GRB 221009A: The BOAT Burns, Eric; Svinkin, Dmitry; Fenimore, Edward ...
Astrophysical journal. Letters,
03/2023, Volume:
946, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract 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.
We report measurements of a terrestrial gamma ray flash (TGF) detected by the Fermi Gamma‐ray Burst Monitor that was produced during a negative cloud‐to‐ground (CG) lightning leader. This is the ...first report of a downward directed TGF occurring during a CG flash but detected by a space‐based instrument. The gamma ray photons are produced 3 ms preceding a return stroke (−146 kA) and are essentially simultaneous with an isolated low frequency radio pulse. Based on timing, the pulse is estimated to initiate at approximately 6 km altitude, and its polarity indicates downward moving negative charge, the opposite of regular satellite‐detected upward TGFs. A likely scenario is that the runaway electrons accelerate into the upper, positively charged end of the leader in a high field region, with the reverse positron beam generating upward gamma rays detectable from space. A search for similar waveform features indicates that this type of downward CG‐TGF may occur prior to 1% of high peak current CG strokes. Extrapolating gives a global rate of 5–10% of previously known TGFs and potentially a significant fraction of global TGFs.
Key Points
A TGF detected by Fermi GBM occurred 3 ms before a −CG stroke during the descending negative leader, coincident with a 120 μs radio pulse
The radio pulse polarity indicates that it is likely a downward TGF produced at ~6 km altitude with a reverse positron beam detected by Fermi GBM
This type of downward CG‐TGF may occur prior to 1% of high‐intensity CG strokes, constituting 5–10% of the previously known TGF population
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 multipulsed 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.
The Hunga Tonga–Hunga Ha’apai submarine volcano recently resumed activity. Violent eruptions on 2022 January 14th and 15th launched a tall ash plume that produced extremely high lightning rates. Here ...we report a terrestrial gamma-ray flash (TGF) that was produced by the volcanic lightning and observed from space by the Fermi Gamma-ray Burst Monitor (GBM). Observations by radio lightning networks and especially by the Geostationary Lightning Mapper (GLM) show that the only lightning close enough to produce a TGF detectable by Fermi GBM was from the volcano’s plume. With the observing duration of Fermi, observing a single TGF is consistent with the hypothesis that the volcanic lightning of this eruption produced TGFs at the average rate of thunderstorm lightning. The observation of a strong TGF from space also indicates that the electric field was oriented so as to accelerate electrons upward.
Many of the details of how terrestrial gamma‐ray flashes (TGFs) are produced, including their association with upward‐propagating in‐cloud lightning leader channels, remain poorly understood. ...Measurements of the low‐frequency radio emissions associated with TGF production continue to provide unique views and key insights into the electrodynamics of this process. Here we report further details on the connection between energetic in‐cloud pulses (EIPs) and TGFs. With coordinated measurements from both ground‐based radio sensors and space‐based gamma‐ray detectors on the Fermi and Reuven Ramaty High Energy Solar Spectroscopic Imager spacecraft, we find that all ten +EIPs that occurred within the searched space‐and‐time window are associated with simultaneous TGFs, including two new TGFs that were not previously identified by the gamma‐ray measurements alone. The results in this study not only solidify the tight connection between +EIPs and TGFs, but also demonstrate the practicability of detecting a subpopulation of TGFs with ground‐based radio sensors alone.
Plain Language Summary
Terrestrial gamma‐ray flashes (TGFs) are kinds of high‐energy emissions produced during thunderstorms and are almost exclusively detected with spacecraft‐based gamma‐ray detectors. Because of the strong atmospheric gamma‐ray attenuation from the low‐altitude atmosphere and the geometry‐driven short horizontal detection range, the ground detection of TGFs with gamma‐ray detectors is challenging. Recently a class of distinct radio emissions during thunderstorms, called energetic in‐cloud pulses (EIPs), was found to be closely linked to the production of some TGFs. In this study, we present several additional lines of strong evidence that strengthen the connection between a subpopulation of TGFs and EIPs. Importantly, by identifying EIPs from radio signals, we found two new TGFs that were previously unreported from space‐based detection. This demonstrates that some TGFs can be detected from the radio measurements alone when the spacecraft‐based detectors are unavailable.
Key Points
Positive polarity energetic in‐cloud pulses (+EIPs) produce terrestrial gamma‐ray flashes (TGFs) with high‐to‐certain probability (74%–100%)
New TGFs previously missed by space‐based detectors were found by ground detection of +EIPs
Demonstrated that a subset of TGFs can be found from remote ground‐based radio detection alone
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 ratio (S/N) and a simple monotonic appearance at low S/N. We minimize this effect by studying six very bright GRB pulses (S/N 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, rehardening 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 forward and backward 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 relative to the emission of the monotonic component.
Abstract
We report observations of the optical counterpart of the long gamma-ray burst (GRB) GRB 230812B and its associated supernova (SN) SN 2023pel. The proximity (
z
= 0.36) and high energy (
E
γ
...,iso
∼ 10
53
erg) make it an important event to study as a probe of the connection between massive star core collapse and relativistic jet formation. With a phenomenological power-law model for the optical afterglow, we find a late-time flattening consistent with the presence of an associated SN. SN 2023pel has an absolute peak
r
-band magnitude of
M
r
= −19.46 ± 0.18 mag (about as bright as SN 1998bw) and evolves on quicker timescales. Using a radioactive heating model, we derive a nickel mass powering the SN of
M
Ni
= 0.38 ± 0.01
M
⊙
and a peak bolometric luminosity of
L
bol
∼ 1.3 × 10
43
erg s
−1
. We confirm SN 2023pel’s classification as a broad-line Type Ic SN with a spectrum taken 15.5 days after its peak in the
r
band and derive a photospheric expansion velocity of
v
ph
= 11,300 ± 1600 km s
−1
at that phase. Extrapolating this velocity to the time of maximum light, we derive the ejecta mass
M
ej
= 1.0 ± 0.6
M
⊙
and kinetic energy
E
KE
=
1.3
−
1.2
+
3.3
×
10
51
erg
. We find that GRB 230812B/SN 2023pel has SN properties that are mostly consistent with the overall GRB-SN population. The lack of correlations found in the GRB-SN population between SN brightness and
E
γ
,iso
for their associated GRBs across a broad range of 7 orders of magnitude provides further evidence that the central engine powering the relativistic ejecta is not coupled to the SN powering mechanism in GRB-SN systems.
We developed a framework merging unsupervised and supervised machine learning to classify lightning radio signals, and applied it to the possible detection of terrestrial gamma‐ray flashes (TGFs). ...Recent studies have established a tight connection between energetic in‐cloud pulses (EIPs, >150 kA) and a subset of TGFs, enabling continuous and large‐scale ground‐based TGF detection. However, even with a high peak current threshold, it is time‐consuming to manually search for EIPs in a background of many non‐EIP events, and it becomes even more difficult when a lower peak current threshold is used. Machine learning classifiers are an effective tool. Beginning with unsupervised learning, spectral clustering is performed on the low‐dimensional features extracted by an autoencoder from raw radio waveforms, showing that +EIPs naturally constitute a distinct class of waveform and 6%–7% of the total population. The clustering results are used to form a labeled data set (∼10,000 events) to further train supervised convolutional neural network (CNN) that targets for +EIPs. Our CNN models identify on average 95.2% of true +EIPs with accuracy up to 98.7%, representing a powerful tool for +EIP classification. The pretrained CNN classifier is further applied to identify lower peak current EIPs (LEIPs, >50 kA) from a larger data set (∼30,000 events). Among 10 LEIPs coincident with Fermi TGF observations, 2 previously reported TGFs and 2 unreported but suspected TGFs are found, while the majority are not associated with detectable TGFs. In addition, unsupervised clustering is found to reflect characteristics of the ionosphere reflection height and its effect on radio wave propagation.
Plain Language Summary
In this study, we developed a machine learning‐based method to classify lightning radio signals. The method uses unsupervised and supervised machine learning to distinguish different types of signals with high accuracy. The focus of the study is to identify energetic in‐cloud pulses (EIPs) that are associated with a subset of lightning‐related terrestrial gamma‐ray flashes (TGFs). The method successfully identified 95.2% of true EIPs with up to 98.7% accuracy, and discovered new TGF events that were not previously reported. Additionally, the method revealed insights into the ionosphere and radio wave propagation. This method can be useful for studying lightning and other related phenomena.
Key Points
A framework merging unsupervised clustering and supervised convolutional neural network (CNN) for lightning classification is developed
Clustering of positive polarity energetic lightning radio pulses (>150 kA) identifies three processes: +EIPs (6%–7%), +NBEs, and +CGs
CNNs detect 95.2% of manually identified +EIPs with up to 98.7% accuracy, enabling studying EIP‐TGF link with lower peak current (>50 kA)
GRB 221009A, The BOAT Burns, Eric; Svinkin, Dmitry; Fenimore, Edward ...
arXiv.org,
03/2024
Paper, Journal Article
Open access
GRB 221009A has been referred to as the Brightest Of All Time (the 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 \(\sim99\)th percentile of the known distribution. We explore how such a burst can be powered and discuss potential implications for ultra-long 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, while it almost certainly not the BOAT over all of cosmic history, it may be the brightest gamma-ray burst since human civilization began.
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.
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