Searching Signals in Chinese Ancient Records for the 14^{14}C Increases in AD 774-775 and in AD 992-993

According to the analysis of the $^{14}$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 $\gamma$-ray energy about 7$\times{}$10$^{24}$erg 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 $^{14}$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 $\gamma$-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 $\gamma$-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 $> 10$ GeV. The $> 10$ GeV emission had a duration about twice that of the soft $\gamma$-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 $20-1500 \mathrm{~Hz}$. 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

Constraining the Mass of the Photon with Gamma-Ray Bursts

One of the cornerstones of modern physics is Einstein's special relativity, with its constant speed of light and zero photon mass assumptions. Constraint on the rest mass m_{\gamma} of photons is a fundamental way to test Einstein's theory, as well as other essential electromagnetic and particle theories. Since non-zero photon mass can give rise to frequency-(or energy-) dependent dispersions, measuring the time delay of photons with different frequencies emitted from explosive astrophysical events is an important and model-independent method to put such a constraint. The cosmological gamma-ray bursts (GRBs), with short time scales, high redshifts as well as broadband prompt and afterglow emissions, provide an ideal testbed for m_{\gamma} constraints. In this paper we calculate the upper limits of the photon mass with GRB early time radio afterglow observations as well as multi-band radio peaks, thus improve the results of Schaefer (1999) by nearly half an order of magnitude.Comment: 25 pages, 2 tables, Accepted by Journal of High Energy Astrophysic