arXiv subjects

Jin-Song Deng

Publications and source records attributed to Jin-Song Deng.

15 recordsLinked to original sources

arXiv2026

SVOM/VT: Instrument Overview, Science Objectives, and First-Year Performance

The 44-cm Visible Telescope (VT) aboard the Space-based Variable Objects Monitor (SVOM) is a dual-band (400-650 nm and 650-1000 nm) instrument designed to detect and characterize the optical counterparts of gamma-ray bursts (GRBs) and other high-energy transients. This paper presents the VT's design, scientific objectives, observing strategies, and both space- and ground-based data processing pipelines, along with its first-year in-orbit performance. In-orbit commissioning tests confirm a sensitivity of 22.5 AB mag (300 s exposure), extendable to $\sim\!24$ AB mag through stacking. This performance enables the VT to monitor over 100 GRBs in its first year with an exceptional $\sim\!80\%$ detection rate for \textit{SVOM}/ECLAIRS-triggered bursts and ToO-observed bursts from other missions (e.g., \textit{Swift, Fermi, Einstein Probe (EP)}), outperforming \textit{Swift}/UVOT's $\sim\!40\%$ detection rate. Beyond its exceptional detection efficiency, the VT played a key role in identifying high-redshift GRBs-most notably GRB 250314A (z = 7.3). Its deep upper limits at long wavelengths (up to 1 $μ$m) were pivotal in guiding follow-up observations with large ground-based telescopes, enabling crucial near-infrared (NIR) detections. With its rapid response, deep sensitivity, and real-time processing capabilities, the VT is a key instrument for GRB research in \textit{SVOM}-era, enabling critical studies of GRB optical afterglows, circumburst environments, relativistic jet dynamics, and the origins of optically dark bursts.

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arXiv2026

SVOM/VT: Preliminary Calibration Analysis

We present the in-orbit calibration of the Visible Telescope (VT), one of the key instruments aboard the Space Variable Objects Monitor (SVOM) mission for gamma-ray burst (GRB) studies. Using Gaia Data Release 3 (DR3) as a reference, the VT achieves an astrometric precision better than 0.03'' for bright stars, degrading to ~0.25'' for faint targets. Shortly after launch, contamination was detected, reducing system transmission by ~40%. An initial bake-out successfully restored performance, but gradual recontamination caused transmission to decline by ~20% over the following 100 days before stabilizing. Despite this effect, routine standard star observations maintain precise zero-point calibration, ensuring a photometric stability of 0.02 mag. Using synthetic stellar spectra, we derived photometric transformations to the Gaia, SDSS, and Johnson-Cousins systems with typical residuals of 0.03 mag. These results demonstrate the VT system's capability and reliability in calibrating GRBs and other transients.

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arXiv2026

SVOM/VT: Overview of data processing and GRB identifications with X-band data

VT (the Visible Telescope) is an optical telescope onboard the SVOM (Space-based Multi-band Astronomical Variable Objects Monitor) mission, specifically designed to detect optical counterparts of gamma-ray bursts (GRBs), study their afterglows, and select high-redshift candidates. It performs rapid follow-up observations simultaneously in two channels either via autonomous platform slewing or Target of Opportunity (ToO) observations. The science images acquired by VT and transmitted via the X-band downlink system are designated as VT X-band data. This paper provides an overview of GRB optical afterglow identifications with VT and describes the ground-based processing pipeline for VT X-band data, including preprocessing, astrometric calibration, and photometry. Up to 2025 December 3, VT has followed up 111 GRBs triggered by SVOM or external missions. The overall detection rate of optical counterparts is approximately 75%. Specifically, for bursts detected by SVOM/ECLAIRs, the detection rate is 77% when observed by VT within 30 minutes after the burst. A slightly higher detection rate of 81% is achieved for GRBs triggered by external missions through rapid ToO observations with a mid-time of less than 3 hours.

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arXiv2026

SVOM/VT: Flight Model Verification and Pre-launch Testing

This paper presents pre-launch testing and calibration results for the SVOM/VT (Space-based Variable Objects Monitor, Visible Telescope) Flight Model (FM), validating its performance under simulated space conditions through thermal vacuum cycling, energy concentration analysis, stray light suppression, and CCD/electronics calibrations (gain, noise, quantum efficiency). The results confirm full compliance with design requirements: stray light suppression achieves point-source transmittance $<10^{-7}$ at $30^\circ$ off-axis, thermal control maintains stable CCD temperatures ($-75^\circ$C for the red channel, $-65^\circ$C for the blue channel), and detection sensitivity meets the limiting magnitude of 22.50 (SNR $>$ 3 with 300 seconds exposure). Early in-orbit tests further validate performance, yielding limiting magnitudes of 22.70 (V-band, red) and 22.78 (blue), consistent with pre-launch specifications.

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arXiv2026

SVOM/VT: Real-Time Onboard Data Processing

The SVOM Visible Telescope (VT) is critical for the rapid identification of gamma-ray burst (GRB) optical counterparts, particularly for high-redshift candidates that require immediate infrared spectroscopic follow-up. To address the stringent bandwidth constraints of the VHF downlink while ensuring real-time data availability, we developed the VT Onboard Data Processing Pipeline (VOPP).This paper details the software architecture, algorithms, and hardware implementation of VOPP using an FPGA and a CPU. The pipeline performs essential real-time tasks, including image quality assessment, dark and flat-field correction, and optimized image stacking to mitigate cosmic ray contamination and variable background noise. Furthermore, it generates compact source catalogs and highly compressed 1-bit images to facilitate rapid downlink.In-flight performance analysis confirms the pipeline's robustness, demonstrating the availability of VT VHF data for 78 percent of promptly slewed SVOM GRBs, with 56 percent leading to the identification of optical counterparts, typically within 18 minutes post-trigger.

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arXiv2026

SVOM/VT: On-ground processing of VT-VHF data

The VT--VHF data comprise three types of onboard-processed data results generated from four sequential observational sequences and transmitted to the ground via a Very High Frequency (VHF) downlink. On the ground, these data are processed by three successive pipelines: the pre-processing pipeline, the VT--VHF data processing pipeline (VVPP), and the VT afterglow candidate pipeline (VTAC). These pipelines perform packet decoding, astrometric and photometric calibration, and afterglow candidate identification, respectively. This paper describes the architecture and operational implementation of the VT--VHF ground processing system and assesses its end-to-end performance using the first year of SVOM operations. These data enable rapid identification of GRB optical counterparts. Early detections, while the source is still optically bright, facilitate spectroscopic redshift measurements. Dual-band colors provide preliminary redshift constraints and help identify high-redshift candidates, whereas non-detections in both bands may indicate very high redshift, significant extinction, or intrinsically dark bursts. In-orbit operations show that the VT--VHF ground processing system successfully identifies optical afterglow candidates for a significant fraction of ECLAIRs triggers with available VT--VHF data, demonstrating its robustness and readiness.

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arXiv2026

SVOM/C-GFT: Instrumentation and Performances on the SVOM Alerts

The Chinese Ground Follow-up Telescope (C-GFT) is an optical facility upgraded to support the Space Variable Objects Monitor mission (\textit{SVOM}). Located at the Jilin Observation Station, it is capable of rapidly identifying and monitoring the optical counterparts of Gamma-Ray Bursts (GRBs). The 1.2-m telescope is equipped with two switchable focal-plane instruments: the prime-focus wide-field LATIOS camera and the Cassegrain-focus three-channel CATCH camera. In this paper, we present a system overview, including the observatory, the telescope, the instrumentation, the automated operational framework managed by the Operations Center, and the data processing pipelines. We also report the performance results obtained during over one year of \textit{SVOM}'s post-launch operations. The results demonstrate that the system meets its design specifications and delivers robust observational and operational performance.

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arXiv2025

GRB 240715A: Revealing Novel Intrinsic Mechanism by Different Individual Pulse

The Space-based multiband astronomical Variable Objects Monitor (SVOM), detected its first short gamma-ray burst, GRB 240715A, in-flight, which was jointly observed by Fermi. Based on observational data of SVOM/GRM and Fermi/GBM, we perform a comprehensive temporal and spectral analysis for individual pulse in the prompt emission of this burst, and novel characteristics are revealed. Firstly, opposite evolutions of spectral lag are found in the first and third pulse of this burst. Second, the large negative lag of the first pulse is an outlier in short GRB sample, especially when the pulse duration is considered. Spectral analysis shows that the negative lag of the first pulse is caused by the evolution of spectrum index, and is irrelevant to Epeak, which is inconsistent with the previous study. The intrinsic mechanism is probably attributed to electron cooling in the decaying magnetic field, which leads to the continuous hardening of the spectrum index and results in negative lag. Furthermore, spectral analysis also shows that the third pulse is more likely to be described by a quasi-thermal spectrum, indicating the existence of photospheric emission. It is difficult to explain how the synchrotron radiation appears before photospheric emission in a single GRB and some assumptions are discussed.

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arXiv2025

GRB 240825A: Early Reverse Shock and Its Physical Implications

Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space- and ground-based telescopes/instruments, covering wavelengths from NIR/optical to X-ray and GeV, and spanning from the prompt emission to the afterglow phase triggered by Swift and Fermi. The early afterglow observations were carried out by SVOM/C-GFT, and spectroscopic observations of the afterglow by GTC, VLT, and TNG determined the redshift of the burst ($z = 0.659$) later.A comprehensive analysis of the prompt emission spectrum observed by Swift-BAT and Fermi-GBM/LAT reveals a rare and significant high-energy cutoff at ~76 MeV. Assuming this cutoff is due to $γγ$ absorption allows us to place an upper limit on the initial Lorentz factor, $Γ_0 < 245$. The optical/NIR and GeV afterglow light curves be described by the standard external shock model, with early-time emission dominated by a reverse shock (RS) and a subsequent transition to forward shock (FS) emission. Our afterglow modelling yields a consistent estimate of the initial Lorentz factor ($Γ_{\rm 0} \sim 234$). Furthermore, the RS-to-FS magnetic field ratio ($\mathcal{R}_B \sim 302$) indicates that the reverse shock region is significantly more magnetized than the FS region. An isotropic-equivalent kinetic energy of $E_{\text{k,iso}} = 5.25 \times 10^{54}$ erg is derived, and the corresponding $γ$-ray radiation efficiency is estimated to be $η_γ$ = 3.1%. On the other hand, the standard afterglow model can not reproduce the X-ray light curve of GRB 240825A, calling for improved models to characterize all multiwavelength data.

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arXiv2016

Very Bright Prompt and Reverse Shock Emission of GRB 140512A

We report our observations of very bright prompt optical and reverse shock (RS) optical emission of GRB 140512A and analyze its multi-wavelength data observed with the {\em Swift} and {\em Fermi} missions. It is found that the joint optical-X-ray-gamma-ray spectrum with our first optical detection (R=13.09 mag) at $T_0+136$ seconds during the second episode of the prompt gamma-rays can be fit by a single power-law with index $-1.32\pm 0.01$. Our empirical fit to the afterglow lightcurves indicates that the observed bright optical afterglow with R=13.00 mag at the peak time is consistent with predictions of the RS and forward shock (FS) emission of external shock models. Joint optical-X-ray afterglow spectrum is well fit with an absorbed single power-law, with an index evolving with time from $-1.86\pm 0.01$ at the peak time to $-1.57\pm 0.01$ at late epoch, which could be due to the evolution of the ratio of the RS to FS emission fluxes. We fit the lightcurves with standard external models, and derive the physical properties of the outflow. It is found that the ratio $R_B\equivε_{\rm B, r}/ε_{\rm B, f}$ is 8187, indicating a high magnetization degree in the RS region. Measuring the relative radiation efficiency with $R_e\equivε_{\rm e, r}/ε_{\rm e, f}$, we have $R_e= 0.02$, implying the radiation efficiency of the RS is much lower than that in FS. We also show that the $R_B$ of GRBs 990123, 090102, and 130427A are similar to that of GRB 140512A and their apparent difference may be mainly attributed to the difference of the jet kinetic energy, initial Lorentz factor, and medium density among them.

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arXiv2016

GRB 110530A: Peculiar Broad Bump and Delayed Plateau in Early Optical Afterglows

We report our very early optical observations of GRB 110530A and investigate its jet properties together with its X-ray afterglow data. A peculiar broad onset bump followed by a plateau is observed in its early R band afterglow lightcurve. The optical data in the other bands and the X-ray data are well consistent with the temporal feature of the R band lightcurve. Our joint spectral fits of the optical and X-ray data show that they are in the same regime, with a photon index of $\sim 1.70$. The optical and X-ray afterglow lightcurves are well fitted with the standard external shock model by considering a delayed energy injection component. Based on our modeling results, we find that the radiative efficiency of the GRB jet is $\sim 1\%$ and the magnetization parameter of the afterglow jet is $<0.04$ with the derived extremely low $ε_B$ (the fraction of shock energy to magnetic field) of $(1.64\pm 0.25)\times 10^{-6}$. These results indicate that the jet may be matter dominated. Discussion on delayed energy injection from accretion of late fall-back material of its pre-supernova star is also presented.

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arXiv2016

NUV Star Catalogue from the Lunar-based Ultraviolet Telescope Survey. First Release

We present a star catalogue extracted from the Lunar-based Ultraviolet Telescope (LUT) survey program. LUT's observable sky area is a circular belt around the Moon's north pole, and the survey program covers a preferred area for about 2400 deg$^2$ which includes a region of the Galactic plane. The data is processed with an automatic pipeline which copes with stray light contamination, artificial sources, cosmic rays, flat field calibration, photometry and so on. In the first release version, the catalogue provides high confidence sources which have been cross-identified with Tycho-2 catalogue. All the sources have signal-to-noise ratio larger than 5, and the corresponding magnitude limit is typically 14.4 mag, which can be deeper as ~16 mag if the stray light contamination is in the lowest level. A total number of 86,467 stars are recorded in the catalogue. The full catalogue in electronic form is available on line.

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arXiv2015

Multi-Wavelength Observations of GRB 111228A and Implications for the Fireball and its environment

Observations of very early multi-wavelength afterglows are critical to reveal the properties of the radiating fireball and its environment as well as the central engine of gamma-ray bursts (GRBs). We report our optical observations of GRB 111228A from 95 sec to about 50 hours after the burst trigger and investigate its properties of the prompt gamma-rays and the ambient medium using our data and the data observed with {\em Swift} and {\em Fermi} missions. Our joint optical and X-ray spectral fits to the afterglow data show that the ambient medium features as low dust-to-gas ratio. Incorporating the energy injection effect, our best fit to the afterglow lightcurves with the standard afterglow model via the Markov Chain Monte Carlo (MCMC) technique shows that $ε_e=(6.9\pm 0.3)\times 10^{-2}$, $ε_B=(7.73\pm 0.62)\times 10^{-6}$, $E_{\rm K}=(6.32\pm 0.86)\times 10^{53}\rm erg$, $n=0.100\pm 0.014$ cm$^{-3}$. The low medium density likely implies that the afterglow jet may be in a halo or in a hot ISM. Achromatic shallow decay segment observed in the optical and X-ray bands is well explained with the long-lasting energy injection from the central engine, which would be a magnetar with a period of about 1.92 ms inferred from the data. The $E_p$ of its time-integrated prompt gamma-ray spectrum is $\sim 26$ KeV. Using the initial Lorentz factor ($Γ_0=476^{+225}_{-237}$) derived from our afterglow model fit, it is found that GRB 111228A satisfies the $L_{\rm iso}-E_{\rm p,z}-Γ_0$ relation and bridges the typical GRBs and low luminosity GRBs in this relation.

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arXiv2015

Data Processing Pipeline for Pointing Observations of Lunar-based Ultraviolet Telescope

We describe the data processing pipeline developed to reduce the pointing observation data of Lunar-based Ultraviolet Telescope (LUT), which belongs to the Chang'e-3 mission of the Chinese Lunar Exploration Program. The pointing observation program of LUT is dedicated to monitor variable objects in a near-ultraviolet (245-345 nm) band. LUT works in lunar daytime for sufficient power supply, so some special data processing strategies have been developed for the pipeline. The procedures of the pipeline include stray light removing, astrometry, flat fielding employing superflat technique, source extraction and cosmic rays rejection, aperture and PSF photometry, aperture correction, and catalogues archiving, etc. It has been intensively tested and works smoothly with observation data. The photometric accuracy is typically ~0.02 mag for LUT 10 mag stars (30 s exposure), with errors come from background noises, residuals of stray light removing, and flat fielding related errors. The accuracy degrades to be ~0.2 mag for stars of 13.5 mag which is the 5σ detection limit of LUT.

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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.

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