We present the result of a search of the Milagro sky map for spatial correlations with sources from a subset of the recent Fermi Bright Source List (BSL). The BSL consists of the 205 most significant ...sources detected above 100 MeV by the Fermi Large Area Telescope. We select sources based on their categorization in the BSL, taking all confirmed or possible Galactic sources in the field of view of Milagro. Of the 34 Fermi sources selected, 14 are observed by Milagro at a significance of 3 standard deviations or more. We conduct this search with a new analysis which employs newly optimized gamma-hadron separation and utilizes the full eight-year Milagro data set. Milagro is sensitive to gamma rays with energy from 1 to 100 TeV with a peak sensitivity from 10 to 50 TeV depending on the source spectrum and declination. These results extend the observation of these sources far above the Fermi energy band. With the new analysis and additional data, multi-TeV emission is definitively observed associated with the Fermi pulsar, J2229.0+6114, in the Boomerang pulsar wind nebula (PWN). Furthermore, an extended region of multi-TeV emission is associated with the Fermi pulsar, J0634.0+1745, the Geminga pulsar.
ABSTRACT
We present the first results from a very deep Chandra X‐ray observation of the core of the Perseus cluster of galaxies. A pressure map reveals a clear thick band of high pressure around the ...inner radio bubbles. The gas in the band must be expanding outwards and the sharp front to it is identified as a shock front, yet we see no temperature jump across it; indeed, there is more soft emission behind the shock than in front of it. We conclude that in this inner region either thermal conduction operates efficiently or the co‐existing relativistic plasma seen as the radio mini‐halo is mediating the shock. If common, isothermal shocks in cluster cores mean that we cannot diagnose the expansion speed of radio bubbles from temperature measurements alone. They can at times expand more rapidly than currently assumed without producing significant regions of hot gas. Bubbles may also be significantly more energetic. The pressure ripples found in earlier images are identified as isothermal sound waves. A simple estimate based on their amplitude confirms that they can be an effective distributed heat source able to balance radiative cooling. We see multiphase gas with about 109 M⊙ at a temperature of about 0.5 keV. Much, but not all, of this X‐ray emitting cooler gas is spatially associated with the optical filamentary nebula around the central galaxy, NGC 1275. A residual cooling flow of about 50 M⊙ yr−1 may be taking place. A channel is found in the pressure map along the path of the bubbles, with indications found of outer bubbles. The channel connects in the south (S) with a curious cold front.
Using Chandra X-ray observations of nine nearby, X-ray luminous elliptical galaxies with good optical velocity dispersion measurements, we show that a tight correlation exists between the Bondi ...accretion rates calculated from the observed gas temperature and density profiles and estimated black hole masses, and the power emerging from these systems in relativistic jets. The jet powers, which are inferred from the energies and time-scales required to inflate cavities observed in the surrounding X-ray emitting gas, can be related to the accretion rates using a power-law model of the form log (PBondi/1043 erg s−1) =A+B log (Pjet/1043 erg s−1), with A= 0.65 ± 0.16 and B= 0.77 ± 0.20. Our results show that a significant fraction of the energy associated with the rest mass of material entering the Bondi accretion radius (2.2+1.0−0.7 per cent, for Pjet= 1043 erg s−1) eventually emerges in the relativistic jets. The data also hint that this fraction may rise slightly with increasing jet power. Our results have significant implications for studies of accretion, jet formation and galaxy formation. The observed tight correlation suggests that the Bondi formulae provide a reasonable description of the accretion process in these systems, despite the likely presence of magnetic pressure and angular momentum in the accreting gas. The similarity of the PBondi and Pjet values argues that a significant fraction of the matter entering the accretion radius flows down to regions close to the black holes, where the jets are presumably formed. The tight correlation between PBondi and Pjet also suggests that the accretion flows are approximately stable over time-scales of a few million years. Our results show that the black hole ‘engines’ at the hearts of large elliptical galaxies and groups can feed back sufficient energy to stem cooling and star formation, leading naturally to the observed exponential cut off at the bright end of the galaxy luminosity function.
We report on a deep, multiwavelength study of the galaxy cluster MACS J1931.8−2634 using Chandra X-ray, Subaru optical and Very Large Array 1.4-GHz radio data. This cluster (z= 0.352) harbours one of ...the most X-ray luminous cool cores yet discovered, with an equivalent mass, cooling rate within the central
is ∼700 M⊙ yr−1. Unique features observed in the central core of MACS J1931.8−2634 hint to a wealth of past activity that has greatly disrupted the original cool core. The X-ray and optical data suggest oscillatory motion of the cool core along a roughly north-south direction. We also observe a spiral of relatively cool, dense, X-ray emitting gas connected to the cool core, as well as highly elongated intracluster light (ICL) surrounding the cD galaxy. For a cluster with such a high-nominal cooling rate, this cluster is missing the central metallicity peak almost always seen in the cool-core clusters, which suggest bulk transport of cool gas out to large distances from the centre. Extended radio emission is observed surrounding the central active galactic nucleus (AGN), elongated in the east-west direction, spatially coincident with X-ray cavities. The power input required to inflate these 'bubbles' is estimated from both the X-ray and radio emission to reside between P
jet∼ 4-14 × 1045 erg s−1, putting it among the most powerful jets ever observed. This combination of a powerful AGN outburst and bulk motion of the cool core has resulted in two X-ray bright ridges to form to the north and south of the central AGN at a distance of approximately 25 kpc. The northern ridge has spectral characteristics typical of cool cores: it contains low-temperature high-density metal-rich gas and is consistent with being a remnant of the cool core after it was disrupted by the AGN and bulk motions. It is also the site of Hα filaments and young stars. The X-ray spectroscopic cooling rate associated with this ridge is ∼165 M⊙ yr−1, which agrees with the estimate of the star formation rate from broad-band optical imaging (∼170 M⊙ yr−1). MACS J1931.8−2634 appears to harbour one of the most profoundly disrupted low-entropy cores observed in a cluster, and offers new insights into the survivability of cool cores in the context of hierarchical structure formation.
Iron-sulfur (Fe-S) clusters are unique, redox-active co-factors ubiquitous throughout cellular metabolism. Fe-S cluster synthesis, trafficking, and coordination result from highly coordinated, ...evolutionarily conserved biosynthetic processes. The initial Fe-S cluster synthesis occurs within the mitochondria; however, the maturation of Fe-S clusters culminating in their ultimate insertion into appropriate cytosolic/nuclear proteins is coordinated by a late-acting cytosolic iron-sulfur assembly (CIA) complex in the cytosol. Several nuclear proteins involved in DNA replication and repair interact with the CIA complex and contain Fe-S clusters necessary for proper enzymatic activity. Moreover, it is currently hypothesized that the late-acting CIA complex regulates the maintenance of genome integrity and is an integral feature of DNA metabolism. This review describes the late-acting CIA complex and several 4Fe-4S DNA metabolic enzymes associated with maintaining genome stability.
We present the first example of binary microlensing for which the parameter measurements can be verified (or contradicted) by future Doppler observations. This test is made possible by a confluence ...of two relatively unusual circumstances. First, the binary lens is bright enough (I = 15.6) to permit Doppler measurements. Second, we measure not only the usual seven binary-lens parameters, but also the 'microlens parallax' (which yields the binary mass) and two components of the instantaneous orbital velocity. Thus, we measure, effectively, six 'Kepler+1' parameters (two instantaneous positions, two instantaneous velocities, the binary total mass, and the mass ratio). Since Doppler observations of the brighter binary component determine five Kepler parameters (period, velocity amplitude, eccentricity, phase, and position of periapsis), while the same spectroscopy yields the mass of the primary, the combined Doppler + microlensing observations would be overconstrained by 6 + (5 + 1) -- (7 + 1) = 4 degrees of freedom. This makes possible an extremely strong test of the microlensing solution. We also introduce a uniform microlensing notation for single and binary lenses, define conventions, summarize all known microlensing degeneracies, and extend a set of parameters to describe full Keplerian motion of the binary lenses.
We present new Chandra images of the X-ray emission from the core of the Perseus cluster of galaxies. The total observation time is now 1.4 Ms. New depressions in X-ray surface brightness are ...discovered to the north of NGC 1275, which we interpret as old rising bubbles. They imply that bubbles are long-lived and do not readily breakup when rising in the hot cluster atmosphere. The existence of a 300 kpc long NNW-SSW bubble axis means there cannot be significant transverse large-scale flows exceeding 100 km s−1. Interesting spatial correlations are seen along that axis in early deep radio maps. A semicircular cold front about 100 kpc west of the nucleus is seen. It separates an inner disturbed region dominated by the activity of the active nucleus of NGC 1275 from the outer region where a subcluster merger dominates.
Abstract
T
2
* relaxation is an intrinsic magnetic resonance imaging (MRI) parameter that is sensitive to local magnetic field inhomogeneities created by the deposition of endogenous paramagnetic ...material (e.g. iron). Recent studies suggest that T
2
* mapping is sensitive to iron oxidation state. In this study, we evaluate the spin state-dependence of T
2
* relaxation using T
2
* mapping. We experimentally tested this physical principle using a series of phantom experiments showing that T
2
* relaxation times are directly proportional to the spin magnetic moment of different transition metals along with their associated magnetic susceptibility. We previously showed that T
2
* relaxation time can detect the oxidation of Fe
2+
. In this paper, we demonstrate that T
2
* relaxation times are significantly longer for the diamagnetic, d
10
metal Ga
3+
, compared to the paramagnetic, d
5
metal Fe
3+
. We also show in a cell culture model that cells supplemented with Ga
3+
(S = 0) have a significantly longer relaxation time compared to cells supplemented with Fe
3+
(S = 5/2). These data support the hypothesis that dipole–dipole interactions between protons and electrons are driven by the strength of the electron spin magnetic moment in the surrounding environment giving rise to T
2
* relaxation.
This paper presents the development and performance evaluation of a compact-converter-based power supply for plasma dielectric barrier discharge (DBD) devices. The developed power supply is designed ...to meet weight and size requirements for applications in aeronautical systems. Multistage and multilevel switch-mode converters are employed to construct the power supply. The multistage part of the power supply is constructed from multiple dc-dc boost converters that have their inputs fed by rechargeable batteries. The outputs of the dc-dc converters are used to feed different levels of a single phase cascaded H-bridge (CHB) multilevel dc-ac converter. The switching signals for the CHB dc-ac converter are generated to facilitate the adjustments of the magnitude and/or frequency of the output voltage. Such adjustments are set to allow manipulating the generated plasma body force. A prototype for the multistage multilevel power supply is constructed for performance evaluation using a fiberglass DBD device. Performance results show an effective generation and control of plasma body force, which can be achieved by a modular, lightweight, and compact size power supply.
We present an analysis of the 2-10 keV X-ray emission associated with the active galactic nuclei (AGN) in brightest cluster galaxies (BCGs). Our sample consists of 32 BCGs that lie in highly X-ray ...luminous cluster of galaxies (
3\times 10^{44}\,{\rm erg}\,{\rm s}^{-1}\,$>
) in which AGN-jetted outflows are creating and sustaining clear X-ray cavities. Our sample covers the redshift range 0 < z < 0.6 and reveals strong evolution in the nuclear X-ray luminosities, such that the black holes in these systems have become on average at least 10 times fainter over the last 5 Gyr. Mindful of potential selection effects, we propose two possible scenarios to explain our results: (1) either that the AGN in BCGs with X-ray cavities are steadily becoming fainter, or more likely, (2) that the fraction of these BCGs with radiatively efficient nuclei is decreasing with time from roughly 60 per cent at z 0.6 to 30 per cent at z 0.1. Based on this strong evolution, we predict that a significant fraction of BCGs in z 1 clusters may host quasars at their centres, potentially complicating the search for such clusters at high redshift. In analogy with black hole binaries and based on the observed Eddington ratios of our sources, we further propose that the evolving AGN population in BCGs with X-ray cavities may be transiting from a canonical low/hard state, analogous to that of X-ray binaries, to a quiescent state over the last 5 Gyr.
PDF
