J/A+A/702/A95 Fermi/GBM GRB minimum variability timescales (Maccary+, 2025)
Gamma-ray burst minimum variability timescales with Fermi/GBM.
Maccary R., Guidorzi C., Camisasca A.E., Maistrello M., Kobayashi S.,
Amati L., Bazzanini L., Bulla M., Ferro L., Frontera F., Tsvetkova A.
<Astron. Astrophys. 702, A95 (2025)>
=2025A&A...702A..95M 2025A&A...702A..95M (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays ; GRB
Keywords: methods: statistical - gamma-ray burst: general
Abstract:
Gamma-ray bursts (GRBs) have traditionally been classified by duration
into long (LGRBs) and 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 be sometimes
misleading. Recently, the minimum variability timescale (MVT) has
emerged as a key metric for classifying GRBs.
We calculate 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 compare our results with other MVT
definitions. We update the MVT-T 90 plane and analyse peculiar events
like long-duration merger candidates 211211A, 230307A, and other short
GRBs with extended emission (SEE-GRBs). We also examine extragalactic
magnetar giant flares (MGFs) and explore possible new correlations
with peak energy. Methods. We used the mepsa algorithm to identify the
shortest pulse in each GRB light curve and measure its FWHM. We
calculated the MVT for around 3700 GRBs, 177 of which with
spectroscopically known redshift.
SEE-GRBs and SGRBs share similar MVTs (from few tens to a few hundreds
of ms), indicating a common progenitor, while extragalactic MGFs
exhibit even shorter values (from few ms to few tens of ms). Our MVT
estimation method consistently yields higher values than another
existing technique, the latter aligning with the pulse rise time. For
LGRBs, we confirmed the correlations of MVT with peak luminosity and
Lorentz factor.
We confirmed that, although MVT alone cannot determine the GRB
progenitor, it is a valuable tool when combined with other indicators,
helping to flag long-duration mergers and distinguish MGFs from
typical SGRBs.
Description:
We started with 3792 GRBs triggered by Fermi/GBM from 14
July 2008 to 11 June 2024, keeping 3720 of them, the others being
not entirely covered by time tagged events (TTE) data. Some very
bright GRBs, such as 221009A and 130427A were also removed owing to
their brightness, which saturated the NaI detectors.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 92 3379 GRBs of our sample
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- GRB GRB name (GRBYYMMDDX format)
11 A1 --- n_GRB [*] * for GRB not appear with a GCN-style
name in the literature
13- 35 A23 --- Fermi Fermi/GBM trigger ID
37- 44 F8.5 s FWHM Minimum variability timescale (MVT)
46- 54 F9.5 s e_FWHM [] Negative error on the MVT
56- 63 F8.5 s E_FWHM Positive error on the MVT
65- 72 F8.3 s t90 T90 duration
74- 77 F4.1 --- Npeaks ? Number of peaks in the GRB light curve
79- 86 F8.6 --- z ? Redshift
88- 92 A5 --- Class Classification of the GRB (1)
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Note (1): Classification as follows:
I = Type I
II = Type II
SEE = SEE-GRB
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Acknowledgements:
Romain Maccary, romain.maccary(at)edu.unife.it
(End) Patricia Vannier [CDS] 08-Sep-2025