The Shape of Spectral Breaks in Gamma-Ray Burst Afterglows

By J. Granot, R. Sari. 2001

523 citations recorded by the source corpus.

Gamma-ray burst afterglows are well described by synchrotron emission from relativistic blast waves expanding into an external medium. The blast wave is believed to amplify the magnetic field and accelerate the electrons into a power-law distribution of energies promptly behind the shock. These electrons then cool both adiabatically and by emitting synchrotron and inverse Compton radiation. The resulting spectra are known to consist of several power-law segments, which smoothly join at certain break frequencies. Here, we give a complete description of all possible spectra under those assumptions and find that there are five possible regimes, depending on the ordering of the break frequencies. The flux density is calculated by integrating over all of the contributions to a given photon arrival time from all of the shocked region using the Blandford & McKee solution. This allows us to calculate more accurate expressions for the value of these break frequencies and describe the shape of the spectral breaks around them. This also provides the shape of breaks in the light curves caused by the passage of a break frequency through the observed band. These new, more exact, estimates are different from more simple calculations by typically a factor of a few, and they describe some new regimes that were previously ignored.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/a90f995dbe957d865f79d56157abcaac99b0813c

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In Astronomy and Astrophysics

1. Bing Zhang
2. E. Berger
3. B. Metzger
4. Pawan Kumar
5. E. Liang
6. E. Nakar
7. W. Fong
8. Binbin Zhang

Citations in the corpus

• GRB 080503: IMPLICATIONS OF A NAKED SHORT GAMMA-RAY BURST DOMINATED BY EXTENDED EMISSION (2008, unknown): “For a νX ≈ 10 18 Hz (corresponding to ∼ 4 keV) this suggests νc(11 hr) & 10 20 Hz, which in turn (using the expression for νc from Granot & Sari 2002) implies n .”
• JET BREAKS AND ENERGETICS OF Swift GAMMA-RAY BURST X-RAY AFTERGLOWS (2008, background): “All of the analytical closure relations assume a simple spectrum with sharp breaks, whereas in reality these breaks are likely smooth (Granot & Sari 2002).”
• Evidence for a Canonical Gamma-Ray Burst Afterglow Light Curve in the Swift XRT Data (2005, background): “…the typical Lorentz factor for a given observed time as that just behind the shock at the radius corresponding to the outer edge of the afterglow image (Granot & Sari 2002) gives C ¼ 4(4 k)/(5 4) and in turn, (t) ¼ 6:68(E52=n0) 1=8½tdays=(1þ z) 3=8 (k ¼ 0); 4:90(E52=A ) 1=4½tdays=(1þ z) 1=4 (k ¼…”
• AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS (2010, background): “…broken power laws with three characteristic frequencies: νa, the frequency below which the radiation is self-absorbed; νm, the characteristic frequency of the emitting electrons; and νc, the frequency above which electrons are able to cool efficiently through radiation (e.g., Granot & Sari 2002).”
• Probing the cosmic reionization history and local environment of gamma‐ray bursts through radio dispersion (2003, methodology): “We follow standard prescriptions for the synchrotron emission from electrons accelerated by a relativistic shock decelerating in the ambient medium (Sari, Piran & Narayan 1998, Wijers & Galama 1999, Panaitescu & Kumar 2000), with particular attention to self-absorption (see also Granot & Sari 2002).”
• The afterglow of GRB 021004: surfing on density waves (2002, background): “The code takes fully into account the light travel-time effects, and assumes standard synchrotron emission equations to compute the comoving frame intensity (Panaitescu & Kumar 2000; Granot & Sari 2002).”
• The optical afterglow of the short gamma-ray burst associated with GW170817 (2018, unknown): “This is in contrast to the cocoon model, where there would be a longer continued rise and shallower decay afterwards, as t ∼ t in the relativistic regime, consistent with near-spherical ejecta.(55) Continued monitoring of the source to very late times will distinguish between the two scenarios.”
• A DECADE OF SHORT-DURATION GAMMA-RAY BURST BROADBAND AFTERGLOWS: ENERGETICS, CIRCUMBURST DENSITIES, AND JET OPENING ANGLES (2015, methodology): “In addition to these four parameters,Fν,i is also dependent on the redshift, luminosity distance,νi , time after the burst,δt, and the value ofp; the exact dependencies are provided in Granot & Sari (2002).”
• The sub-energetic γ-ray burst GRB 031203 as a cosmic analogue to the nearby GRB 980425 (2004, methodology): “As a next step, we applied the simplest afterglow mode”
• A Decline in the X-Ray through Radio Emission from GW170817 Continues to Support an Off-axis Structured Jet (2018, background): “We observe no evidence for a steepening of the X-ray spectral index from βx to βx+0.5, predicted when the synchrotron cooling frequency passes below the X-ray band (Granot & Sari 2002).”
• Short-hard gamma-ray bursts (2007, background): “(17) A detailed discussion of the light curve in cases of other orders of the break frequencies can be found in Granot & Sari (2002) while the case of 1 p 2 is discussed in Dai & Cheng (2001).”
• Late-Time Radio Observations of 68 Type Ibc Supernovae: Strong Constraints on Off-Axis Gamma-Ray Bursts (2005, methodology): “A Semi-analytic Model In modeling the afterglow emission from an off-axis GRB jet, we adopt the standard framework for a adiabatic blastwave expanding into either a uniform or wind stratified medium (Sari 1997; Granot & Sari 2002).”
• A complete reference of the analytical synchrotron external shock models of gamma-ray bursts (2013, background): “, 1999), which smooths the spectral and temporal breaks (Granot and Sari, 2002).”
• The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VI. Radio Constraints on a Relativistic Jet and Predictions for Late-time Emission from the Kilonova Ejecta (2017, methodology): “Here we utilize the standard afterglow synchrotron model in a constant density medium (Granot & Sari 2002), as expected for a BNS progenitor.”