A radio and infrared exploration of the Cygnus X-3 environments

To confirm, or rule out, the possible hot spot nature of two previously detected radio sources in the vicinity of the Cygnus X-3 microquasar. We present the results of a radio and near infrared exploration of the several arc-minute field around the well known galactic relativistic jet source Cygnus X-3 using the Very Large Array and the Calar Alto 3.5~m telescope. The data this paper is based on do not presently support the hot spot hypothesis. Instead, our new observations suggest that these sources are most likely background or foreground objects. Actually, none of them appears to be even barely extended as would be expected if they were part of a bow shock structure. Our near infrared observations also include a search for extended emission in the Bracket $\gamma$ (2.166 $\mu$m) and $H_{2}$ (2.122 $\mu$m) lines as possible tracers of shocked gas in the Cygnus X-3 surroundings. The results were similarly negative and the corresponding upper limits are reported.Comment: Accepted for publication in A&A; 5 pages, 4 figure

Chandra X-ray counterpart of KS 1741-293

We aim to investigate the nature of the high energy source KS 1741-293 by revisiting the radio and infrared associations proposed in the early 1990s. Our work is mostly based on the analysis of modern survey and archive data, including the NRAO, MSX, 2MASS and Chandra archives, and catalogues. We also have obtained deep CCD optical observations by ourselves. The coincidence of KS 1741-293 with an extended radio and far-infrared source, tentatively suggested in 1994, is no longer supported by modern observational data. Instead, a Chandra source is the only peculiar object found to be consistent with all high-energy error circles of KS 1741-293 and we propose it to be its most likely X-ray counterpart. We also report the existence of a non-thermal radio nebula in the vicinity of the KS 1741-293 position with the appearance of a supernova remnant. The possibility of being associated to this X-ray binary is discussed.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in Astronomy & Astrophysic

An X-ray study of the SNR G344.7-0.1 and the central object CXOU J170357.8-414302

Aims. We report results of an X-ray study of the supernova remnant (SNR) G344.7-0.1 and the point-like X-ray source located at the geometrical center of the SNR radio structure. Methods. The morphology and spectral properties of the remnant and the central X-ray point-like source were studied using data from the XMM-Newton and Chandra satellites. Archival radio data and infrared Spitzer observations at 8 and 24 $\mu$m were used to compare and study its multi-band properties at different wavelengths. Results. The XMM-Newton and Chandra observations reveal that the overall X-ray emission of G344.7-0.1 is extended and correlates very well with regions of bright radio and infrared emission. The X-ray spectrum is dominated by prominent atomic emission lines. These characteristics suggest that the X-ray emission originated in a thin thermal plasma, whose radiation is represented well by a plane-parallel shock plasma model (PSHOCK). Our study favors the scenario in which G344.7-0.1 is a 6 x 10^3 year old SNR expanding in a medium with a high density gradient and is most likely encountering a molecular cloud on the western side. In addition, we report the discovery of a soft point-like X-ray source located at the geometrical center of the radio SNR structure. The object presents some characteristics of the so-called compact central objects (CCO). However, its neutral hydrogen absorption column (N_{H}) is inconsistent with that of the SNR. Coincident with the position of the source, we found infrared and optical objects with typical early-K star characteristics. The X-ray source may be a foreground star or the CCO associated with the SNR. If this latter possibility were confirmed, the point-like source would be the farthest CCO detected so far and the eighth member of the new population of isolated and weakly magnetized neutron stars.Comment: 9 pages, 8 figures, accepted for publication in Astronomy and Astrophysics. Higher resolution figures can be seen on A&

A Verilog-A Based Fractional Frequency Synthesizer Model for Fast and Accurate Noise Assessment

This paper presents a new strategy to simulate fractional frequency synthesizer behavioral models with better performance and reduced simulation time. The models are described in Verilog-A with accurate phase noise predictions and they are based on a time jitter to power spectral density transformation of the principal noise sources in a synthesizer. The results of a fractional frequency synthesizer simulation is compared with state of the art Verilog-A descriptions showing a reduction of nearly 20 times. In addition, experimental results of a fractional frequency synthesizer are compared to the simulation results to validate the proposed model

Discovery of faint double-peak Halpha emission in the halo of low redshift galaxies

Aiming at the detection of cosmological gas being accreted onto galaxies of the local Universe, we examined the Halpha emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (\musew ) with observable Halpha (redshift < 0.42). An exhaustive screening of the corresponding Halpha images led us to select 118 reliable Halpha emitting gas clouds. The signals are faint, with a surface brightness of 10**(-17.3 pm 0.3) erg/s/cm2/arcsec2. Through statistical tests and other arguments, we ruled out that they are created by instrumental artifacts, telluric line residuals, or high redshift interlopers. Around 38% of the time, the Halpha line profile shows a double peak with the drop in intensity at the rest-frame of the central galaxy, and with a typical peak-to-peak separation of the order of pm 200 km/s. Most line emission clumps are spatially unresolved. The mass of emitting gas is estimated to be between one and 10**(-3) times the stellar mass of the central galaxy. The signals are not isotropically distributed; their azimuth tends to be aligned with the major axis of the corresponding galaxy. The distances to the central galaxies are not random either. The counts drop at a distance > 50 galaxy radii, which roughly corresponds to the virial radius of the central galaxy. We explore several physical scenarios to explain this Halpha emission, among which accretion disks around rogue intermediate mass black holes fit the observations best.Comment: pay attention to the last sentence of the abstract! Accepted for publication in Ap

Ionized and neutral gas in the peculiar star/cluster complex in NGC 6946

The characteristics of ionized and HI gas in the peculiar star/cluster complex in NGC 6946, obtained with the 6-m telescope (BTA) SAO RAS, the Gemini North telescope, and the Westerbork Synthesis Radio Telescope (WSRT), are presented. The complex is unusual as hosting a super star cluster, the most massive known in an apparently non-interacting giant galaxy. It contains a number of smaller clusters and is bordered by a sharp C-shaped rim. We found that the complex is additionally unusual in having peculiar gas kinematics. The velocity field of the ionized gas reveals a deep oval minimum, ~300 pc in size, centered 7" east of the supercluster. The Vr of the ionized gas in the dip center is 100 km/s lower than in its surroundings, and emission lines within the dip appear to be shock excited. This dip is near the center of an HI hole and a semi-ring of HII regions. The HI (and less certainly, HII) velocity fields reveal expansion, with the velocity reaching ~30 km/s at a distance about 300 pc from the center of expansion, which is near the deep minimum position. The super star cluster is at the western rim of the minimum. The sharp western rim of the whole complex is plausibly a manifestation of a regular dust arc along the complex edge. Different hypotheses about the complex and the Vr depression origins are discussed, including a HVC/dark mini-halo impact, a BCD galaxy merging, and a gas outflow due to release of energy from the supercluster stars.Comment: MN RAS, accepte

Pauli graphs when the Hilbert space dimension contains a square: why the Dedekind psi function ?

We study the commutation relations within the Pauli groups built on all decompositions of a given Hilbert space dimension $q$, containing a square, into its factors. Illustrative low dimensional examples are the quartit ($q=4$) and two-qubit ($q=2^2$) systems, the octit ($q=8$), qubit/quartit ($q=2\times 4$) and three-qubit ($q=2^3$) systems, and so on. In the single qudit case, e.g. $q=4,8,12,...$, one defines a bijection between the $\sigma (q)$ maximal commuting sets [with $\sigma[q)$ the sum of divisors of $q$] of Pauli observables and the maximal submodules of the modular ring $\mathbb{Z}_q^2$, that arrange into the projective line $P_1(\mathbb{Z}_q)$ and a independent set of size $\sigma (q)-\psi(q)$ [with $\psi(q)$ the Dedekind psi function]. In the multiple qudit case, e.g. $q=2^2, 2^3, 3^2,...$, the Pauli graphs rely on symplectic polar spaces such as the generalized quadrangles GQ(2,2) (if $q=2^2$) and GQ(3,3) (if $q=3^2$). More precisely, in dimension $p^n$ ($p$ a prime) of the Hilbert space, the observables of the Pauli group (modulo the center) are seen as the elements of the $2n$-dimensional vector space over the field $\mathbb{F}_p$. In this space, one makes use of the commutator to define a symplectic polar space $W_{2n-1}(p)$ of cardinality $\sigma(p^{2n-1})$, that encodes the maximal commuting sets of the Pauli group by its totally isotropic subspaces. Building blocks of $W_{2n-1}(p)$ are punctured polar spaces (i.e. a observable and all maximum cliques passing to it are removed) of size given by the Dedekind psi function $\psi(p^{2n-1})$. For multiple qudit mixtures (e.g. qubit/quartit, qubit/octit and so on), one finds multiple copies of polar spaces, ponctured polar spaces, hypercube geometries and other intricate structures. Such structures play a role in the science of quantum information.Comment: 18 pages, version submiited to J. Phys. A: Math. Theo