Constraints on Cold H_2 Clouds from Gravitational Microlensing Searches

It has been proposed that the Galaxy might contain a population of cold clouds in numbers sufficient to account for a substantial fraction of the total mass of the Galaxy. These clouds would have masses of the order of 10^{-3} Solar mass and sizes of the order of 10 AU. We consider here the lensing effects of such clouds on the light from background stars. A semianalytical formalism for calculation of the magnification event rate produced by such gaseous lensing is developed, taking into account the spatial distribution of the dark matter in the Galaxy, the velocity distribution of the lensing clouds and source stars, and motion of the observer. Event rates are calculated for the case of gaseous lensing of stars in the Large Magellanic Cloud and results are directly compared with the results of the search for gravitational microlensing events undertaken by the MACHO collaboration. The MACHO experiment strongly constrains the properties of the proposed molecular clouds, but does not completely rule them out. Future monitoring programs will either detect or more strongly constrain this proposed population.Comment: 36 pages, 9 figures, 1 table, typos corrected, minor change

CMB as a possible new tool to study the dark baryons in galaxies

Baryons constitute about 4% of our universe, but most of them are missing and we do not know where and in what form they are hidden. This constitute the so-called missing baryon problem. A possibility is that part of these baryons are hidden in galactic halos. We show how the 7-year data obtained by the WMAP satellite may be used to trace the halo of the nearby giant spiral galaxy M31. We detect a temperature asymmetry in the M31 halo along the rotation direction up to about 120 kpc. This could be the first detection of a galactic halo in microwaves and may open a new way to probe hidden baryons in these relatively less studied galactic objects using high accuracy CMB measurements.Comment: 8 pages, presented at the III Italian-Pakistani Workshop on Relativistic Astrophysics, Lecce, June 20-22, 2011; to be published in Journal of Physics: Conference Serie

Prevalence and Properties of Dark Matter in Elliptical Galaxies

Given the recently deduced relationship between X-ray temperatures and stellar velocity dispersions (the "T-sigma relation") in an optically complete sample of elliptical galaxies (Davis & White 1996), we demonstrate that L>L_* ellipticals contain substantial amounts of dark matter in general. We present constraints on the dark matter scale length and on the dark-to-luminous mass ratio within the optical half-light radius and within the entire galaxy. For example, we find that minimum values of dark matter core radii scale as r_dm > 4(L_V/3L_*)^{3/4}h^{-1}_80 kpc and that the minimum dark matter mass fraction is >~20% within one optical effective radius r_e and is >~39-85% within 6r_e, depending on the stellar density profile and observed value of beta_spec. We also confirm the prediction of Davis & White (1996) that the dark matter is characterized by velocity dispersions that are greater than those of the luminous stars: sigma_dm^2 ~ 1.4-2 sigma_*^2. The T-sigma relation implies a nearly constant mass-to-light ratio within six half-light radii: M/L_V ~ 25h_80 M_sun/L_V_sun. This conflicts with the simplest extension of CDM theories of large scale structure formation to galactic scales; we consider a couple of modifications which can better account for the observed T-sigma relation.Comment: 27 pages AASTeX; 15 PostScript figures; to appear in Ap

XMM-Newton observation of MACHO 104.20906.960: a dwarf nova candidate with a 2 h period

The binaries known as cataclysmic variables are particular binary systems in which the primary star (a white dwarf) accretes material from a secondary via Roche-lobe mechanism. Usually, these objects have orbital period of a few hours so that a detailed temporal analysis can be performed. Here, we present Chandra ${\it XMM}$-Newton observations of a dwarf nova candidate identified in the past by optical observations towards the galactic Bulge and labeled as MACHO 104.20906.960. After a spectral analysis, we used the Lomb-Scargle technique for the period search and evaluated the confidence level using Monte-Carlo simulations. In this case, we found that the $X$-ray source shows a period of $2.03_{-0.07}^{+0.09}$ hours (3$\sigma$ error) so that it is most likely a system of interacting objects. The modulation of the signal was found with a confidence level of $>$99%. The spectrum can be described by a two thermal plasma components with X-ray flux in the 0.3--10 keV energy band of $1.77_{-0.19}^{+0.16}\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$. We find that the distance of the source is approximately 1 kpc thus corresponding to a luminosity $L_{X}\simeq 2\times 10^{31}$ erg s$^{-1}$.Comment: 2008, in press on New Astronomy, (http://www.elsevier.com/wps/find/journaldescription.cws_home/601274/description#description); XMM-Newton observation of MACHO 104.20906.960: a dwarf nova candidate with a 2 h perio

Estimating the parameters of the Sgr A* black hole

The measurement of relativistic effects around the galactic center may allow in the near future to strongly constrain the parameters of the supermassive black hole likely present at the galactic center (Sgr A*). As a by-product of these measurements it would be possible to severely constrain, in addition, also the parameters of the mass-density distributions of both the innermost star cluster and the dark matter clump around the galactic center.Comment: Accepted for publication on General Relativity and Gravitation, 2010. 11 Pages, 1 Figur

Probing the mass function of halo dark matter via microlensing

The simplest interpretation of the microlensing events observed towards the Large Magellanic Clouds is that approximately half of the mass of the Milky Way halo is in the form of MAssive Compact Halo Objects with $M \sim 0.5 M_{\odot}$. It is not possible, due to limits from star counts and chemical abundance arguments, for faint stars or white dwarves to comprise such a large fraction of the halo mass. This leads to the consideration of more exotic lens candidates, such as primordial black holes, or alternative lens locations. If the lenses are located in the halo of the Milky Way, then constraining their mass function will shed light on their nature. Using the current microlensing data we find, for four halo models, the best fit parameters for delta-function, primordial black hole and various power law mass functions. The best fit primordial black hole mass functions, despite having significant finite width, have likelihoods which are similar to, and for one particular halo model greater than, those of the best fit delta functions . We then use Monte Carlo simulations to investigate the number of microlensing events necessary to determine whether the MACHO mass function has significant finite width. If the correct halo model is known, then $\sim$ 500 microlensing events will be sufficient, and will also allow determination of the mass function parameters to $\sim 5$.Comment: 28 pages including 14 figures, version to appear in ApJ, minor changes to discussio

The X-ray eclipse of the dwarf nova HT CAS observed by the XMM-Newton satellite: spectral and timing analysis

A cataclysmic variable is a binary system consisting of a white dwarf that accretes material from a secondary object via the Roche-lobe mechanism. In the case of long enough observation, a detailed temporal analysis can be performed, allowing the physical properties of the binary system to be determined. We present an XMM-Newton observation of the dwarf nova HT Cas acquired to resolve the binary system eclipses and constrain the origin of the X-rays observed. We also compare our results with previous ROSAT and ASCA data. After the spectral analysis of the three EPIC camera signals, the observed X-ray light curve was studied with well known techniques and the eclipse contact points obtained. The X-ray spectrum can be described by thermal bremsstrahlung of temperature $kT_1=6.89 \pm 0.23$ keV plus a black-body component (upper limit) with temperature $kT_2=30_{-6}^{+8}$ eV. Neglecting the black-body, the bolometric absorption corrected flux is $F^{\rm{Bol}}=(6.5\pm 0.1)\times10^{-12}$ erg s$^{-1}$ cm$^{-2}$, which, for a distance of HT Cas of 131 pc, corresponds to a bolometric luminosity of $(1.33\pm 0.02)\times10^{31}$ erg s$^{-1}$. The study of the eclipse in the EPIC light curve permits us to constrain the size and location of the X-ray emitting region, which turns out to be close to the white dwarf radius. We measure an X-ray eclipse somewhat smaller (but only at a level of $\simeq 1.5 \sigma$) than the corresponding optical one. If this is the case, we have possibly identified the signature of either high latitude emission or a layer of X-ray emitting material partially obscured by an accretion disk.Comment: Accepted for publication on Astronomy and Astrophysics, 200

General Relativistic Electromagnetic Fields of a Slowly Rotating Magnetized Neutron Star. I. Formulation of the equations

We present analytic solutions of Maxwell equations in the internal and external background spacetime of a slowly rotating magnetized neutron star. The star is considered isolated and in vacuum, with a dipolar magnetic field not aligned with the axis of rotation. With respect to a flat spacetime solution, general relativity introduces corrections related both to the monopolar and the dipolar parts of the gravitational field. In particular, we show that in the case of infinite electrical conductivity general relativistic corrections due to the dragging of reference frames are present, but only in the expression for the electric field. In the case of finite electrical conductivity, however, corrections due both to the spacetime curvature and to the dragging of reference frames are shown to be present in the induction equation. These corrections could be relevant for the evolution of the magnetic fields of pulsars and magnetars. The solutions found, while obtained through some simplifying assumption, reflect a rather general physical configuration and could therefore be used in a variety of astrophysical situations.Comment: A few typos corrected; matches the versions in MNRA

Epithelial–mesenchymal transition in an EcPV2-positive vulvar squamous cell carcinoma of a mare

BackgroundVulvar squamous cell carcinoma (VSCC) has been recently associated with Equus caballus papillomavirus type 2 (EcPV2) infection. Still, few reports concerning this disease are present in the literature. ObjectiveTo describe a case of naturally occurring EcPV2-induced VSCC, by investigating tumour ability in undergoing the epithelial-to-mesenchymal transition (EMT). Study designCase report. MethodsA 13-year-old Haflinger mare was referred for a rapidly growing vulvar mass. After surgical excision, the mass was submitted to histopathology and molecular analysis. Histopathological diagnosis was consistent with a VSCC. Real-time qPCR, real-time reverse transcriptase (RT)-qPCR and RNAscope were carried out to detect EcPV2 infection and to evaluate E6/E7 oncogenes expression. To highlight the EMT, immunohistochemistry (IHC) was performed. Expression of EMT-related and innate immunity-related genes was investigated through RT-qPCR. ResultsReal-time qPCR, RT-qPCR and RNAscope confirmed EcPV2 DNA presence and expression of EcPV2 oncoproteins (E6 and E7) within the neoplastic vulvar lesion. IHC highlighted a cadherin switch together with the expression of the EMT-related transcription factor HIF1 & alpha;. With RT-qPCR, significantly increased gene expression of EBI3 (45.0 & PLUSMN; 1.62, p < 0.01), CDH2 (2445.3 & PLUSMN; 0.39, p < 0.001), CXCL8 (288.7 & PLUSMN; 0.40, p < 0.001) and decreased gene expression of CDH1 (0.3 & PLUSMN; 0.57, p < 0.05), IL12A (0.04 & PLUSMN; 1.06, p < 0.01) and IL17 (0.2 & PLUSMN; 0.64, p < 0.05) were detected. Main limitationsLack of ability to generalise and danger of over-interpretation. ConclusionThe results obtained were suggestive of an EMT event occurring within the neoplastic lesion

XMM-Newton and Swift observations of WZ Sge: spectral and timing analysis

WZ Sagittae is the prototype object of a subclass of dwarf novae, with rare and long (super)outbursts, in which a white dwarf primary accretes matter from a low mass companion. High-energy observations offer the possibility of a better understanding of the disk-accretion mechanism in WZ Sge-like binaries. We used archival XMM-Newton and Swift data to characterize the X-ray spectral and temporal properties of WZ Sge in quiescence. We performed a detailed timing analysis of the simultaneous X-ray and UV light curves obtained with the EPIC and OM instruments on board XMM-Newton in 2003. We employed several techniques in this study, including a correlation study between the two curves. We also performed an X-ray spectral analysis using the EPIC data, as well as Swift/XRT data obtained in 2011. We find that the X-ray intensity is clearly modulated at a period of about 28.96 s, confirming previously published preliminary results. We find that the X-ray spectral shape of WZ Sge remains practically unchanged between the XMM-Newton and Swift observations. However, after correcting for inter-stellar absorption, the intrinsic luminosity is estimated to be about 2.65X10^ 30 erg/s/cm^2 and 1.57X10^30 erg/s/cm^2 in 2003 and 2011, respectively. During the Swift/XRT observation, the observed flux is a factor of about 2 lower than that observed by XMM-Newton, but is similar to the quiescent levels observed various times before the 2001 outburst.Comment: Accepted for publication on A&A.10 pages, 9 figure