197 citations · 1k across the 27 of their papers we have counts for
28 papers
A Universal Physics Defining the Radiation Spectra of Blazars and Gamma-Ray Bursts
Z. Lucas Uhm, Sang-Sung Lee, Bing Zhang +5
Blazars and gamma-ray bursts (GRBs) are both cosmic beacons of extreme energy release powered by relativistic jets. However, they originate from tremendously different environments…
Multiwavelength Afterglow Analysis of GRB 221009A: Unveiling the Evolution of a Cooling Break in a Wind-like Medium
Donggeun Tak, Z. Lucas Uhm, Gregory S. H. Paek +8
Gamma-ray bursts (GRBs) are the most energetic explosions in the universe, and their afterglow emission provides an opportunity to probe the physics of relativistic shock waves in…
Impact of Ejecta Temperature and Mass on the Strength of Heavy Element Signatures in Kilonovae
Donggeun Tak, Z. Lucas Uhm, James H. Gillanders
A kilonova, the electromagnetic emission produced by compact binary mergers, is formed through a delicate interplay of physical processes, involving r-process nucleosynthesis and i…
Exploring the Impact of Ejecta Velocity Profile on Kilonova Evolution: Diversity of the Kilonova Lightcurves
Donggeun Tak, Z. Lucas Uhm, James H. Gillanders
A kilonova is a short-lived explosive event in the universe, resulting from the merger of two compact objects. Despite its importance as a primary source of heavy elements through…
Temporal and Spectral Evolution of Gamma-ray Burst Broad Pulses: Identification of High Latitude Emission in the Prompt Emission
Donggeun Tak, Z. Lucas Uhm, Judith Racusin +5
We perform a detailed analysis on broad pulses in bright Gamma-ray bursts (GRBs) to understand the evolution of GRB broad pulses. Using the temporal and spectral properties, we tes…
Evidence of High-latitude Emission in the Prompt Phase of GRBs: How Far from the Central Engine are the GRBs Produced?
Z. Lucas Uhm, Donggeun Tak, Bing Zhang +5
One of the difficulties in nailing down the physical mechanism of gamma-ray bursts (GRBs) comes from the fact that there has been no clear observational evidence on how far from th…
Bright gamma-ray flares observed in GRB131108A
Donggeun Tak, Z. Lucas Uhm, Bing Zhang
GRB 131108A is a bright long Gamma-Ray Burst (GRB) detected by the Large Area Telescope and the Gamma-ray Burst Monitor on board the Fermi Gamma-ray Space Telescope. Dedicated temp…
Multiple Components in the Broadband -ray Emission of the Short GRB 160709A
Donggeun Tak, Sylvain Guiriec, Z. Lucas Uhm +3
GRB 160709A is one of the few bright short gamma-ray bursts detected by both the Gamma-ray Burst Monitor and the Large Area Telescope on board the - $Te…
"Double-tracking" Characteristic of the Spectral Evolution of GRB 131231A: Synchrotron Origin?
Liang Li, Jin-Jun Geng, Yan-Zhi Meng +6
The characteristics of the spectral evolution of the prompt emission of gamma-ray bursts (GRBs), which are closely related to the radiation mechanism (synchrotron or photosphere),…
Toward an understanding of GRB prompt emission mechanism: II. Patterns of peak energy evolution and their connection to spectral lags
Z. Lucas Uhm, Bing Zhang, Judith Racusin
The prompt emission phase of gamma-ray bursts (GRBs) exhibits two distinct patterns of the peak-energy () evolution, i.e., time-resolved spectral analyses of spectra of…
Towards an understanding of GRB prompt emission mechanism: I. The origin of spectral lags
Z. Lucas Uhm, Bing Zhang
Despite decades of investigations, the physical mechanism that powers the bright prompt -ray emission from gamma-ray bursts (GRBs) is still not identified. One important observa…
A Statistical Study of GRB X-ray Flares: Evidence of Ubiquitous Bulk Acceleration in the Emission Region
Lan-Wei Jia, Z. Lucas Uhm, Bing Zhang
When emission in a conical relativistic jet ceases abruptly (or decays sharply), the observed decay light curve is controlled by the high-latitude "curvature effect". Recently, Uhm…
Evidence of Bulk Acceleration of the GRB X-ray Flare Emission Region
Z. Lucas Uhm, Bing Zhang
Applying our recently-developed generalized version of the high-latitude emission theory to the observations of X-ray flares in gamma-ray bursts (GRBs), we present here clear obser…
Synchrotron Origin of the Typical GRB Band Function - A Case Study of GRB 130606B
Bin-Bin Zhang, Z. Lucas Uhm, Valerie Connaughton +2
We perform a time-resolved spectral analysis of GRB 130606B within the framework of a fast-cooling synchrotron radiation model with magnetic field strength in the emission region d…
On the Curvature Effect of a Relativistic Spherical Shell
Z. Lucas Uhm, Bing Zhang
We consider a relativistic spherical shell and calculate its spectral flux as received by a distant observer. Using two different methods, we derive a simple analytical expression…
Dynamics and Afterglow Light Curves of GRB Blast Waves Encountering a Density Bump or Void
Z. Lucas Uhm, Bing Zhang
We investigate the dynamics and afterglow light curves of gamma-ray burst (GRB) blast waves that encounter various density structures (such as bumps, voids, or steps) in the surrou…
The optical rebrightening of GRB100814A: an interplay of forward and reverse shocks?
Massimiliano De Pasquale, N. P. M. Kuin, S. Oates +36
We present a wide dataset of gamma-ray, X-ray, UVOIR, and radio observations of the Swift GRB100814A. At the end of the slow decline phase of the X-ray and optical afterglow, this…
Fast cooling synchrotron radiation in a decaying magnetic field and -ray burst emission mechanism
Z. Lucas Uhm, Bing Zhang
Synchrotron radiation of relativistic electrons is an important radiation mechanism in many astrophysical sources. In the sources where the synchrotron cooling time scale is…
On the Non-existence of a Sharp Cooling Break in GRB Afterglow Spectra
Z. Lucas Uhm, Bing Zhang
Although the widely-used analytical afterglow model of gamma-ray bursts (GRBs) predicts a sharp cooling break in its afterglow spectrum, the GRB observations so far rarely sh…
Dynamics and Afterglow Light Curves of GRB Blast Waves with a Long-lived Reverse Shock
Z. Lucas Uhm, Bing Zhang, Romain Hascoet +3
We perform a detailed study on the dynamics of a relativistic blast wave with the presence of a long-lived reverse shock (RS). Although a short-lived RS has been widely considered,…
GRB100814A as a member of the growing set of bursts with sudden optical rebrightening
Massimiliano De Pasquale, N. P. Kuin, S. Oates +22
We present the gamma-ray, X-ray, optical and radio data for GRB100814A. At the end of the slow decline phase of the X-ray and optical afterglow, a sudden and prominent rebrightenin…
Was the "naked burst" GRB 050421 really naked ?
R. Hascoët, Z. L. Uhm, R. Mochkovitch +1
A few long gamma-ray bursts such as GRB 050421 show no afterglow emission beyond the usual initial steep decay phase. It has been suggested that these events correspond to "naked"…
Is GRB afterglow emission intrinsically anisotropic ?
A. M. Beloborodov, F. Daigne, R. Mochkovitch +1
The curvature of a relativistic blast wave implies that its emission arrives to observers with a spread in time. This effect is believed to wash out fast variability in the lightcu…
A Semi-analytic Formulation for Relativistic Blast Waves with a Long-lived Reverse Shock
Z. Lucas Uhm
This paper performs a semi-analytic study of relativistic blast waves in the context of gamma-ray bursts (GRBs). Although commonly used in a wide range of analytical and numerical…