212 research outputs found
A broken "-intensity" relation caused by the evolving photosphere emission and the nature of the extraordinarily bright GRB~230307A
GRB~230307A is one of the brightest gamma-ray bursts detected so far. With
the excellent observation of GRB~230307A by Fermi-GBM, we can reveal the
details of the prompt emission evolution. As found in high-time-resolution
spectral analysis, the early low-energy spectral indices () of this
burst exceed the limit of synchrotron radiation (), and gradually
decreases with the energy flux (). A tight
correlation anyhow holds within the whole duration of the burst, where is the spectral peak energy. Such evolution pattern of and with intensity is called ``double tracking". For the relation,
we find a log Bayes factor 210 in favor of a smoothly broken power-law
function over a linear function in log-linear space. We call this particular
relation as broken ``-intensity", and interpret it as the
evolution of the ratio of thermal and non-thermal components, which is also the
evolution of the photosphere. We also show that GRB 230307A with a duration of
, if indeed at a redshift of , is likely a neutron star
merger event (i.e., it is intrinsically ``short"). Intriguingly, different from
GRB 060614 and GRB 211211A, this long event is not composed of a hard spike
followed by a soft tail, suggesting that the properties of the prompt emission
light curves are not a good tracer of the astrophysical origins of the bursts.
The other possibility of would point toward very peculiar nature of
both GRB 230307A and its late time thermal-like emission.Comment: 14 pages, 6 figures, 1 table. We have excluded the GBM instrument
pile-up time interval in the data analysis and also discussed the nature of
this even
A Unified Geometric Model of Repeating and Non-Repeating Fast Radio Bursts
Fast radio bursts (FRBs) are millisecond-duration extragalactic radio
transients. They apparently fall into repeaters and non-repeaters. However,
such a classification has lacked a motivation on the physical picture. Here we
propose a unified geometric model to distinguish between the repeaters and
non-repeaters, in which the quasi-tangential (QT) propagation effect within the
magnetospheric polar cap of a neutron star is considered. In this model, the
non-repeaters arise from the sources whose emitting region has a smaller impact
angle with respect to the magnetic axis, while the repeaters come from the
sources whose emitting region has a larger impact angle. The observational
discriminant polarization properties between the repeaters and non-repeaters
are an important clue to verifying this unified geometric model since the
polarization is sensitive to the QT propagation effect. Moreover, our model
effectively explains all of the other discriminant properties, including
bandwidth, duration, peak luminosity, energy, brightness temperature,
time-frequency downward drifting, and repetition rate, providing compelling
evidence for the magnetospheric origin of FRBs.Comment: 16 pages, 8 figure
Multi-frequency test of dark matter annihilation into long-lived particles in Sirius
New long-lived particles produced at the colliders may escape from
conventional particle detectors. Using satellites or ground telescopes, we can
detect the photons generated from the annihilation of the star-captured dark
matter into a pair of long-lived particles. When the propagation length of
these long-lived particles surpasses the interplanetary distance between the
Sun and Jupiter, it becomes unfeasible to detect such dark matter signals
originating from the Sun or Jupiter on Earth. Our analysis of the dark
matter-induced photons produced by prompt radiation, inverse Compton
scattering, and synchrotron radiation mechanisms reveals that a decay length of
about pc for long-lived particles is required for maximum
detectability. We investigate the parameters that allow the long-lived
particle's lifetime to be consistent with Big Bang nucleosynthesis while also
allowing it to escape the confines of our solar system. The Sirius system is
proposed as a promising target for the indirect detection of such long-lived
particles. Utilizing the prompt, inverse Compton scattering, and synchrotron
radiation, upper limits on the dark matter-proton spin-independent and
spin-dependent cross section are estimated with the Fermi-LAT null-signal
observation and the capabilities of the upcoming Square Kilometre Array radio
telescope.Comment: 30 pages, 6 figures, JCAP accepte
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