as well as the lower bound on maximal gravitational mass of non-rotating NSs govern the constraints on $\hat{p}_3$ and $\hat{p}_4$. Using posterior samples of pressure parameters and some universal relations, we further investigate how the current data sets can advance our understanding of tidal deformability ($Λ$), moment of inertia ($I$) and binding energy ($BE$) of NSs. For a canonical mass of $1.4M_\odot$, we have $I_{1.4} = {1.43}^{+0.30}_{-0.13} \times 10^{38}~{\rm kg \cdot m^2}$, $Λ_{1.4} = 390_{-210}^{+280}$ , $R_{1.4} = 11.8_{-0.7}^{+1.2}~{\rm km}$ and $BE_{1.4} = {0.16}^{+0.01}_{-0.02} M_{\odot}$ if the constraints from the nuclear data and the gravitational wave data have been jointly applied. For the joint analysis of gravitational wave data and the LMXB data, we have $I_{1.4} = {1.28}^{+0.15}_{-0.08} \times 10^{38}~{\rm kg \cdot m^2}$, $Λ_{1.4} = 220_{-90}^{+90}$, $R_{1.4} = 11.1_{-0.6}^{+0.7}~{\rm km}$ and $BE_{1.4} = {0.18}^{+0.01}_{-0.01} M_{\odot}$. These results suggest that the current constraints on $Λ$ and $R$ still suffer from significant systematic uncertainties, while $I_{1.4}$ and $BE_{1.4}$ are better constrained.

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arXiv2019

Probing local cosmic rays using Fermi-LAT observation of a mid-latitude region in the third Galactic quadrant

The $γ$-ray observation of interstellar gas provides a unique way to probe the cosmic rays (CRs) outside the solar system. In this work, we use an updated version of Fermi-LAT data and recent multi-wavelength tracers of interstellar gas to re-analyze a mid-latitude region in the third Galactic quadrant and estimate the local CR proton spectrum. Two $γ$-ray production cross section models for $pp$ interaction, the commonly used one from Kamae et al. (2006) and the up-to-date one from Kafexhiu et al. (2014), are adopted separately in the analysis. Both of them can well fit the emissivity and the derived proton spectra roughly resemble the direct measurements from AMS-02 and Voyager 1, but rather different spectral parameters are indicated. A break at $4\pm1~{\rm GeV}\;c^{-1}$ is shown if the cross section model by Kamae et al. (2006) is adopted. The resulting spectrum is $\lesssim 20\%$ larger than the AMS-02 observation above $15~\rm GeV$ and consistent with the de-modulated spectrum within $2\%$. The proton spectrum based on the cross section model of Kafexhiu et al. (2014) is about $1.4-1.8$ times that of AMS-02 at $2-100~\rm GeV$, however the difference decreases to $20\%$ below $10~\rm GeV$ with respect to the de-modulated spectrum. A spectral break at $20\pm11~{\rm GeV}\;c^{-1}$ is required in this model. An extrapolation down to $300~\rm MeV$ is performed to compare with the observation of Voyager 1, and we find a deviation of $\lesssim 2.5σ$ for both the models. In general, an approximately consistent CR spectrum can be obtained using $γ$-ray observation nowadays, but we still need a better $γ$-ray production cross section model to derive the parameters accurately.

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arXiv2019

GW170817: The energy extraction process of the off-axis relativistic outflow and the constraint on the equation of state of neutron stars

As revealed recently by the modeling of the multi-wavelength data of the emission following GW170817/GRB 170817A, there was an off-axis energetic relativistic outflow component launched by this historic double neutron star merger event. In this work we use the results of these modeling to examine the energy extraction process of the central engine. We show that the magnetic process (i.e., the Blandford-Znajek mechanism) is favored, while the neutrino process usually requires a too massive accretion disk if the duration of the central engine activity is comparable to the observed $T_{90}$ of GRB 170817A, unless the timescale of the central engine activity is less than $\sim$ 0.2s. We propose that the GRB observations are helpful to constrain the combined tidal parameter $\tildeΛ$, and by adopting the accretion disk mass distribution estimated in BZ mechanism, the $90\%$ credible interval of $\tildeΛ$ for the progenitor of GW170817 is inferred as $309-954$.

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arXiv2019

Late afterglow emission statistics: a clear link between GW170817 and bright short GRBs

GW170817, the first neutron star merger event detected by advanced LIGO/Virgo detectors, was associated with an underluminous short duration GRB 170817A. In this work we compare the forward shock afterglow emission of GW170817/GRB 170817A to other luminous short GRBs (sGRBs) with both a known redshift and an afterglow emission lasting at least one day after the burst. In the rapid decay phase, the afterglow emission of the bright sGRBs and GW170817/GRB 170817A form a natural and continuous sequence, though separated by an observation time gap. If viewed on-axis, the forward shock afterglow emission of GW170817/GRB 170817A would be among the brightest ones detected so far. This provides a strong evidence for the GW170817-like merger origin of bright sGRBs, and suggests that the detection of the forward shock afterglow emission of most neutron star merger events are more challenging than the case of GW170817 since usually the mergers will be more distant and the viewing angles are plausibly higher.

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arXiv2018

HESS J1640-465 -- a Gamma-ray emitting pulsar wind nebula ?

HESS J1640-465 is an extended TeV $γ$-ray source and its $γ$-ray emission whether from the shell of a supernova remnant (SNR) or a pulsar wind nebula (PWN) is still under debate. We reanalyze the GeV $γ$-ray data in the field of HESS J1640-465 using eight years of Pass 8 data recorded by the Fermi Large Area Telescope. An extended GeV $γ$-ray source positionally coincident with HESS J1640-465 is found. Its photon spectrum can be described by a power-law with an index of $1.42\pm0.19$ in the energy range of 10-500 GeV, and smoothly connects with the TeV spectrum of HESS J1640-465. The broadband spectrum of HESS J1640-465 can be well fit by a leptonic model with a broken power-law spectrum of electrons with an exponential cut-off at $\sim$ 300 TeV. The spectral properties of HESS J1640-465 are broadly consistent with the characteristics of other sources identified as PWNe, such as the correlations between high-energy luminosity ratios and the physical parameters of pulsar, including spin-down luminosity $\dot{E}$ and characteristic age $τ_c$. All these pieces of evidence support that the $γ$-ray emission of HESS J1640-465 may originate from the PWN powered by PSR J1640-4631 rather than the shell of the SNR G338.3-0.0.

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arXiv2018

Studies on cosmic ray nuclei with Voyager, ACE and AMS-02: I. local interstellar spectra and solar modulation

The acceleration of cosmic ray particles and their propagation in the Milky Way and the heliosphere tangle with each other, leading to complexity and degeneracy of the modeling of Galactic cosmic rays (GCRs). The recent measurements of the GCR spectra by Voyager-1 from outside of the heliosphere gave a first direct observation of GCRs in the local interstellar (LIS) environment. Together with the high-precision data near the Earth taken by ACE and AMS-02, we derive the LIS spectra of Helium, Lithium, Beryllium, Boron, Carbon, and Oxygen nuclei from a few MeV/n to TeV/n, using a non-parameterization method. These LIS spectra are helpful in further studying the injection and propagation parameters of GCRs. The nearly 20 years of data recorded by ACE are used to determine the solar modulation parameters over the solar cycles 23 and 24, based on the force-field approximation. We find general agreements of the modulation potential with the results inferred from neutron monitors and other cosmic ray data.

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arXiv2018

Total gravitational mass of the Galactic Double Neutron Star systems: evidence for a bimodal distribution

So far, in total 15 double neutron star systems (DNSs) with a reliable measurement of the total gravitational mass ($M_{\rm T}$) have been detected in the Galaxy. In this work we study the distribution of $M_{\rm T}$. The data prefer the double Gaussian distribution over a single Gaussian distribution and the low and high mass populations center at $M_{\rm T}\sim 2.58M_\odot$ and $\sim 2.72M_\odot$, respectively. The progenitor stars of GW170817 have a $M_{\rm T}=2.74^{+0.04}_{-0.01}M_\odot$, falling into the high mass population. With a local neutron star merger rate of $\sim 10^{3}~{\rm Gpc^{-3}~yr^{-1}}$, supposing the $M_{\rm T}$ of those merging neutron stars also follow the double Gaussian distribution, the upcoming runs of the advanced LIGO/Virgo will soon detect some events with a $M_{\rm T}\lesssim 2.6M_\odot$ that can effectively probe the equation of state of the neutron stars and the distribution function is expected to be reliably reconstructed in the next decade.

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arXiv2018

GW170817 and the prospect of forming supramassive remnants in neutron star mergers

The gravitational wave data of GW170817 favor the equation of state (EoS) models that predict compact neutron stars (NSs), consistent with the radius constraints from X-ray observations. Motivated by such a remarkable progress, we examine the fate of the remnants formed in NS mergers and focus on the roles of the angular momentum and the mass distribution of the binary NSs. In the mass shedding limit (for which the dimensionless angular momentum equals to the Keplerian value, i.e., $j=j_{\rm Kep}$), the adopted { seven EoS models, except H4 and ALF2,} yield supramassive NSs in more than half of the mergers. However, for $j\lesssim 0.7j_{\rm Kep}$, the presence or absence of a non-negligible fraction of supramassive NSs formed in the mergers depends sensitively on both the EoS and the mass distribution of the binary systems. The NS mergers with a total gravitational mass $\leq 2.6M_\odot$ are found to be able to shed valuable light on both the EoS model and the angular momentum of the remnants if supramassive NSs are still absent. We have also discussed the uncertainty on estimating the maximum gravitational mass of non-rotating NSs ($M_{\rm max}$) due to the unknown $j$ of the pre-collapse remnants. With the data of GW170817 and the assumption of the mass loss of $0.03M_\odot$, we have $M_{\rm max}<(2.19,~2.32)M_\odot$ (90\% confidence level) for $j=(1.0,~0.8)j_{\rm Kep}$, respectively.

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arXiv2018

Neutrinos from Choked Jets Accompanied by Type-II Supernovae

The origin of the IceCube neutrinos is still an open question. Upper limits from diffuse gamma-ray observations suggest that the neutrino sources are either distant or hidden from gamma-ray observations. It is possible that the neutrinos are produced in jets that are formed in the core-collapsing massive stars and fail to break out, the so-called choked jets. We study neutrinos from the jets choked in the hydrogen envelopes of red supergiant stars. Fast photo-meson cooling softens the neutrino spectrum, making it difficult to explain the PeV neutrinos observed by IceCube in a one-component scenario, but a two-component model can explain the spectrum. Furthermore, we predict that a newly born jet-driven type-II supernova may be observed to be associated with a neutrino burst detected by IceCube.

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arXiv2018

Short GRBs: opening angles, local neutron star merger rate and off-axis events for GRB/GW association

The jet breaks in the afterglow lightcurves of short gamma-ray bursts (SGRBs), rarely detected so far, are crucial for estimating the half-opening angles of the ejecta ($θ_{\rm j}$) and hence the neutron star merger rate. In this work we report the detection of jet decline behaviors in GRB 150424A and GRB 160821B and find $θ_{\rm j}\sim 0.1$ rad. Together with five events reported before 2015 and other three "identified" recently (GRB 050709, GRB 060614 and GRB 140903A), we have a sample consisting of nine SGRBs and one long-short GRB with reasonably estimated $θ_{\rm j}$. In particular, three {\it Swift} bursts in the sample have redshifts $z\leq 0.2$, with which we estimate the local neutron star merger rate density {to be $\sim 1109^{+1432}_{-657}~{\rm Gpc^{-3}~yr^{-1}}$ or $162^{+140}_{-83} {\rm Gpc^{-3}yr^{-1}}$ if the narrowly-beamed GRB 061201 is excluded}. Inspired by the typical $θ_{\rm j}\sim 0.1$ rad found currently, we further investigate whether the off-beam GRBs (in the uniform jet model) or the off-axis events (in the structured jet model) can significantly enhance the GRB/GW association or not. For the former the enhancement is at most moderate, while for the latter the enhancement can be much greater and a high GRB/GW association probability of $\sim 10\%$ is possible. We also show that the data of GRB 160821B may contain a macronova/kilonova emission component with a temperature of $\sim 3100$ K at $\sim 3.6$ days after the burst and more data are needed to ultimately clarify.

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arXiv2018

How Special Is GRB 170817A?

GRB 170817A is the first short gamma-ray burst (GRB) with direct detection of the gravitational-wave radiation and also the spectroscopically identified macronova emission (i.e., AT 2017gfo). The prompt emission of this burst, however, is underluminous in comparison with the other short GRBs with known redshift. In this work, we examine whether GRB 170817A is indeed unique. We firstly show that GRB 130603B/macronova may be the on-axis "analogs" of GRB 170817A/AT 2017gfo, and the extremely dim { but long-lasting} afterglow emission of GRB 170817A may suggest a low number density ($\sim 10^{-5}~{\rm cm^{-3}}$) of its circumburst medium { and a structured outflow}. We then discuss whether GRB 070923, GRB 080121, GRB 090417A, GRB 111005A, and GRB 170817A form a new group of very nearby underluminous GRBs originated from neutron star mergers. If the short events GRB 070923, GRB 080121, and GRB 090417A are indeed at a redshift of $\sim 0.076,~0.046,~0.088$, respectively, their isotropic energies of the prompt emission are $\sim 10^{47}$ erg and thus comparable to the other two events. The non-detection of optical counterparts of GRB 070923, GRB 080121, GRB 090417A, and GRB 111005A, however, strongly suggests that the macronovae from neutron star mergers are significantly diverse in luminosities or, alternatively, there is the other origin channel (for instance, the white dwarf and black hole mergers). We finally suggest that GW170817/GRB 170817A are likely not alone and similar events will be detected by the upgraded/upcoming gravitational-wave detectors and the electromagnetic monitors.

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arXiv2018

Detection of the Characteristic Pion-Decay Signature in the Molecular Clouds

The $γ$-ray emission from molecular clouds is widely believed to have a hadronic origin, while unequivocal evidence is still lacking. In this work, we analyze the Fermi-LAT Pass 8 publicly available data accumulated from 2008 August 4 to 2017 June 29 and report the significant detection of a characteristic $π^0$-decay feature in the $γ$-ray spectra of the molecular clouds Orion A and Orion B. This detection provides a direct evidence for the hadronic origin of their $γ$-ray emission.

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arXiv2018

GRB 111005A at Z = 0.0133 and the Prospect of Establishing Long-short GRB/GW Association

GRB 111005A, one long duration gamma-ray burst (GRB) occurred within a metal-rich environment that lacks massive stars with $M_{\rm ZAMS}\geq 15M_\odot$, is not coincident with supernova emission down to stringent limit and thus should be classified as a "long-short" GRB (lsGRB; also known as SN-less long GRB or hybrid GRB), like GRB 060505 and GRB 060614. In this work we show that in the neutron star merger model, the non-detection of the optical/infrared emission of GRB 111005A requires a sub-relativistic neutron-rich ejecta with the mass of $\leq 0.01~M_\odot$, (significantly) less massive than that of GRB 130603B, GRB 060614 and GRB 050709. The lsGRBs are found to have a high rate density and the neutron star merger origin model can be unambiguously tested by the joint observations of the second generation gravitational wave (GW) detectors and the full-sky gamma-ray monitors such as Fermi-GBM and the proposing GECAM. If no lsGRB/GW association is observed in 2020s, alternative scenarios have to be systematically investigated. With the detailed environmental information achievable for the very-nearby events, a novel kind of merger or explosion origin may be identified.

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arXiv2017

GW170817/GRB 170817A/AT2017gfo association: some implications for physics and astrophysics

On 17 August 2017, a gravitational wave event (GW170817) and an associated short gamma-ray burst (GRB 170817A) from a binary neutron star merger had been detected. The followup optical/infrared observations also identified the macronova/kilonova emission (AT2017gfo). In this work we discuss some implications of the remarkable GW170817/GRB 170817A/AT2017gfo association. We show that the $\sim 1.7$s time delay between the gravitational wave (GW) and GRB signals imposes very tight constraint on the superluminal movement of gravitational waves (i.e., the relative departure of GW velocity from the speed of light is $\leq 4.3\times 10^{-16}$) or the possible violation of weak equivalence principle (i.e., the difference of the gamma-ray and GW trajectories in the gravitational field of the galaxy and the local universe should be within a factor of $\sim 3.4\times 10^{-9}$). The so-called Dark Matter Emulators and a class of contender models for cosmic acceleration ("Covariant Galileon") are ruled out, too. The successful identification of Lanthanide elements in the macronova/kilonova spectrum also excludes the possibility that the progenitors of GRB 170817A are a binary strange star system. The high neutron star merger rate (inferred from both the local sGRB data and the gravitational wave data) together with the significant ejected mass strongly suggest that such mergers are the prime sites of heavy r-process nucleosynthesis.

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arXiv2017

Possible correlations between the emission properties of short GRBs and their offsets from the host galaxies

Short Gamma-Ray Bursts(SGRBs) are widely believed to be from mergers of binary compact objects involving at least one neutron star and hence have a broad range of spatial offsets from their host galaxies. In this work we search for possible correlations between the emission properties of 18 SGRBs and their offsets from the host galaxies. The SGRBs with and without extended emission do not show significant difference between their offset distribution, in agreement with some previous works. There are however possible correlations between the optical and X-ray afterglow emission and the offsets. The underlying physical origins are examined.

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arXiv2017

The SNR Puppis A Revisited with Seven Years of Fermi Large Area Telescope Observations

Puppis A is a very famous and extensively studied supernova remnant (SNR) that shows strong evidence of shock-cloud interaction. We re-analyze the GeV $γ$-ray emission of it using seven years Pass 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT). The morphology of the $γ$-ray emission is more compatible with that of the thermal X-ray and IR emissions than the radio image, which suggests a possible correlation between the gamma-ray emitting region and dense clouds. The $γ$-ray spectrum in the energy range of 1-500 GeV shows a break at $7.92\pm1.91$ GeV with the photon indices of $1.81\pm0.08$ below the break and $2.53\pm0.12$ above the break, which can naturally explain the lack of TeV $γ$-ray emission from Puppis A. The multi-wavelength observations favor a hadronic origin for the $γ$-ray emission.

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