526 research outputs found
Exploring Io's atmospheric composition with APEX: first measurement of 34SO2 and tentative detection of KCl
The composition of Io's tenuous atmosphere is poorly constrained. Only the
major species SO2 and a handful of minor species have been positively
identified, but a variety of other molecular species should be present, based
on thermochemical equilibrium models of volcanic gas chemistry and the
composition of Io's environment. This paper focuses on the spectral search for
expected yet undetected molecular species (KCl, SiO, S2O) and isotopes (34SO2).
We analyze a disk-averaged spectrum of a potentially line-rich spectral window
around 345 GHz, obtained in 2010 at the APEX-12m antenna (Atacama Pathfinder
EXperiment). Using different models assuming either extended atmospheric
distributions or a purely volcanically-sustained atmosphere, we tentatively
measure the KCl relative abundance with respect to SO2 and derive a range of
4x10^{-4}-8x10^{-3}. We do not detect SiO or S2O and present new upper limits
on their abundances. We also present the first measurement of the 34S/32S
isotopic ratio in gas phase on Io, which appears to be twice as high as the
Earth and ISM reference values. Strong lines of SO2 and SO are also analyzed to
check for longitudinal variations of column density and relative abundance. Our
models show that, based on their predicted relative abundance with respect to
SO2 in volcanic plumes, both the tentative KCl detection and SiO upper limit
are compatible with a purely volcanic origin for these species.Comment: Accepted for publication in ApJ. 11 pages, 4 figure
Interferometric imaging of the high-redshift radio galaxy, 4C60.07: An SMA, Spitzer and VLA study reveals a binary AGN/starburst
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Blackwell / RAS. DOI: 10.1111/j.1365-2966.2008.13811.xPeer reviewe
First Detection of Millimeter/Submillimeter Extragalactic H2O Maser Emission
We report the first detection of an extragalactic millimeter wavelength H2O
maser at 183 GHz towards NGC 3079 using the Submillimeter Array (SMA), and a
tentative submillimeter wave detection of the 439 GHz maser towards the same
source using the James Clerk Maxwell Telescope (JCMT). These H2O transitions
are known to exhibit maser emission in star-forming regions and evolved stars.
NGC 3079 is a well-studied nuclear H2O maser source at 22 GHz with a
time-variable peak flux density in the range 3 -- 12 Jy. The 183 GHz H2O maser
emission, with peak flux density 0.5 Jy (7 detection), also
originates from the nuclear region of NGC 3079 and is spatially coincident with
the dust continuum peak at 193 GHz (53 mJy integrated). Peak emission at both
183 and 439 GHz occurs in the same range of velocity as that covered by the 22
GHz spectrum. We estimate the gas to dust ratio of the nucleus of NGC 3079 to
be 150, comparable to the Galactic value of 160. Discovery of maser
emission in an active galactic nucleus beyond the long-known 22 GHz transition
opens the possibility of future position-resolved radiative transfer modeling
of accretion disks and outflows pc from massive black holes.Comment: 12 pages, 3 figures, ApJ Letters accepte
Unusual Flaring Activity in the Blazar PKS 1424-418 during 2008-2011
Context. Blazars are a subset of active galactic nuclei (AGN) with jets that
are oriented along our line of sight. Variability and spectral energy
distribution (SED) studies are crucial tools for understanding the physical
processes responsible for observed AGN emission.
Aims. We report peculiar behaviour in the bright gamma-ray blazar PKS
1424-418 and use its strong variability to reveal information about the
particle acceleration and interactions in the jet. Methods. Correlation
analysis of the extensive optical coverage by the ATOM telescope and nearly
continuous gamma-ray coverage by the Fermi Large Area Telescope is combined
with broadband, time-dependent modeling of the SED incorporating supplemental
information from radio and X-ray observations of this blazar.
Results. We analyse in detail four bright phases at optical-GeV energies.
These flares of PKS 1424-418 show high correlation between these energy ranges,
with the exception of one large optical flare that coincides with relatively
low gamma-ray activity. Although the optical/gamma-ray behaviour of PKS
1424-418 shows variety, the multiwavelength modeling indicates that these
differences can largely be explained by changes in the flux and energy spectrum
of the electrons in the jet that are radiating. We find that for all flares the
SED is adequately represented by a leptonic model that includes inverse Compton
emission from external radiation fields with similar parameters.
Conclusions. Detailed studies of individual blazars like PKS 1424-418 during
periods of enhanced activity in different wavebands are helping us identify
underlying patterns in the physical parameters in this class of AGN.Comment: accepted for publication in A&
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