XMM-Newton observations of the Coma cluster relic 1253+275

Using XMM Newton data, we investigate the nature of the X-ray emission in the radio relic 1253+275 in the Coma cluster. We determine the conditions of the cluster gas to check current models of relic formation, and we set constraints on the intracluster magnetic field. Both imaging and spectral analysis are performed, and the X-ray emission is compared with the radio emission. We found that the emission is of thermal origin and is connected to the sub-group around NGC 4839. The best-fit gas temperature in the region of the relic and in its vicinity is in the range 2.8 - 4.0 keV, comparable to the temperature of the NGC 4839 sub-group. We do not detect any high temperature gas, resulting from a possible shock in the region of the Coma relic. We therefore suggest that the main source of energy for particles radiating in the radio relic is likely to be turbulence. From the X-ray data, we can also set a flux upper limit of 3.2 x 10e-13 erg/cm^2 s, in the 0.3 - 10 keV energy range, to the non-thermal emission in the relic region. This leads to a magnetic field B > 1.05 microG.Comment: 4 pages, 2 figures, Accepted for publication in A&A Letter

The XMM-Newton Ω\Omega Project

The abundance of high-redshift galaxy clusters depends sensitively on the matter density \OmM and, to a lesser extent, on the cosmological constant $\Lambda$. Measurements of this abundance therefore constrain these fundamental cosmological parameters, and in a manner independent and complementary to other methods, such as observations of the cosmic microwave background and distance measurements. Cluster abundance is best measured by the X-ray temperature function, as opposed to luminosity, because temperature and mass are tightly correlated, as demonstrated by numerical simulations. Taking advantage of the sensitivity of XMM-Newton, our Guaranteed Time program aims at measuring the temperature of the highest redshift (z>0.4) SHARC clusters, with the ultimate goal of constraining both \OmM and $\Lambda$.Comment: To appear in the Proceedings of the XXI Moriond Conference: Galaxy Clusters and the High Redshift Universe Observed in X-rays, edited by D. Neumann, F. Durret, & J. Tran Thanh Va

Looking for reference genes for real-time quantitative PCR experiments in Rhodnius prolixus (Hemiptera: Reduviidae)

Abstract Quantitative real-time PCR (qPCR) has become one of the most used techniques to measure gene expression. However, normalization of gene expression data against reference genes is essential, although these are usually used without any kind of validation. The expression of seven genes was compared in organs of Rhodnius prolixus under diverse conditions, using published software to test gene expression stability. Rp18S and elongation factor 1 (RpEF -1) were the most reliable genes for normalization in qPCR when gene expression in different organs was compared. Moreover, both genes were found to be the best references when transcript levels were compared in the posterior midgut of insects infected with Trypanosoma cruzi. Rp18S was also the best reference gene in the fat bodies of unfed and fed insects. By contrast, RpEF-1 was found to be the best reference gene for comparison between posterior midguts, and RpMIP or RpActin should be used to compare gene expression in the ovaries. Although Rp18S is indicated here as the best reference in most cases, reports from the literature show that it is difficult to find an optimum reference gene. Nevertheless, validation of candidate genes to be taken as references is important when new experimental conditions are tested to avoid incorrect data interpretation

The distant galaxy cluster CL0016+16: X-ray analysis up to R200R_{200}

To study the mass distribution of galaxy clusters up to their Virial radius, CL0016+16 seems to be a good candidate,since it is a bright massive cluster, previously considered as being dynamically relaxed. Using XMM-Newton observations of CL0016+16, we performed a careful X-ray background analysis, and we detected convincingly its X-ray emission up to $R_{200}$. We then studied its dynamical state with a detailed 2D temperature and surface brightness analysis of the inner part of the cluster. Using the assumption of both spherical symmetry and hydrostatic equilibrium (HE) we can determine the main cluster parameters: total mass, temperature profile, surface brightness profile and $\beta$-parameter. We also build a temperature map which clearly exhibits departure from spherical symmetry in the centre. To estimate the influence of these perturbations onto our total mass estimate, we also compute the total mass in the framework of the HE approach, but this time with various temperature profiles obtained in different directions. These various total mass estimates are consistent with each other. The temperature perturbations are clear signatures of ongoing merger activity. We also find significant residuals after subtracting the emissivity map by a 2D $\beta$-model fit. We conclude that, although CL0016+16 shows clear signs of merger activity and departure from spherical symmetry in the centre, its X-ray emissivity can be detected up to $R_{200}$ and the corresponding mass $M_{200}$ can be computed directly. It is therefore a good candidate to study cosmological scaling laws as predicted by the theory.Comment: 11 pages, 17 figures, Accepted for publication in A&

Measuring Cluster Temperature Profiles with XMM/EPIC

Using the PV observation of A1795, we illustrate the capability of XMM-EPIC to measure cluster temperature profiles, a key ingredient for the determination of cluster mass profiles through the equation of hydrostatic equilibrium. We develop a methodology for spatially resolved spectroscopy of extended sources, adapted to XMM background and vignetting characteristics. The effect of the particle induced background is discussed. A simple unbiased method is proposed to correct for vignetting effects, in which every photon is weighted according to its energy and location on the detector. We were able to derive the temperature profile of A1795 up to 0.4 times the virial radius. A significant and spatially resolved drop in temperature towards the center (r<200 kpc) is observed, which corresponds to the cooling flow region of the cluster. Beyond that region, the temperature is constant with no indication of a fall-off at large radii out to 1.2 Mpc.Comment: 7 pages, 8 figures, Accepted for publication in A&A (special Letter issue on XMM

Spatially resolved X-ray spectroscopy and modeling of the nonthermal emission of the PWN in G0.9+0.1

We performed a spatially resolved spectral X-ray study of the pulsar wind nebula (PWN) in the supernova remnant G0.9+0.1. Furthermore we modeled its nonthermal emission in the X-ray and very high energy (VHE, E > 100 GeV) gamma-ray regime. Using Chandra ACIS-S3 data, we investigated the east-west dependence of the spectral properties of G0.9+0.1 by calculating hardness ratios. We analyzed the EPIC-MOS and EPIC-pn data of two on-axis observations of the XMM-Newton telescope and extracted spectra of four annulus-shaped regions, centered on the region of brightest emission of the source. A radially symmetric leptonic model was applied in order to reproduce the observed X-ray emission of the inner part of the PWN. Using the optimized model parameter values obtained from the X-ray analysis, we then compared the modeled inverse Compton (IC) radiation with the published H.E.S.S. gamma-ray data. The spectral index within the four annuli increases with growing distance to the pulsar, whereas the surface brightness drops. With the adopted model we are able to reproduce the characteristics of the X-ray spectra. The model results for the VHE gamma radiation, however, strongly deviate from the H.E.S.S. data.Comment: 8 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Serotonin regulates an acyl-CoA-binding protein (ACBP) gene expression in the midgut of Rhodnius prolixus

Abstract Acyl-CoA esters have many intracellular functions, acting as energy source, substrate for metabolic processes and taking part in cell signaling. The acyl-CoA-binding protein (ACBP), a highly conserved 10 kDa intracellular protein, binds long- and medium-chain acyl-CoA esters with very high affinity, directing them to specific metabolic routes and protecting them from hydrolysis. An ACBP gene sequence was identified in the genome of Rhodnius prolixus. This ACBP gene (RpACBP-1) was expressed in all analyzed tissues and quantitative PCR showed that expression was highest in posterior midgut. In this tissue, ACBP gene expression increased in the first day after blood meal (∼10-fold) and then decreased to unfed levels in the seventh day after meal. Injection of serotonin (5-hydroxytryptamine; 5-HT), a neuroamine released in the hemolymph after the start of feeding, increased the expression of this gene in the midgut of unfed females, reaching levels similar to those observed in fed insects. This effect of injected 5-HT was inhibited by spiperone, an antagonist of 5-HT mammalian receptors, that was also able to block the physiological increase in RpACBP-1 expression observed after feeding. Injection of cholera toxin or dibutyryl-cAMP also resulted in the stimulation of this gene expression. These data reveal a transcriptional regulatory mechanism in R. prolixus, that is triggered by 5-HT. In this way, a novel role for 5-HT is proposed, as a regulator of ACBP gene expression and, consequently, taking part in the control of lipid metabolism

XMM-Newton spectral analysis of the Pulsar Wind Nebula within the composite SNR G0.9+0.1

We present a study of the composite supernova remnant G0.9+0.1 based on observations by XMM-Newton. The EPIC spectrum shows diffuse X-ray emission from the region corresponding to the radio shell. The X-ray spectrum of the whole Pulsar Wind Nebula is well fitted by an absorbed power-law model with a photon index Gamma ~ 1.9 and a 2-10 keV luminosity of about 6.5 X 10^34 d^2_10 erg s^-1 (d_10 is the distance in units of 10 kpc). However, there is a clear softening of the X-ray spectrum with distance from the core, which is most probably related to the finite lifetime of the synchrotron emitting electrons. This is fully consistent with the plerionic interpretation of the Pulsar Wind Nebula, in which an embedded pulsar injects energetic electrons into its surrounding region. At smaller scales, the eastern part of the arc-like feature, which was first revealed by Chandra observations, shows indications of a hard X-ray spectrum with a corresponding small photon index (Gamma=1.0 +- 0.7), while the western part presents a significantly softer spectrum (Gamma=3.2 +- 0.7). A possible explanation for this feature is fast rotation and subsequent Doppler boosting of electrons: the eastern part of the torus has a velocity component pointing towards the observer, while the western part has a velocity component in the opposite direction pointing away from the observer.Comment: 8 pages, 7 figures, A&A in pres

RXJ0256.5+0006: a merging cluster of galaxies at z=0.36 observed with XMM-Newton

(abridged) We present a study based on XMM data of RX J0256.5+0006, a medium distant (z=0.36) galaxy cluster found in the Bright SHARC catalog. The intracluster medium shows a bimodal structure: one main cluster component and a substructure in the west. Despite the indication of interaction we do not find any sign of temperature gradients. Due to the non-symmetric form of the main cluster we extract surface brightness profiles in different sectors around its centre. We see large variations between the profiles, which we quantify by beta-model fitting. The corresponding r_c's vary between 0.1-0.5Mpc and the beta's between 0.5-1.2. The variations of the beta-model parameters indicate that the main cluster is not entirely relaxed. This hypothesis is strengthened by the fact that the cluster is over-luminous with respect to the (z-evolving) L_x-T relation found for nearby clusters. Comparing our profiles to the reference emission measure profile of Arnaud et al., we find that only the profile extracted north-east (NE) of the main cluster centre is similar to this reference profile. This indicates that only the NE profile is representative for the relaxed part of this cluster component. Using this profile and the spectroscopically fitted temperature of T=4.9^+0.5_-0.4keV we find M_500~4 10^14 solar masses. This value is in agreement with the value obtained using the z-evolving M_500-T relation from the HIFLUGCS sample. For the gas mass fraction we find f_g~18-20% which is in good agreement with other work. We also develop a simple on-axis merger model for the cluster. Together with a simple ram pressure model we find that the most likely physical distance of the subcluster to the main cluster lies between 0.6<d<1.0Mpc. We find for the ratio of subcluster to main cluster mass values between 20-30%.Comment: 19 pages including 19 figures (including 4 figures in jpg and png format), accepted for publication in A&