R. Rekola

Multiepoch multiwavelength spectra and models for blazar 3C 279

Of the blazars detected by EGRET in GeV γ-rays, 3C 279 is not only the best observed by EGRET but also one of the best monitored at lower frequencies. We have assembled 11 spectra, from GHz radio through GeV γ-rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data taken during the high states in early 1999 and early 2000. All of the spectra show substantial γ-ray contribution to the total luminosity of the object; in a high state, the γ-ray luminosity dominates over that at all other frequencies by a factor of more than 10. There is no clear pattern of time correlation; different bands do not always rise and fall together, even in the optical, X-ray, and γ-ray bands. The spectra are modeled using a leptonic jet, with combined synchrotron self-Compton plus external Compton γ-ray production. Spectral variability of 3C 279 is consistent with variations of the bulk Lorentz factor of the jet, accompanied by changes in the spectral shape of the electron distribution. Our modeling results are consistent with the UV spectrum of 3C 279 being dominated by accretion disk radiation during times of low γ-ray intensity.

Twenty years monitoring of extragalactic sources at 22, 37 and 87 GHz

Long term monitoring results from mid 1995 to the end of 2000 of quasar observations at 22, 37 and 87 GHz done at the Metsahovi radio observatory are presented. Approximately 15 700 observations are published here.

Day-Scale Variability of 3C?279 and Searches for Correlations in Gamma-Ray, X-Ray, and Optical Bands

Light curves of 3C 279 are presented in optical (R band), X-rays (RXTE/PCA), and γ rays (CGRO/EGRET) for 1999 January-February and 2000 January-March. During both of those epochs the γ-ray levels were high and all three observed bands demonstrated substantial variation, on timescales as short as 1 day. Correlation analyses provided no consistent pattern, although a rather significant optical/γ-ray correlation was seen in 1999, with a γ-ray lag of ~2.5 days, and there are other suggestions of correlations in the light curves. For comparison, correlation analysis is also presented for the γ-ray and X-ray light curves during the large γ ray flare in 1996 February and the two γ-bright weeks leading up to it; the correlation at that time was strong, with a γ-ray/X-ray offset of no more than 1 day.

Surface Brightness Fluctuation Distances for Nearby Dwarf Elliptical Galaxies

We obtained deepB andR-band CCD images for the dwarf elliptical (dE) galaxies DDO 44, UGC 4998, KK98 77, DDO 71, DDO 113, and UGC 7356 at the Nordic Optical Telescope. Employing Fourier analysis technique we measure stellar R-band surface brightness fluctuations (SBFs) and magnitudes in 29 dierent elds of the galaxies. Independent tip of the red giant branch distances for DDO 44, KK98 77, DDO 71 are used to convert their set of apparent into absolute SBF magnitudes. The results are combined with the corresponding local (B R) colours and compared with the (B R) MR relation for mainly old, metal-poor stellar populations as predicted by Wortheys population synthesis models using Padova isochrones. While the colour dependency of the theoretical relation is conrmed by the empirical data, we nd a systematic zero point oset between observations and theory in the sense that models are too faint by 0:13 (0:02) mag. Based on these ndings we establish a new semiempirical calibration of the SBF method as distance indicator for dE galaxies with an estimated uncertainty of10%. Taking rst advantage of the improved calibration, we determine SBF distances for the other three early-type dwarfs UGC 4998, DDO 113, and UGC 7356. Although found in the M 81 group region, previous velocity measurements suggested UGC 4998 is a background galaxy. This picture is conrmed by our SBF distance of 10: 5( 0:9) Mpc. We can further identify DDO 113 as a faint stellar system at the near side of the Canes Venatici I (CVn I) cloud at a distance of 3: 1( 0:3) Mpc. The second CVn I member in our sample, UGC 7356, lies at 6: 7( 0:6) Mpc and spatially close to NGC 4258 (M 106). We derive BR surface brightness proles and colour gradients for all dwarfs and determine photometric and S ersic parameters. Finally, we discuss two non-stellar objects in DDO 71 and UGC 7356 which may resemble globular clusters.

New distances of unresolved dwarf elliptical galaxies in the vicinity of the Local Group

We present Surface Brightness Fluctuation distances of nine early-type dwarf galaxies and the SO galaxy NGC 4150 in the Local Volume based on deep B- and R-band CCD images obtained with the 2.56 m Nordic Optical Telescope. Typically, six stellar fields at various galactocentric distances have been chosen for each galaxy as appropriately free of foreground stars and other contaminants, and Fourier analysed to determine the distances, which are found to lie in the range of 3 to 16 Mpc. The SBF method is thus demonstrated to efficiently measure distances from the ground with mid-aperture telescopes for galaxies for which only the tip of the red giant branch method in combination with the Hubble Space Telescope has been available until now. We obtained the following distance moduli: 28.11 ± 0.15 mag (or 4.2 ± 0.3 Mpc) for UGC 1703, 27.61 ± 0.17 mag for 3.3 ± 0.3 Mpc) for KDG 61, 29.00 ± 0.27 mag (or 6.3 ± 0.8 Mpc) for UGCA 200, 27.74 ± 0.18 mag (or 3.5 ± 0.3 Mpc) for UGC 5442, 30.22 ± 0.17 mag (or 11.1 ± 0.9 Mpc) for UGC 5944, 30.79 ± 0.11 mag (or 14.4 ± 0.7 Mpc) for NGC 4150, 31.02 ± 0.25 mag (or 16.0 ± 1.9 Mpc) for BTS 128, 29.27 ± 0.16 mag (or 7.1 ± 0.6 Mpc) for UGC 7639, 30.19 ± 0.23 mag (or 10.9 ± 1.2 Mpc) for UGC 8799 with an alternative distance of 30.61 ± 0.26 mag (or 13.2 ± 1.7 Mpc), and 29.60 ± 0.20 mag (or 8.3 ± 0.8 Mpc) for UGC 8882.

DEEP Ks-NEAR-INFRARED SURFACE PHOTOMETRY OF 80 DWARF IRREGULAR GALAXIES IN THE LOCAL VOLUME

We present deep near-infrared (K_s) images and surface photometry for 80 dwarf irregular galaxies (dIs) within ~5 Mpc of the Milky Way. The galaxy images were obtained at five different facilities between 2004 and 2006. The image reductions and surface photometry have been performed using methods specifically designed for isolating faint galaxies from the high and varying near-infrared sky level. Fifty-four of the 80 dIs have surface brightness profiles which could be fit to a hyperbolic-secant (sech) function, while the remaining profiles could be fit to the sum of a sech and a Gaussian function. From these fits, we have measured central surface brightnesses, scale lengths, and integrated magnitudes. This survey is part of a larger study of the connection between large-scale structure and the global properties of dIs, the hypothesized building-blocks of more massive galaxies.

More than 160 near Earth asteroids observed in the EURONEAR network

Astrometry is mandatory in order to acquire the positional information necessary to define and improve orbits of NEAs and PHAs and to study their trajectories through the solar system, especially in the vicinity of Earth. Photometry is required to derive some physical information about NEAs and PHAs. In order to achieve these objectives, the main method of research of the EURONEAR is the follow-up programme of objects selected by a few criteria, carried out mostly at 1m-class telescopes endowed with medium and large field cameras. 162 NEAs summing more than 1,500 individual positions were observed for a total time of 55 nights in both visiting mode and regular runs using nine telescopes located in four countries. The observations were reduced promptly and reported to the Minor Planet Centre (MPC) which validated and included them in the MPC and NEODyS databases following the improvement of their orbital elements. For one binary NEA we acquired photometry and were able to determine its orbital and rotational periods. Complementary to the follow-up work, as many as 500 unknown moving objects consistent with new Main Belt asteroids and one possible NEA were discovered in the analyzed fields. Our positions present 1′′ precision with an accuracy of 0.2-0.4′′ , sufficient for achieving our immediate main goals. The observations and data reduction were conducted by our network members, which included some students and amateurs supervised by professional astronomers. In most cases, we increased the observational arcs decreasing the uncertainties in the orbits, while in some cases the new positions allowed us to recover some bodies endangered to be lost, defining their orbits.