Two Classes of Gamma-ray Bursts Distinguished within the First Second of Their Prompt Emission

Abstract

Studies of Gamma-Ray Burst (GRB) properties, such as duration and spectral hardness, have found evidence for additional classes, beyond the short/hard and long/soft prototypes, using model-dependent methods. In this paper, a model-independent approach was used to analyse the gamma-ray light curves of large samples of GRBs detected by BATSE, Swift/BAT and Fermi/GBM. All the features were extracted from the GRB time profiles in four energy bands using the Stationary Wavelet Transform and Principal Component Analysis. t-distributed Stochastic Neighbourhood Embedding (t-SNE) visualisation of the features revealed two distinct groups of Swift/BAT bursts using the T100 interval with 64 ms resolution data. When the same analysis was applied to 4 ms resolution data, two groups were seen to emerge within the first second (T1) post-trigger. These two groups primarily consisted of short/hard (Group 1) and long/soft (Group 2) bursts, and were 95% consistent with the groups identified using the T100 64 ms resolution data. Kilonova candidates, arising from compact object mergers, were found to belong to Group 1, while those events with associated supernovae fell into Group 2. Differences in cumulative counts between the two groups in the first second, and in the minimum variability timescale, identifiable only with the 4 ms resolution data, may account for this result. Short GRBs have particular significance for multi-messenger science as a distinctive EM signature of a binary merger, which may be discovered by its gravitational wave emissions. Incorporating the T1 interval into classification algorithms may support the rapid classification of GRBs, allowing for an improved prioritisation of targets for follow-up observations.

Correlation in Gamma Ray Burst Time Delays between Pairs of Radio Photons

“…). This redshift is small enough so much that, one can easily apply the usual Hubble Law 4 to determine the distance to this event without the need (e.g.) for Wright's [41] online cosmology calculator.…”

“…For example-in recent times, astrophysical phenomenon such as the time delays observed in Gamma Ray Bursts (GRBs) (see e.g., Refs. [4]- [14]) and Fast Radio Bursts (FRBs) (see e.g., Refs. [7] [15] [16] [17] [18]) have brought to the fore of physics this very idea that the Photon may not be massless as we have long assumed.…”

Two Dimensional Clustering of Swift/BAT and Fermi/GBM Gamma-ray Bursts

“…Fourier analysis of the Swift/BAT GRB light curves by Jespersen et al [101] identified two classes of bursts. Following on from the analysis presented in this paper is a wavelet-based feature extraction analysis of GRB light curves from Swift/BAT, BATSE and Fermi/GBM (Salmon et al [102], in preparation).…”

New detailed characterization of the residual luminescence emitted by the GAGG:Ce scintillator crystals for the HERMES Pathfinder mission

“…In [224], the authors propose a study on Fermi, BATSE, and Swift datasets, where GRB lightcurves are preprocessed using a wavelet transform, followed by PCA and GMM clustering. Although the cluster separation is not distinct in all datasets, two groups consistently emerge.…”