arXiv subjects

J. -J. Geng

Publications and source records attributed to J. -J. Geng.

4 recordsLinked to original sources

arXiv2026

An invariant energy release hierarchy in a repeating fast radio burst

Fast radio bursts (FRBs) are luminous millisecond radio transients whose physical origin remains unsettled. A key diagnostic is whether their burst-energy distributions retain characteristic physical scales that are intrinsic and temporally stable within an individual engine. Here we report a 3.2-year monitoring campaign of the hyperactive repeater FRB~20220529 with FAST and Parkes, yielding more than 1,300 bursts spanning nearly five orders of magnitude in spectral energy density. The cumulative burst-rate distribution is described by an exponential-plus-power-law (EXP+PL) form, linking a low-energy exponential component with characteristic scale (E_0) to a scale-free bright-end tail. This scale remains invariant despite the burst rate declining by more than an order of magnitude, revealing a stable dissipation scale decoupled from the source's macroscopic trigger activity. Within a magnetar interpretation, this phenomenology is consistent with localized sub-critical reconnection episodes coexisting with plasmoid-mediated magnetic avalanches in a twisted magnetosphere. The invariant (E_0) constrains the dissipation region to the inner-to-middle magnetosphere and reveals a robust energy-release hierarchy beneath the variable activity of repeating FRBs, providing an observational benchmark for relativistic reconnection in an ultra-magnetized neutron-star environment.

astro-ph.HE↗

arXiv2025

An extremely soft and weak fast X-ray transient associated with a luminous supernova

Long gamma-ray bursts (LGRBs), including their subclasses of low-luminosity GRBs (LL-GRBs) and X-ray flashes (XRFs) characterized by low spectral peak energies, are known to be associated with broad-lined Type Ic supernovae (SNe Ic-BL), which result from the core collapse of massive stars that lose their outer hydrogen and helium envelopes. However, the soft and weak end of the GRB/XRF population remains largely unexplored, due to the limited sensitivity to soft X-ray emission. Here we report the discovery of a fast X-ray transient, EP250108a, detected by the Einstein Probe (EP) in the soft X-ray band at redshift $z = 0.176$, which was followed up by extensive multiband observations. EP250108a shares similar X-ray luminosity as XRF\,060218, the prototype of XRFs, but it extends GRBs/XRFs down to the unprecedentedly soft and weak regimes, with its $E_{\rm peak} \lesssim 1.8\,\mathrm{keV}$ and $E_{\rm iso} \lesssim 10^{49}\, \mathrm{erg}$, respectively. Meanwhile, EP250108a is found to be associated with SN\,2025kg, one of the most luminous and possibly magnetar-powered SNe Ic-BL detected so far. Modeling of the well-sampled optical light curves favors a mildly relativistic outflow as the origin of this event. This discovery demonstrates that EP, with its unique capability, is opening a new observational window into the diverse outcomes of death of massive stars.

astro-ph.HE↗

arXiv2024

Soft X-ray prompt emission from a high-redshift gamma-ray burst EP240315a

Long gamma-ray bursts (GRBs) are believed to originate from core collapse of massive stars. High-redshift GRBs can probe the star formation and reionization history of the early universe, but their detection remains rare. Here we report the detection of a GRB triggered in the 0.5--4 keV band by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated as EP240315a, whose bright peak was also detected by the Swift Burst Alert Telescope and Konus-Wind through off-line analyses. At a redshift of $z=4.859$, EP240315a showed a much longer and more complicated light curve in the soft X-ray band than in gamma-rays. Benefiting from a large field-of-view ($\sim$3600 deg$^2$) and a high sensitivity, EP-WXT captured the earlier engine activation and extended late engine activity through a continuous detection. With a peak X-ray flux at the faint end of previously known high-$z$ GRBs, the detection of EP240315a demonstrates the great potential for EP to study the early universe via GRBs.

astro-ph.HE↗

arXiv2021

81 New Candidate Fast Radio Bursts in Parkes Archive

We have searched for weak fast radio burst (FRB) events using a database containing 568,736,756 transient events detected using the Parkes radio telescope between 1997 and 2001. In order to classify these pulses, and to identify likely FRB candidates, we used a machine learning algorithm based on ResNet. We identified 81 new candidate FRBs and provide details of their positions, event times, and dispersion measures. These events were detected in only one beam of the Parkes multibeam receiver. We used a relatively low S/N cutoff threshold when selecting these bursts and some have dispersion measures only slightly exceeding the expected Galactic contribution. We therefore present these candidate FRBs as a guide for follow-up observations in the search for repeating FRBs.

astro-ph.HE↗