1,571 research outputs found
Doppler effect of gamma-ray bursts in the fireball framework
The influence of the Doppler effect in the fireball framework on the spectrum
of gamma-ray bursts is investigated. The study shows that the shape of the
expected spectrum of an expanding fireball remains almost the same as that of
the corresponding rest frame spectrum for constant radiations of the
bremsstrahlung, Comptonized, and synchrotron mechanisms as well as for that of
the GRB model. The peak flux spectrum and the peak frequency are obviously
correlated. When the value of the Lorentz factor becomes 10 times larger, the
flux of fireballs would be several orders of magnitude larger. The expansion
speed of fireballs is a fundamental factor of the enhancement of the flux of
gamma-ray bursts.Comment: 19 pages, 13 figure
Distinguishing RBL-like objects and XBL-like objects with the peak emission frequency of the overall energy spectrum
We investigate quantitatively how the peak emission frequency of the overall
energy spectrum is at work in distinguishing RBL-like and XBL-like objects. We
employ the sample of Giommi et al. (1995) to study the distribution of BL
Lacertae objects with various locations of the cutoff of the overall energy
spectrum. We find that the sources with the cutoff located at lower frequency
are indeed sited in the RBL region of the plane,
while those with the cutoff located at higher frequency are distributed in the
XBL region. For a more quantitative study, we employ the BL Lacertae samples
presented by Sambruna et al. (1996), where, the peak emission frequency, , of each source is estimated by fitting the data with a parabolic function.
In the plot of we find that, in the four different
regions divided by the line and the line,
all the RBL-like objects are inside the upper left region, while most XBL-like
objects are within the lower right region. A few sources are located in the
lower left region. No sources are in the upper right region. This result is
rather quantitative. It provides an evidence supporting what Giommi et al.
(1995) suggested: RBL-like and XBL-like objects can be distinguished by the
difference of the peak emission frequency of the overall energy spectrum.Comment: 7 pages, 2 figure
The disappearance of a narrow Mg II absorption system in quasar SDSS J165501.31+260517.4
In this letter, we present for the first time, the discovery of the
disappearance of a narrow Mg II absorption system
from the spectra of quasar SDSS J165501.31+260517.4 (). This
absorber is located at , and has a velocity offset of
with respect to the quasar. According to the velocity
offset and the line variability, this narrow Mg II
absorption system is likely intrinsic to the quasar. Since the corresponding UV
continuum emission and the absorption lines of another narrow Mg II
absorption system at are very
stable, we think that the disappearance of the absorption system is unlikely to
be caused by the change in ionization of absorption gas. Instead, it likely
arises from the motion of the absorption gas across the line of sight
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