Discovery of a new branch of the Taurid meteoroid stream as a real source of potentially hazardous bodies

Taurid meteor shower produces prolonged but usually low activity every October and November. In some years, however, the activity is significantly enhanced. Previous studies based on long-term activity statistics concluded that the enhancement is caused by a swarm of meteoroids locked in 7:2 resonance with Jupiter. Here we present precise data on 144 Taurid fireballs observed by new digital cameras of the European Fireball Network in the enhanced activity year 2015. Orbits of 113 fireballs show common characteristics and form together a well defined orbital structure, which we call new branch. We found that this branch is characterized by longitudes of perihelia lying between 155.9-160o and latitudes of perihelia between 4.2-5.7o. Semimajor axes are between 2.23-2.28 AU and indeed overlap with the 7:2 resonance. Eccentricities are in wide range 0.80-0.90. The orbits form a concentric ring in the inner solar system. The masses of the observed meteoroids were in a wide range from 0.1 g to more than 1000 kg. We found that all meteoroids larger than 300 g were very fragile, while those smaller than 30 g were much more compact. Based on orbital characteristics, we argue that asteroids 2015 TX24 and 2005 UR, both of diameters 200-300 meters, are direct members of the new branch. It is therefore very likely that the new branch contains also numerous still not discovered objects of decameter or even larger size. Since asteroids of sizes of tens to hundreds meters pose a treat to the ground even if they are intrinsically weak, impact hazard increases significantly when the Earth encounters the Taurid new branch every few years. Further studies leading to better description of this real source of potentially hazardous objects, which can be large enough to cause significant regional or even continental damage on the Earth, are therefore extremely important.Comment: 24 pages, 22 figures, 5 tables. Accepted in Astronomy and Astrophysic

Statistics of Cosmological Black Hole Jet Sources: Blazar Predictions for GLAST

A study of the statistics of cosmological black-hole jet sources is applied to EGRET blazar data, and predictions are made for GLAST. Black-hole jet sources are modeled as collimated relativistic plasma outflows with radiation beamed along the jet axis due to strong Doppler boosting. The comoving rate density of blazar flares is assumed to follow a blazar formation rate (BFR), modeled by analytic functions based on astronomical observations and fits to EGRET data. The redshift and size distributions of gamma-ray blazars observed with EGRET, separated into BL Lac object (BL) and flat spectrum radio quasar (FSRQ) distributions, are fit with monoparametric functions for the distributions of the jet Lorentz factor \Gamma, comoving directional power l'_e, and spectral slope. A BFR factor ~10 x greater at z ~ 1 than at present is found to fit the FSRQ data. A smaller comoving rate density and greater luminosity of BL flares at early times compared to the present epoch fits the BL data. Based on the EGRET observations, ~1000 blazars consisting of ~800 FSRQs and FR2 radio galaxies and ~200 BL Lacs and FR1 radio galaxies will be detected with GLAST during the first year of the mission. Additional AGN classes, such as hard-spectrum BL Lacs that were mostly missed with EGRET, could add more GLAST sources. The FSRQ and BL contributions to the EGRET gamma-ray background at 1 GeV are estimated at the level of ~10 - 15% and ~2 - 4%, respectively. EGRET and GLAST sensitivities to blazar flares are considered in the optimal case, and a GLAST analysis method for blazar detection is outlined.Comment: 17 pages, 9 figures, ApJ, in press, v.660, May 1, 2007 (minor changes from previous version

Point-like gamma ray sources as signatures of distant accelerators of ultra high energy cosmic rays

We discuss the possibility of observing distant accelerators of ultra high energy cosmic rays in synchrotron gamma rays. Protons propagating away from their acceleration sites produce extremely energetic electrons during photo-pion interactions with cosmic microwave background photons. If the accelerator is embedded in a magnetized region, these electrons will emit high energy synchrotron radiation. The resulting synchrotron source is expected to be point-like and detectable in the GeV-TeV energy range if the magnetic field is at the nanoGauss level.Comment: 4 pages 2 figures. To be published in PR

Data on 824 fireballs observed by the digital cameras of the European Fireball Network in 2017-2018. I. Description of the network, data reduction procedures, and the catalog

A catalog of 824 fireballs (bright meteors), observed by a dedicated network of all-sky digital photographic cameras in central Europe in the years 2017-2018 is presented. The status of the European Fireball Network, established in 1963, is described. The cameras collect digital images of meteors brighter than an absolute magnitude of about -2 and radiometric light curves with a high temporal resolution of those brighter than a magnitude ~ -4. All meteoroids larger than 5 grams, corresponding to sizes of about 2 cm, are detected regardless of their entry velocity. High-velocity meteoroids are detected down to masses of about 0.1 gram. The largest observed meteoroid in the reported period 2017-2018 had a mass of about 100 kg and a size of about 40 cm. The methods of data analysis are explained and all catalog entries are described in detail. The provided data include the fireball date and time, atmospheric trajectory and velocity, the radiant in various coordinate systems, heliocentric orbital elements, maximum brightness, radiated energy, initial and terminal masses, maximum encountered dynamic pressure, physical classification, and possible shower membership. Basic information on the fireball spectrum is available for some bright fireballs (apparent magnitude < -7). A simple statistical evaluation of the whole sample is provided. The scientific analysis is presented in an accompanying paper.Comment: accepted in Astronomy and Astrophysic

The AGASA/SUGAR Anisotropies and TeV Gamma Rays from the Galactic Center: A Possible Signature of Extremely High-energy Neutrons

Recent analysis of data sets from two extensive air shower cosmic ray detectors shows tantalizing evidence of an anisotropic overabundance of cosmic rays towards the Galactic Center (GC) that ``turns on'' around $10^{18}$ eV. We demonstrate that the anisotropy could be due to neutrons created at the Galactic Center through charge-exchange in proton-proton collisions, where the incident, high energy protons obey an $\sim E^{-2}$ power law associated with acceleration at a strong shock. We show that the normalization supplied by the gamma-ray signal from EGRET GC source 3EG J1746-2851 -- ascribed to pp induced neutral pion decay at GeV energies -- together with a very reasonable spectral index of 2.2, predicts a neutron flux at $\sim 10^{18}$ eV fully consistent with the extremely high energy cosmic ray data. Likewise, the normalization supplied by the very recent GC data from the HESS air-Cerenkov telescope at \~TeV energies is almost equally-well compatible with the $\sim 10^{18}$ eV cosmic ray data. Interestingly, however, the EGRET and HESS data appear to be themselves incompatible. We consider the implications of this discrepancy. We discuss why the Galactic Center environment can allow diffusive shock acceleration at strong shocks up to energies approaching the ankle in the cosmic ray spectrum. Finally, we argue that the shock acceleration may be occuring in the shell of Sagittarius A East, an unusual supernova remnant located very close to the Galactic Center. If this connection between the anisotropy and Sagittarius A East could be firmly established it would be the first direct evidence for a particular Galactic source of cosmic rays up to energies near the ankle.Comment: 57 pages, 2 figure

EGRET Observations of the Extragalactic Gamma Ray Emission

The all-sky survey in high-energy gamma rays (E$>$30 MeV) carried out by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma-Ray Observatory provides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation as well an almost uniformly distributed component that is generally believed to originate outside the Galaxy. Through a careful study and removal of the Galactic diffuse emission, the flux, spectrum and uniformity of the extragalactic emission is deduced. The analysis indicates that the extragalactic emission is well described by a power law photon spectrum with an index of -(2.10+-0.03) in the 30 MeV to 100 GeV energy range. No large scale spatial anisotropy or changes in the energy spectrum are observed in the deduced extragalactic emission. The most likely explanation for the origin of this extragalactic high-energy gamma-ray emission is that it arises primarily from unresolved gamma-ray-emitting blazars.Comment: 19 pages latex, 10 figures, accepted for publication in Ap