899 research outputs found
Searching Signals in Chinese Ancient Records for the C Increases in AD 774-775 and in AD 992-993
According to the analysis of the C content of two Japanese trees over
a period of approximately 3000 years at high time resolution, Miyake (2012)
found a rapid increase at AD 774-775 and later on at AD 992-993 (Miyake 2013).
This corresponds to a high-energy event happened within one year that input
-ray energy about 710erg to the Earth, leaving the
origin a mystery. Such strong event should have an unusual optical counterpart,
and have been recorded in historical literature. We searched Chinese historical
materials around AD 744-775 and AD 992-993, but no remarkable event was found
except a violent thunderstorm in AD 775. However, the possibility of a
thunderstorm containing so much energy is still unlikely. We conclude the event
caused the C increase is still unclear. This event most probably has no
optical counterpart, and short gamma-ray burst, giant flare of a soft gamma-ray
repeater and terrestrial -ray flash may all be the candidates.Comment: 8 pages, 3 figure
Expected high energy emission from GRB 080319B and origins of the GeV emission of GRBs 080514B, 080916C and 081024B
We calculate the high energy (sub-GeV to TeV) prompt and afterglow emission
of GRB 080319B that was distinguished by a naked-eye optical flash and by an
unusual strong early X-ray afterglow. There are three possible sources for high
energy emission: the prompt optical and -ray photons IC scattered by
the accelerated electrons, the prompt photons IC scattered by the early
external reverse-forward shock electrons, and the higher band of the
synchrotron and the synchrotron self-Compton emission of the external shock.
There should have been in total {hundreds} high energy photons detectable for
the Large Area Telescope (LAT) onboard the Fermi satellite, and {tens} photons
of those with energy GeV. The GeV emission had a duration about
twice that of the soft -rays. AGILE could have observed these energetic
signals if it was not occulted by the Earth at that moment. The physical
origins of the high energy emission detected in GRB 080514B, GRB 080916C and
GRB 081024B are also discussed. These observations seem to be consistent with
the current high energy emission models.Comment: Accepted for publication in MNRAS, the interpretation of GRB 080916C
has been extended, main conclusions are unchange
Constraining the bulk Lorentz factor from the photosphere emission
We propose a direct and model-independent method to constrain the Lorentz
factor of a relativistically expanding object, like gamma-ray bursts. Only the
measurements, such as thermal component of the emission, the distance and the
variable time scale of the light curve, are used. If the uncertainties are
considered, we will obtain lower limits of the Lorentz factor instead. We apply
this method to GRB 090618 and get a lower limit of the Lorentz factor to be 22.
The method can be used to any relativistically moving object, such as gamma-ray
bursts, blazars, and soft gamma-ray repeaters, providing the thermal component
of the emission being observed.Comment: 10 pages, 1 figur
Directed search for continuous gravitational waves from the possible kilonova remnant G4.8+6.2
G4.8+6.2 was proposed as a possible kilonova remnant associated with the
Korean guest star of AD 1163 in our Milky Way galaxy. Its age is about 860
years according to the historical record. If a neutron star was left in the
center of G4.8+6.2, this young neutron star may radiate strong continuous
gravitational waves, which could beat the indirect age-based upper limit with
current LIGO sensitivity. In this work, we searched such continuous
gravitational waves in the frequency band . This search
used two days of LIGO O3b data from the Hanford and Livingston detectors. While
no signal was found, we placed upper limits on the gravitational wave strain.
For comparison we also showed the latest results of all-sky searches obtained
with various search pipelines. With upgrading of the LIGO detectors, it will
provide the opportunity to see whether a black hole or a neutron star is
harbored inside G4.8+6.2.Comment: 8 pages, 6 figures, 1 tables, Accepted for publication in Physical
Review
Constraint on the relativistic motion of fast radio bursts based on the maximal electric field
Fast radio bursts (FRBs) are millisecond radio signals from cosmological
distances. As they propagate, FRBs can interact with ambient photons and
initiate a quantum cascade that can limit the electric field strength. This
paper examines whether some observed bright and brief FRBs may challenge this
limit if the source is not relativistic. The size of a static FRB source is
estimated as , where is the time scale of the FRB and denotes
the speed of light. But for a relativistic source moving at the Lorentz factor
, the size is . Using an FRB catalog, we plot
the luminosity-duration distribution. Most FRBs fall below the limit for a
static source, but two events have higher luminosity and shorter duration. This
suggests these bursts may originate from relativistic sources, although more
data is needed to confirm this.Comment: 4 pages, 1figur
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