GRB minimum variability timescale with Insight-HXMT and Swift: implications for progenitor models, dissipation physics and GRB classifications

The dissipation process of GRB prompt emission is still unknown. Study of temporal variability may provide a unique way to discriminate the imprint of the inner engine activity from geometry and propagation related effects. We define the minimum variability timescale (MVT) as the shortest duration of individual pulses that shape a light curve for a sample of GRBs and test correlations with peak luminosity, Lorentz factor, and jet opening angle. We compare these correlations with predictions from recent numerical simulations for a relativistic structured -- possibly wobbling -- jet and assess the value of MTV as probe of prompt-emission physics. We used the peak detection algorithm mepsa to identify the shortest pulse within a GRB time history and estimate its full width half maximum (FWHM). We applied this framework to two sets of GRBs: Swift (from 2005 to July 2022) and Insight-HXMT (from June 2017 to July 2021, including 221009A). We then selected 401 GRBs with measured z to test for correlations. On average short GRBs have significantly shorter MVT than long GRBs. The MVT distribution of short GRBs with extended emission such as 060614 and 211211A is compatible only with that of short GRBs. This provides a new clue on the progenitor's nature. The MVT for long GRBs anticorrelates with peak luminosity. We confirm the anticorrelation with the Lorentz factor and find a correlation with the jet opening angle as estimated from the afterglow, along with an inverse correlation with the number of pulses. The MVT can identify the emerging putative new class of long GRBs that are suggested to be produced by compact binary mergers. For otherwise typical long GRBs, the different correlations between MVT and peak luminosity, Lorentz factor, jet opening angle, and number of pulses can be explained within the context of structured, possibly wobbling, weakly magnetised relativistic jets. (summarised)Comment: 18 pages, 15 figures, accepted by A&

A set of distinctive properties ruling the prompt emission of GRB 230307A and other long γ-ray bursts from compact object mergers

Short gamma-ray bursts (SGRBs), occasionally followed by a long and spectrally soft extended emission, are associated with compact object mergers (COMs). Yet, a few recent long GRBs (LGRBs) show compelling evidence for a COM origin, in contrast with the massive-star core-collapse origin of most LGRBs. While possible COM indicators were found, such as the minimum variability timescale (MVT), a detailed and unique characterisation of their γ-ray prompt emission that may help identify and explain their deceptively long profile is yet to be found. Here we report the discovery of a set of distinctive properties that rule the temporal and spectral evolution of GRB 230307A, a LGRB with evidence for a COM origin. Specifically, the sequence of pulses that make up its profile is characterised by an exponential evolution of (i) flux intensities, (ii) waiting times between adjacent pulses, (iii) pulse durations, and (iv) spectral peak energy. Analogous patterns are observed in the prompt emission of other long COM candidates. The observed evolution of gamma-ray pulses would imply that a relativistic jet is colliding with more slowly expanding material. This contrasts with the standard internal shock model for typical LGRBs, in which dissipation occurs at random locations within the jet itself. We tentatively propose a few simple toy models that may explain these properties and are able to reproduce the overall time profile

Gamma-ray burst minimum variability timescales with Fermi/GBM

Context. Gamma-ray bursts (GRBs) have traditionally been classified by duration as long (LGRBs) or short (SGRBs), with the former believed to originate from massive star collapses and the latter from compact binary mergers. However, events such as the SGRB 200826A (coming from a collapsar) and the LGRBs 211211A and 230307A (associated with a merger) suggest that duration-based classification could sometimes be misleading. Recently, the minimum variability timescale (MVT) has emerged as a key metric for classifying GRBs. Aims. We calculated the MVT, defined as the full width at half maximum (FWHM) of the narrowest pulse in the light curve, using an independent dataset from Fermi/GBM, and we compared our results with other MVT definitions. We updated the MVT-T90 plane and analysed peculiar events such as long-duration merger candidates 211211A, 230307A, and other short GRBs with extended emission (SEE-GRBs). We also examined extragalactic magnetar giant flares (MGFs) and explored possible new correlations with peak energy. Methods. We used the MEPSA algorithm to identify the shortest pulse in each GRB light curve and measured its FWHM. We calculated the MVT for around 3700 GRBs, 177 of which have spectroscopically known redshift. Results. The SEE-GRBs and SGRBs share similar MVTs (from a few tens of to a few hundred milliseconds, indicating a common progenitor, while extragalactic MGFs exhibit even shorter values (from a few milliseconds to a few tens of milliseconds). Our MVT estimation method consistently yields higher values than another existing technique, the latter aligning with the pulse rise time. For LGRBs, we confirm the correlations of MVT with peak luminosity and Lorentz factor. Conclusions. We confirm that although MVT alone cannot determine the GRB progenitor, it is a valuable tool when combined with other indicators, as it helps flag long-duration mergers and distinguish MGFs from typical SGRBs

New results on the gamma-ray burst variability–luminosity relation

Context. At the dawn of the gamma–ray burst (GRB) afterglow era, a Cepheid-like correlation was discovered between the time variability V and the isotropic-equivalent peak luminosity Liso of the prompt emission of about a dozen long GRBs with measured redshift available at that time. Soon afterwards, the correlation was confirmed in a sample of about 30 GRBs, even though it was affected by significant scatter. Unlike the minimum variability timescale (MVT), V measures the relative power of short-to-intermediate timescales. Aims. We aim to test the correlation using about 200 long GRBs with spectroscopically measured redshift, detected by Swift, Fermi, and Konus/WIND, for which both observables can be accurately estimated. Methods. The variability for all selected GRBs was calculated according to the original definition using the 64 ms background-subtracted light curves of Swift/BAT (Fermi/GBM) in the 15–150 (8–900) keV energy passband. Peak luminosities were either taken from the literature or derived from modelling broad-band spectra acquired with either Konus/WIND or Fermi/GBM. Results.The statistical significance of the correlation has weakened to ≲2%, mostly due to the appearance of a number of smooth and luminous GRBs that are characterised by a relatively small V. At odds with most long GRBs, three out of four long-duration merger candidates have high V and low Liso. Conclusions. The luminosity is more tightly connected with shortest timescales measured by MVT than the short to intermediate timescales measured by V. We discuss the implications for internal dissipation models and the role of the e± photosphere. We identified a few smooth GRBs with a single broad pulse and low V that might have an external shock origin, in contrast with most GRBs. The combination of high variability (V ≳ 0.1), low luminosity Liso ≲ 1051 erg s−1, and short MVT (≲0.1 s) could be a good indicator for a compact binary merger origin

Water-Resources Investigations Report 80-57

This report analyses resistivity and porosity logs to determine water-quality trends in carbonate aquifers. It contains tables and other figures

Sir Christopher Wren’s Towers of London: The Affordances of ArcGIS Spatial Analysis for Studying Visibility in the Early Modern London Skyline with the Spire of St. Bride’s Church

After the Great Fire of 1666 decimated London, Sir Christopher Wren was commissioned to oversee the reconstruction of parish churches, St. Paul’s Cathedral, and numerous infrastructure and architecture projects in the city. Though his plan for the city’s layout was rejected, Wren’s work on parish churches and the city cathedral stamped his mark on the urban fabric of London. His steeples, towers, and domes elevated English Baroque architectural features into the skyline. Wren is one of the most well-known and biographed British architects; yet while his London parish churches have been extensively studied by architectural historians, there is little scholarship of how his churches were spatially situated and observed from the ground level in the early modern period. The Wren parish churches have instead been discussed within the historical context of the arrival of Renaissance treatises and knowledge in England, as well as the urban history of London’s reconstruction after the Great Fire. This project is localized to St. Bride’s Church, Fleet Street, and asks how its steeple was viewed and experienced in the early modern period. To this end, the neighborhood around St. Bride’s was schematically recreated in ArcGIS Pro to enable spatial analyses. The results of these analyses indicate that the visibility of St. Bride’s was impeded along Fleet Street in the eponymous parish by the ad hoc spatiality of in the early-modern period, as it continues to be in the contemporary day; instead, St. Martin and St. Paul’s were visible. Furthermore, the spatial analyses revealed that the steeple of St. Bride was observable from Ludgate in the neighboring parish of St. Martin. This thesis discusses these results as interparish visibility, and evaluates what these analyses suggest about the early modern neighborhood surrounding St. Bride’s. </p