We present the systematic spectral analyses of gamma-ray bursts (GRBs) detected by the Fermi Gamma-Ray Burst Monitor during its first ten years of operation. This catalog contains two types of spectra: time-integrated spectral fits and spectral fits at the brightest time bin, from 2297 GRBs, resulting in a compendium of over 18,000 spectra. The four different spectral models used for fitting the spectra were selected based on their empirical importance to the shape of many GRBs. We describe in detail our procedure and criteria for the analyses, and present the bulk results in the form of parameter distributions both in the observer frame and in the GRB rest frame. 941 GRBs from the first four years have been refitted using the same methodology as that of the 1356 GRBs in years five through ten. The data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.

We report the discovery of the unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image, and Neutron Star Interior Composition Explorer Mission. This energetic GRB was located relatively nearby (z = 0.151), allowing for sustained observations of the afterglow. The large X-ray luminosity and low Galactic latitude (b = 4.°3) make GRB 221009A a powerful probe of dust in the Milky Way. Using echo tomography, we map the line-of-sight dust distribution and find evidence for significant column densities at large distances (≳10 kpc). We present analysis of the light curves and spectra at X-ray and UV–optical wavelengths, and find that the X-ray afterglow of GRB 221009A is more than an order of magnitude brighter at T 0 + 4.5 ks than that from any previous GRB observed by Swift. In its rest frame, GRB 221009A is at the high end of the afterglow luminosity distribution, but not uniquely so. In a simulation of randomly generated bursts, only 1 in 104 long GRBs were as energetic as GRB 221009A; such a large E γ,iso implies a narrow jet structure, but the afterglow light curve is inconsistent with simple top-hat jet models. Using the sample of Swift GRBs with redshifts, we estimate that GRBs as energetic and nearby as GRB 221009A occur at a rate of ≲1 per 1000 yr—making this a truly remarkable opportunity unlikely to be repeated in our lifetime.

We analyze pulse properties of Short gamma-ray bursts (GRBs) from a new catalog containing 434 pulses from 387 BATSE Time-Tagged Event (TTE) GRBs. Short GRB pulses exhibit correlated properties of duration, fluence, hardness, and amplitude, and they evolve hard-to-soft while undergoing similar triple-peaked light curves similar to those found in Long/Intermediate bursts. We classify pulse light curves using their temporal complexities, demonstrating that Short GRB pulses exhibit a range of complexities from smooth to highly variable. Most of the bright, hard, chaotic emission seen in complex pulses seems to represent a separate highly-variable emission component. Unlike Long/Intermediate bursts, as many as 90% of Short GRBs are single-pulsed. However, emission in Short multi-pulsed bursts is coupled such that the first pulse's duration is a predictor of both the interpulse separation and subsequent pulse durations. These results strongly support the idea that external shocks produce the prompt emission seen in Short GRBs. The similarities between the triple-peaked structures and spectral evolution of Long, Short, and Intermediate GRBs then suggests that external shocks are responsible for the prompt emission observed in all GRB classes. In addition to these findings, we identify a new type of gamma-ray transient in which peak amplitudes occur at the end of the burst rather than at earlier times. Some of these "Crescendo" bursts are preceded by rapid-fire "Staccato" pulses, whereas the remaining are preceded by a variable episode that could be unresolved staccato pulses.

We demonstrate that the 'smoke' of limited instrumental sensitivity smears out structure in gamma-ray burst (GRB) pulse light curves, giving each a triple-peaked appearance at moderate signal-to-noise and a simple monotonic appearance at low signal-to-noise. We minimize this effect by studying six very bright GRB pulses (signal-to-noise generally > 100), discovering surprisingly that each exhibits complex time-reversible wavelike residual structures. These 'mirrored' wavelike structures can have large amplitudes, occur on short timescales, begin/end long before/after the onset of the monotonic pulse component, and have pulse spectra that generally evolve hard to soft, re-hardening at the time of each structural peak. Among other insights, these observations help explain the existence of negative pulse spectral lags, and allow us to conclude that GRB pulses are less common, more complex, and have longer durations than previously thought. Because structured emission mechanisms that can operate forwards and backwards in time seem unlikely, we look to kinematic behaviors to explain the time-reversed light curve structures. We conclude that each GRB pulse involves a single impactor interacting with an independent medium. Either the material is distributed in a bilaterally symmetric fashion, the impactor is structured in a bilaterally symmetric fashion, or the impactor's motion is reversed such that it returns along its original path of motion. The wavelike structure of the time-reversible component suggests that radiation is being both produced and absorbed/deflected dramatically, repeatedly, and abruptly from the monotonic component.

GRB 221009A has been referred to as the brightest of all time (BOAT). We investigate the veracity of this statement by comparing it with a half century of prompt gamma-ray burst observations. This burst is the brightest ever detected by the measures of peak flux and fluence. Unexpectedly, GRB 221009A has the highest isotropic-equivalent total energy ever identified, while the peak luminosity is at the ∼99th percentile of the known distribution. We explore how such a burst can be powered and discuss potential implications for ultralong and high-redshift gamma-ray bursts. By geometric extrapolation of the total fluence and peak flux distributions, GRB 221009A appears to be a once-in-10,000-year event. Thus, it is almost certainly not the BOAT over all of cosmic history;  it may be the brightest gamma-ray burst since human civilization began.