arXiv subjects

A. Moiseev

Publications and source records attributed to A. Moiseev.

36 records · Page 2Linked to original sources

arXiv2008

Two New Large Separation Gravitational Lenses from SDSS

We present discovery images, together with follow-up imaging and spectroscopy, of two large separation gravitational lenses found by our survey for wide arcs (the CASSOWARY). The survey exploits the multicolor photometry of the Sloan Digital Sky Survey to find multiple blue components around red galaxies. CASSOWARY~2 (or "the Cheshire Cat") is composed of two massive early-type galaxies at z = 0.426 and 0.432 respectively lensing two background sources, the first a star-forming galaxy at z = 0.97 and the second a high redshift galaxy (z> 1.4). There are at least three images of the former source and probably four or more of the latter, arranged in two giant arcs. The mass enclosed within the larger arc of radius 11 arcsecs is about 33 x 10^{12} solar masses. CASSOWARY~3 comprises an arc of three bright images of a z = 0.725 source, lensed by a foreground elliptical at z = 0.274. The radius of the arc is about 4 arcsecs and the enclosed mass is 2.5 x 10^{12} solar masses. Together with earlier discoveries like the Cosmic Horseshoe and the 8 O'Clock Arc, these new systems, with separations intermediate between the arcsecond separation lenses of typical strong galaxy lensing and the larger separation cluster lenses, probe the very high end of the galaxy mass function.

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arXiv2007

The Cosmic Horseshoe: Discovery of an Einstein Ring around a Giant Luminous Red Galaxy

We report the discovery of an almost complete Einstein ring of diameter 10" in Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5). Spectroscopic data from the 6m telescope of the Special Astrophysical Observatory reveals that the deflecting galaxy has a line-of-sight velocity dispersion in excess of 400 km/s and a redshift of 0.444, whilst the source is a star-forming galaxy with a redshift of 2.379. From its color and luminosity, we conclude that the lens is an exceptionally massive Luminous Red Galaxy (LRG) with a mass within the Einstein radius of 5 x 10^12 solar masses. This remarkable system provides a laboratory for probing the dark matter distribution in LRGs at distances out to 3 effective radii, and studying the properties of high redshift star-forming galaxies.

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arXiv2007

Emitting gas regions in Mrk 493: An extensive Fe II line emission region

We performed 3D spectroscopic observations of Mrk 493 in order to investigate the Fe II emitting region and their possible connection with the Hydrogen emitting region. We found that there is a strong Fe II emission in an extensive region ~ 4" x 4" around Sy 1 nucleus. The Fe II line width indicates that these lines are originated in an intermediate line region.

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arXiv2006

An Outbursting Protostar of the FU~Orionis type in the Cygnus OB7 Molecular Cloud

Context: To follow the early evolution of stars we need to understand how young stars accrete and eject mass. It is generally assumed that the FU Orionis phenomenon is related to the variations in the disk accretion, but many questions remain still open, in particular because of the rarity of FU Ori type stars. Aims: We explore here the characteristics of the outburst and of the environment of one new object, discovered recently in the in the active star formation region containing RNO127, within the Cygnus OB7 dark cloud complex. Methods: We present an extensive optical and near-infrared study of a new candidate of FU Orionis object, including its direct imaging, spectroscopy and scanning Fabry-Perot interferometry. Results: The source, associated with the variable reflection nebula, underwent prodigious outburst. The "Braid" nebula, which appeared in 2000, as is indicated by its name, consists of two intertwined features, illuminated by the outburst. Subsequent NIR observations revealed the bright source, which was not visible on 2MASS images, and its estimated brightening was more than 4 magnitudes. Optical and infrared spectral data show features, which are necessary for the system to be referred to as a FUor object. The bipolar optical flow directed by the axis of nebula also was found. Various estimates give the November/December 1999 as the most probable date for the eruption.

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arXiv2006

Modeling the star formation history in the ring galaxy Arp 10 with the help of spectral indices

We use long-slit spectra obtained with the 6-m telescope BTA (Russian Academy of Sciences) to investigate the history of star formation in the peculiar ring galaxy Arp 10. The radial distributions of quasi-Lick spectral indices are calculated from the observed spectra and are compared with the model spectra, the latter are generated using the Starburst99 population synthesis code. Our model includes an outward propagating density wave which triggers star formation in the gas disk, and an old stellar disk. The metallicity of both old and young stellar populations is a function of radius. We show that a mix of the young and old populations is required to explain the radial distribution of the spectral indices. The density wave propagates outward with a moderate speed (of order 40 km/s), and the metallicities of both young and old populations decrease with the radius. The model indices corresponding to the alpha-elements require somewhat higher metallicities as compared to the Fe-peak elements. We acknowledge partial support from grant RFBR 04-02-16518.

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arXiv2004

Hadronic Calibration of the ATLAS Liquid Argon End-Cap Calorimeter in the Pseudorapidity Region 1.6 < |eta| < 1.8 in Beam Tests

A full azimuthal phi-wedge of the ATLAS liquid argon end-cap calorimeter has been exposed to beams of electrons, muons and pions in the energy range 6 GeV <= E <= 200 GeV at the CERN SPS. The angular region studied corresponds to the ATLAS impact position around the pseudorapidity interval 1.6 < |eta| < 1.8. The beam test set-up is described. A detailed study of the performance is given as well as the related intercalibration constants obtained. Following the ATLAS hadronic calibration proposal, a first study of the hadron calibration using a weighting ansatz is presented. The results are compared to predictions from Monte Carlo simulations, based on GEANT 3 and GEANT 4 models.

physics.ins-det↗

arXiv2002

Gamma Ray Large Area Space Telescope (GLAST) Balloon Flight Data Handling Overview

The GLAST Balloon Flight Engineering Model (BFEM) represents one of 16 towers that constitute the Large Area Telescope (LAT), a high-energy (>20 MeV) gamma-ray pair-production telescope being built by an international partnership of astrophysicists and particle physicists for a satellite launch in 2006. The prototype tower consists of a Pb/Si pair-conversion tracker (TKR), a CsI hodoscopic calorimeter (CAL), an anti-coincidence detector (ACD) and an autonomous data acquisition system (DAQ). The self-triggering capabilities and performance of the detector elements have been previously characterized using positron, photon and hadron beams. External target scintillators were placed above the instrument to act as sources of hadronic showers. This paper provides a comprehensive description of the BFEM data-reduction process, from receipt of the flight data from telemetry through event reconstruction and background rejection cuts. The goals of the ground analysis presented here are to verify the functioning of the instrument and to validate the reconstruction software and the background-rejection scheme.

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arXiv2002

Precise Measurements of Atmospheric Muon Fluxes with the BESS Spectrometer

The vertical absolute fluxes of atmospheric muons and muon charge ratio have been measured precisely at different geomagnetic locations by using the BESS spectrometer. The observations had been performed at sea level (30 m above sea level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada. The vertical cutoff rigidities in Tsukuba (36.2 N, 140.1 E) and in Lynn Lake (56.5 N, 101.0 W) are 11.4 GV and 0.4 GV, respectively. We have obtained vertical fluxes of positive and negative muons in a momentum range from 0.6 to 20 GeV/c with systematic errors less than 3 % in both measurements. By comparing the data collected at two different geomagnetic latitudes, we have seen an effect of cutoff rigidity. The dependence on the atmospheric pressure and temperature, and the solar modulation effect have been also clearly observed. We also clearly observed the decrease of charge ratio of muons at low momentum side with at higher cutoff rigidity region.

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arXiv2002

The Composition of Cosmic Rays at the Knee

The observation of a small change in spectral slope, or 'knee' in the fluxes of cosmic rays near energies 10^15 eV has caused much speculation since its discovery over 40 years ago. The origin of this feature remains unknown. A small workshop to review some modern experimental measurements of this region was held at the Adler Planetarium in Chicago, USA in June 2000. This paper summarizes the results presented at this workshop and the discussion of their interpretation in the context of hadronic models of atmospheric airshowers.

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arXiv2002

Measurements of Cosmic-ray Low-energy Antiproton and Proton Spectra in a Transient Period of the Solar Field Reversal

The energy spectra of cosmic-ray low-energy antiprotons and protons have been measured by BESS in 1999 and 2000, during a period covering the solar magnetic field reversal. Based on these measurements, a sudden increase of the antiproton to proton flux ratio following the solar magnetic field reversal was observed, and it generally agrees with a drift model of the solar modulation.

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arXiv2000

The origin of cosmic rays: What can GLAST say ?

Gamma rays in the band from 30 MeV to 300 GeV, used in combination with direct measurements and with data from radio and X-ray bands, provide a powerful tool for studying the origin of Galactic cosmic rays. Gamma-ray Large Area Space Telescope (GLAST) with its fine 10-20 arcmin angular resolution will be able to map the sites of acceleration of cosmic rays and their interactions with interstellar matter. It will provide information that is necessary to study the acceleration of energetic particles in supernova shocks, their transport in the interstellar medium and penetration into molecular clouds.

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arXiv2000

Precise Measurement of Cosmic-Ray Proton and Helium Spectra with the BESS Spectrometer

We report cosmic-ray proton and helium spectra in energy ranges of 1 to 120 GeV and 1 to 54 GeV/nucleon, respectively, measured by a balloon flight of the BESS spectrometer in 1998. The magnetic-rigidity of the cosmic-rays was reliably determined by highly precise measurement of the circular track in a uniform solenoidal magnetic field of 1 Tesla. Those spectra were determined within overall uncertainties of +-5 % for protons and +- 10 % for helium nuclei including statistical and systematic errors.

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arXiv1999

Anticoincidence Detector for GLAST

The Gamma-ray Large Area Space Telescope (GLAST) is now being designed by a number of collaborating institutions. It will study the cosmic gamma radiation from 20 MeV to 300 GeV with high precision and sensitivity, greatly expanding on the important EGRET results. One of the key systems of the instrument, the Anticoincidence Detector (ACD), is designed to reject the majority of charged particles, which are the background for any gamma-ray experiment. The ACD of EGRET has suffered from the self-veto effect when the products of the high energy photon interactions in the instrument's calorimeter cause a veto signal in the anticoincidence detector (backsplash effect), resulting in the degradation of the efficiency for high energy (> 5 GeV) gamma rays. To avoid this effect, the ACD for GLAST is divided into many scintillating tiles with wave-shifting fiber readout. The design of this detector along with the beam test and simulation results are given in this paper.

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arXiv1999

Detection of Galactic Dark Matter by GLAST

The mysterious dark matter has been a subject of special interest to high energy physicists, astrophysicists and cosmologists for many years. According to theoretical models, it can make up a significant fraction of the mass of the Universe. One possible form of galactic dark matter, Weakly Interacting Massive Particles (WIMPs), could be detected by their annihilation into monoenergetic gamma-ray line(s). This paper will demonstrate that the Gamma-ray Large Area Space Telescope (GLAST), scheduled for launch in 2005 by NASA, will be capable of searching for these gamma-ray lines in the energy range from 20 GeV to ~500 GeV and will be sufficiently sensitive to test a number of models. The required instrument performance and its capability to reject backgrounds to the required levels are explicitly discussed.

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arXiv1999

Interstellar Low Energy Antiprotons as a Probe of Dark Matter and Primordial Black Holes

Cosmic ray antiprotons can originate from dark matter annihilating into quarks that subsequently decay into antiprotons. Evaporation of primordial black holes also can produce a significant antiproton flux. Since the spectrum of secondary antiprotons from cosmic ray interactions peaks at ~ 2 GeV and goes down sharply at lower energy, there is a window at energies < 1 GeV in which to look for excess antiprotons as a signature of these exotic antiproton sources. However, in the vicinity of the Earth low energy particles are strongly modulated by the solar wind, which makes any analysis ambiguous. The adverse effects of the solar wind can be avoided by placing a low energy antiproton spectrometer aboard an interstellar probe. The theoretical predictions are reviewed and the preliminary design of a light-weight, low-power instrument to make the measurements and a summary of the anticipated results are given in this paper.

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arXiv1999

Precision Measurement of Cosmic-Ray Antiproton Spectrum

The energy spectrum of cosmic-ray antiprotons has been measured in the range 0.18 to 3.56 GeV, based on 458 antiprotons collected by BESS in recent solar-minimum period. We have detected for the first time a distinctive peak at 2 GeV of antiprotons originating from cosmic-ray interactions with the interstellar gas. The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation. Future BESS flights toward the solar maximum will help us to study the solar modulation and the propagation in detail and to search for primary antiproton components.

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arXiv1999

Beam Test of Gamma-ray Large Area Space Telescope Components

A beam test of GLAST (Gamma-ray Large Area Space Telescope) components was performed at the Stanford Linear Accelerator Center in October, 1997. These beam test components were simple versions of the planned flight hardware. Results on the performance of the tracker, calorimeter, and anti-coincidence charged particle veto are presented.

physics.ins-det↗

arXiv1998

Measurement of Low-Energy Cosmic-Ray Antiprotons at Solar Minimum

The absolute fluxes of the cosmic-ray antiprotons at solar minimum are measured in the energy range 0.18 to 1.4 GeV, based on 43 events unambiguously detected in BESS '95 data. The resultant energy spectrum appears to be flat below 1 GeV, compatible with a possible admixture of primary antiproton component with a soft energy spectrum, while the possibility of secondary antiprotons alone explaining the data cannot be excluded with the present accuracy. Further improvement of statistical accuracy and extension of the energy range are planned in future BESS flights.

astro-ph↗