arXiv subjects

Jin-Da Li

Publications and source records attributed to Jin-Da Li.

5 recordsLinked to original sources

arXiv2024

Polarization of gamma-ray burst afterglows in the context of non-axisymmetric structured jets

As the most energetic explosion in the universe, gamma-ray bursts (GRBs) are usually believed to be generated by relativistic jets. Some mechanisms (e.g. internal non-uniform magnetic dissipation processes or the precession of the central engine) may generate asymmetric jet structures, which is characterized by multiple fluctuations in the light curve of afterglow. Since the jet's structure introduces asymmetry in radiation around the line of sight (LOS), it is naturally expected that polarization will be observable. In this work, we reveal the polarization characteristics of gamma-ray burst afterglows with a non-axisymmetric structured jet. Our results show that the afterglow signal generally exhibits polarization, with the degree and evolution influenced by the specific jet structure, observing frequency, and the line of sight (LOS). The polarization degree is notably higher when the LOS is outside the jet. This degree fluctuates over time as different regions of radiation alternate in their dominance, which is accompanied by the rotation of the polarization angle and further reflects the intricate nature of the jet. Regarding its evolution over frequency, the polarization degree displays significant fluctuations at spectral breaks, with the polarization angle possibly undergoing abrupt changes. These features may provide strong evidence for future identification of potential GRBs with asymmetric jet structures.

astro-ph.HE↗

arXiv2024

Multiple rebrightenings in the optical afterglow of GRB 210731A: evidence for an asymmetric jet

The broadband afterglow of Gamma-ray bursts (GRBs) is usually believed to originate from the synchrotron radiation of electrons accelerated by the external shock of relativistic jets. Therefore, the jet structure should have a significant impact on the GRB afterglow features. The latest observations indicate that the GRB jets may possess intricate structures, such as Gaussian structure, power-law structure, or jet-cocoon structure. Most recently, an abnormal afterglow of GRB 210731A has raised extensive attention, whose optical afterglow exhibites multiple rebrightening phenomena within 4 hours, posing a serious challenge to the standard afterglow model. Here we intend to interpret the characteristics of GRB 210731A afterglows within the framework of non-axisymmetric structured jets, where multiple distinct peaks in the afterglow light curve are caused by the uneven distribution of energy and velocity within the jet in the azimuth angle direction. Through Monte Carlo Markov Chain fitting, we show that a three-component asymmetric structured jet can well explain the multi-band afterglow data. The energy difference among the three components is about 1.5 orders of magnitude, with higher-energy components exhibiting slower speeds. The radiation contribution of each component has sequentially dominated the light curve of the afterglow, resulting in multiple peaks, with the highest peak occurring at the latest time. We suggest that in the future, polarization observations should be conducted on afterglows with multiple brightening signatures, which will help to effectively distinguish the structured jet model from other alternative models, such as energy injection, and ultimately help to determine the true configuration of jets.

astro-ph.HE↗

arXiv2023

Characteristics of gamma-ray burst afterglows in the context of non-axisymmetric structured jets

As the most energetic explosions in the Universe, gamma-ray bursts (GRBs) are commonly believed to be generated by relativistic jets. Recent observational evidence suggests that the jets producing GRBs are likely to have a structured nature. Some studies have suggested that non-axisymmetric structured jets may be formed through internal non-uniform magnetic dissipation processes or the precession of the central engine. In this study, we analyze the potential characteristics of GRB afterglows within the framework of non-axisymmetric structured jets. We simplify the profile of the asymmetric jet as a step function of the azimuth angle, dividing the entire jet into individual elements. By considering specific cases, we demonstrate that the velocity, energy, and line-of-sight direction of each jet element can greatly affect the behaviour of the overall light curve. The radiative contributions from multiple elements may lead to the appearance of multiple distinct peaks or plateaus in the light curve. Furthermore, fluctuations in the rising and declining segments of each peak can be observed. These findings establish a theoretical foundation for future investigations into the structural characteristics of GRBs by leveraging GRB afterglow data.

astro-ph.HE↗

arXiv2022

The Peculiar Precursor of a Gamma-Ray Burst from a Binary Merger Involving a Magnetar

The milestone discovery of GW 170817-GRB 170817A-AT 2017gfo has shown that gravitational wave (GW) could be produced during the merger of neutron star-neutron star/black hole and that in electromagnetic (EM) wave a gamma-ray burst (GRB) and a kilonova (KN) are generated in sequence after the merger. Observationally, however, EM property before the merger phase is still unclear. Here we report a peculiar precursor in a KN-associated long-duration GRB 211211A, providing evidence of the EM before the merger. This precursor lasts $\sim$ 0.2 s, and the waiting time between the precursor and the main burst is $\sim$ 1 s, comparable to that between GW 170817 and GRB 170817A. The spectrum of the precursor could be well fit with a non-thermal cutoff power-law model instead of a blackbody. Especially, a $\sim$22 Hz Quasi-Periodic Oscillation candidate ($\sim 3\sigma$) is detected in the precursor. These temporal and spectral properties indicate that this precursor is probably produced by a catastrophic flare accompanying with magnetoelastic or crustal oscillations of a magnetar in binary compact merger. The strong magnetic field of the magnetar can also account for the prolonged duration of GRB 211211A. However, it poses a challenge to reconcile the rather short lifetime of a magnetar with the rather long spiraling time of a binary neutron star system only by the GW radiation before merger.

astro-ph.HE↗

arXiv2021

Identifications of RR Lyrae stars and Quasars from the simulated data of Mephisto-W Survey

We have investigated the feasibilities and accuracies of the identifications of RR Lyrae stars and quasars from the simulated data of the Multi-channel Photometric Survey Telescope (Mephisto) W Survey. Based on the variable sources light curve libraries from the Sloan Digital Sky Survey (SDSS) Stripe 82 data and the observation history simulation from the Mephisto-W Survey Scheduler, we have simulated the $uvgriz$ multi-band light curves of RR Lyrae stars, quasars and other variable sources for the first year observation of Mephisto-W Survey. We have applied the ensemble machine learning algorithm Random Forest Classifier (RFC) to identify RR Lyrae stars and quasars, respectively. We build training and test samples and extract ~ 150 features from the simulated light curves and train two RFCs respectively for the RR Lyrae star and quasar classification. We find that, our RFCs are able to select the RR Lyrae stars and quasars with remarkably high precision and completeness, with $purity$ = 95.4 per cent and $completeness$ = 96.9 per cent for the RR Lyrae RFC and $purity$ = 91.4 per cent and $completeness$ = 90.2 per cent for the quasar RFC. We have also derived relative importances of the extracted features utilized to classify RR Lyrae stars and quasars.

astro-ph.IM↗