18 research outputs found
The whole earth blazar telescope campaign on the intermediate BL Lac object 3C 66A in 2007-2008
Prompted by a high optical state in 2007 September, the Whole Earth Blazar Telescope consortium organized an intensive optical, near-IR (JHK) and radio observing campaign on the intermediate BL Lac object 3C 66A throughout the fall and winter of 2007-2008. In this paper, we present data from 28 observatories in 12 countries, covering the observing season from late 2007 July through 2008 February. The source remained in a high optical state throughout the observing period and exhibited several bright flares on timescales of 10 days. This included an exceptional outburst around 2007 September 15-20, reaching a peak brightness at R 13.4. Our campaign revealed microvariability with flux changes up to |dR/dt| 0.02 mag hr-1. Our observations do not reveal evidence for systematic spectral variability in the overall high state covered by our campaign, in agreement with previous results. In particular, we do not find evidence for spectral hysteresis in 3C 66A for which hints were found in an earlier campaign in a somewhat lower flux state. We also did not find any evidence for spectral lags in the discrete correlation functions between different optical bands. We infer a value of the magnetic field in the emission region of B 19 e 2/7B τ-6/7h D 13/71 G, where eB is the magnetic field equipartition fraction, τh is the shortest observed variability timescale in units of hours, and D 1 is the Doppler factor in units of 10. From the lack of systematic spectral variability, we can derive an upper limit on the Doppler factor, D ≤ 28 τ-1/8h e 3/16B. This is in perfect agreement with superluminal motion measurements with the VLBI/VLBA of βapp ≤ 27 and argues against models with very high Lorentz factors of Γ ≳ 50, required for a one-zone synchrotron-self-Compton interpretation of some high-frequency-peaked BL Lac objects detected at TeV γ-ray energies. © 2009 The American Astronomical Society
The correlated optical and radio variability of BL Lacertae - WEBT data analysis 1994-2005
Since 1997, BL Lacertae has undergone a phase of high optical activity, with
the occurrence of several prominent outbursts. Starting from 1999, the Whole
Earth Blazar Telescope (WEBT) consortium has organized various multifrequency
campaigns on this blazar, collecting tens of thousands of data points. One of
the main issues in the study of this huge dataset has been the search for
correlations between the optical and radio flux variations, and for possible
periodicities in the light curves. The analysis of the data assembled during
the first four campaigns (comprising also archival data to cover the period
1968-2003) revealed a fair optical-radio correlation in 1994-2003, with a delay
of the hard radio events of ~100 days. Moreover, various statistical methods
suggested the existence of a radio periodicity of ~8 years. In 2004 the WEBT
started a new campaign to extend the dataset to the most recent observing
seasons, in order to possibly confirm and better understand the previous
results. In this campaign we have collected and assembled about 11000 new
optical observations from twenty telescopes, plus near-IR and radio data at
various frequencies. Here, we perform a correlation analysis on the long-term
R-band and radio light curves. In general, we confirm the ~100-day delay of the
hard radio events with respect to the optical ones, even if longer (~200-300
days) time lags are also found in particular periods. The radio
quasi-periodicity is confirmed too, but the "period" seems to progressively
lengthen from 7.4 to 9.3 years in the last three cycles. The optical and radio
behaviour in the last forty years suggests a scenario where geometric effects
play a major role. In particular, the alternation of enhanced and suppressed
optical activity (accompanied by hard and soft radio events, respectively) ca
Multifrequency variability of the blazar AO 0235+164 the WEBT campaign in 2004-2005 and long-term SED analysis
A huge multiwavelength campaign targeting the blazar AO 0235+164 was
organized by the Whole Earth Blazar Telescope (WEBT) in 2003-2005 to study the
variability properties of the source. Monitoring observations were carried out
at cm and mm wavelengths, and in the near-IR and optical bands, while three
pointings by the XMM-Newton satellite provided information on the X-ray and UV
emission. We present the data acquired during the second observing season,
2004-2005, by 27 radio-to-optical telescopes. They reveal an increased near-IR
and optical activity with respect to the previous season. Increased variability
is also found at the higher radio frequencies, down to 15 GHz, but not at the
lower ones. The radio (and optical) outburst predicted to peak around
February-March 2004 on the basis of the previously observed 5-6 yr
quasi-periodicity did not occur. The analysis of the optical light curves
reveals now a longer characteristic time scale of 8 yr, which is also present
in the radio data. The spectral energy distributions corresponding to the
XMM-Newton observations performed during the WEBT campaign are compared with
those pertaining to previous pointings of X-ray satellites. Bright, soft X-ray
spectra can be described in terms of an extra component, which appears also
when the source is faint through a hard UV spectrum and a curvature of the
X-ray spectrum. Finally, there might be a correlation between the X-ray and
optical bright states with a long time delay of about 5 yr, which would require
a geometrical interpretation
The high activity of 3C 454.3 in autumn 2007: Monitoring by the WEBT during the AGILE detection
The quasar-type blazar 3C 454.3 underwent a phase of high activity in summer
and autumn 2007, which was intensively monitored in the radio-to-optical bands
by the Whole Earth Blazar Telescope (WEBT). The gamma-ray satellite AGILE
detected this source first in late July, and then in November-December 2007. In
this letter we present the multifrequency data collected by the WEBT and
collaborators during the second AGILE observing period, complemented by a few
contemporaneous data from UVOT onboard the Swift satellite. The aim is to trace
in detail the behaviour of the synchrotron emission from the blazar jet, and to
investigate the contribution from the thermal emission component. Optical data
from about twenty telescopes have been homogeneously calibrated and carefully
assembled to construct an R-band light curve containing about 1340 data points
in 42 days. This extremely well-sampled optical light curve allows us to follow
the dramatic flux variability of the source in detail. In addition, we show
radio-to-UV spectral energy distributions (SEDs) at different epochs, which
represent different brightness levels. In the considered period, the source
varied by 2.6 mag in a couple of weeks in the R band. Many episodes of fast
(i.e. intranight) variability were observed, most notably on December 12, when
a flux increase of about 1.1 mag in 1.5 hours was detected, followed by a steep
decrease of about 1.2 mag in 1 hour. The contribution by the thermal component
is difficult to assess, due to the uncertainties in the Galactic, and possibly
also intrinsic, extinction in the UV band. However, polynomial fitting of
radio-to-UV SEDs reveals an increasing spectral bending going towards fainter
states, suggesting a UV excess likely due to the thermal emission from the
accretion disc
Nuclear and mitochondrial sequences confirm complex colonization patterns and clear species boundaries for flightless weevils in the Galápagos archipelago
Nuclear sequence data were collected from endemic Galápagos species and an introduced close relative, and contrasted with mitochondrial DNA sequences, continuing investigation into the colonization history and modes of diversification in the weevil genus Galapaganus. The current combined phylogeny together with previously published penalized likelihood age estimates builds a complex picture of the archipelago's colonization history. The present reconstruction relies on submerged platforms to explain the early divergence of the young southern Isabela endemics or the Española or San Cristobal populations. Diversity is later built through inter-island divergence starting on older islands and continuing on two simultaneous tracks towards younger islands. The amount of diversity generated through intra-island processes is skewed towards older islands, suggesting that island age significantly influences diversity. Phylogenetic concordance between nuclear and mitochondrial datasets and well-supported monophyletic species in mitochondrial derived topologies appear to reject the possibility of inter-species hybridization. These clear species boundaries might be related to the tight host associations of adult weevils in discrete ecological zones. If shared hosts facilitate hybridization, then host- or habitat-promoted divergences could prevent it, even in the case of species that share islands, since the altitudinal partitioning of habitats minimizes range overlap