J/MNRAS/454/L31 GRB prompt emission fitted with the DREAM model (Ahlgren+, 2015)
Confronting GRB prompt emission with a model for subphotospheric dissipation.
Ahlgren B., Larsson J., Nymark T., Ryde F., Pe'er A.
<Mon. Not. R. Astron. Soc., 454, L31-L35 (2015)>
=2015MNRAS.454L..31A 2015MNRAS.454L..31A (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays ; Models
Keywords: radiation mechanisms: thermal - gamma-ray burst: general -
gamma-ray burst: individual: GRB 090618 -
gamma-ray burst: individual: GRB 100724B
Abstract:
The origin of the prompt emission in gamma-ray bursts (GRBs) is still
an unsolved problem and several different mechanisms have been
suggested. Here, we fit Fermi GRB data with a photospheric emission
model which includes dissipation of the jet kinetic energy below the
photosphere. The resulting spectra are dominated by Comptonization and
contain no significant contribution from synchrotron radiation. In
order to fit to the data, we span a physically motivated part of the
model's parameter space and create DREAM (Dissipation with Radiative
Emission as A table Model), a table model for XSPEC. We show that this
model can describe different kinds of GRB spectra, including GRB 090618,
representing a typical Band function spectrum, and GRB 100724B,
illustrating a double peaked spectrum, previously fitted with a
Band+blackbody model, suggesting they originate from a similar
scenario. We suggest that the main difference between these two types
of bursts is the optical depth at the dissipation site.
Description:
We illustrate the application of the DREAM model by fitting it to two
different, bright Fermi GRBs; GRB 090618 and GRB 100724B. While GRB 090618
is well fitted by a Band function, GRB 100724B was the first example of a
burst with a significant additional BB component (Guiriec et al.
2011ApJ...727L..33G 2011ApJ...727L..33G). GRB 090618 is analysed using Gamma-ray Burst Monitor
(GBM) data (Meegan et al. 2009ApJ...702..791M 2009ApJ...702..791M) from the NaI and BGO
detectors. For GRB 100724B, we used GBM data from the NaI and BGO detectors
as well as Large Area Telescope Low Energy (LAT-LLE) data. For both
bursts we selected NaI detectors seeing the GRB at an off-axis angle
lower than 60° and the BGO detector as being the best aligned of the
two BGO detectors. The spectra were fitted in the energy ranges
8-1000 keV (NaI), 200-40000 keV (BGO) and 30-1000 MeV (LAT-LLE).
Objects:
-------------------------------------------------------------
RA (ICRS) DE Designation(s)
-------------------------------------------------------------
19 36 01.80 +78 21 07.1 GRB 090618 = Fermi bn090618353
07 58 +75.9 GRB 100724B = Fermi bn100724029
-------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 92 81 Best-fitting parameters for GRB 090618 fitted
with the DREAM model
table2.dat 92 31 Best-fitting parameters for GRB 100724B fitted
with the DREAM model
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See also:
J/ApJ/754/121 : GRBs from Fermi/GBM and LAT (The Fermi Team, 2012)
J/ApJ/756/112 : Fermi/GBM GRB time-resolved spectral analysis (Lu+, 2012)
J/A+A/573/A81 : Spectral properties of energetic GRBs (Yu+, 2015)
J/A+A/588/A135 : Fermi/GBM GRB time-resolved spectral catalog (Yu+, 2016)
J/ApJ/818/18 : Jet angles and gamma-ray energetics estimations
(Goldstein+, 2016)
J/ApJS/223/28 : The third Fermi/GBM GRB catalog (6yr) (Bhat+, 2016)
Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 5 F5.1 s b_Time Time interval, lower value
7- 11 F5.1 s B_Time Time interval, upper value
13- 15 I3 --- pgstat [233/670] pgstat value
17- 19 I3 --- dof [240/383] Degrees of freedom
21- 25 F5.2 --- tau Optical depth τ
27- 31 F5.2 --- E_tau Upper limit uncertainty in tau
33- 36 F4.2 --- e_tau Lower limit uncertainty in tau
38- 42 F5.1 --- Gamma Bulk flow Lorentz factor Γ
44- 47 F4.1 --- E_Gamma Upper limit uncertainty in Gamma
49- 52 F4.1 --- e_Gamma Lower limit uncertainty in Gamma
54- 60 F7.3 10-59W L0.52 Luminosity (L0,52=L010-52erg/s) (1)
62- 67 F6.3 10-59W E_L0.52 Upper limit uncertainty in L0.52
69- 74 F6.3 10-59W e_L0.52 Lower limit uncertainty in L0.52
76- 80 F5.3 --- epsilon Dissipated energy εd (2)
82- 86 F5.3 --- E_epsilon Upper limit uncertainty in epsilon
88- 92 F5.3 --- e_epsilon Lower limit uncertainty in epsilon
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Note (1): The luminosity, L0,52, corresponds to the amount of energy we have
in the spectrum as well as the comoving proton number density.
Note (2): εd is pegged at its lowest value in table1.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 02-Jan-2018