14 research outputs found
Low frequency follow up of radio halos and relics in the GMRT Radio Halo Cluster Survey
We performed GMRT low frequency observations of the radio halos, relics and
new candidates belonging to the GMRT Radio Halo Cluster Sample first observed
at 610 MHz. High sensitivity imaging was performed using the GMRT at 325 MHz
and 240 MHz. The properties of the diffuse emission in each cluster were
compared to our 610 MHz images and/or literature information available at other
frequencies, in order to derive the integrated spectra over a wide frequency
range.Beyond the classical radio halos, whose spectral index is in the
range (S), we found sources with
. This result supports the idea that the spectra of the
radiating particles in radio halos is not universal, and that inefficient
mechanisms of particle acceleration are responsible for their origin. We also
found a variety of brightness distributions, i.e. centrally peaked as well as
clumpy halos. Even though the thermal and relativistic plasma tend to occupy
the same cluster volume, in some cases a positional shift between the radio and
X-ray peaks of emission is evident. Our observations also revealed the
existence of diffuse cluster sources which cannot be easily classified either
as halos or relics. New candidate relics were found in A1300 and in A1682, and
in some clusters "bridges" of radio emission have been detected, connecting the
relic and radio halo emission. Combining our new data with literature
information, we derived the LogL-LogP correlation for
radio halos, and investigated the possible trend of the spectral index of radio
halos with the temperature of the intracluster medium.Comment: 19 pages, 10 figures, 5 tables, accepted for publication on A&
A shock front in the merging galaxy cluster Abell 754: X-ray and radio observations
We present new Chandra X-ray and Giant Meterwave Radio Telescope (GMRT) radio
observations of the nearby merging galaxy cluster Abell 754. Our X-ray data
confirm the presence of a shock front by obtaining the first direct measurement
of a gas temperature jump across the X-ray brightness edge previously seen in
the imaging data. A754 is only the fourth galaxy cluster with confirmed merger
shock fronts, and it has the weakest shock of those, with a Mach number
M=1.57+0.16-0.12. In our new GMRT observation at 330 MHz, we find that the
previously-known centrally located radio halo extends eastward to the position
of the shock. The X-ray shock front also coincides with the position of a radio
relic previously observed at 74 MHz. The radio spectrum of the post-shock
region, using our radio data and the earlier results at 74 MHz and 1.4 GHz, is
very steep. We argue that acceleration of electrons at the shock front directly
from thermal to ultrarelativistic energies is problematic due to energy
arguments, while reacceleration of preexisting relativistic electrons is more
plausible.Comment: 10 pages, 8 figures, "emulateapj" format. Submitted to Ap
Intraring allostery controls the function and assembly of a hetero‐oligomeric class II chaperonin
Class II chaperonins are essential multisubunit complexes that aid the folding of nonnative proteins in the cytosol of archaea and eukarya. They use energy derived from ATP to drive a series of structural rearrangements that enable polypeptides to fold within their central cavity. These events are regulated by an elaborate allosteric mechanism in need of elucidation. We employed mutagenesis and experimental analysis in concert with in silico molecular dynamics simulations and interface-binding energy calculations to investigate the class II chaperonin from Thermoplasma acidophilum. Here we describe the effects on the asymmetric allosteric mechanism and on hetero-oligomeric complex formation in a panel of mutants in the ATP-binding pocket of the α and β subunits. Our observations reveal a potential model for a nonconcerted folding mechanism optimized for protecting and refolding a range of nonnative substrates under different environmental conditions, starting to unravel the role of subunit heterogeneity in this folding machine and establishing important links with the behavior of the most complex eukaryotic chaperonins.—Shoemark, D. K., Sessions, R. B., Brancaccio, A., Bigotti, M. G. Intraring allostery controls the function and assembly of a hetero-oligomeric class II chaperonin
Progress with the LOFAR Imaging Pipeline
One of the science drivers of the new Low Frequency Array (LOFAR) is
large-area surveys of the low-frequency radio sky. Realizing this goal requires
automated processing of the interferometric data, such that fully calibrated
images are produced by the system during survey operations. The LOFAR Imaging
Pipeline is the tool intended for this purpose, and is now undergoing
significant commissioning work. The pipeline is now functional as an automated
processing chain. Here we present several recent LOFAR images that have been
produced during the still ongoing commissioning period. These early LOFAR
images are representative of some of the science goals of the commissioning
team members.Comment: 11 pages, 6 figures. Accepted for publication in proceedings of
"ISKAF2010 Science Meeting", PoS(ISKAF2010)05
Hide and seek between Andromeda's halo, disk, and giant stream
Photometry in B, V (down to V ~ 26 mag) is presented for two 23' x 23' fields
of the Andromeda galaxy (M31) that were observed with the blue channel camera
of the Large Binocular Telescope during the Science Demonstration Time. Each
field covers an area of about 5.1kpc x 5.1kpc at the distance of M31 ((m-M)o ~
24.4 mag), sampling, respectively, a northeast region close to the M31 giant
stream (field S2), and an eastern portion of the halo in the direction of the
galaxy minor axis (field H1). The stream field spans a region that includes
Andromeda's disk and the giant stream, and this is reflected in the complexity
of the color magnitude diagram of the field. One corner of the halo field also
includes a portion of the giant stream. Even though these demonstration time
data were obtained under non-optimal observing conditions the B photometry,
acquired in time-series mode, allowed us to identify 274 variable stars (among
which 96 are bona fide and 31 are candidate RR Lyrae stars, 71 are Cepheids,
and 16 are binary systems) by applying the image subtraction technique to
selected portions of the observed fields. Differential flux light curves were
obtained for the vast majority of these variables. Our sample includes mainly
pulsating stars which populate the instability strip from the Classical
Cepheids down to the RR Lyrae stars, thus tracing the different stellar
generations in these regions of M31 down to the horizontal branch of the oldest
(t ~ 10 Gyr) component.Comment: 59 pages, 26 figures, 12 tables, ApJ in pres
Characterization of the SKA1-Low prototype station Aperture Array Verification System 2
The low frequency component of the Square Kilometre Array (SKA1-Low) will be an aperture phased array located at the Murchison Radio-astronomy Observatory (MRO) site in Western Australia. It will be composed of 512 stations, each consisting of 256 log-periodic dual-polarized antennas, and will operate in the low frequency range (50 to 350 MHz) of the SKA bandwidth. The Aperture Array Verification System 2 (AAVS2), operational since late 2019, is the last full-size engineering prototype station deployed at the MRO site before the start of the SKA1-Low construction phase. The aim of this paper is to characterize the station performance through commissioning observations at six different frequencies (55, 70, 110, 160, 230, and 320 MHz) collected during its first year of activities. We describe the calibration procedure, present the resulting all-sky images and their analysis, and discuss the station calibratability and system stability. Using the difference imaging method, we also derive estimates of the SKA1-Low sensitivity for the same frequencies and compare them with those obtained through electromagnetic simulations across the entire telescope bandwidth, finding good agreement (within 13%). Moreover, our estimates exceed the SKA1-Low requirements at all considered frequencies by up to a factor of ∼2.3. Our results are very promising and allow for an initial validation of the AAVS2 prototype station performance, which is an important step toward the coming SKA1-Low telescope construction and science
Circulating Molecular Chaperones in Subjects with Amnestic Mild Cognitive Impairment and Alzheimer's Disease: Data from the Zabùt Aging Project
Molecular chaperones play essential roles in many processes such as cell differentiation, tissue homeostasis, and organ remodeling. Recent data indicate that chaperones can act as cytoprotectants for brain cells during the progression of neurodegenerative diseases, including Alzheimer's disease (AD). However, very few data on the levels of chaperones in dementia, including its prodromal phases, have been reported. In this study, we used biological samples and epidemiological data collected during the Zabùt Aging Project (a prospective, community-based, cohort study of normal/pathological aging conducted in Sicily, Italy, with a follow-up of ten years) to determine if there is an association between plasma levels of the chaperones Hsp60, Hsp70, and Hsp90 with amnestic mild cognitive impairment (aMCI) and AD. Twenty-six aMCI individuals, 26 AD and 26 controls, matched for age and sex, were enrolled. After adjustment for education subjects with AD showed significantly higher levels of Hsp60 than aMCI (OR = 1.16, 95% CI 1.04-1.30) and controls (OR = 1.12, 95% CI 1.03-1.22), while Hsp70 was significantly higher only in AD (OR = 1.84, 95% CI 1.09-3.10) than controls. In contrast, circulating levels of Hsp90 were significantly diminished in aMCI (OR = 0.69, 95% CI 0.52-0.91) and AD (OR = 0.51, 95% CI 0.35-0.75) compared to controls. However, these results were no longer significant after adjustment for multiple comparisons. Although the results lost significance after adjustment for multiple comparisons, they are encouraging despite the smallness of the sample and new studies should be carried out with larger populations to determine to what extent sequential measurement of serum chaperones in aMCI and AD can be trusted as indicators of disease status and progression
LOFAR and APERTIF Surveys of the Radio Sky : Probing Shocks and Magnetic Fields in Galaxy Clusters
At very low frequencies, the new pan-European radio telescope LOFAR is opening the last unexplored window of the electromagnetic spectrum for astrophysical studies. The revolutionary APERTIF-phased arrays that are about to be installed on the Westerbork radio telescope (WSRT) will dramatically increase the survey speed for the WSRT. Combined surveys with these two facilities will deeply chart the northern sky over almost two decades in radio frequency from similar to 15 up to 1400 MHz. Here we briefly describe some of the capabilities of these new facilities and what radio surveys are planned to study fun-damental issues related to the formation and evolution of galaxies and clusters of galaxies. In the second part we briefly review some recent observational results directly showing that diffuse radio emission in clusters traces shocks due to cluster mergers. As these diffuse radio sources are relatively bright at low frequencies, LOFAR should be able to detect thousands of such sources up to the epoch of cluster formation. This will allow addressing many question about the origin and evolution of shocks and magnetic fields in clusters. At the end we briefly review some of the first and very preliminary LOFAR results on clusters.Peer reviewe