arXiv subjects

Jian-Yan Wei

Publications and source records attributed to Jian-Yan Wei.

45 records · Page 3Linked to original sources

arXiv2015

Optical light curve of GRB 121011A: a textbook for the onset of GRB afterglow in a mixture of ISM and wind-type medium

We reported the optical observations of GRB 121011A by 0.8-m TNT telescope at Xinglong observatory, China. The light curve of optical afterglow shows a smooth and featureless bump during the epoch of $\sim$130 sec and $\sim$5000 sec with a rising index of $1.57\pm0.28$ before the break time of $539\pm44$ sec, and a decaying index of about $1.29\pm0.07$ up to the end of our observations. Meanwhile, the X-ray light curve decays in a single power-law with a slop of about $1.51\pm0.03$ observed by $XRT$ onboard ${\rm} Swift$ from 100 sec to about 10000 sec after the burst trigger. The featureless optical light curve could be understood as an onset process under the external-shock model. The typical frequency has been below or near the optical one before the deceleration time, and the cooling frequency is located between the optical and X-ray wavelengths. The external medium density has a transition from a mixed stage of ISM and wind-type medium before the peak time to the ISM at the later phase. The joint-analysis of X-ray and optical light curves shows that the emission from both frequencies are consistent with the prediction of the standard afterglow model without any energy injections, indicating that the central engine has stopped its activity and does not restart anymore after the prompt phase.

astro-ph.HE↗

arXiv2015

A Correlated Study of Optical and X-ray Afterglows of GRBs

We study an extensive sample of 87 GRBs for which there are well sampled and simultaneous optical and X-ray light-curves. We extract the cleanest possible signal of the afterglow component, and compare the temporal behaviors of the X-ray light-curve, observed by Swift XRT, and optical data, observed by UVOT and ground-based telescopes for each individual burst. Overall we find 62\% GRBs that are consistent with the standard afterglow model. When more advanced modeling is invoked, up to 91\% of the bursts in our sample may be consistent with the external shock model. A large fraction of these bursts are consistent with occurring in a constant interstellar density medium (ISM) (61\%) while only 39\% of them occur in a wind-like medium. Only 9 cases have afterglow light-curves that exactly match the standard fireball model prediction, having a single power law decay in both energy bands which are observed during their entire duration. In particular, for the bursts with chromatic behavior additional model assumptions must be made over limited segments of the light-curves in order for these bursts to fully agree with the external shock model. Interestingly, for 54\% of the X-ray and 40\% of the optical band observations the end of the shallow decay ($t^{\sim-0.5}$) period coincides with the jet break ($t^{\sim-p}$) time, causing an abrupt change in decay slope. The fraction of the burst that consistent with the external shock model is independent of the observational epochs in the rest frame of GRBs. Moreover, no cases can be explained by the cooling frequency crossing the X-ray or optical band.

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arXiv2014

A double neutron star merger origin for the cosmological relativistic fading source PTF11agg?

The Palomar Transient Factory (PTF) team recently reported the discovery of a rapidly fading optical transient source, PTF11agg. A long-lived scintillating radio counterpart was identified, but the search for a high energy counterpart showed negative results. The PTF team speculated that PTF11agg may represent a new class of relativistic outbursts. Here we suggest that a neutron star (NS)-NS merger system with a supra-massive magnetar central engine could be a possible source to power such a transient, if our line of sight is not on the jet axis direction of the system. These systems are also top candidates for gravitational wave sources to be detected in the advanced LIGO/Virgo era. We find that the PTF11agg data could be explained well with such a model, suggesting that at least some gravitational wave bursts due to NS-NS mergers may be associated with such a bright electromagnetic counterpart without a γ-ray trigger.

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arXiv2013

A Comprehensive Study of Gamma-Ray Burst Optical Emission: III. Brightness Distributions and Luminosity Functions of Optical Afterglows

We continue our systematic statistical study on optical afterglow data of gamma-ray bursts (GRBs). We present the apparent magnitude distributions of early optical afterglows at different epochs (t= 10^2 s, t = 10^3 s, and 1 hour) for the optical lightcurves of a sample of 93 GRBs (the global sample), and for sub-samples with an afterglow onset bump or a shallow decay segment. For the onset sample and shallow decay sample we also present the brightness distribution at the peak time t_{p} and break time t_{b}, respectively. All the distributions can be fit with Gaussian functions. We further perform Monte Carlo simulations to infer the luminosity function of GRB optical emission at the rest-frame time 10^3 seconds, t_{p}, and t_{b}, respectively. Our results show that a single power-law luminosity function is adequate to model the data, with indices -1.40+/-0.10, -1.06+/- 0.16, and -1.54\+/- 0.22, respectively. Based on the derived rest-frame 10^3 s luminosity function, we generate the intrinsic distribution of the R-band apparent magnitude M_{R} at the observed time 10^{3} seconds post trigger, which peaks at M_{R}=22.5 mag. The fraction of GRBs whose R-band magnitude is fainter than 22 mag, and 25 mag and at the observer time 10^3 seconds are ~63% and ~25%, respectively. The detection probabilities of the optical afterglows with ground-based robotic telescopes and UVOT onboard {Swift} are roughly consistent with that inferred from this intrinsic M_{R} distribution, indicating that the variations of the dark GRB fraction among the samples with different telescopes may be due to the observational selection effect, although the existence of an intrinsically dark GRB population cannot be ruled out.

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arXiv2013

A Comprehensive Study of Gamma-Ray Burst Optical Emission: II. Afterglow Onset and Late Re-Brightening Components

We continue our systematic statistical study of various components in gamma-ray burst (GRB) optical lightcurves. We decompose the early onset bump and the late re-brightening bump with empirical fits and analyze their statistical properties. Among the 146 GRBs that have well-sampled optical lightcurves, the onset and re-brightening bumps are observed in 38 and 26 GRBs, respectively. It is found that the typical rising and decaying slopes for both the onset and re-brightening bumps are ~1.5 and -1.15, respectively. No early onset bumps in the X-ray band are detected to be associated with the optical onset bumps, while an X-ray re-brightening bump is detected for half of the re-brightening optical bumps. The peak luminosity is anti-correlated with the peak time, L_p\propto t_{p}^{-1.81+/-0.32} and L_p\propto t_{p}^{-0.83+/-0.17} for the onset and re-brightening bumps, respectively. Both L_p and the isotropic energy release of the onset bumps are correlated with E_{γ, iso}, whereas no similar correlation is found for the re-brightening bumps. Taking the onset bumps as probes for the properties of the fireballs and their ambient medium, we find that the typical power-law index of the relativistic electrons is 2.5 and the medium density profile behaves as n\propto r^{-1} within the framework of the synchrotron external shock models. With the medium density profile obtained from our analysis, we also confirm the correlation between initial Lorentz factor (Γ_0) and E_{γ, iso} in our previous work. The jet component that produces the re-brightening bump seems to be on-axis and independent of the prompt emission jet component. Its typical kinetic energy budget would be about one order of magnitude larger than the prompt emission component, but with a lower Γ_0, typically several tens.

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arXiv2012

A Comprehensive Study of Gamma-Ray Burst Optical Emission: I. Flares and Early Shallow Decay Component

Well-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are compiled from the literature. By empirical fitting we identify eight possible emission components and summarize the results in a "synthetic" lightcurve. Both optical flare and early shallow-decay components are likely related to long-term central engine activities. We focus on their statistical properties in this paper. Twenty-four optical flares are obtained from 19 GRBs. The isotropic R-band energy is smaller than 1% of $E_{γ, \rm iso}$. The relation between isotropic luminosities of the flares and gamma-rays follows $L^{\rm F}_{\rm R, iso}\propto L_{γ, \rm iso}^{1.11\pm 0.27}$. Later flares tend to be wider and dimmer, i.e., $w^{\rm F}\sim t^{\rm F}_{\rm p}/2$ and $L^{\rm F}_{\rm R, iso}\propto [t^{\rm F}_{\rm p}/(1+z)]^{-1.15\pm0.15}$. The detection probability of the optical flares is much smaller than that of X-ray flares. An optical shallow decay segment is observed in 39 GRBs. The relation between the break time and break luminosity is a power-law, with an index of $-0.78\pm 0.08$, similar to that derived from X-ray flares. The X-ray and optical breaks are usually chromatic, but a tentative correlation is found. We suggest that similar to the prompt optical emission that tracks $γ$-rays, the optical flares are also related to the erratic behavior of the central engine. The shallow decay component is likely related to a long-lasting spinning-down central engine or piling up of flare materials onto the blastwave. Mixing of different emission components may be the reason of the diverse chromatic afterglow behaviors.

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arXiv2010

Simulations on High-z Long Gamma-Ray Burst Rate

Since the launch of Swift satellite, the detections of high-z (z>4) long gamma-ray bursts (LGRBs) have been rapidly growing, even approaching the very early Universe (the record holder currently is z=8.3). The observed high-z LGRB rate shows significant excess over that estimated from the star formation history. We investigate what may be responsible for this high productivity of GRBs at high-z through Monte Carlo simulations, with effective Swif/BAT trigger and redshift detection probabilities based on current Swift/BAT sample and CGRO/BATSE LGRB sample. We compare our simulations to the Swift observations via log N-log P, peak luminosity (L) and redshift distributions. In the case that LGRB rate is purely proportional to the star formation rate (SFR), our simulations poorly reproduce the LGRB rate at z>4, although the simulated log N-log P distribution is in good agreement with the observed one. Assuming that the excess of high-z GRB rate is due to the cosmic metallicity evolution or unknown LGRB rate increase parameterized as (1+z)^delta, we find that although the two scenarios alone can improve the consistency between our simulations and observations, incorporation of them gives much better consistency. We get 0.2 4 (~15% of GRBs in current Swift LGRB sample based on our simulations), a window for very early Universe is opening by Swift and up-coming SVOM missions.

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arXiv2010

The ROSAT Bright Source 1RXS J201607.0+251645: An Active Algol-type Binary

1RXS J201607.0251645 is identified to be an eclipsing binary for the first time. We present the preliminary observations in V band with the 0.6-m telescope for three years and the extensive observations in V and R band with the 0.8-m telescope for six nights respectively. The light curve of the system is EB type. Five light minimum times were obtained and the orbital period of 0.388058d(0.00044d) is determined. The photometric solution given by the 2003-version Wilson-Devinney program suggests the binary is a semi-detached system with the photometric mass ratio 0.895(0.006), which probably comprise a G5 primary and an oversize K5 secondary. The less massive component has completely filled up its Roche lobe, while the other almost fills its Roche lobe with the filling factor of 93.4%. The system shows a varying O'Connell effect in its phase folded diagrams from 2005 to 2007, and is X-ray luminous with log(LXLbol)3.27. Possible mechanisms to account for these two phenomena are discussed. Finally, we infer the binary may be in thermal oscillation predicted by thermal relaxation oscillation (TRO) theory or may evolve into a contact binary.

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arXiv2006

Photometric monitoring of the ROSAT selected weak-line T Tauri stars in the Taurus-Auriga field

We monitored the light variations of 22 weak-line T Tauri stars (WTTS) discovered among the X-ray sources in the field of the Taurus-Auriga cloud. The photometric variability of 12 out of these WTTS samples is confirmed. They are all proved to be in periodic variations. By using the methods of the Phase Dispersion Minimization (PDM) and Fourier analysis, the rotational periods of these stars were determined based on this observation. Most of them are found to be shorter than one day. This gives further evidences for the spin up of solar-type stars as predicted by models of angular momentum evolution of pre-main sequence stars.

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