“Double-tracking” Characteristics of the Spectral Evolution of GRB 131231A: Synchrotron Origin?. (arXiv:1901.04925v2 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Li_L/0/1/0/all/0/1">Liang Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Geng_J/0/1/0/all/0/1">Jin-Jun Geng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Meng_Y/0/1/0/all/0/1">Yan-Zhi Meng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wu_X/0/1/0/all/0/1">Xue-Feng Wu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Huang_Y/0/1/0/all/0/1">Yong-Feng Huang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_Y/0/1/0/all/0/1">Yu Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moradi_R/0/1/0/all/0/1">Rahim Moradi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Uhm_Z/0/1/0/all/0/1">Z. Lucas Uhm</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_B/0/1/0/all/0/1">Bing Zhang</a>
The characteristics of the spectral evolution of the prompt emission of
gamma-ray bursts (GRBs), which is closely related to the radiation mechanism
(synchrotron or photosphere), is still an unsolved subject. Here, by performing
the detailed time-resolved spectral fitting of GRB 131231A, which has a very
bright and well-defined single pulse, some interesting spectral evolution
features have been found. (i) Both the low-energy spectral index $alpha$ and
the peak energy $E_{rm pk}$ exhibit the “flux-tracking” pattern
(“double-tracking” characteristics). (ii) The parameter relations, i.e.,
$F$(the energy flux)-$alpha$, $F$-$E_{rm pk}$, and $E_{rm pk}$-$alpha$,
along with the analogous Yonetoku $E_{rm pk}$-$L_{gamma,rm iso}$ relation
for the different time-resolved spectra, show strong monotonous (positive)
correlations, both in the rising and the decaying phases. (iii) The values of
$alpha$ do not exceed the synchrotron limit ($alpha$= -2/3) in all slices
across the pulse, favoring the synchrotron origin. We argue that the one-zone
synchrotron emission model with the emitter streaming away at a large distance
from the central engine can explain all these special spectral evolution
characteristics.
The characteristics of the spectral evolution of the prompt emission of
gamma-ray bursts (GRBs), which is closely related to the radiation mechanism
(synchrotron or photosphere), is still an unsolved subject. Here, by performing
the detailed time-resolved spectral fitting of GRB 131231A, which has a very
bright and well-defined single pulse, some interesting spectral evolution
features have been found. (i) Both the low-energy spectral index $alpha$ and
the peak energy $E_{rm pk}$ exhibit the “flux-tracking” pattern
(“double-tracking” characteristics). (ii) The parameter relations, i.e.,
$F$(the energy flux)-$alpha$, $F$-$E_{rm pk}$, and $E_{rm pk}$-$alpha$,
along with the analogous Yonetoku $E_{rm pk}$-$L_{gamma,rm iso}$ relation
for the different time-resolved spectra, show strong monotonous (positive)
correlations, both in the rising and the decaying phases. (iii) The values of
$alpha$ do not exceed the synchrotron limit ($alpha$= -2/3) in all slices
across the pulse, favoring the synchrotron origin. We argue that the one-zone
synchrotron emission model with the emitter streaming away at a large distance
from the central engine can explain all these special spectral evolution
characteristics.
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