45,750 research outputs found
Evidence from the Very Long Baseline Array that J1502SE/SW are Double Hotspots, not a Supermassive Binary Black Hole
SDSS J150243.09+111557.3 is a merging system at z = 0.39 that hosts two
confirmed AGN, one unobscured and one dust-obscured, offset by several
kiloparsecs. Deane et al. recently reported evidence from the European VLBI
Network (EVN) that the dust-obscured AGN exhibits two flat-spectrum radio
sources, J1502SE/SW, offset by 26 mas (140 pc), with each source being
energized by its own supermassive black hole (BH). This intriguing
interpretation of a close binary BH was reached after ruling out a
double-hotspot scenario, wherein both hotspots are energized by a single,
central BH, a configuration occuring in the well-studied Compact Symmetric
Objects. When observed with sufficient sensitivity and resolution, an object
with double hotspots should have an edge-brightened structure. We report
evidence from the Very Long Baseline Array (VLBA) for just such a structure in
an image of the obscured AGN with higher sensitivity and resolution than the
EVN images. We thus conclude that a double-hotspot scenario should be
reconsidered as a viable interpretation for J1502SE/SW, and suggest further
VLBA tests of that scenario. A double-hotspot scenario could have broad
implications for feedback in obscured AGNs. We also report a VLBA detection of
high-brightness-temperature emssion from the unobscured AGN that is offset
several kiloparsecs from J1502SE/SW.Comment: 12 pages, 1 figure, accepted by ApJL on 2014 July 2
The relative abundance of neon and magnesium in the solar corona
A technique is proposed for specifically determining the relative solar coronal abundance of neon and magnesium. The relative abundance is calculated directly from the relative intensity of the resonance lines of Ne X (12.134A) and Mg XI (9.169A) without the need for the development of a detailed model of the thermal structure of the corona. Moderate resolution Bragg crystal spectrometer results from the OVI-10 satellite were used to determine a coronal neon to magnesium relative abundance of 1.47 + or - 0.38. The application of this technique to a recent higher resolution rocket observation gave an abundance ratio of approximately 0.93 + or - 0.15
Effects of Quasi-Static Aberrations in Faint Companion Searches
We present the first results obtained at CFHT with the TRIDENT infrared
camera, dedicated to the detection of faint companions close to bright nearby
stars. The camera's main feature is the acquisition of three simultaneous
images in three wavelengths (simultaneous differential imaging) across the
methane absorption bandhead at 1.6 micron, that enables a precise subtraction
of the primary star PSF while keeping the companion signal. The main limitation
is non-common path aberrations between the three optical paths that slightly
decorrelate the PSFs. Two types of PSF calibrations are combined with the
differential simultaneous imaging technique to further attenuate the PSF:
reference star subtraction and instrument rotation to smooth aberrations. It is
shown that a faint companion with a DeltaH of 10 magnitudes would be detected
at 0.5 arcsec from the primary.Comment: 12 pages, 10 figures, to appear in Astronomy with High Contrast
Imaging, EAS Publications Serie
Relative coronal abundances derived from X-ray observations 3: The effect of cascades on the relative intensity of Fe (XVII) line fluxes, and a revised iron abundance
Permitted lines in the optically thin coronal X-ray spectrum were analyzed to find the distribution of coronal material, as a function of temperature, without special assumptions concerning coronal conditions. The resonance lines of N, O, Ne, Na, Mg, Al, Si, S, and Ar which dominate the quiet coronal spectrum below 25A were observed. Coronal models were constructed and the relative abundances of these elements were determined. The intensity in the lines of the 2p-3d transitions near 15A was used in conjunction with these coronal models, with the assumption of coronal excitation, to determine the Fe XVII abundance. The relative intensities of the 2p-3d Fe XVII lines observed in the corona agreed with theoretical prediction. Using a more complete theoretical model, and higher resolution observations, a revised calculation of iron abundance relative to hydrogen of 0.000026 was made
The effect of the quasar H1821+643 on the surrounding intracluster medium: revealing the underlying cooling flow
We present a detailed study of the thermodynamic properties of the
intracluster medium of the only low redshift galaxy cluster to contain a highly
luminous quasar, H1821+643. The cluster is a highly massive, strong cool core
cluster. We find that the ICM entropy around the quasar is significantly lower
than that of other similarly massive strong cool core clusters within the
central 80 kpc, and that the entropy lies significantly below the extrapolated
baseline entropy profile from hierarchical structure formation. By comparing
the scaled temperature profile with those of other strong cool core clusters of
similar total mass, we see that the entropy deficiency is due to the central
temperature being significantly lower. This suggests that the presence of the
quasar in the core of H1821+643 has had a dramatic cooling effect on the
intracluster medium around it. We find that, if the quasar was brighter in the
past, Compton cooling by radiation from the quasar may have caused the low
entropy and temperature levels in the ICM around the quasar. Curiously, the
gradients of the steep central temperature and entropy decline are in
reasonable agreement with the profiles expected for a constant pressure cooling
flow. It is possible that the system has been locked into a Compton cooled
feedback cycle which prevents energy release from the black hole heating the
gas sufficiently to switch it off, leading to the formation of a huge (~3x10^10
solar mass) supermassive black hole.Comment: 8 pages, 10 figures. Accepted for publication in MNRA
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