Stepwise e-Participation

Molinari, Francesco; Kunstelj, Mateja; Todorovski, Ljupčo

doi:10.4018/978-1-4666-0116-1.ch021

Cited by 19 publications

(53 citation statements)

References 6 publications

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“…The bulk Lorentz factor has been derived in various ways (e.g. Lithwick & Sari 2001; Molinari et al 2007; Xue, Fan & Wei 2009; Zou & Piran 2009) and Γ i ∼ 300 seems quite reasonable. R γ can be estimated by ∼2Γ 2 i c δ t .…”

Section: Thermal Radiation Expected In Standard Internal Shock Modementioning

confidence: 94%

The spectrum of γ-ray burst: a clue

Fan¹

2010

Monthly Notices of the Royal Astronomical Society

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In this work, we numerically calculate the thermal radiation efficiency of the baryonic outflow. The possible outflow acceleration in the transparent stage, which lowers thermal radiation efficiency, has been taken into account. In the standard internal shock model for the prompt emission, the fast shells should move with a typical Lorentz factor ∼5 Γi otherwise the γ‐ray burst (GRB) efficiency will be in disagreement with the observations, where Γi is the bulk Lorentz factor of the shocked/emitting region. The photosphere radius of these fast shells is small and the thermal radiation is too strong to be effectively outshone by the internal shock emission. This is particularly the case for some extremely bright events having Γi∼ 103, like GRBs 080319B and 080916C. The absence of a distinct thermal component in the spectrum of most GRBs challenges the standard internal shock model and may suggest a non‐baryonic (magnetic) outflow component. Though the magnetic outflow model seems favoured by more and more data, it can hardly reproduce the typical GRB spectrum. In the photosphere‐gradual magnetic dissipation scenario, the spectrum cuts off at ∼1 GeV, too low to account for the observations of GRBs 080916C. In the sudden magnetic energy dissipation model, the low‐energy spectrum is expected to be Fν∝ν−1/2, too soft to be consistent with the data Fν∝ν0. We speculate that the low‐energy spectrum puzzle could be unveiled by the mechanism that particles, in the magnetic dissipation process, are repeatedly accelerated.

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Section: Thermal Radiation Expected In Standard Internal Shock Modementioning

confidence: 94%

The spectrum of γ-ray burst: a clue

Fan¹

2010

Monthly Notices of the Royal Astronomical Society

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Section: Introductionmentioning

confidence: 99%

“…As an example, using this method Sari & Piran (1999a) constrained Γ 0 of GRB 990123 to be ∼200. Molinari et al (2007) and Jin & Fan (2007) estimated, using the early optical afterglow, Γ 0 to be ∼400 for both GRB 060418 and GRB 060607A. Thermal emission escapes from the fireball's photospheric when it becomes optically thin. The observations of a thermal component would, therefore, allow us to infer the Lorentz factor at this time (Nakar, Piran & Sari 2005; Pe'er et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Lorentz factor constraint from the very early external shock of the gamma-ray burst ejecta

Zou

Piran

2010

Monthly Notices of the Royal Astronomical Society

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While it is generally agreed that the emitting regions in gamma‐ray bursts move ultra‐relativistically towards the observer, different estimates of the initial Lorentz factors, Γ0, lead to different at times conflicting estimates. We show here that the quiet periods in which the signals goes down below the instrumental thresholds put strong upper limits on the values of Γ0. According to the standard internal–external shock model, an external shock should develop during the prompt stage. This external shock radiates in the hard X‐rays to soft gamma‐rays bands and this emission should be seen as a smooth background signal. The observed deep minima indicate that this contribution is negligible. This limits, in turn, Γ0. We obtain upper limits on Γ0 for several bursts with typical values around hundreds. We compare these values with those obtained by the other methods, which typically yield lower limits. The results are marginally consistent leaving only a narrow range of allowed values for Γ0.

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“… The three GRBs that show prominent late X‐ray flares but without a simultaneous optical flare apparent in the afterglow light curve. Top: GRB 060418; middle: 060607a (both from Molinari et al 2007); bottom: GRB 060904b; blue triangles are BAT data extrapolated to the X‐ray band, magenta squares are XRT data and red circles are optical data (from Rykoff et al 2009). …”

Section: Late‐jet–cocoon Interactionmentioning

confidence: 99%

The late jet in gamma-ray bursts and its interactions with a supernova ejecta and a cocoon

Shen

Kumar

Piran

2010

Monthly Notices of the Royal Astronomical Society

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Late X‐ray flares observed in X‐ray afterglows of gamma‐ray bursts (GRBs) suggest late central engine activities at a few minutes to hours after the burst. A few unambiguously confirmed cases of supernova associations with nearby long GRBs imply that an accompanying supernova‐like component might be a common feature in all long GRB events. These motivate us to study the interactions of a late jet, responsible for an X‐ray flare, with various components in a stellar explosion, responsible for a GRB. These components include a supernova shell‐like ejecta and a cocoon that was produced when the main jet producing the GRB itself was propagating through the progenitor star. We find that the interaction between the late jet and the supernova ejecta may produce a luminous (up to 1049 erg s−1) thermal X‐ray transient lasting for ∼10 s. The interaction between the late jet and the cocoon produces synchrotron self‐absorbed non‐thermal emission, with the observed peak X‐ray flux density from 0.001 μJy to 1 mJy at 1 keV and a peak optical flux density from 0.01 μJy to 0.1 Jy (for a redshift z= 2). The light curve due to the late‐jet–cocoon interaction has a very small pulse‐width‐to‐time ratio, Δt/t≈ 0.01–0.5, where t is the pulse peak time since the burst trigger. Identifying these features in current and future observations would open a new frontier in the study of GRB progenitor stars.

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Stepwise e-Participation

Cited by 19 publications

References 6 publications

The spectrum of γ-ray burst: a clue

The spectrum of γ-ray burst: a clue

Lorentz factor constraint from the very early external shock of the gamma-ray burst ejecta

The late jet in gamma-ray bursts and its interactions with a supernova ejecta and a cocoon

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