42,620 research outputs found
Second Repeating FRB 180814.J0422+73: Ten-year Fermi-LAT Upper Limits and Implications
The second repeating fast radio burst source, FRB 180814.J0422+73, was detected recently by the CHIME collaboration. We use the ten-year Fermi Large Area Telescope archival data to place a flux upper limit in the energy range of 100 MeV−10 GeV at the position of the source, which is ~1.1 × 10−11 erg cm−2 s−1 for a six-month time bin on average, and ~2.4 × 10−12 erg cm−2 s−1 for the entire ten-year time span. For the maximum redshift of z = 0.11, the ten-year upper limit of luminosity is ~7.3 × 1043 erg s−1. We utilize these upper limits to constrain the fast radio burst (FRB) progenitor and central engine. For the rotation-powered young magnetar model, the upper limits can pose constraints on the allowed parameter space for the initial rotational period and surface magnetic field of the magnetar. We also place significant constraints on the kinetic energy of a relativistic external shock wave, ruling out the possibility that there existed a gamma-ray burst (GRB) beaming toward Earth during the past ten years as the progenitor of the repeater. The case of an off-beam GRB is also constrained if the viewing angle is not much greater than the jet opening angle. All of these constraints are more stringent if FRB 180814.J0422+73 is at a closer distance
Equilibrium and equilibration in a gluon plasma with improved matrix elements
The hot and dense matter created in the early stage of a relativistic heavy
ion collision is composed mainly of gluons. Radiative processes can play an
important role for the thermalization of such partonic systems. The simplest
parton number changing processes are commonly described by the Gunion-Bertsch
formula. We show that the cross section from the exact matrix element for the
lowest order radiative process could be significantly smaller than that based
on the Gunion-Bertsch formula. In light of this, we discuss the role of
radiative processes on the equilibrium and equilibration of a gluon plasma.Comment: Presented at the 25th International Nuclear Physics Conference (INPC
2013), Florence, Italy, 2-7 June 201
Central Engine Memory of Gamma-Ray Bursts and Soft Gamma-Ray Repeaters
Gamma-ray Bursts (GRBs) are bursts of -rays generated from
relativistic jets launched from catastrophic events such as massive star core
collapse or binary compact star coalescence. Previous studies suggested that
GRB emission is erratic, with no noticeable memory in the central engine. Here
we report a discovery that similar light curve patterns exist within individual
bursts for at least some GRBs. Applying the Dynamic Time Warping (DTW) method,
we show that similarity of light curve patterns between pulses of a single
burst or between the light curves of a GRB and its X-ray flare can be
identified. This suggests that the central engine of at least some GRBs carries
"memory" of its activities. We also show that the same technique can identify
memory-like emission episodes in the flaring emission in Soft Gamma-Ray
Repeaters (SGRs), which are believed to be Galactic, highly magnetized neutron
stars named magnetars. Such a phenomenon challenges the standard black hole
central engine models for GRBs, and suggest a common physical mechanism behind
GRBs and SGRs, which points towards a magnetar central engine of GRBs.Comment: 7 pages, 4 figures, ApJ Letters in pres
Dependence of Temporal Properties on Energy in Long-Lag, Wide-Pulse Gamma-Ray Bursts
We employed a sample compiled by Norris et al. (2005, ApJ, 625, 324) to study
the dependence of the pulse temporal properties on energy in long-lag,
wide-pulse gamma-ray bursts. Our analysis shows that the pulse peak time, rise
time scale and decay time scale are power law functions of energy, which is a
preliminary report on the relationships between the three quantities and
energy. The power law indexes associated with the pulse width, rise time scale
and decay time scale are correlated and the correlation between the indexes
associated with the pulse width and the decay time scale is more obvious. In
addition, we have found that the pulse peak lag is strongly correlated with the
CCF lag, but the centroid lag is less correlated with the peak lag and CCF lag.
Based on these results and some previous investigations, we tend to believe
that all energy-dependent pulse temporal properties may come from the joint
contribution of both the hydrodynamic processes of the outflows and the
curvature effect, where the energy-dependent spectral lag may be mainly
dominated by the dynamic process and the energy-dependent pulse width may be
mainly determined by the curvature effect.Comment: 20 pages, 7 figures, added references, matched to published version,
accepted for publication in PAS
Is It Desirable for Asian Economies to Hold More Asian Assets in Their Foreign Exchange Reserves?—The People’s Republic of China’s Answer
The author calculates the return on the major Asian currency denominated long-term government bonds in terms of a basket of the People’s Republic of China’s (PRC) imports of goods and services, namely the real return on those assets from the PRC’s perspective. He shows that it is desirable for the PRC to substitute Asian currency denominated government bonds for US Treasury bills to maintain the purchasing power of its foreign exchange reserves.foreign exchange reserves; currency basket; asian currencies
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