E. Marilli

The unprecedented optical outburst of the quasar 3C 454.3 : The WEBT campaign of 2004-2005

Context. The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting more than 1 year and culminating in spring 2005. The maximum brightness detected was

Multifrequency monitoring of the blazar 0716+714 during the GASP-WEBT-AGILE campaign of 2007

R=12.0

Results of WEBT, VLBA and RXTE monitoring of 3C 279 during 2006-2007 ⋆

, which represents the most luminous quasar state thus far observed (

Further identification of ROSAT all-sky survey sources in Orion

M_B \sim -31.4

Newly discovered active binaries in the RasTyc sample of stellar X-ray sources , I. Orbital and physical parameters of six new binaries

). Aims. In order to follow the emission behaviour of the source in detail, a large multiwavelength campaign was organized by the Whole Earth Blazar Telescope (WEBT). Methods. Continuous optical, near-IR and radio monitoring was performed in several bands. ToO pointings by the Chandra and INTEGRAL satellites provided additional information at high energies in May 2005. Results. The historical radio and optical light curves show different behaviours. Until about 2001.0 only moderate variability was present in the optical regime, while prominent and long-lasting radio outbursts were visible at the various radio frequencies, with higher-frequency variations preceding the lower-frequency ones. After that date, the optical activity increased and the radio flux is less variable. This suggests that the optical and radio emissions come from two separate and misaligned jet regions, with the inner optical one acquiring a smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index behaviour (generally redder-when-brighter) during the outburst suggests the presence of a luminous accretion disc. A huge mm outburst followed the optical one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux started to increase in early 2005 and reached a maximum at the end of our observing period (end of September 2005). VLBA observations at 43 GHz during the summer confirm the brightening of the radio core and show an increasing polarization. An exceptionally bright X-ray state was detected in May 2005, corresponding to the rising mm flux and suggesting an inverse-Compton nature of the hard X-ray spectrum. Conclusions. A further multifrequency monitoring effort is needed to follow the next phases of this unprecedented event.

ROTATION PERIODS OF OPEN-CLUSTER STARS. III

Aims. Since the CGRO operation in 1991–2000, one of the primary unresolved questions about the blazar γ -ray emission has been its possible correlation with the low-energy (in particular optical) emission. To help answer this problem, the Whole Earth Blazar Telescope (WEBT) consortium has organized the GLAST-AGILE Support Program (GASP) to provide the optical-to-radio monitoring data to be compared with the γ -ray detections by the AGILE and GLAST satellites. This new WEBT project started in early September 2007, just before a strong γ -ray detection of 0716+714 by AGILE. Methods. We present the GASP-WEBT optical and radio light curves of this blazar obtained in July–November 2007, about various AGILE pointings at the source. We construct NIR-to-UV spectral energy distributions (SEDs), by assembling GASP-WEBT data together with UV data from the Swift ToO observations of late October. Results. We observe a contemporaneous optical-radio outburst, which is a rare and interesting phenomenon in blazars. The shape of the SEDs during the outburst appears peculiarly wavy because of an optical excess and a UV drop-and-rise. The optical light curve is well sampled during the AGILE pointings, showing prominent and sharp flares. A future cross-correlation analysis of the optical and AGILE data will shed light on the expected relationship between these flares and the γ -ray events.

The star formation in the L1615/L1616 Cometary Cloud

Context. The quasar 3C 279 is among the most extreme blazars in terms of luminosity and variability of flux at all wavebands. Its vari ations in flux and polarization are quite complex and therefore require intensive monitoring observations at multiple wavebands to characterise and interpret the observed changes. Aims. In this paper, we present radio-to-optical data taken by the WEBT, supplemented by our VLBA and RXTE observations, of 3C 279. Our goal is to use this extensive database to draw inferences regarding the physics of the relativistic jet. Methods. We assemble multifrequency light curves with data from 30 ground-based observatories and the space-based instruments SWIFT (UVOT) and RXTE, along with linear polarization vs. time in the optical R band. In addition, we present a sequence of 22 images (with polarization vectors) at 43 GHz at resolution 0.15 milliarcse c, obtained with the VLBA. We analyse the light curves and polarization, as well as the spectral energy distributions at different epochs, corresponding to different brightness states. Results. We find that the IR-optical-UV continuum spectrum of the vari able component corresponds to a power law with a constant slope of−1.6, while in the 2.4‐10 keV X-ray band it varies in slope from−1.1 to−1.6. The steepest X-ray spectrum occurs at a flux minimum. Durin g a decline in flux from maximum in late 2006, the optical and 43 GHz core po larization vectors rotate by∼ 300 ◦ . Conclusions. The continuum spectrum agrees with steady injection of relativistic electrons with a power-law energy distribution of slope−3.2 that is steepened to−4.2 at high energies by radiative losses. The X-ray emission at flux minimum comes most likely from a new component that starts in an upstream section of the jet where inverse Compton scattering of seed photons from outside the jet is important. The rotation of the polarization vector implies that the jet contains a helical magnetic field that extends ∼ 20 pc past the 43 GHz core.

The high activity of 3C 454.3 in autumn 2007. Monitoring by the WEBT during the AGILE detection

We report on the identification of 22 ROSAT All-Sky Survey (RASS) X-ray sources distributed in the general direc- tion of the Orion star-forming region. The X-ray sample contains sources from the ROSAT bright source catalogue and from previous detections. The optical identifications are based on intermediate-resolution spectroscopy and UBV Johnson photom- etry using a 1m-class telescope. The strengths of the Hα ,N a D2 and lithium lines for the stellar counterparts are evaluated applying the spectral subtraction technique, using templates of the same spectral type. Radial velocities of the optical coun- terparts are also reported. Thirteen of the optical counterparts show the lithium absorption line in their spectra and have radial velocities consistent with the Orion star forming region. Four of these objects can be classified as new bona-fide T Tauri stars.

A spectroscopic survey of the youngest field stars in the solar neighbourhood - I. The optically bright sample

We present the first results from follow-up optical observations, both photometric and spectroscopic, of stellar X-ray sources, selected from theRasTyc sample, resulting from the cross-correlation of ROSAT All-Sky Survey (RASS) and TYCHO catalogues. In particular, we report on the discovery of six late-type binaries, for which we obtained good radial velocity curves and solved their orbits. We performed an automatic spectral classification of both single-lined and double-lined binaries with codes developed by us and found two binaries composed of two main-sequence stars and four binaries with an evolved (giant or subgiant) component. Filled-in or pure emission Hα profiles indicative of a moderate or high level of chromospheric activity were observed. In nearly all the systems, we also detected a photometric modulation ascribable to surface inhomogeneities that is correlated with the orbital period, suggesting a synchronization between rotational and orbital periods. The position on the HR diagram of the components of the five sources with a known parallax indicates three binaries containing only main-sequence stars and two single-lined systems with a giant component. The kinematical properties of two, or possibly four, of the observed systems are consistent with a young disk population.

REM near-IR and optical photometric monitoring of pre-main sequence stars in Orion - Rotation periods and starspot parameters

We present the results from a photometric monitoring program of 21 stars observed during 1992 in the Pleiades and Alpha Persei open clusters. Period determinations for 16 stars are given, 13 of which are the first periods reported for these stars. Brightness variations for an additional five cluster stars are also given. One K dwarf member of the Alpha Per cluster is observed to have a period of rotation of only 4.39 hrs, perhaps the shortest period currently known among BY Dra variables. The individual photometric measurements have been deposited with the NSSDC. Combining current X-ray flux determinations with known photometric periods, we illustrate the X-ray activity/rotation relation among Pleiades K dwarfs based on available data.