140 research outputs found
Intranight variability of 3C 454.3 during its 2010 November outburst
Context. 3C 454.3 is a very active flat spectrum radio quasar (blazar) that
has undergone a recent outburst in all observed bands, including the optical.
Aims. In this work we explore the short-term optical variability of 3C 454.3
during its outburst by searching for time delays between different optical
bands. Finding one would be important for understanding the evolution of the
spectrum of the relativistic electrons, which generate the synchrotron jet
emission.
Methods. We performed photometric monitoring of the object by repeating
exposures in different optical bands (BVRI). Occasionally, different telescopes
were used to monitor the object in the same band to verify the reliability of
the smallest variations we observed.
Results. Except on one occasion, where we found indications of a lag of the
blue wavelengths behind the red ones, the results are inconclusive for most of
the other cases. There were either no structures in the light curves to be able
to search for patterns, or else different approaches led to different
conclusions.Comment: 4 pages, 4 figures. Accepted for publication in A&
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Xanthates: Metabolism by Flavoprotein-Containing Monooxygenases and Antimycobacterial Activity.
Ethionamide (ETH) plays a central role in the treatment of tuberculosis in patients resistant to the first-line drugs. The ETH, thioamide, and thiourea class of antituberculosis agents are prodrugs that are oxidatively converted to their active S-oxides by the mycobacterial flavin-dependent monooxygenase (EtaA) of Mycobacterium tuberculosis, thus initiating the chain of reactions that result in inhibition of mycolic acid biosynthesis and cell lysis. As part of a search for new lead candidates, we report here that several xanthates are oxidized by purified EtaA to S-oxide metabolites (perxanthates), which are implicated in the antimycobacterial activity of these compounds. This process, which is analogous to that responsible for activation of ETH, is also catalyzed by human flavoprotein monooxygenase 3. EtaA was not inhibited in a time-dependent manner during the reaction. Xanthates with longer alkyl chains were oxidized more efficiently. EtaA oxidized octyl-xanthate (Km = 5 ”M; Vmax = 1.023 nmolP/min; kcat = 5.2 molP/min/molE) more efficiently than ETH (194 ”M; 1.46 nmolP/min; 7.73 nmolP/min/molE, respectively). Furthermore, the in vitro antimycobacterial activity of four xanthates against M. tuberculosis H37Hv was higher (minimum inhibitory concentration of around 1 ”M) than that of ETH (12 ”M)
Discovery of a new photometric sub-class of faint and fast classical novae
We present photometric and spectroscopic follow-up of a sample of
extragalactic novae discovered by the Palomar 60-inch telescope during a search
for "Fast Transients In Nearest Galaxies" (P60-FasTING). Designed as a fast
cadence (1-day) and deep (g < 21 mag) survey, P60-FasTING was particularly
sensitive to short-lived and faint optical transients. The P60-FasTING nova
sample includes 10 novae in M31, 6 in M81, 3 in M82, 1 in NGC2403 and 1 in
NGC891. This significantly expands the known sample of extragalactic novae
beyond the Local Group, including the first discoveries in a starburst
environment. Surprisingly, our photometry shows that this sample is quite
inconsistent with the canonical Maximum Magnitude Rate of Decline (MMRD)
relation for classical novae. Furthermore, the spectra of the P60-FasTING
sample are indistinguishable from classical novae. We suggest that we have
uncovered a sub-class of faint and fast classical novae in a new phase space in
luminosity-timescale of optical transients. Thus, novae span two orders of
magnitude in both luminosity and time. Perhaps, the MMRD, which is
characterized only by the white dwarf mass, was an over-simplification. Nova
physics appears to be characterized by quite a rich four-dimensional parameter
space in white dwarf mass, temperature, composition and accretion rate.Comment: Submitted to ApJ, 12 pages. High resolution version at
http://www.astro.caltech.edu/~mansi/msFasting.pd
Effects of Aronia melanocarpa fruit juice on exploratory behaviour and locomotor activity in rats
The main bioactive substances in Aronia melanocarpa fruit juice (AMFJ) are polyphenols (flavonoids, procyanidins, and phenolic acids). A great number of polyphenols are able to traverse the blood-brain barrier. In recent years more attention is drawn to the ability of these substances to influence central nervous system functions. The aim of the present study was to investigate the effects of AMFJ on exploratory behaviour and locomotor activity in male Wistar rats. AMFJ was administered orally for 7, 14, 21, and 30 days at three increasing doses (2.5, 5, and 10 ml kgâ1). The changes in exploratory behaviour and locomotor activity were recorded in an Opto Varimex apparatus. It was found that the low doses of AMFJ (2.5 and 5 ml kgâ1) for all treatment periods did not significantly affect exploratory behaviour and locomotor activity of rats compared to the saline-treated controls. AMFJ at the highest dose of 10 ml kgâ1 had no significant effect on exploration and locomotion for the treatment periods of 7 and 14 days, while for the periods of 21 and 30 days it significantly decreased the number of horizontal and vertical movements, which might be the result of a sedative effect. At all the doses and testing periods, AMFJ did not disturb the progressive decrease in motor behaviour, suggesting habituation
Black sea observing system
The ultimate goal of modern operational oceanography are end user oriented products with high scientific quality. Beneficiaries are the governmental services, coast and offshore based enterprises and research institutions that make use of the products generated by operational oceanography. Direct users are coastal managers, shipping, search and rescue, oil spill combat, offshore industry, ports, fishing, tourism, and recreation industry. Indirect beneficiaries, through climate forecasting based on ocean observations, are food, energy, water and medical suppliers. Availability of updated information on the actual state as well as forecast of marine environment is essential for the success and safety of maritime operations in the offshore industry. Various systems for the collection and presentation of marine data for the needs of different users have been developed and put in operation in the Black Sea. The systems are located both along the coast and in the open sea and the information they provide is used by both the maritime industry and the widest range of users. The Black Sea Monitoring and Forecasting Center in the frame of the Copernicus Marine Service is providing regular and systematic information about the physical state of the ocean, marine ecosystem and wave conditions in the Black Sea area, assimilating observations, keeping efficient operations, advanced technology and high quality modeling products. Combining and optimizing in situ, remote sensing, modeling and forecasting into a Black Sea observing system is a task that has to be solved, and that will allow to get a more complete and comprehensive picture of the state of the marine environment as well as to forecast future changes of physical and biogeochemical state of the Black Sea and the Black Sea ecosystem
Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006--2007 outburst
The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the
radio and optical bands. Moreover, an extra emission component contributing to
the UV and soft X-ray flux was detected, whose nature is not yet clear. A
predicted optical outburst was observed in late 2006/early 2007. We here
present the radio-to-optical WEBT light curves during the outburst, together
with UV data acquired by Swift in the same period. We found the optical
outburst to be as strong as the big outbursts of the past: starting from late
September 2006, a brightness increase of 5 mag led to the outburst peak in
February 19-21, 2007. We also observed an outburst at mm and then at cm
wavelengths, with an increasing time delay going toward lower frequencies
during the rising phase. Cross-correlation analysis indicates that the 1 mm and
37 GHz flux variations lagged behind the R-band ones by about 3 weeks and 2
months, respectively. These short time delays suggest that the corresponding
jet emitting regions are only slightly separated and/or misaligned. In
contrast, during the outburst decreasing phase the flux faded contemporaneously
at all cm wavelengths. This abrupt change in the emission behaviour may suggest
the presence of some shutdown mechanism of intrinsic or geometric nature. The
behaviour of the UV flux closely follows the optical and near-IR one. By
separating the synchrotron and extra component contributions to the UV flux, we
found that they correlate, which suggests that the two emissions have a common
origin.Comment: 9 pages, 7 figures, in press for Astronomy and Astrophysic
A new activity phase of the blazar 3C 454.3. Multifrequency observations by the WEBT and XMM-Newton in 2007-2008
We present and analyse the WEBT multifrequency observations of 3C 454.3 in
the 2007-2008 observing season, including XMM-Newton observations and near-IR
spectroscopic monitoring, and compare the recent emission behaviour with the
past one. In the optical band we observed a multi-peak outburst in July-August
2007, and other faster events in November 2007 - February 2008. During these
outburst phases, several episodes of intranight variability were detected. A mm
outburst was observed starting from mid 2007, whose rising phase was
contemporaneous to the optical brightening. A slower flux increase also
affected the higher radio frequencies, the flux enhancement disappearing below
8 GHz. The analysis of the optical-radio correlation and time delays, as well
as the behaviour of the mm light curve, confirm our previous predictions,
suggesting that changes in the jet orientation likely occurred in the last few
years. The historical multiwavelength behaviour indicates that a significant
variation in the viewing angle may have happened around year 2000. Colour
analysis reveals a complex spectral behaviour, which is due to the interplay of
different emission components. All the near-IR spectra show a prominent Halpha
emission line, whose flux appears nearly constant. The analysis of the
XMM-Newton data indicates a correlation between the UV excess and the
soft-X-ray excess, which may represent the head and the tail of the big blue
bump, respectively. The X-ray flux correlates with the optical flux, suggesting
that in the inverse-Compton process either the seed photons are synchrotron
photons at IR-optical frequencies or the relativistic electrons are those that
produce the optical synchrotron emission. The X-ray radiation would thus be
produced in the jet region from where the IR-optical emission comes.Comment: 10 pages, 12 figures (7 included in the text, 5 in GIF format),
accepted for publication in A&
WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008. Unveiling different emission components
In 2007-2008 we carried out a new multiwavelength campaign of the Whole Earth
Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the
XMM-Newton satellite, to study its emission properties. The source was
monitored in the optical-to-radio bands by 37 telescopes. The brightness level
was relatively low. Some episodes of very fast variability were detected in the
optical bands. The X-ray spectra are well fitted by a power law with photon
index of about 2 and photoelectric absorption exceeding the Galactic value.
However, when taking into account the presence of a molecular cloud on the line
of sight, the data are best fitted by a double power law, implying a concave
X-ray spectrum. The spectral energy distributions (SEDs) built with
simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations
suggest that the peak of the synchrotron emission lies in the near-IR band, and
show a prominent UV excess, besides a slight soft-X-ray excess. A comparison
with the SEDs corresponding to previous observations with X-ray satellites
shows that the X-ray spectrum is extremely variable. We ascribe the UV excess
to thermal emission from the accretion disc, and the other broad-band spectral
features to the presence of two synchrotron components, with their related SSC
emission. We fit the thermal emission with a black body law and the non-thermal
components by means of a helical jet model. The fit indicates a disc
temperature greater than 20000 K and a luminosity greater than 6 x 10^44 erg/s.Comment: 11 pages, 7 figures, accepted for publication in A&
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