Previously unremarkable, the extragalactic radio source GB 1310+487 showed a gamma-ray flare on 2009 November 18, reaching a daily flux of ~10^-6 photons/cm^2/s at energies E>100 MeV and becoming one of the brightest GeV sources for about two weeks.
Its optical spectrum is not typical for a blazar, instead, it resembles those of narrow emission-line galaxies. We investigate changes of the objects radio-to-GeV spectral energy distribution (SED) during and after the prominent GeV flare with the aim to determine the nature of the object and constrain the origin of the variable high-energy emission. The data collected by the Fermi and AGILE satellites at gamma-ray energies, Swift at X-ray and ultraviolet, Kanata, NOT, and Keck telescopes at optical, OAGH and WISE at infrared, and IRAM 30m, OVRO 40m, Effelsberg 100m, RATAN-600, and VLBA at radio, are analysed together to trace the SED evolution on timescales of months. The gamma-ray/radio-loud narrow-line active galactic nucleus (AGN) is located at redshift z=0.638. It is shining through an unrelated foreground galaxy at z=0.500. The AGN light is likely amplified by a factor of a few because of gravitational lensing. The AGN SED shows a two-humped structure typical of blazars and gamma-ray-loud NLSy1 galaxies, with the high-energy (inverse-Compton) emission dominating by more than an order of magnitude over the low-energy (synchrotron) emission during gamma-ray flares. The difference between the two SED humps is smaller during the low-activity state. Fermi observations reveal a strong correlation between the gamma-ray flux and spectral index, with the hardest spectrum observed during the brightest gamma-ray state. If the gamma-ray flux is a mixture of synchrotron self-Compton (SSC) and external Compton (EC) emission, the observed GeV spectral variability may result from varying relative contributions of these two emission components.
Single-zone synchrotron self-Compton and external Compton models are widely used to explain broad-band Spectral Energy Distributions (SEDs) of blazars from infrared to gamma-rays. These models bear obvious similarities to the homogeneous synchrotron
cloud model which is often applied to explain radio emission from individual components of parsec-scale radio jets. The parsec-scale core, typically the brightest and most compact feature of blazar radio jet, could be the source of high-energy emission. We report on ongoing work to test this hypothesis by deriving the physical properties of parsec-scale radio emitting regions of twenty bright Fermi blazars using dedicated 5-43 GHz VLBA observations and comparing these parameters to results of SED modeling.
We report the discovery of CoRoT 102980178 (R.A.= 06:50:12.10, Dec.= -02:41:21.8, J2000) an Algol-type eclipsing binary system with a pulsating component (oEA). It was identified using a publicly available 55 day long monochromatic lightcurve from th
e CoRoT initial run dataset (exoplanet field). Eleven consecutive 1.26m deep total primary and the equal number of 0.25m deep secondary eclipses (at phase 0.50) were observed. The following light elements for the primary eclipse were derived: HJD_MinI= 2454139.0680 + 5.0548d x E. The lightcurve modeling leads to a semidetached configuration with the photometric mass ratio q=0.2 and orbital inclination i=85 deg. The out-of-eclipse lightcurve shows ellipsoidal variability and positive OConnell effect as well as clear 0.01m pulsations with the dominating frequency of 2.75 c/d. The pulsations disappear during the primary eclipses, which indicates the primary (more massive) component to be the pulsating star. Careful frequency analysis reveals the second independent pulsation frequency of 0.21 c/d and numerous combinations of these frequencies with the binary orbital frequency and its harmonics. On the basis of the CoRoT lightcurve and ground based multicolor photometry, we favor classification of the pulsating component as a gamma Doradus type variable, however, classification as an SPB star cannot be excluded.
The spatially resolved broad-band spectroscopy with Very Long Baseline Interferometry (VLBI) is one of the few methods that can probe the physical conditions inside blazar jets. We report on measurements of the magnetic field strength in parsec-scale
radio structures of selected bright Fermi blazars, based on fitting the synchrotron spectrum to VLBA images made at seven frequencies in a 4.6 -- 43.2 GHz range. Upper limits of B <= 10^-2 -- 10^2 G (observers frame) could be placed on the magnetic field strength in 13 sources. Hard radio spectra (-0.5 <= a <= +0.1, S_nu ~ nu^a) observed above the synchrotron peak may either be an indication of a hard energy spectrum of the emitting electron population or result from a significant inhomogeneity of the emitting region.
We investigate the sample of 213 GPS sources selected from simultaneous multi-frequency 1-22 GHz observations obtained with RATAN-600 radio telescope. We use publicly available data to characterize parsec-scale structure of the selected sources. Amon
g them we found 121 core dominated sources, 76 Compact Symmetric Object (CSO) candidates (24 of them are highly probable), 16 sources have complex parsec-scale morphology. Most of GPS galaxies are characterized by CSO-type morphology and lower observed peak frequency (~1.8 GHz). Most of GPS quasars are characterized by core-jet-type morphology and higher observed peak frequency (~3.6 GHz). This is in good agreement with previous results. However, we found a number of sources for which the general relation CSO - galaxy, core-jet - quasar does not hold. These sources deserve detailed investigation. Assuming simple synchrotron model of a homogeneous cloud we estimate characteristic magnetic field in parsec-scale components of GPS sources to be B ~ 10 mG.
We describe a new sample of 226 GPS (GHz-Peaked Spectrum) source candidates selected using simultaneous 1-22 GHz multi-frequency observations with the RATAN-600 radio telescope. Sixty objects in our sample are identified as GPS source candidates for
the first time. The candidates were selected on the basis of their broad-band radio spectra only. We discuss the spectral and variability properties of selected objects of different optical classes.
We initiated digitization of the Moscow collection of astronomical plates using flatbed scanners. Techniques of photographic photometry of the digital images were applied, enabling an effective search for new variable stars. Our search for new variab
les among 140000 stars in the 10 x 5 degrees northern half of the field centered at 66 Oph, photographed with the Sternberg Institutes 40-cm astrograph in 1976--1995, gave 274 new discoveries, among them: 2 probable Population II Cepheids; 81 eclipsing variables; 5 high-amplitude Delta Scuti stars (HADSs); 82 RR Lyr stars; 62 red irregular variables and 41 red semiregular stars; 1 slow irregular variable not red in color. Light elements were determined for periodic variable stars. We detected about 30 variability suspects for follow-up CCD observations, confirmed 11 stars from the New Catalogue of Suspected Variable Stars, and derived new light elements for 2 stars already contained in the General Catalogue of Variable Stars.
We present the discovery and CCD observations of the first eclipsing binary with a Type II Cepheid component in our Galaxy. The pulsation and orbital periods are found to be 4.1523 and 51.38 days, respectively, i.e. this variable is a system with the
shortest orbital period among known Cepheid binaries. Pulsations dominate the brightness variations. The eclipses are assumed to be partial. The EB-subtype eclipsing light curve permits to believe that the binarys components are non-spherical.
