Xiang-Gao Wang

We report multiwavelength observations and theoretical modeling of the afterglow of gamma-ray burst (GRB) 151027A. The object exhibits a complete evolutionary sequence, including prompt gamma-ray and optical emission, an initial optical onset bump, an optical rebrightening, a late-time supernova bump, an X-ray flare, and two distinct X-ray plateaus. GRB 151027A exhibits nearly all characteristic features observed in GRB afterglows. Such a rich set of features within a single event is exceptionally rare. We show that the first X-ray plateau followed by a rapid decay can be attributed to the collapse of a newly formed magnetar to form a black hole. The second X-ray plateau can be explained by fallback accretion. We find that the energy-injection model successfully reproduces the optical rebrightening of GRB 151027A. The late-time optical bump is well described by a ⁵⁶ Ni-powered supernova light curve. GRB 151027A presents a complete physical picture for GRB phenomenology, whereas reconstructing such a comprehensive picture previously required the statistical analysis of multiple GRBs.

Context. On December 6, 2024, 1ES 1959+650, one of the X-ray brightest blazars known, underwent a high-amplitude X-ray outburst detected by SVOM, the first such discovery with this mission. The source was subsequently monitored with SVOM and Swift from December 2024 to March 2025. Aims. We report the detection and multiwavelength follow-up of this event, and describe the temporal and spectral evolution observed during the campaign. Methods. We analyzed data from SVOM/MXT, SVOM/ECLAIRs, and Swift /XRT using log-parabola models to track flux and spectral variability. Results. We detected the source in a bright state over the 0.3–50 keV range. During the three months of monitoring, the X-ray flux varied significantly, and showed episodes of spectral hardening at high flux levels. The spectral curvature evolved more irregularly and did not show a clear trend with flux. The synchrotron peak of the spectral energy distribution shifts to higher energies when the flux increases. Conclusions. This event constitutes the first blazar outburst discovered in X-rays by SVOM. The coordinated follow-up with Swift provided continuous coverage of the flare and highlights the strong complementarity of the two missions for time-domain studies of blazars. The flare shows no clear signatures of either Fermi I or Fermi II acceleration, suggesting a mixed Fermi I and II scenario.

It is known that there is an association between long gamma-ray bursts and supernovae (SNe), and study of these SNe is important for exploring the death of massive stars. Here, we investigate GRB 171205A/SN 2017iuk (at redshift z = 0.0368) by fitting multiband light curves and modeling the SN 2017iuk spectra with SYNAPPS. The light curve of GRB 171205A/SN 2017iuk shows a long plateau, not only in X-rays but also in optical bands. This plateau may be from the late-time contribution of a magnetar central engine. We use a magnetar spindown model, ⁵⁶ Ni model, and cooling model to fit the multiband light curves. The best-fitting results reveal the total SN ejected mass M ej = 4.6 0 − 0.70 + 1.20 M ⊙ , Ni mass M Ni = 0.3 1 − 0.03 + 0.05 M ⊙ , and total kinetic energy E _K ≈ 3.14 × 10 ⁵² erg, consistent with the average values inferred for other gamma-ray burst-SNe. The best-fitting photospheric velocities are 14,700 and 11,400 km s ⁻¹ , and the photospheric temperatures are 9900 and 11,800 K, at +7.2 and +13.2 days (respectively). From our light curves and spectral analysis, we suggest that the central engine of GRB 171205A/SN 2017iuk is likely to be a magnetar, with initial spin period P 0 = 70.6 1 − 0.97 + 0.62 ms and surface magnetic field at the pole B p = 3.8 4 − 0.61 + 0.33 × 1 0 15 G .

We present the first X-ray polarimetric observation of the extreme high-synchrotron-peaked blazar 1ES 1101–232, conducted by the Imaging X-ray Polarimetry Explorer (IXPE). The data analysis incorporates simultaneous and quasi-simultaneous observations from the Swift X-Ray Telescope and NuSTAR. Our results reveal a significant detection of X-ray polarization in the 2–6 keV band at a confidence level (CL) of 6.6 σ , with a polarization degree of Π _X = 17.9% ± 2.7% and an electric vector position angle (EVPA) of ψ _X = 10 . ° 0 ± 4 . ° 4. An even higher polarization degree of Π _X = 38.9% ± 9.1% with an EVPA of ψ _X = 13 . ° 9 ± 6 . ° 7 is observed within a narrower time interval, at a CL of 4.3 σ . During the IXPE observational campaign, the X-ray spectrum of 1ES 1101–232 exhibits a clear soft-to-hard spectral evolution in the 0.3–10 keV band, although no significant flux variability is detected. Additionally, a clockwise hysteresis loop is identified in the flux–photon index plane. These findings collectively indicate that the X-ray emission from 1ES 1101–232 originates in a region characterized by a well-ordered magnetic field through synchrotron radiation.

Type IIn supernovae (SNe IIn) are a subclass of core-collapse SNe in which strong interactions occur between the ejecta and dense circumstellar material, creating ideal conditions for the production of high-energy neutrinos. This makes them promising candidate sources of neutrinos. In this work, we conduct an association study between 163 SNe IIn observed by the Zwicky Transient Facility and 138 neutrino alert events detected by the IceCube Neutrino Observatory. After excluding alerts with poor localization, we find two SNe that are spatiotemporally coincident with neutrino events. IC 231027A and IC 250421A coincide with the positions of SN 2023syz and SN 2025cbj, respectively, within their localization uncertainties, and the neutrino arrival times are delayed by 38 days and 61 days relative to the discovery times of the corresponding SNe. Using Monte Carlo simulations, we estimate that the probability of two such events occurring by chance in our sample is p ∼ 0.67%, suggesting that they may originate from genuine physical associations, though the result is not yet statistically significant. Our model calculations, however, indicate that the likelihood of a neutrino originating from IC 231027A is low, implying that the association between IC 231027A and SN 2023syz is likely coincidental. Nevertheless, under optimistic parameters, the probability of detecting a neutrino from the whole SNe IIn sample could reach ≳6%, indicating that detecting neutrino emission from the SNe population may be possible. Our study provides a systematic analysis, combining statistical analysis and model calculations, to assess whether interacting supernovae can serve as potential sources of neutrino emission.

Investigating the correlation between the tidal disruption event (TDE) population and IceCube neutrinos could help us better understand whether TDEs could be potential high-energy neutrino emitters. In this paper, we perform a systematic search for TDEs that are associated with neutrinos in a sample including 143 IceCube neutrino alert events and 52 TDEs classified by the Zwicky Transient Facility Bright Transient Survey. Furthermore, considering that the TDEs/TDE candidates reported as potential IceCube neutrino emitters are all accompanied by infrared (IR) echo emission, we further select TDEs with IR echoes from these 52 TDEs as a subsample to examine their correlation with neutrinos. Based on the Wide-field Infrared Survey Explorer mission database, seven TDEs are identified as having IR echoes. Then we employ Monte Carlo simulations to quantify the correlation between the TDE sample/subsample and IceCube neutrinos. Finally, after considering spatial and temporal criteria, the seven TDEs with IR echoes show the most significant correlation at the 2.46σ confidence level. If we tentatively further take the time delay factor into account, the correlation enhances to the 2.66σ confidence level. The correlation is primarily contributed by two TDEs: AT2019dsg and AT2019azh. The latter’s association with a neutrino alert, IC230217A, is newly reported in this work. We discuss the possible physical connection between AT2019azh and the neutrino event IC230217A.

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, Γ₀ < 245. The optical/NIR and GeV afterglow light curves can 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 modeling yields a consistent estimate of the initial Lorentz factor (Γ₀ ∼ 234). Furthermore, the RS-to-FS magnetic field ratio ( R B ∼ 302 ) indicates that the RS region is significantly more magnetized than the FS region. An isotropic-equivalent kinetic energy of E _k,iso = 5.25 × 10⁵⁴ 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 cannot reproduce the X-ray light curve of GRB 240825A, calling for improved models to characterize all multiwavelength data.

GRB 170519A was discovered by the Swift Burst Alert Telescope (BAT) and then observed by the Swift X-Ray Telescope, Swift UltraViolet and Optical Telescope, and ground-based telescopes. We report Lick Katzman Automatic Imaging Telescope observations of GRB 170519A and make temporal analysis and spectral joint fits of its multiwavelength light curves. The observations present a relatively complete afterglow structure, including two X-ray flares (Flares I and II), optical onset (Slice 1), normal decay (Slices 2 and 3), and a possible jet break. The spectrum of the bright X-ray flare (Flare II) indicates that a thermal component exists at t = 190–240 s. The blackbody (BB) emits in the photospheric radius R _ph ∼ 10¹¹ cm, and its temperature (kT) decreases with time from 1.08 to 0.37 keV, while its Lorentz factor of BB (Γ_BB) decreases with time from 67.71 to 46.70. The luminosity of the BB (L _BB), kT, and Γ_BB follows the relations L _BB ∝ kT ^2.49±0.03 and Γ BB ∝ L BB 0.27 . In the optical light curves, there is an onset bump in the early-time afterglow, rising with an index α _O,1 ≈ −0.43 and peaking ∼1174.9 s since the BAT trigger. The bump then decays with α _O,2 ≈ 0.88 in the normal decay phase, and the X-ray flux decays with a similar index of α _X,1 ≈ 0.95. There is no obvious spectral evolution in the normal decay phases, with photon index Γ ˆ = 1.86 and 1.92 in Slices 2 and 3, respectively. We find that the multiwavelength light curves of the GRB 170519A afterglow can be well fitted by an external shock with time-dependent ϵ _B . In the early afterglow, the value of ϵ _B decays rapidly from 4.29 × 10⁻² to 8.23 × 10⁻³.