14,205 research outputs found
Stochastic model of optical variability of BL Lacertae
We use optical photometric and polarimetric data of BL Lacertae that cover a
period of 22 years to study the variability of the source. The long-term
observations are employed for establishing parameters of a stochastic model
consisting of the radiation from a steady polarized source and a number of
variable components with different polarization parameters, proposed by
Hagen-Thorn et al. earlier. We infer parameters of the model from the
observations using numerical simulations based on a Monte Carlo method, with
values of each model parameter selected from a Gaussian distribution. We
determine the best set of model parameters by comparing model distributions to
the observational ones using the chi-square criterion. We show that the
observed photometric and polarimetric variability can be explained within a
model with a steady source of high polarization, ~40%, and with direction of
polarization parallel to the parsec scale jet, along with 10+-5 sources of
variable polarization.Comment: 4 pages, 10 figures, published by Astronomy and Astrophysics; v2:
typos correcte
The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation
We present the results of polarimetric ( band) and multicolor photometric
() observations of the blazar AO 0235+16 during an outburst in 2006
December. The data reveal a short timescale of variability (several hours),
which increases from optical to near-IR wavelengths; even shorter variations
are detected in polarization. The flux density correlates with the degree of
polarization, and at maximum degree of polarization the electric vector tends
to align with the parsec-scale jet direction. We find that a variable component
with a steady power-law spectral energy distribution and very high optical
polarization (30-50%) is responsible for the variability. We interpret these
properties of the blazar withina model of a transverse shock propagating down
the jet. In this case a small change in the viewing angle of the jet, by
, and a decrease in the shocked plasma compression by a factor of
1.5 are sufficient to account for the variability.Comment: 22 pages, 8 figures, accepted for Ap
Life in Extraterrestrial Environments Quarterly Status Report No. 4, 15 Nov. 1965 - 15 Feb. 1966
Bacillus spore germination in simulated Martian environmen
Life in extraterrestrial environments Quarterly status report, 1 Sep. - 30 Nov. 1967
Importance of Bacillus cereus and Staphylococcus aureus survival and growth to extraterrestrial planetary contaminatio
Life in extraterrestrial environments Final report, 16 Feb. 1968 - 14 Jul. 1969
Ultraviolet irradiation of microorganisms in simulated Martian environmen
Life in extraterrestrial environments Quarterly status report, Feb. 15 - May 15, 1966
Simulated Martian atmospheric and ecological effects on Bacillus cereus spore germinatio
Life in Extraterrestrial Environments Quarterly Status Report, 15 Feb. - 15 May 1965
Growth response of Bacillus cereus and subtilis cells subjected to modified Martian environment with freeze cycles of different duration
Life in extraterrestrial environments Quarterly status report, 15 Aug. - 15 Nov. 1965
Effect of extraterrestrial environment on bacteri
Life in extraterrestrial environments Quarterly status report, Nov. 15, 1966 - Feb. 15, 1967
Simulated Martian environment growth experiments conducted with Staphylococcus aureu
LIFE IN EXTRATERRESTRIAL ENVIRONMENTS
Life in extraterrestrial environments - simulation of martian environment and survival of microorganism
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