Improvement of the all-weather profiler

The article considers the issues of improving the quality of vertical wind profile measurements. In order to make these measurements under any meteorological conditions, data from profilometers operating in different wave ranges, from optical to centimetre, are combined. At the same time, the resolving power of the latter is considerably inferior to that of the former. We propose a way to improve the quality of measurements in the radio band by applying a new method of information processing, using estimates of the width of the spectrum and the peculiarities of their spatial distribution.

Constraints on Optical Emission of FAST-detected FRB 20181130B with GWAC Synchronized Observations

Multiwavelength simultaneous observations are essential to the constraints on the origin of fast radio bursts (FRBs). However, it is a significant observational challenge due to the nature of FRBs as transients with a radio millisecond duration, which occur randomly in the sky regardless of time and position. Here, we report the search for short-time fast optical bursts in the Ground-based Wide Angle Camera (GWAC) archived data associated with FRB 20181130B, which were detected by the Five-hundred-meter Aperture Spherical radio Telescope and recently reported. No new credible sources were detected in all single GWAC images with an exposure time of 10 s, including images with coverage of the expected arrival time in optical wavelength by taking the high dispersion measurements into account. Our results provide a limiting magnitude of 15.43 ± 0.04 mag in the R band, corresponding to a flux density of 1.66 Jy or 8.35 mag in AB system by assuming that the duration of the optical band is similar to that of the radio band of about 10 ms. This limiting magnitude makes the spectral index of α < 0.367 from optical to radio wavelength. The possible existence of longer-duration optical emission was also investigated with upper limits of 0.33 Jy (10.10 mag), 1.74 mJy (15.80 mag), and 0.16 mJy (18.39 mag) for the durations of 50 ms, 10 s, and 6060 s, respectively. This undetected scenario could be partially attributed to the shallow detection capability, as well as the high inferred distance of FRB 20181130B and the low fluence in radio wavelength. The future detectability of optical flashes associated with nearby and bright FRBs are also discussed in this paper.

Constraining the axion–photon coupling using radio data of the Bullet cluster

Axion is one of the most popular candidates of the cosmological dark matter. Recent studies considering the misalignment production of axions suggest some benchmark axion mass ranges near $$m_a \sim 20$$ m a ∼ 20 μeV. For such axion mass, the spontaneous decay of axions can give photons in radio band frequency $$\nu \sim 1{-}3$$ ν ∼ 1 - 3 GHz, which can be detected by radio telescopes. In this article, we show that using radio data of galaxy clusters would be excellent to constrain axion dark matter. Specifically, by using radio data of the Bullet cluster (1E 0657-55.8), we find that the upper limit of the axion–photon coupling constant can be constrained to $$g_{a \gamma \gamma } \sim 10^{-12}{-}10^{-11}$$ g a γ γ ∼ 10 - 12 - 10 - 11 GeV$$^{-1}$$ - 1 for $$m_a \sim 20$$ m a ∼ 20 μeV, which is tighter than the limit obtained by the CERN Axion Solar Telescope (CAST).

Simultaneous Radio and Optical Polarimetry of GRB 191221B Afterglow

Gamma-ray bursts (GRBs) are the most luminous gamma-ray transients in the universe, and are utilized as probes of early stars, gravitational wave counterparts, and collision less shock physics. For understanding the fundamental physical quantities of GRB jets and their environments as well as their emission mechanism, coordinated multi-wavelength (semi-)simultaneous measurements are crucial as the global communities demonstrated in the past three decades. In spite of studies on polarimetry of GRBs in individual wavelengths that characterized intriguing properties of prompt emission and afterglow, no coordinated multi-wavelength measurements has yet been performed. Here, we report the first coordinated simultaneous polarimetry in the optical and radio bands for the afterglow associated to the typical long GRB 191221B. Our observations successfully caught the radio emission, which is not affected by synchrotron self-absorption, and show that the emission is depolarized in the radio band in comparison with the optical one. This result excludes a simple one-zone model that the polarization degree is nearly constant above the synchrotron self-absorption frequency, and has important implications for plasma-scale turbulent magnetic fields and existence of cool electrons. Our simultaneous polarization angle measurement supports the latter model rather than the former one. The existence of cool electrons increases the estimate of the total jet energy by a factor of > 2 for this typical GRB. Further coordinated multi-wavelength polarimetric campaigns would improve our understanding of the total jet energies and magnetic field configurations in the emission regions of various types of GRBs, which are required to comprehend the mass scales of their progenitor systems and the physics of collisionless shocks.

In-Orbit Measurements and Analysis of Radio Interference in the UHF Amateur Radio Band from the LUME-1 Satellite

Radio interference in the uplink makes communication to satellites in the UHF amateur radio band (430–440 MHz) challenging for any satellite application. Interference measurements and characterisation can improve the robustness and reliability of the communication system design. Most published results focus on average power spectrum measurements and heatmaps. We apply a low complexity estimator on an SDR (Software-Defined Radio) to study the interference’s dispersion and temporal variation on-board a small satellite as an alternative. Measuring the Local Mean Envelope (LME) variability with different averaging window lengths enables the estimation of time variability of the interference. The coefficient of variation for the LME indicates how much the signals vary in time and the spread in magnitudes. In this article, theoretical analysis, simulations, and laboratory results were used to validate this measurement method. In-orbit measurements were performed on-board the LUME-1 satellite. Band-limited interference with pulsed temporal behaviour and a high coefficient of variation was detected over North America, Europe, and the Arctic, where space-tracking radars are located. Wide-band pulsed interference with high time variability was also detected over Europe. These measurements show why operators that use a communication system designed for Additive White Gaussian Noise (AWGN) at power levels obtained from heatmaps struggle to command their satellites.

Mobile Network Performance and Technical Feasibility of LTE-Powered Unmanned Aerial Vehicle

Conventional and license-free radio-controlled drone activities are limited to a line-of-sight (LoS) operational range. One of the alternatives to operate the drones beyond the visual line-of-sight (BVLoS) range is replacing the drone wireless communications system from the conventional industrial, scientific, and medical (ISM) radio band to a licensed cellular-connected system. The Long Term Evolution (LTE) technology that has been established for the terrestrial area allows command-and-control and payload communications between drone and ground station in real-time. However, with increasing height above the ground, the radio environment changes, and utilizing terrestrial cellular networks for drone communications may face new challenges. In this regard, this paper aims to develop an LTE-based control system prototype for low altitude small drones and investigate the feasibility and performance of drone cellular connectivity at different altitudes with measuring parameters such as latency, handover, and signal strength. The measurement results have shown that by increasing flight height from ground to 170 m the received signal power and the signal quality levels were reduced by 20 dBm and 10 dB respectively, the downlink data rate decreased to 70%, and latency increased up to 94 ms. It is concluded that although the existing LTE network can provide a minimum requirement for drone cellular connectivity, further improvements are still needed to enhance aerial coverage, eliminate interference, and reduce network latency.

Rapid-response radio observations of short GRB 181123B with the Australia Telescope Compact Array

We introduce the Australia Telescope Compact Array (ATCA) rapid-response mode by presenting the first successful trigger on the short-duration gamma-ray burst (GRB) 181123B. Early-time radio observations of short GRBs may provide vital insights into the radio afterglow properties of Advanced LIGO- and Virgo-detected gravitational wave events, which will in turn inform follow-up strategies to search for counterparts within their large positional uncertainties. The ATCA was on target within 12.6 hr post-burst, when the source had risen above the horizon. While no radio afterglow was detected during the 8.3 hr observation, we obtained force-fitted flux densities of 7 ± 12 and 15 ± 11μJy at 5.5 and 9 GHz, respectively. Afterglow modelling of GRB 181123B showed that the addition of the ATCA force-fitted radio flux densities to the Swift X-ray Telescope detections provided more stringent constraints on the fraction of thermal energy in the electrons (log $\epsilon _e = -0.75^{+0.39}_{-0.40}$ rather than log $\epsilon _e = -1.13^{+0.82}_{-1.2}$ derived without the inclusion of the ATCA values), which is consistent with the range of typical εe derived from GRB afterglow modelling. This allowed us to predict that the forward shock may have peaked in the radio band ∼10 days post-burst, producing detectable radio emission ≳ 3 − 4 days post-burst. Overall, we demonstrate the potential for extremely rapid radio follow-up of transients and the importance of triggered radio observations for constraining GRB blast wave properties, regardless of whether there is a detection, via the inclusion of force-fitted radio flux densities in afterglow modelling efforts.

An early peak in the radio light curve of short-duration gamma-ray burst 200826A

ABSTRACT We present the results of radio observations from the eMERLIN telescope combined with X-ray data from Swift for the short-duration gamma-ray burst (GRB) 200826A, located at a redshift of 0.71. The radio light curve shows evidence of a sharp rise, a peak around 4–5 d post-burst, followed by a relatively steep decline. We provide two possible interpretations based on the time at which the light curve reached its peak. (1) If the light curve peaks earlier, the peak is produced by the synchrotron self-absorption frequency moving through the radio band, resulting from the forward shock propagating into a wind medium and (2) if the light curve peaks later, the turnover in the light curve is caused by a jet break. In the former case we find a minimum equipartition energy of ∼3 × 1047 erg and bulk Lorentz factor of ∼5, while in the latter case we estimate the jet opening angle of ∼9–16°. Due to the lack of data, it is impossible to determine which is the correct interpretation, however due to its relative simplicity and consistency with other multiwavelength observations which hint at the possibility that GRB 200826A is in fact a long GRB, we prefer the scenario one over scenario two.