J/ApJ/720/1146 Spectral analysis of GRBs (Lu+, 2010)
The Ep-flux correlation in the rising and decaying phases of gamma-ray burst
pulses: evidence for viewing angle effect?
Lu R.-J., Hou S.-J., Liang E.-W.
<Astrophys. J., 720, 1146-1154 (2010)>
=2010ApJ...720.1146L 2010ApJ...720.1146L
ADC_Keywords: Gamma rays
Keywords: gamma-ray burst: general - methods: data analysis -
radiation mechanisms: non-thermal
Abstract:
A time-resolved spectral analysis for a sample of 22 intense, broad
gamma-ray burst (GRB) pulses from the Compton Gamma Ray Observatory
(CGRO)/BATSE GRB sample is presented. We fit the spectra with the Band
function and investigate the correlation between the observed flux (F)
and the peak energy (Ep) of the νfν spectrum in the rising
and decaying phases of these pulses. Two kinds of Ep evolution
trends, i.e., hard-to-soft (two-thirds of the pulses in our sample)
and Ep-tracing-F (one-third of the pulses in our sample), are
observed in pulses from different GRBs and even from different pulses
of the same burst. No dependence of spectral evolution feature on the
pulse shape is found. A tight F-Ep positive correlation is observed
in the decaying phases, with a power-law index ∼2.2, which is much
shallower than that expected from the curvature effect. In the rising
phase, the observed F is either correlated or anti-correlated with
Ep, depending on the spectral evolution feature, and the power-law
index of the correlation is dramatically different among pulses. More
than 80% of the low-energy photon indices in the time-resolved
spectra, whose Ep's are anti-correlated with F during the rising
phase, violate the death line of the synchrotron radiation,
disfavoring the synchrotron radiation model for these gamma rays. The
F-Ep correlation, especially for those GRBs with Ep-tracking-F
spectral evolution, may be due to the viewing angle and jet structure
effects. In this scenario, the observed F-Ep correlation in the
rising phase may be due to the line of sight toward a structured jet
(or jetter) moving from off-beam to on-beam, and both the on-beam
emission and the delayed photons from high latitude of the GRB
fireball contribute to the decaying phase, resulting in a shallower
slope of the observed F-Ep correlation than that predicted by the
pure curvature effect.
Description:
We make use of the data observed with BATSE. Kaneko et al. (2006, Cat.
J/ApJS/166/298) presented a sample of 8459 time-resolved burst spectra
for 350 bright GRBs observed with BATSE. Our sample of GRB pulses is
taken from this sample. We obtained the spectra data from the
following Web site: http://www.batse.msfc.nasa.gov/~kaneko/.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 70 296 Spectral fits with the Band function
table2.dat 50 22 Power-law indices of the F∝EpKr(Kd)
relation for the pulses in our sample
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See also:
IX/20 : The Fourth BATSE Burst Revised Catalog (Paciesas+ 1999)
J/ApJ/704/1405 : Testing the Epeak-Eiso relation for GRBs (Krimm+, 2009)
J/ApJS/166/298 : Spectral catalog of bright BATSE gamma-ray bursts (Kaneko+,
2006)
J/ApJ/609/935 : Gamma-ray burst formation rate (Yonetoku+, 2004)
J/ApJS/126/19 : BATSE gamma-ray burst spectral catalog. I. (Preece+, 2000)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Trig Trigger number
6- 11 F6.3 s tstart Starting time
13- 18 F6.3 s tend Ending time
20- 26 F7.2 keV Ep Peak energy Ep
28- 33 F6.2 keV e_Ep Uncertainty in Ep
35- 39 F5.2 --- alpha Low energy power law index α
41- 45 F5.2 --- e_alpha Uncertainty in alpha
47- 52 F6.2 --- beta High energy power law index β
54- 58 F5.2 --- e_beta Uncertainty in beta
60- 64 F5.2 nW/m2 Flux Flux in the 30keV-10MeV band (10-6erg/s/cm2)
66- 70 F5.2 nW/m2 e_Flux Uncertainty in Flux
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Byte-by-byte Description of file:table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Trig Trigger number (1)
5 A1 --- n_Trig [ht] Evolution group (2)
7- 13 F7.4 --- Kr ? κr value in rising phase (3)
15- 19 F5.3 --- e_Kr ? Kr uncertainty
21- 26 F6.3 --- rr ? Correlation coefficient in rising phase
28- 29 I2 --- Nr ? Number of the data points in rising phase
31- 35 F5.3 --- Kd ? κd value in decaying phase (3)
37- 41 F5.3 --- e_Kd ? Kd uncertainty
43- 47 F5.3 --- rd ? Correlation coefficient in decaying phase
49- 50 I2 --- Nd ? Number of the data points in decaying phase
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Note (1): Trigger 1625 added by CDS.
Note (2): Flag as follows:
h = hard-to-soft evolution group
t = Ep-tracing-flux evolution group
See section 3 for further details.
Note (3): the correlation between the flux F and the peak energy Ep is
fitted by the power laws F∝EpKr and F∝EpKd
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 29-Jun-2012