We report the discovery of bright, fast, radio flashes lasting tens of seconds with the AARTFAAC high-cadence all-sky survey at 60 MHz. The vast majority of these coincide with known, bright radio sources that brighten by factors of up to 100 during such an event. We attribute them to magnification events induced by plasma near the Earth, most likely in the densest parts of the ionosphere. They can occur both in relative isolation, during otherwise quiescent ionospheric conditions, and in large clusters during more turbulent ionospheric conditions. Using a toy model, we show that the likely origin of the more extreme (up to a factor of 100 or so) magnification events likely originate in the region of peak electron density in the ionosphere, at an altitude of 300-400 km. Distinguishing these events from genuine astrophysical transients is imperative for future surveys searching for low frequency radio transient at timescales below a minute.
The displacement of star images by atmospheric refraction observed by an Earth-bound telescope is dominated by a familiar term proportional to the product of the tangent of the zenith angle by the refractivity at the ground. The manuscript focuses on the torsion of the ray path through the atmosphere in a model of atmospheric layers above the ellipsoidal Earth surface, induced by the two slightly different principal curvatures along N--S and E--W pointing directions. This breaking of the azimuthal symmetry effects apparent places at the sub-milliarcsecond scale at optical and infrared waveleng…
The results of observations with the MASTER-SHOK robotic wide-field optical cameras onboard the Lomonosov Space Observatory carried out in 2016 are presented. In all, the automated transient detection system transmitted 22 181 images of moving objects with signal-to-noise ratios greater than 5 to the Earth. Approximately 84% of these images are identified with well-known artificial Earth satellites (including repeated images of the same satellite) and fragments of such satellites (space debris), according to databases of known satellites. The remaining 16% of the images are relate to uncatalog…
Transient PULSE: Code for the Transient Propagation of UltraLight (pseudo)Scalars to Earth
University of Delaware（特拉华大学）；High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；The University of Tokyo（东京大学）；Graduate University for Advanced Studies (SOKENDAI)（高级研究大学院大学）
Earth-Projected Clustering of Historical Optical Transients in the Palomar Observatory Sky Survey-I (POSS-I)
Vanderbilt University Medical Center（范德堡大学医学中心）；KTH Royal Institute of Technology and Stockholm University（瑞典皇家理工学院和斯德哥尔摩大学）；CERIST Constantine（康斯坦丁科学文化研究与调解研究中心）；Independent Researcher（独立研究者）；Instituto de Astrofísica de Canarias（加那利群岛天体物理学研究所）
An optical transient candidate of $\lesssim$ 2-second duration captured by wide-field video observations
Nihon University（日本大学）；The University of Tokyo（东京大学）；National Astronomical Observatory of Japan, National Institutes of Natural Sciences（日本国立天文台，日本国立自然科学研究院）；Kiso Observatory, Institute of Astronomy, Graduate School of Science, The University of Tokyo（木曾天文台，东京大学理学研究科天文学系）
We describe ZStreak, a semi-real-time pipeline specialized in detecting small, fast-moving near-Earth asteroids (NEAs) that is currently operating on the data from the newly-commissioned Zwicky Transient Facility (ZTF) survey. Based on a prototype originally developed by Waszczak et al. (2017) for the Palomar Transient Factory (PTF), the predecessor of ZTF, ZStreak features an improved machine-learning model that can cope with the $10\times$ data rate increment between PTF and ZTF. Since its first discovery on 2018 February 5 (2018 CL), ZTF/ZStreak has discovered $45$ confirmed new NEAs over a…
qCMOS detectors and the case of hypothetical primordial black holes in the solar system, near earth objects, transients, and other high cadence observations
Old, digitized astronomical images taken before the human spacefaring age offer a unique view of the sky devoid of known artificial satellites. In this paper, we have carried out the first optical searches ever for non-terrestrial artifacts near the Earth following the method proposed in Villarroel et al. (2022). We use images contained in the First Palomar Sky Survey to search for simultaneous (during a plate exposure time) transients that in addition to being point-like, are aligned. We provide a shortlist of the most promising candidates of aligned transients, that must be examined with the…
Science Talent Training Center（科学人才培训中心）；Palo Alto Senior High School（帕洛阿尔托高级中学）；Shanghai Astronomical Observatory（上海天文台）
Although many near-Earth objects have been found by ground-based telescopes, some fast-moving ones, especially those near detection limits, have been missed by observatories. We developed a convolutional neural network for detecting faint fast-moving near-Earth objects. It was trained with artificial streaks generated from simulations and was able to find these asteroid streaks with an accuracy of 98.7% and a false positive rate of 0.02% on simulated data. This program was used to search image data from the Zwicky Transient Facility (ZTF) in four nights in 2019, and it identified six previousl…
Modelling Palomar Transients: Constraints from Reflection Geometry and Orbital Altitude
Nordita, KTH Royal Institute of Technology and Stockholm University（诺尔迪塔，皇家理工学院和斯德哥尔摩大学）；Society of UAP Studies（不明飞行物研究学会）；Science of the Matter Division, Research Unit in Scientific Mediation, CERIST, Constantine, Algeria（物质科学部，科学调解研究单位，CERIST，阿尔及利亚君士坦丁）；Department of Anesthesiology, Vanderbilt University Medical Center（麻醉学系，范德堡大学医学中心）
A considerable fraction of incident high-energy photons from astrophysical transients such as Gamma-Ray Bursts (GRBs) is Compton scattered by the Earth's atmosphere. These photons, sometimes referred to as the "reflection component", contribute to the signal detected by space-borne X-ray/$γ$-ray instruments. The effectiveness and reliability of source parameters such as position, flux, spectra, and polarization, inferred by these instruments are therefore highly dependent on the accurate estimation of this scattered component. Current missions use dedicated response matrices to account for the…
We present DeepStreaks, a convolutional-neural-network, deep-learning system designed to efficiently identify streaking fast-moving near-Earth objects that are detected in the data of the Zwicky Transient Facility (ZTF), a wide-field, time-domain survey using a dedicated 47 sq. deg camera attached to the Samuel Oschin 48-inch Telescope at the Palomar Observatory in California, United States. The system demonstrates a 96-98% true positive rate, depending on the night, while keeping the false positive rate below 1%. The sensitivity of DeepStreaks is quantified by the performance on the test data…
Reflections from objects in Earth orbit can produce sub-second, star-like optical flashes similar to astrophysical transients. Reflections have historically caused false alarms for transient surveys, but the population has not been systematically studied. We report event rates for these orbital flashes using the Evryscope Fast Transient Engine, a low-latency transient detection pipeline for the Evryscopes. We select single-epoch detections likely caused by Earth satellites and model the event rate as a function of both magnitude and sky position. We measure a rate of $1800^{+600}_{-280}$ sky$^…
Testing 3D hydrodynamic models of stellar atmospheres is feasible by retrieving spectral line shapes across stellar disks, using differential spectroscopy during exoplanet transits. From synthetic data at hyper-high spectral resolution, characteristic patterns for FeI and FeII lines were identified in Paper IV from 3D models spanning T=3964-6726K (spectral types approx. K8V-F3V). The observability of patterns among lines of different strength, excitation potential and ionization level are now examined, as observed at ordinary spectral resolutions and in the presence of noise. Time variability …
Thousands of active artificial objects are orbiting around Earth along with much more non-operational ones -- derelict satellites or rocket bodies, collision debris, or spacecraft payloads, significant part of them being uncatalogued. They all impact observations of the sky by ground-based telescopes by producing a large number of streaks polluting the images, as well as generating false alerts hindering the search for new astrophysical transients. While the former threat for astronomy is widely discussed nowadays in regard of rapidly growing satellite mega-constellations, the latter one -- fa…
From near-Earth asteroids to superluminous supernovae and counterparts to gravitational wave sources, the Zwicky Transient Facility will soon scan the night sky for transient phenomena.
Most searches for alien radio transmission have focused on finding omni-directional or purposefully earth-directed beams of enduring duration. However, most of the interesting signals so far detected have been transient and non-repeatable in nature. These signals could very well be the first data points in an ever-growing data base of such signals used to construct a probabilistic argument for the existence of extraterrestrial intelligence. This paper looks at the effect base rate bias could have on deciding which signals to include in such an archive based upon the likely assumption that our …
As radio telescopes become more sensitive, the damaging effects of radio frequency interference (RFI) become more apparent. Near radio telescope arrays, RFI sources are often easily removed or replaced; the challenge lies in identifying them. Transient (impulsive) RFI is particularly difficult to identify. We propose a novel dictionary-based approach to transient RFI identification. RFI events are treated as sequences of sub-events, drawn from particular labelled classes. We demonstrate an automated method of extracting and labelling sub-events using a dataset of transient RFI. A dictionary of…
LOFAR, the "low-frequency array", will be one of the first in a new generation of radio telescopes and Square Kilometer Array (SKA) pathfinders that are highly flexible in capability because they are largely software driven. LOFAR will not only open up a mostly unexplored spectral window, the lowest frequency radio light observable from the Earth's surface, but it will also be an unprecented tool with which to monitor the transient radio sky over a large field of view and down to timescales of milliseconds or less. Here we discuss LOFAR's current and upcoming capabilities for observing fast tr…
