arXiv subjects

Jun-Jie Wei

Publications and source records attributed to Jun-Jie Wei.

At least 73 records · Page 4Linked to original sources

arXiv2019

Model-independent Distance Calibration and Curvature Measurement using Quasars and Cosmic Chronometers

We present a new model-independent method to determine the spatial curvature and to mitigate the circularity problem affecting the use of quasars as distance indicators. The cosmic-chronometer measurements are used to construct the curvature-dependent luminosity distance $D^{\rm cal}_{L}(Ω_{K},z)$ using a polynomial fit. Based on the reconstructed $D^{\rm cal}_{L}(Ω_{K},z)$ and the known ultraviolet versus X-ray luminosity correlation of quasars, we simultaneously place limits on the curvature parameter $Ω_{K}$ and the parameters characterizing the luminosity correlation function. This model-independent analysis suggests that a mildly closed Universe ($Ω_{K}=-0.918\pm0.429$) is preferred at the $2.1σ$ level. With the calibrated luminosity correlation, we build a new data set consisting of 1598 quasar distance moduli, and use these calibrated measurements to test and compare the standard $Λ$CDM model and the $R_{\rm h}=ct$ universe. Both models account for the data very well, though the optimized flat $Λ$CDM model has one more free parameter than $R_{\rm h}=ct$, and is penalized more heavily by the Bayes Information Criterion. We find that $R_{\rm h}=ct$ is slightly favoured over $Λ$CDM with a likelihood of $\sim57.7\%$ versus 42.3\%.

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arXiv2019

The time-resolved spectra of photospheric emission from a structured jet for gamma-ray bursts

The quasi-thermal components found in many Fermi gamma-ray bursts (GRBs) imply that the photosphere emission indeed contributes to the prompt emission of many GRBs. But whether the observed spectra empirically fitted by the Band function or cutoff power law, especially the spectral and peak energy ($E_{p}$) evolutions can be explained by the photosphere emission model alone needs further discussion. In this work, we investigate in detail the time-resolved spectra and $E_{p}$ evolutions of photospheric emission from a structured jet, with an inner-constant and outer-decreasing angular Lorentz factor profile. Also, a continuous wind with a time-dependent wind luminosity has been considered. We show that the photosphere spectrum near the peak luminosity is similar to the cutoff power-law spectrum. The spectrum can have the observed average low-energy spectral index $α$ $ \sim -1$, and the distribution of the low-energy spectral index in our photosphere model is similar to that observed ($-2\lesssim $ $α\lesssim 0$). Furthermore, the two kinds of spectral evolutions during the decay phase, separated by the width of the core ($θ_{c}$), are consistent with the time-resolved spectral analysis results of several Fermi multi-pulse GRBs and single-pulse GRBs, respectively. Also, for this photosphere model we can reproduce the two kinds of observed $E_{p}$ evolution patterns rather well. Thus, by considering the photospheric emission from a structured jet, we reproduce the observations well for the GRBs best fitted by the cutoff power-law model for the peak-flux spectrum or the time-integrated spectrum.

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arXiv2019

Constraining the Evolution of the Baryon Fraction in the IGM with FRB and H(z) data

Extragalactic dispersion measures (DMs) obtained from observations of fast radio bursts (FRBs) are an excellent tool for probing intergalactic medium (IGM) and for conducting cosmography. However, the DM contribution from the IGM (${\rm DM_{IGM}}$) depends on the fraction of baryon mass in the IGM, $f_{\rm IGM}$, which is not properly constrained. As $f_{\rm IGM}(z)$ is geometrically related to the Hubble parameter $H(z)$ and ${\rm DM_{IGM}}(z)$, here we propose that combining two independent measurements of FRBs and $H(z)$ in similar redshift ranges provides a novel and cosmology-free method to constrain the evolution of $f_{\rm IGM}(z)$. Under the assumption that $f_{\rm IGM}$ is evolving with redshift in a functional form, we forecast that the evolution of $f_{\rm IGM}(z)$ can be well inferred in a combined analysis of $\sim3000$ ${\rm DM_{IGM}}(z)$ derived from FRBs and $\sim50$ $H(z)$ derived from the Hubble parameter data. Though the efficiency of our method is not as good as that of the other model-independent method involving the joint measurements of DM and luminosity distance of FRBs, our method offers a new model-independent way to constrain $f_{\rm IGM}(z)$.

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arXiv2019

The Luminosity Function and Formation Rate of A Complete Sample of Long Gamma-Ray Bursts

We study the luminosity function and formation rate of long gamma-ray bursts (GRBs) by using a maximum likelihood method. This is the first time this method is applied to a well-defined sample of GRBs that is complete in redshift. The sample is composed of 99 bursts detected by the $Swift$ satellite, 81 of them with measured redshift and luminosity for a completeness level of $82\%$. We confirm that a strong redshift evolution in luminosity (with an evolution index of $δ=2.22^{+0.32}_{-0.31}$) or in density ($δ=1.92^{+0.20}_{-0.21}$) is needed in order to reproduce the observations well. But since the predicted redshift and luminosity distributions in the two scenarios are very similar, it is difficult to distinguish between these two kinds of evolutions only on the basis of the current sample. Furthermore, we also consider an empirical density case in which the GRB rate density is directly described as a broken power-law function and the luminosity function is taken to be non-evolving. In this case, we find that the GRB formation rate rises like $(1+z)^{3.85^{+0.48}_{-0.45}}$ for $z\leq2$ and is proportional to $(1+z)^{-1.07^{+0.98}_{-1.12}}$ for $z\geq2$. The local GRB rate is $1.49^{+0.63}_{-0.64}$ Gpc$^{-3}$ yr$^{-1}$. The GRB rate may be consistent with the cosmic star formation rate (SFR) at $z\leq2$, but shows an enhancement compared to the SFR at $z\geq2$.

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arXiv2019

The Energy Function and Cosmic Formation Rate of Fast Radio Bursts

Fast radio bursts (FRBs) are intense radio transients whose physical origin remains unknown. Therefore, it is of crucial importance to use a model-independent method to obtain the energy function and cosmic formation rate directly from the observational data. Based on current samples from the Parkes and ASKAP telecsopes, we determine, for the first time, the energy function and formation rate of FRBs by using the Lynden-Bell $\rm C^{-}$ method. The energy function derived from the Parkes sample is a broken power law, however it is a simple power law for the ASKAP sample. For Parkes sample, we derive the formation rate which is roughly consistent with the star formation rate up to $z\sim1.7$, with a local formation rate of $\dot ρ(0) \simeq (3.2\pm 0.3)\; \times {10^4}\;{\rm{Gp}}{\rm{c}^{ - 3}}{\rm{y}}{\rm{r}^{ - 1}}$ above a detection threshold of $2\,{\rm{Jyms}}$. For ASKAP sample, we find that the formation rate evolves much faster than the star formation rate up to $z\sim0.7$, namely $\dot ρ(z) \propto {(1 + z)^{6.9 \pm 1.9}}$, with a local formation rate of $\dot ρ(0) \simeq (4.6\pm 0.8)\; \times {10^3}\;{\rm{Gp}}{\rm{c}^{ - 3}}{\rm{y}}{\rm{r}^{ - 1}}$ above a detection threshold of $51\,{\rm{Jyms}}$. This might be a important clue for the physical origin of FRBs.

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arXiv2019

Precision Test of the Weak Equivalence Principle from Gamma-Ray Burst Polarization

If the weak equivalence principle (WEP) is broken, the measured values of the parametrized post-Newtonian parameter $γ$ from photons with left- and right-handed circular polarizations should differ slightly, leading to the arrival-time difference of these two circular components. Thus, the polarization vector of a linearly polarized light may rotate during the propagation. The rotation angle of the polarization vector depends on both the photon energy and the distance of the source. It is believed that if the rotation angle differs by more than $π/2$ over an energy range, then the net polarization of the signal would be significantly suppressed and could not be as high as the observed level. Thus, the detection of highly polarized photons implies that the relative rotation angle ($ΔΘ$) should not be too large. In this paper, we give a detailed calculation on the evolution of gamma-ray burst (GRB) polarization arising from a possible violation of the WEP, and we find that more than $60\%$ of the initial polarization degree can be conserved even if $ΔΘ$ is larger than $π/2$. In addition, to tightly constrain the WEP violation, GRBs with harder spectra and polarization observations in a wider energy range seem to be favored. Applying our formulas to the measurements of linear polarization from GRB 110721A and GRB 061122, we obtain strict limits on the differences of the $γ$ values as low as $Δγ<1.3\times10^{-33}$ and $Δγ<0.8\times10^{-33}$. These provide the most stringent limits to date on a deviation from the WEP, improving at least 6 orders of magnitude over previous bounds.

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arXiv2019

New constraints on Lorentz invariance violation with polarized gamma-ray bursts

Lorentz invariance violations (LIV) can yield vacuum birefringence, which results in an energy-dependent rotation of the polarization vector of linearly polarized emission from astrophysical sources. It is believed that if the relative rotation angle ($ΔΘ$) of the polarization vector of high energy photons with respect to that of low energy photons is larger than $π/2$, then the net polarization of the signal would be significantly depleted and could not be as high as the observed level. Hence, the measurement of high polarization implies that $ΔΘ$ should not be too large. In this work, we assemble recent detections of prompt emission polarization in gamma-ray bursts (GRBs), all of whom have high detection significance. Following the method shown in Lin et al. (2016), we give a detailed calculation on the polarization evolution arising from the LIV effect for each GRB, and confirm that, even if $ΔΘ$ is approaching to $π/2$, the net polarization is not severely suppressed, and more than 60\% of the initial polarization can be conserved. Applying this method to our GRB polarimetric data, we improve existing sensitivities to LIV involving photons by factors ranging from two to ten. In addition, we prove that our constraints are not greatly affected by uncertainties in the spectral parameters of GRBs.

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arXiv2019

Cosmology-independent estimate of the fraction of baryon mass in the IGM from fast radio burst observations

The excessive dispersion measure (DM) of fast radio bursts (FRBs) has been proposed to be a powerful tool to study intergalactic medium (IGM) and to perform cosmography. One issue is that the fraction of baryons in the IGM, $f_{\rm IGM}$, is not properly constrained. Here we propose a method of estimating $f_{\rm IGM}$ using a putative sample of FRBs with the measurements of both DM and luminosity distance $d_{\rm L}$. The latter can be obtained if the FRB is associated with a distance indicator (e.g. a gamma-ray burst or a gravitational wave event), or the redshift $z$ of the FRB is measured and $d_{\rm L}$ at the corresponding $z$ is available from other distance indicators (e.g. type Ia supernovae) at the same redshift. Since $d_{\rm L}/{\rm DM}$ essentially does not depend on cosmological parameters, our method can determine $f_{\rm IGM}$ independent of cosmological parameters. We parameterize $f_{\rm IGM}$ as a function of redshift and model the DM contribution from a host galaxy as a function of star formation rate. Assuming $f_{\rm IGM}$ has a mild evolution with redshift with a functional form and by means of Monte Carlo simulations, we show that an unbiased and cosmology-independent estimate of the present value of $f_{\rm IGM}$ with a $\sim 12\%$ uncertainty can be obtained with 50 joint measurements of $d_{\rm L}$ and DM. In addition, such a method can also lead to a measurement of the mean value of DM contributed from the local host galaxy.

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arXiv2019

Unbiased Cosmic Opacity Constraints from Standard Sirens and Candles

The observation of Type Ia supernovae (SNe Ia) plays an essential role in probing the expansion history of the universe. But the possible presence of cosmic opacity can degrade the quality of SNe Ia. The gravitational-wave (GW) standard sirens, produced by the coalescence of double neutron stars and black hole--neutron star binaries, provide an independent way to measure the distances of GW sources, which are not affected by cosmic opacity. In this paper, we first propose that combining the GW observations of third-generation GW detectors with SN Ia data in similar redshift ranges offers a novel and model-independent method to constrain cosmic opacity. Through Monte Carlo simulations, we find that one can constrain the cosmic opacity parameter $κ$ with an accuracy of $σ_κ\sim0.046$ by comparing the distances from 100 simulated GW events and 1048 current Pantheon SNe Ia. The uncertainty of $κ$ can be further reduced to $\sim0.026$ if 800 GW events are considered. We also demonstrate that combining 2000 simulated SNe Ia and 1000 simulated GW events could result in much severer constraints on the transparent universe, for which $κ=0.0000\pm0.0044$. Compared to previous opacity constraints involving distances from other cosmic probes, our method using GW standard sirens and SN Ia standard candles at least achieves competitive results.

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arXiv2019

Multimessenger Tests of Einstein's Weak Equivalence Principle and Lorentz Invariance with a High-energy Neutrino from a Flaring Blazar

The detection of the high-energy ($\sim290$ TeV) neutrino coincident with the flaring blazar TXS 0506+056, the first and only $3σ$ neutrino-source association to date, provides new, multimessenger tests of the weak equivalence principle (WEP) and Lorentz invariance. Assuming that the flight time difference between the TeV neutrino and gamma-ray photons from the blazar flare is mainly caused by the gravitational potential of the Laniakea supercluster of galaxies, we show that the deviation from the WEP for neutrinos and photons is conservatively constrained to have an accuracy of $10^{-6}-10^{-7}$, which is 3--4 orders of magnitude better than previous results placed by MeV neutrinos from supernova 1987A. In addition, we demonstrate that the association of the TeV neutrino with the blazar flare sets limits on the energy scales of quantum gravity for both linear and quadratic violations of Lorentz invariance (LIV) to $E_{\rm QG, 1}>3.2\times10^{15}-3.7\times10^{16}$ GeV and $E_{\rm QG, 2}>4.0\times10^{10}-1.4\times10^{11}$ GeV. These improve previous limits on both linear and quadratic LIV energy scales in neutrino propagation by 5--7 orders of magnitude.

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arXiv2018

Model-independent Curvature Determination from Gravitational-Wave Standard Sirens and Cosmic Chronometers

The detection of gravitational waves (GWs) provides a direct way to measure the luminosity distance, which enables us to probe cosmology. In this paper, we continue to expand the application of GW standard sirens in cosmology, and propose that the spatial curvature can be estimated in a model-independent way by comparing the distances from future GW sources and current cosmic-chronometer observations. We expect an electromagnetic counterpart of the GW event to give the source redshift, and simulate hundreds of GW data from the coalescence of double neutron stars and black hole--neutron star binaries using the Einstein Telescope as reference. Our simulations show that, from 100 simulated GW events and 31 current cosmic-chronometer measurements, the error of the curvature parameter $Ω_{K}$ is expected to be constrained at the level of $\sim0.125$. If 1000 GW events are observed, the uncertainty of $Ω_{K}$ would be further reduced to $\sim0.040$. We also find that adding 50 mock $H(z)$ data (consisting of 81 cosmic-chronometer data and 1000 simulated GW events) could result in much tighter constraint on the zero cosmic curvature, for which, $Ω_{K}=-0.002\pm0.028$. Compared to some actual model-independent curvature tests involving the distances from other cosmic probes, this method with GW data achieves constraints with much higher precision.

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arXiv2018

Cosmological Tests with the Joint Lightcurve Analysis

We examine whether a comparison between wCDM and R_h=ct using merged Type Ia SN catalogs produces results consistent with those based on a single homogeneous sample. Using the Betoule et al. (2014) joint lightcurve analysis (JLA) of a combined sample of 613 events from SNLS and SDSS-II, we estimate the parameters of the two models and compare them. We find that the improved statistics can alter the model selection in some cases, but not others. In addition, based on the model fits, we find that there appears to be a lingering systematic offset of ~0.04-0.08 mag between the SNLS and SDSS-II sources, in spite of the cross-calibration in the JLA. Treating wCDM, LCDM and R_h=ct as separate models, we find in an unbiased pairwise statistical comparison that the Bayes Information Criterion (BIC) favors the R_h=ct universe with a likelihood of 82.8% versus 17.2% for wCDM, but the ratio of likelihoods is reversed (16.2% versus 83.8%) when w_de=-1 (i.e., LCDM) and strongly reversed (1.0% versus 99.0%) if in addition k=0 (i.e., flat LCDM). We point out, however, that the value of k is a measure of the net energy (kinetic plus gravitational) in the Universe and is not constrained theoretically, though some models of inflation would drive k to 0 due to an expansion-enforced dilution. Since we here consider only the basic LCDM model, the value of k needs to be measured and, therefore, the pre-assumption of flatness introduces a significant bias into the BIC.

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arXiv2018

Robust Limits on Photon Mass from Statistical Samples of Extragalactic Radio Pulsars

The photon zero-mass hypothesis has been investigated for a long time using the frequency-dependent time delays of radio emissions from astrophysical sources. However, the search for a rest mass of the photon has been hindered by the similarity between the frequency-dependent dispersions due to the plasma and nonzero photon mass effects. Considering the contributions to the observed dispersion measure from both the plasma and nonzero photon mass effects, and assuming the dispersion induced by the plasma effect is an unknown constant, we obtain a robust limit on the photon mass by directly fitting a combination of the dispersion measures of radio sources. Using the observed dispersion measures from two statistical samples of extragalactic pulsars, here we show that at the 68\% confidence level, the constraints on the photon mass can be as low as $m_γ\leq1.51\times10^{-48}~\rm kg\simeq8.47\times10^{-13}~{\rm eV}/c^{2}$ for the sample of 22 radio pulsars in the Large Magellanic Cloud and $m_γ\leq1.58\times10^{-48}~\rm kg\simeq8.86\times10^{-13} {\rm eV}/c^{2}$ for the other sample of 5 radio pulsars in the Small Magellanic Cloud, which are comparable with that obtained by a single extragalactic pulsar. Furthermore, the statistical approach presented here can also be used when more fast radio bursts with known redshifts are detected in the future.

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arXiv2018

The Origin of the Prompt Emission for Short GRB 170817A: Photosphere Emission or Synchrotron Emission?

The first gravitational-wave event from the merger of a binary neutron star system (GW170817) was detected recently. The associated short gamma-ray burst (GRB 170817A) has a low isotropic luminosity ($\sim 10^{47}$ erg s$ ^{-1}$) and a peak energy $E_{p}\sim 145$ keV during the initial main emission between -0.3 and 0.4 s. The origin of this short GRB is still under debate, but a plausible interpretation is that it is due to the off-axis emission from a structured jet. We consider two possibilities. First, since the best-fit spectral model for the main pulse of GRB 170817A is a cutoff power law with a hard low-energy photon index ($α=-0.62_{-0.54}^{+0.49} $), we consider an off-axis photosphere model. We develop a theory of photosphere emission in a structured jet and find that such a model can reproduce a low-energy photon index that is softer than a blackbody through enhancing high-latitude emission. The model can naturally account for the observed spectrum. The best-fit Lorentz factor along the line of sight is $\sim 20$, which demands that there is a significant delay between the merger and jet launching. Alternatively, we consider that the emission is produced via synchrotron radiation in an optically thin region in an expanding jet with decreasing magnetic fields. This model does not require a delay of jet launching but demands a larger bulk Lorentz factor along the line of sight. We perform Markov Chain Monte Carlo fitting to the data within the framework of both models and obtain good fitting results in both cases.

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arXiv2018

Cosmology with Gravitational Wave/Fast Radio Burst Associations

Recently, some theoretical models predicted that a small fraction of fast radio bursts (FRBs) could be associated with gravitational waves (GWs). In this work, we discuss the possibility of using GW/FRB association systems, if commonly detected in the future, as a complementary cosmic probe. We propose that upgraded standard sirens can be constructed from the joint measurements of luminosity distances $D_{L}$ derived from GWs and dispersion measures ${\rm DM_{IGM}}$ derived from FRBs (i.e., the combination $D_{L}\cdot{\rm DM_{IGM}}$). Moreover, unlike the traditional standard-siren approach (i.e., the $D_{L}$ method) and the $\rm DM_{IGM}$ method that rely on the optimization of the Hubble constant $H_0$, this $D_{L}\cdot{\rm DM_{IGM}}$ method has the advantage of being independent of $H_0$. Through Monte Carlo simulations, we prove that the $D_{L}\cdot{\rm DM_{IGM}}$ method is more effective to constrain cosmological parameters than $D_{L}$ or ${\rm DM_{IGM}}$ separately, and enables us to achieve accurate multimessenger cosmology from around 100 GW/FRB systems. Additionally, even if GW/FRB associations are not exist, the methodology developed here can still be applied to those GWs and FRBs that occur at the same redshifts.

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arXiv2017

A Further Test of Lorentz Violation from the Rest-Frame Spectral Lags of Gamma-Ray Bursts

Lorentz invariance violation (LIV) can manifest itself by an energy-dependent vacuum dispersion of light, which leads to arrival-time differences of photons with different energies originating from the same astronomical source. The spectral lags of gamma-ray bursts (GRBs) have been widely used to investigate the possible LIV effect. However, all current investigations used lags extracted in the observer frame only. In this work, we present, for the first time, an analysis of the LIV effect and its redshift dependence in the cosmological rest frame. Using a sample of 56 GRBs with known redshifts, we obtain a robust limit on LIV by fitting their rest-frame spectral lag data both using a maximization of the likelihood function and a minimum $χ^{2}$ statistic. Our analysis indicates that there is no evidence of LIV. Additionally, we test the LIV in different redshift ranges by dividing the full sample into four redshift bins. We also find no evidence for the redshift variation of the LIV effect.

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arXiv2017

Multimessenger tests of the weak equivalence principle from GW170817 and its electromagnetic counterparts

The coincident detection of a gravitational-wave (GW) event GW170817 with electromagnetic (EM) signals (e.g., a short gamma-ray burst SGRB 170817A or a macronova) from a binary neutron star merger within the nearby galaxy NGC 4933 provides a new, multimessenger test of the weak equivalence principle (WEP), extending the WEP test with GWs and photons. Assuming that the arrival time delay between the GW signals from GW170817 and the photons from SGRB 170817A or the macronova is mainly attributed to the gravitational potential of the Milky Way, we demonstrate that the strict upper limits on the deviation from the WEP are $Δγ<1.4\times10^{-3}$ for GW170817/macronova and $Δγ<5.9\times10^{-8}$ for GW170817/SGRB 170817A. A much more severe constraint on the WEP accuracy can be achieved ($\sim0.9\times10^{-10}$) for GW170817/SGRB 170817A when we consider the gravitational potential of the Virgo Cluster, rather than the Milky Way's gravity. This provides the tightest limit to date on the WEP through the relative differential variations of the $γ$ parameter for two different species of particles. Compared with other multimessenger (photons and neutrinos) results, our limit is 7 orders of magnitude tighter than that placed by the neutrinos and photons from supernova 1987A, and is almost as good as or is an improvement of 6 orders of magnitude over the limits obtained by the low-significance neutrinos correlated with GRBs and a blazar flare.

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arXiv2017

Constraining External Reverse Shock Physics of GRBs from ROTSE-III Limits

Assuming that the early optical emission is dominated by the external reverse shock (RS) in the standard model of gamma-ray bursts (GRBs), we intend to constrain RS models with the initial Lorentz factor $Γ_0$ of the outflows based on the ROTSE-III observations. We consider two cases of the RS behavior: the relativistic shock and the non-relativistic shock. For homogeneous interstellar medium (ISM) and wind circum-burst environment, the constraints can be achieved by the fact that the peak flux $F_{\rm ν}$ at the RS crossing time should be lower than the observed upper limit $F_{\rm ν,limit}$. We consider the different spectral regimes that the observed optical frequency $ν_{\rm opt}$ may locate in, which are divided by the orders for the minimum synchrotron frequency $ν_{\rm m}$ and the cooling frequency $ν_{\rm c}$. {\bf Considering the homogeneous and wind environment around GRBs, we find that the relativistic RS case can be constrained by the (upper and lower) limits of $Γ_0$ in a large range from about hundreds to thousands for 36 GRBs reported by ROTSE-III. The constraints on the non-relativistic RS case are achieved with limits of $Γ_0$ for 26 bursts ranging from $\sim 30$ to $\sim 350$.} The lower limits of $Γ_0$ achieved for the relativistic RS model is disfavored based on the previously discovered correlation between the initial Lorentz factor $Γ_0$ and the isotropic gamma-ray energy $E_{\rm γ, iso}$ released in prompt phase.

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