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GRB Emission Mechanism Theory

I am not the best person to reference on this. I am still trying to clarify my understanding


Pure Synchrotron Emission

Shen & Zhang 09 paper 2009, MNRAS 398, 1936 shows that (1) Synchrotron can have the same appearance at gamma, X, but very different manifestations at optical, in four cases. This is the most recent treatment, those below are listed for hisotrical interest. (2) the same paper shows that incredible information, lorentz factor, radius of emission, and B are encoded in the self-absoption frequency (so go measure it!).

Here are the four cases:

Rybicki and Lightman Synchrotron

describe synch. from a power law e- population (fig. 6.12):

low-f rise is nu^+5/2 (eqn. 6.54; optically thick therefore source function)

and decay is nu^-(p-1)/2 (eqn 6.22a; optically think therefore emission function)

… but that's not the applicable spectrum:

Ghisellini+00 discusses pure or standard synch vs. synch+ cooling and inverse compton

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2000MNRAS.313L...1G&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf

The important paper here is Gabriele Ghisellini, Annalisa Celotti and Davide Lazzati MNRAS 2000.

emission is from a quasi-monoenergetic e- population;

F_nu ~ nu^+1/3 up to nu_peak

nu > nu_peak they don't say.

However, with reasonable consideration of cooling, you get a nu^-1/2 in the X-gamma spectrum, because the cooling frequency is now ~ eV.

Here is a figure from a lecture by Tsvi Piran at Caltech http://ned.ipac.caltech.edu/level5/March04/Piran2/Piran8_2.html:

“Figure 22. Synchrotron spectrum of a relativistic shock with a power-law electron distribution. (a) Fast cooling, which is expected at early times (t < t0). The spectrum consists of four segments, identified as A, B, C, D. Self-absorption is important below nua. The frequencies, num, nuc, nua, decrease with time as indicated; the scalings above the arrows correspond to an adiabatic evolution, and the scalings below, in square brackets, to a fully radiative evolution. (b) Slow cooling, which is expected at late times (t > t0). The evolution is always adiabatic. The four segments are identified as E, F, G, H. From [Sari, R., Piran, T., & Narayan, R., 1998, Ap. J. Lett., 497, L17.].”

SSC

Zou, Piran, and Sari 09 are a good reference for SSC http://iopscience.iop.org/1538-4357/692/2/L92/pdf/apjl_692_2_92.pdf

public/emission.txt · Last modified: 2021/01/12 00:50 (external edit)