J/A+A/671/A112 GRB minimum variability timescale (Camisasca+, 2023)
GRB minimum variability timescale with Insight-HXMT and Swift.
Implications for progenitor models, dissipation physics and GRB classifications.
Camisasca A.E., Guidorzi C., Amati L., Frontera F., Song X.Y., Xiao S.,
Xiong S.L., Zhang S.N., Margutti R., Kobayashi S., Mundell C.G., Ge M.Y.,
Gomboc A., Jia S.M., Jordana-Mitjans N., Li C.K., Li X.B., Maccary R.,
Shrestha M., Xue W.C., Zhang S.
<Astron. Astrophys. 671, A112 (2023)>
=2023A&A...671A.112C 2023A&A...671A.112C (SIMBAD/NED BibCode)
ADC_Keywords: GRB ; Redshifts ; Gamma rays
Keywords: radiation mechanisms: non-thermal - relativistic processes -
gamma-ray burst: general - stars: jets
Abstract:
There has been significant technological and scientific progress in
our ability to detect, monitor and model the physics of gamma-ray
bursts (GRBs) over the 50 years since their first discovery. However,
the dissipation process thought to be responsible for their defining
prompt emission is still unknown. Recent efforts have focused on
investigating how the ultrarelativistic jet of the GRB propagates
through the progenitor's stellar envelope, for different initial
composition shapes, jet structures, magnetisation, and -
consequently - possible energy dissipation processes. Study of the
temporal variability - in particular the shortest duration of an
independent emission episode within a GRB - may provide a unique way
to discriminate the imprint of the inner engine activity from geometry
and propagation related effects. The advent of new high-energy
detectors with exquisite time resolution now makes this possible.
We aim to characterise the minimum variability timescale (MVT) defined
as the shortest duration of individual pulses that shape a light curve
for a sample of GRBs in the keV-MeV energy range and test
correlations with other key observables, such as the peak luminosity,
the Lorentz factor, and the 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 temporal variability studies as probes of prompt-emission
dissipation physics.
We used the peak detection algorithm mepsa to identify the shortest
pulse within a GRB time history and preliminarily calibrated mepsa to
estimate the full width half maximum (FWHM) duration. We then applied
this framework to two sets of GRBs: Swift GRBs (from 2005 to July
2022) and Insight Hard Modulation X-ray Telescope (Insight-HXMT) GRBs
(from June 2017 to July 2021, including the exceptional 221009A). We
then selected 401 GRBs with measured redshift to test for
correlations. Results. We confirm that 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 is important because it
provides a new clue on the progenitor's nature. The MVT for long
GRBs with measured redshift anti-correlates with peak luminosity; our
analysis includes careful evaluation of selection effects. We confirm
the anti-correlation with the Lorentz factor and find a correlation
with the jet opening angle as estimated from the afterglow light
curve, 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.
Description:
We proposed a simple definition of minimum variability timescale (MVT)
of GRB prompt emission as the FWHM of the shortest pulse that is
identified through mepsa, a thoroughly tested GRB peak search
algorithm. We applied this method to two independent and complementary
GRB data sets: Swift/BAT and Insight-HXMT/HE, both of which were split
into two groups: Type-I and Type-II GRBs, the former including
SEE-GRBs.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 69 1326 Swift-BAT sample
table2.dat 69 231 Insight-HXMT sample
table5.dat 114 399 Swift-BAT sample with known redshift
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See also:
J/A+A/609/A112 : Bulk Lorentz factors of gamma-ray bursts (Ghirlanda+, 2018)
Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- GRB GRB Name
10- 16 F7.3 s FWHMmin Minimum FWHM
19- 25 F7.3 s e_FWHMmin Negative error on FWHM
28- 34 F7.3 s E_FWHMmin Positive error on FWHM
36- 43 F8.3 s T90 Burst duration between 5% and 95% of
maximum fluence
46- 52 F7.3 s e_T90 ?=-1 Error on T90
57- 61 F5.3 --- z ?=- Redshift
64- 65 I2 --- Npeaks Number of peaks in GRB light curve
67- 69 A3 --- Type GRB Type (1)
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Note (1): GRB Type as follows:
S = short
L = long
SEE = short with extended emission
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- GRB GRB Name
9- 16 E8.3 10-7W Lpeak Peak luminosity (in erg/s)
18- 25 E8.3 10-7W e_Lpeak Error on peak luminosity (in erg/s)
31- 33 I3 --- Gamma0 ?=- Lorentz factor
41- 43 I3 --- e_Gamma0 ?=- Negative error on Lorentz factor
50- 52 I3 --- E_Gamma0 ?=- Positive error on Lorentz factor
58- 60 A3 --- r_Gamma0 Reference for the Lorentz factor (1)
67- 69 I3 --- Gamma0G ?=- Lorentz factor calculated using
Ghirlanda's (2018A&A...609A.112G 2018A&A...609A.112G) data and
prescriptions
76- 78 I3 --- e_Gamma0G ?=- Error on Lorentz factor calculated using
Ghirlanda's data eGamma_0^(G)
83- 87 F5.3 rad thetajISN ?=- Jet opening angle as reported by Zhao et
al. (2020ApJ...900..112Z 2020ApJ...900..112Z) in case of
ISM environment
92- 96 F5.3 rad e_thetajISN ?=- Error on jet opening angle as reported by
Zhao et al. (2020ApJ...900..112Z 2020ApJ...900..112Z) in case of
ISM environment
101-105 F5.3 rad thetajWind ?=- Jet opening angle as reported by Zhao et
al. (2020ApJ...900..112Z 2020ApJ...900..112Z) in case of
Wind environment.
110-114 F5.3 rad e_thetajWind ?=- Error on jet opening angle as reported
by Zhao et al. (2020ApJ...900..112Z 2020ApJ...900..112Z) in case
of Wind environment
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Note (1): References as follows:
L12 = Lu et al., 2012ApJ...751...49L 2012ApJ...751...49L
X16 = Xin et al., 2016ApJ...817..152X 2016ApJ...817..152X
X19 = Xue et al., 2019ApJ...876...77X 2019ApJ...876...77X
X20 = Xie et al., 2020ApJ...896....4X 2020ApJ...896....4X
Y17 = Yi et al., 2017, Journal of High Energy Astrophysics, 13, 1
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Acknowledgements:
Anna Elisa Camisasca, cmsnls(at)unife.it
(End) Patricia Vannier [CDS] 06-Jan-2023