TY - JOUR
T1 - Power density spectra of gamma-ray bursts in the internal shock model
AU - Panaitescu, A.
AU - Spada, M.
AU - Mészáros, P.
N1 - Funding Information:
We have compared our results to those of BSS98 and have identified three possible reasons for the observed deficit of short (dT ≲ 1 s) pulses: (1) the 50–300 keV radiative efficiency of such pulses may be smaller than for longer pulses due to low electron injection fractions and magnetic fields well below equipartition, (2) the short pulses may occur below the photospheric radius, and (3) the short pulses may result from the collision of light shells, carrying little energy, due to a modulation of the ejection LFs. Our study of the power spectra of internal shock GRBs has shown that if the ejection parameters of optically thin winds are totally random, the resulting spectrum is flat, with equal power at low and high frequency. In order to explain the f−5/3 behavior of the observed PDS, the wind must be modulated, such that collisions at large radii release more energy in the observing band than the collisions occurring as small radii. Thus we obtain PDS features similar to those observed mainly by using the dynamics of relativistic winds and not through the turbulence that could develop in them, as hypothesized by BSS98. A modulation of the wind ejection is physically quite plausible, and the fact that it is necessary to introduce this in order to obtain the correct PDS is one indication of the value of the power spectrum as a tool in studying the physics of the GRB “central engine.” This research is supported by NASA NAG5-2857, NSF PHY94-07194, and the CNR. We are grateful to Martin Rees, Marco Salvati, and Steinn Sigurdsson for stimulating comments.
PY - 1999/9/10
Y1 - 1999/9/10
N2 - We simulate gamma-ray bursts arising from internal shocks in relativistic winds, calculate their power density spectrum (PDS), and identify the factors to which the PDS is most sensitive: the wind ejection features, which determine the wind dynamics and its optical thickness, and the energy release parameters, which give the pulse 50-300 keV radiative efficiency. We found that the upper limit on the efficiency of conversion of wind kinetic energy into 50-300 keV photons is ∼1%. Winds with a modulated Lorentz factor distribution of the ejecta yield PDSs that exhibit a -5/3 power law up to ∼1 Hz and have efficiencies ∼10-3, while winds with a random, uniform Lorentz factor ejection must be optically thick to the short-duration pulses to yield the same PDS features and have an overall efficiency around 10-4.
AB - We simulate gamma-ray bursts arising from internal shocks in relativistic winds, calculate their power density spectrum (PDS), and identify the factors to which the PDS is most sensitive: the wind ejection features, which determine the wind dynamics and its optical thickness, and the energy release parameters, which give the pulse 50-300 keV radiative efficiency. We found that the upper limit on the efficiency of conversion of wind kinetic energy into 50-300 keV photons is ∼1%. Winds with a modulated Lorentz factor distribution of the ejecta yield PDSs that exhibit a -5/3 power law up to ∼1 Hz and have efficiencies ∼10-3, while winds with a random, uniform Lorentz factor ejection must be optically thick to the short-duration pulses to yield the same PDS features and have an overall efficiency around 10-4.
UR - https://www.scopus.com/pages/publications/0033543429
UR - https://www.scopus.com/pages/publications/0033543429#tab=citedBy
U2 - 10.1086/312230
DO - 10.1086/312230
M3 - Article
AN - SCOPUS:0033543429
SN - 0004-637X
VL - 522
SP - L105-L108
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 PART 2
ER -