Spectral variability in Swift and Chandra observations of the Ultraluminous source NGC 55 ULX1

NGC 55 ULX1 is a bright Ultraluminous X-ray source located 1.78 Mpc away. We analysed a sample of 20 Swift observations, taken between 2013 April and August, and two Chandra observations taken in 2001 September and 2004 June. We found only marginal hints of a limited number of dips in the light curve, previously reported to occur in this source, although the uncertainties due to the low counting statistics of the data are large. The Chandra and Swift spectra showed clearly spectral variability which resembles those observed in other ULXs. We can account for this spectral variability in terms of changes in both the normalization and intrinsic column density of a two-components model consisting of a blackbody (for the soft component) and a multicolour accretion disc (for the hard component). We discuss the possibility that strong outflows ejected by the disc are in part responsible for such spectral changes.Comment: 9 pages, 6 figure; accepted to be published on MNRA

SARCS strong lensing galaxy groups: I - optical, weak lensing, and scaling laws

We present the weak lensing and optical analysis of the SL2S-ARCS (SARCS) sample of strong lens candidates. The sample is based on the Strong Lensing Legacy Survey (SL2S), a systematic search of strong lensing systems in the photometric Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The SARCS sample focuses on arc-like features and is designed to contain mostly galaxy groups. We briefly present the weak lensing methodology that we use to estimate the mass of the SARCS objects. Among 126 candidates, we obtain a weak lensing detection for 89 objects with velocity dispersions of the Singular Isothermal Sphere mass model ranging from 350 to 1000 km/s with an average value of 600km/s, corresponding to a rich galaxy group (or poor cluster). From the galaxies belonging to the bright end of the group's red sequence (M_i<-21), we derive the optical properties of the SARCS candidates. We obtain typical richnesses of N=5-15 galaxies and optical luminosities of L=0.5-1.5e+12 Lsol (within a radius of 0.5 Mpc). We use these galaxies to compute luminosity density maps, from which a morphological classification reveals that a large fraction of the sample are groups with a complex light distribution, either elliptical or multimodal, suggesting that these objects are dynamically young structures. We finally combine the lensing and optical analyses to draw a sample of 80 most secure group candidates, i.e. weak lensing detection and over-density at the lens position in the luminosity map, to remove false detections and galaxy-scale systems from the initial sample. We use this reduced sample to probe the optical scaling relations in combination with a sample of massive galaxy clusters. We detect the expected correlations over the probed range in mass with a typical scatter of 25% in the SIS velocity dispersion at a given richness or luminosity, making these scaling laws interesting mass proxie

Viabilidade econômica da produção agroecológica de hortaliças no Sistema de Produção Agroecológica Integrada e Sustentável (PAIS) em Juti, Mato Grosso do Sul.

Publicado também na: Revista Brasileira de Agroecologia, v. 6. n. 2, dez. 2011

The Brightest Cluster Galaxy in Abell 85: The Largest Core Known so far

We have found that the brightest cluster galaxy (BCG) in Abell~85, Holm 15A, displays the largest core so far known. Its cusp radius, $r_{\gamma} = 4.57 \pm 0.06$ kpc ($4.26^{\prime\prime}\pm 0.06^{\prime\prime}$), is more than 18 times larger than the mean for BCGs, and $\geq1$ kpc larger than A2261-BCG, hitherto the largest-cored BCG (Postman, Lauer, Donahue, et al. 2012) Holm 15A hosts the luminous amorphous radio source 0039-095B and has the optical signature of a LINER. Scaling laws indicate that this core could host a supermassive black hole (SMBH) of mass $M_{\bullet}\thicksim (10^{9}-10^{11})\,M_{\odot}$. We suggest that cores this large represent a relatively short phase in the evolution of BCGs, whereas the masses of their associated SBMH might be set by initial conditions.Comment: 14 pages, 3 figure, 2 tables, accepted for publication in ApJ Letters on October 6th, 2014, replacement of previous manuscript submitted on May 30th, 2014 to astro-p

Dark matter-baryons separation at the lowest mass scale: the Bullet Group

We report on the X-ray observation of a strong lensing selected group, SL2S J08544-0121, with a total mass of $2.4 \pm 0.6 \times 10^{14}$ $\rm{M_\odot}$ which revealed a separation of $124\pm20$ kpc between the X-ray emitting collisional gas and the collisionless galaxies and dark matter (DM), traced by strong lensing. This source allows to put an order of magnitude estimate to the upper limit to the interaction cross section of DM of 10 cm$^2$ g$^{-1}$. It is the lowest mass object found to date showing a DM-baryons separation and it reveals that the detection of bullet-like objects is not rare and confined to mergers of massive objects opening the possibility of a statistical detection of DM-baryons separation with future surveys.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letters. Typos correcte

The Use of Sonic Frequencies as a Cleaning Agent of Specimens to be Observed by Scanning Electron Microscopy

The presence of mucus and/or cellular debris can obscure the fine morphology of the gastrointestinal or respiratory luminal surface, when observed by scanning electron microscopy. With the intent of obtaining a good cleaning of the mucosal surface without altering the ultrafine morphology of epithelial cells, a new model of sonicator/ultrasonicator is presented. The instrument is supplied with a control system for wave frequency, amplitude and form, and permits a precise regulation of the wave energy. With this instrument it is possible to produce a cleaning effect by using any kind of frequency (either sonic or ultrasonic) and/or amplitude and/or waveform and/or liquid. We report the application of sonic frequencies through water as a fluid for immersion to obtain a gentle and slow removing of mucus and in order to explore the possibility to clean hydrated tissues. With the employment of sonic frequencies (from 5 to 15 kHz modulated by 200 Hz) and water as the immersion fluid, we were able to generate a gentle wave energy which effected an optimal removal of the mucus, with the consequent exposure of a well preserved epithelial surface of rat trachea and small intestine

Cellulose production is coupled to sensing of the pyrimidine biosynthetic pathway via c-di-GMP production by the DgcQ protein of Escherichia coli

Production of cellulose, a stress response-mediated process in enterobacteria, is modulated in Escherichia coli by the activity of the two pyrimidine nucleotide biosynthetic pathways, namely, the de novo biosynthetic pathway and the salvage pathway, which relies on the environmental availability of pyrimidine nitrogenous bases. We had previously reported that prevalence of the salvage over the de novo pathway triggers cellulose production via synthesis of the second messenger c-di-GMP by the DgcQ (YedQ) diguanylate cyclase. In this work, we show that DgcQ enzymatic activity is enhanced by UTP, whilst being inhibited by N-carbamoyl-aspartate, an intermediate of the de novo pathway. Thus, direct allosteric control by these ligands allows full DgcQ activity exclusively in cells actively synthesizing pyrimidine nucleotides via the salvage pathway. Inhibition of DgcQ activity by N-carbamoyl-aspartate appears to be favoured by protein-protein interaction between DgcQ and PyrB, a subunit of aspartate transcarbamylase, which synthesizes N-carbamoyl-aspartate. Our results suggest that availability of pyrimidine bases might be sensed, somehow paradoxically, as an environmental stress by E. coli. We hypothesize that this link might have evolved since stress events, leading to extensive DNA/RNA degradation or lysis of neighbouring cells, can result in increased pyrimidine concentrations and activation of the salvage pathway

Characterizing SL2S galaxy groups using the Einstein radius

We analyzed the Einstein radius, $\theta_E$, in our sample of SL2S galaxy groups, and compared it with $R_A$ (the distance from the arcs to the center of the lens), using three different approaches: 1.- the velocity dispersion obtained from weak lensing assuming a Singular Isothermal Sphere profile ($\theta_{E,I}$), 2.- a strong lensing analytical method ($\theta_{E,II}$) combined with a velocity dispersion-concentration relation derived from numerical simulations designed to mimic our group sample, 3.- strong lensing modeling ($\theta_{E,III}$) of eleven groups (with four new models presented in this work) using HST and CFHT images. Finally, $R_A$ was analyzed as a function of redshift $z$ to investigate possible correlations with L, N, and the richness-to-luminosity ratio (N/L). We found a correlation between $\theta_{E}$ and $R_A$, but with large scatter. We estimate $\theta_{E,I}$ = (2.2 $\pm$ 0.9) + (0.7 $\pm$ 0.2)$R_A$, $\theta_{E,II}$ = (0.4 $\pm$ 1.5) + (1.1 $\pm$ 0.4)$R_A$, and $\theta_{E,III}$ = (0.4 $\pm$ 1.5) + (0.9 $\pm$ 0.3)$R_A$ for each method respectively. We found a weak evidence of anti-correlation between $R_A$ and $z$, with Log$R_A$ = (0.58$\pm$0.06) - (0.04$\pm$0.1)$z$, suggesting a possible evolution of the Einstein radius with $z$, as reported previously by other authors. Our results also show that $R_A$ is correlated with L and N (more luminous and richer groups have greater $R_A$), and a possible correlation between $R_A$ and the N/L ratio. Our analysis indicates that $R_A$ is correlated with $\theta_E$ in our sample, making $R_A$ useful to characterize properties like L and N (and possible N/L) in galaxy groups. Additionally, we present evidence suggesting that the Einstein radius evolves with $z$.Comment: Accepted for publication in Astronomy & Astrophysics. Typos correcte