We examine a method to detect the light speed variation from gamma ray burst data observed by the Fermi Gamma-ray Space Telescope (FGST). We suggest new criteria to determine the characteristic time ...for low energy photons by the energy curve and the average energy curve respectively, and obtain similar results compared with those from the light curve. We offer a new criterion with both the light curve and the average energy curve to determine the characteristic time for low energy photons. We then apply the new criteria to the GBM NaI data, the GBM BGO data, and the LAT LLE data, and obtain consistent results for three different sets of low energy photons from different FERMI detectors.
It is postulated in Einstein's relativity that the speed of light in vacuum is a constant for all observers. However, the effect of quantum gravity could bring an energy dependence of light speed. ...Even a tiny speed variation, when amplified by the cosmological distance, may be revealed by the observed time lags between photons with different energies from astrophysical sources. From the newly detected long gamma ray burst GRB 160509A, we find evidence to support the prediction for a linear form modification of light speed in cosmological space.
Previous researches on high-energy photon events from gamma-ray bursts (GRBs) suggest a light speed variation v(E)=c(1−E/ELV) with ELV=3.6×1017 GeV, together with a pre-burst scenario that ...hight-energy photons come out about 10 seconds earlier than low-energy photons at the GRB source. However, in the Lorentz invariance violating scenario with an energy dependent light speed considered here, high-energy photons travel slower than low-energy photons due to the light speed variation, so that they are usually detected after low-energy photons in observed GRB data. Here we find four high-energy photon events which were observed earlier than low-energy photons from Fermi Gamma-ray Space Telescope (FGST), and analysis on these photon events supports the pre-burst scenario of high energy photons from GRBs and the energy dependence of light speed listed above.
It has been reported that the Large High Altitude Air Shower Observatory (LHAASO) observed very high energy photons from GRB 221009A, with the highest energy reaching 18 TeV. We find that observation ...of such high energy photons is quite nontrivial since extragalactic background light could absorb these photons severely and the flux is too weak to be observed. Therefore we discuss a potential mechanism for us to observe these photons, and suggest that Lorentz invariance violation induced threshold anomaly of the process γγ→e−e+ provides a candidate to explain this phenomenon.
We present a facile route towards a dual single‐atom nanozyme composed of Zn and Mo, which utilizes the non‐covalent nano‐assembly of polyoxometalates, supramolecular coordination complexes as the ...metal‐atom precursor, and a macroscopic amphiphilic aerogel as the supporting substrate. The dual single‐atoms of Zn and Mo have a high content (1.5 and 7.3 wt%, respectively) and exhibit a synergistic effect and a peroxidase‐like activity. The Zn/Mo site was identified as the main active center by X‐ray absorption fine structure spectroscopy and density functional theory calculation. The detection of versatile analytes, including intracellular H2O2, glucose in serum, cholesterol, and ascorbic acid in commercial beverages was achieved. The nanozyme has an outstanding stability and maintained its performance after one year's storage. This study develops a new peroxidase‐like nanozyme and provides a robust synthetic strategy for single‐atom catalysts by utilizing an aerogel as a facile substrate that is capable of stabilizing various metal atoms.
A new synthesis strategy for a dual single‐atom nanozyme has been developed by using a macroscopic polymer aerogel as the supporting substrate and supramolecular coordination complexes/polyoxometalates as the metal precursor. The nanozyme with high catalytic activity and super‐long stability has been applied in the detection of various analytes including intracellular H2O2, glucose in serum, cholesterol, and ascorbic acid in commercial beverages.
We revisit a supersymmetric string model for space-time foam, in which bosonic open-string states, such as photons, can possess quantum-gravity-induced velocity fluctuations in vacuum. We argue that ...the suggestion of light speed variation with lower bound from gamma-ray burst photon time delays can serve as a support for this string-inspired framework, through connecting the experimental finding with model predictions. We also derive the value of the effective quantum-gravity mass in this framework, and give a qualitative study on the model-dependent coefficients. Constraints from birefringent effects and/or photon decays, including the novel γ-decay constraint obtained here from the latest Tibet ASγ near-PeV photon, are also found to be consistent with predictions in such a quantum-gravity scheme. Future observation that can testify further the theory is suggested.
•We analyze the data of photons from gamma-ray bursts (GRBs) with energies higher than 10 GeV.•We unveil a surprising regularity behind the data of these energetic photons.•Such regularity can serve ...to support the energy-dependence of light speed in cosmological space.
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The effect of quantum gravity can bring a tiny light speed variation which is detectable through energetic photons propagating from gamma ray bursts (GRBs) to an observer such as the space observatory. Through an analysis of the energetic photon data of the GRBs observed by the Fermi Gamma-ray Space Telescope (FGST), we reveal a surprising regularity of the observed time lags between photons of different energies with respect to the Lorentz violation factor due to the light speed energy dependence. Such regularity suggests a linear form correction of the light speed v(E)=c(1−E/ELV), where E is the photon energy and ELV=(3.60±0.26)×1017GeV is the Lorentz violation scale measured by the energetic photon data of GRBs. The results support an energy dependence of the light speed in cosmological space.
As a new concept, a self‐crosslink mechanism for hydrothermal synthesis of poly(vinyl alcohol) (PVA) aerogel, assisted by multiwall carbon nanotubes, is reported. PVA, working as a low‐cost and ...commercially available raw material, exempts the complicated synthesis process and reserves its nontoxic nature since no organic crosslinkers are used in the synthesis process. The crosslink density and many other properties of the products can be easily tuned by simply altering the concentration of PVA precursors, which is considered to be another feature of our method. Dehydration between hydroxyl groups occurs in the hydrothermal process, leading to a reverse wettability of the products from hydrophilic to hydrophobic, thus their absorbing capacity for several organic solvents, such as bean oil and crude oil, is investigated. The absorbate has 10–52 times the original weight of the aerogel. As exhibited by the cytotoxic tests, the product has neglectable toxicity, suitable for application in environmental bioengineering. Furthermore, the product can be used as a facile substrate for transformation into conductive aerogel by in situ hybridizing with polypyrrole, showing a conductivity of 0.16 S m−1. As it is rich in hydroxyl groups, the aerogels are believed to be further functionalized by the reactions related to the hydroxyl group.
A self‐crosslink mechanism for one‐pot synthesis of poly(vinyl alcohol)‐based aerogel is reported. No organic crosslinkers are required in the synthesis process and the raw material is low‐cost and commercially available. The products have good absorbing capacity for oil–water separation and meanwhile work as a “substrate” for in situ fabrication of conductive gel by hybridizing with polypyrrole.
The mass domain where massive extrasolar planets and brown dwarfs overlap is still poorly understood due to the paucity of brown dwarfs orbiting close to solar-type stars, the so-called brown dwarf ...desert. In this paper, we collect all available data about close brown dwarfs around solar-type stars and their host stars from literature and study the demographics of the brown dwarf desert. The data clearly show a short period and a medium mass gap in the brown dwarf period-mass distribution diagram (35 < m sin i < 55M
Jup and P < 100 d), representing the 'driest land' in the brown dwarf desert. Observation biases are highly unlikely to cause this gap due to its short period and medium mass, of which brown dwarfs can be easily detected by previous radial velocity surveys. Brown dwarfs above and below this gap have significantly different eccentricity distribution, which not only confirms that this gap is real, but also implies that they may have different origins. Our further statistical study indicates that brown dwarfs below this gap may primarily form in the protoplanetary disc through disc gravitational instability, while brown dwarfs above this gap may dominantly form like a stellar binary through molecular cloud fragmentation. Our discoveries have offered important insights about brown dwarf formation mechanisms and their possible relationships with planet and star formation.
Lorentz invariance violation (LIV) can change the threshold behavior predicted by special relativity and cause threshold anomalies which affect the propagation of cosmic photons. In this work, we ...focus on the threshold anomaly effect on cosmic photon attenuations by extragalactic background light (EBL) and discuss how to identify LIV from observations of very high energy (VHE) photons propagated from long distance in the universe. We point out that the Large High Altitude Air Shower Observatory (LHAASO), one of the most sensitive gamma-ray detector arrays currently operating at TeV and PeV energies, is an ideal facility for performing such LIV searching. We apply the proposed strategy to discuss the newly observed gamma-ray burst GRB 221009A to demonstrate the predictive ability of our suggestions.
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