We report on the correlation between the flux, color and polarization variations on time scales of daysmonths in blazars, and discuss their universal aspects. We performed monitoring of 42 blazars in the optical and near-infrared bands from 2008 to 2010 using TRISPEC attached to the "Kanata" 1.5-m telescope. We found that 28 blazars exhibited "bluer-when-brighter" trends in their whole or a part of time-series data sets. This corresponds to 88% of objects that were observed for > 10 days. Thus, our observation unambiguously confirmed that the "bluer-when-brighter" trend is common in the emission from blazar jets. This trend was apparently generated by a variation component with a constant and relatively blue color and an underlying red component. Prominent short-term flares on time scales of days-weeks tended to exhibit a spectral hysteresis; their rising phases were bluer than their decay phases around the flare maxima. In contrast to the strong flux-color correlation, the correlation of the flux and polarization degree was relatively weak; only 10 objects showed significant positive correlations. Rotations of polarization were detected only in three objects: PKS 1510−089, 3C 454.3, and PKS 1749+096, and possibly in S5 0716+714. We also investigated the dependence of the degree of variability on the luminosity and the synchrotron peak frequency, ν peak . As a result, we found that lower luminosity and higher ν peak objects had smaller variations in their amplitudes both in the flux, color, and polarization degree. Our observation suggests the presence of several distinct emitting sources, which have different variation time-scales, colors, and polarizations. We propose that the energy injection by, for example, internal shocks in relativistic shells is a major factor for blazar variations on time scales of both days and months.
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 R = 12.0, which represents the most luminous quasar state thus far observed (M B ∼ −31.4). 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.
The origin of lithium (Li) and its production process have long been an unsettled question in cosmology and astrophysics. Candidates environments of Li production events or sites suggested by previous studies include big bang nucleosynthesis, interactions of energetic cosmic rays with interstellar matter, evolved low mass stars, novae, and supernova explosions.Chemical evolution models and observed stellar Li abundances suggest that at least half of the present Li abundance may have been produced in red giants, asymptotic giant branch (AGB) stars, and novae [1][2][3] . However, no direct evidence for the supply of Li from stellar ob- High-resolution spectra (R = 90, 000-60, 000) of V339 Del were obtained at four epochs after its outburst (+38, +47, +48, and +52 d). These spectra contain a series of broad emission lines originating from neutral hydrogen (H I, Balmer series) and other permitted transitions of neutral or singly ionized species (e.g., Fe II, He I, Ca II). These emission lines are usually seen in post-outburst spectra of classical novae. Most of these broad emission lines are accompanied by sharp and blue-shifted multiple absorption lines at their blue edges. The typical radial velocity (v rad ) of these highly blue-shifted absorption lines is ∼ −1, 000 km s −1 . Figure 1- There are no Na I D doublet lines, which are often found to be the strongest absorption features in novae within a few weeks after their outbursts 8,10 . We interpret this as indicating that the ionization state of the ejected gas has evolved into a higher stage of excitation before our observing epochs (5-7 weeks). The observed spectral energy distribution of this nova indicates that the shape of the continuous radiation had entered a very hot stage (effective temperature >100,000 K) within 5 weeks after the explosion 11 . Other observed characteristics of this nova (e.g., light curves, optical and UV emission lines) show that it is a typical Fe II nova with a CO white dwarf (WD) 12,13 .Among these absorption line systems, we have noticed two remarkable pairs of absorption features near 312 nm. These correspond to the absorption components originating from transitions 3 at ∼313 nm. These pairs are marked as A, B and C, D, respectively, in Figure 1- The transition probability of the 7 Be II line at 313.0583 nm (log gf = −0.178) is twice as large as that of the 7 Be II at 313.1228 nm (log gf = −0.479) 14 . Due to saturation effects, the ratio of their equivalent widths is expected to be in the range between 2 (no saturation) to 1 (complete saturation). The measured ratios are 1.1 ± 0.3 and 1.6 ± 0.4 for the components at v rad = −1, 268and −1, 103 km s −1 , respectively. These are within the range expected for the doublet, although the values contain some errors ( ∼ < ±25%) due mainly to the uncertainty in the continuum placement.The weaker component at v rad = −1, 268 km s −1 has a ratio closer to complete saturation. This can 4 be interpreted as resulting from the fact that the absorbing gas cloud moving with v rad = −1, 268 km s...
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