A search for evidence of irradiation in Centaurus X-4 during quiescence

We present a study of the neutron star X-Ray Transient Cen X-4. Our aim is to look for any evidence of irradiation of the companion with a detailed analysis of its radial velocity curve, relative contribution of the donor star and Doppler tomography of the main emission lines. To improve our study all our data are compared with a set of simulations that consider different physical parameters of the system, like the disc aperture angle and the mass ratio. We conclude that neither the radial velocity curve nor the orbital variation of the relative donor's contribution to the total flux are affected by irradiation. On the other hand, we do see emission from the donor star at H${\alpha}$ and HeI 5876 which we tentatively attribute to irradiation effects. In particular, the H${\alpha}$ emission from the companion is clearly asymmetric and we suggest is produced by irradiation from the hot-spot. Finally, from the velocity of the HeI 5876 spot we constrain the disc opening angle to alpha=7-14 deg.Comment: 4 pages, 5 figures, accepted for publication in A&A as a R

Deciphering the large-scale environment of radio galaxies in the local Universe: where do they born, grow and die?

The role played by the large-scale environment on the nuclear activity of radio galaxies (RGs), is still not completely understood. Accretion mode, jet power and galaxy evolution are connected with their large-scale environment from tens to hundreds of kpc. Here we present a detailed, statistical, analysis of the large-scale environment for two samples of RGs up to redshifts $z_\mathrm{src}$=0.15. The main advantages of our study, with respect to those already present in the literature, are due to the extremely homogeneous selection criteria of catalogs adopted to perform our investigation. This is also coupled with the use of several clustering algorithms. We performed a direct search of galaxy-rich environments around RGs using them as beacon. To perform this study we also developed a new method that does not appear to suffer by a strong $z_\mathrm{src}$ dependence as other algorithms. We conclude that, despite their radio morphological (FR\,I $vs$ FR\,II) and/or their optical (HERG $vs$ LERG) classification, RGs in the local Universe tend to live in galaxy-rich large-scale environments having similar characteristics and richness. We highlight that the fraction of FR\,Is-LERG, inhabiting galaxy rich environments, appears larger than that of FR\,IIs-LERG. We also found that 5 out of 7 FR\,II-HERGs, with $z_\mathrm{src}\leq$0.11, lie in groups/clusters of galaxies. However, we recognize that, despite the high level of completeness of our catalogs, when restricting to the local Universe, the low number of HERGs ($\sim$10\% of the total FR\,IIs investigated) prevent us to make a strong statistical conclusion about this source class.Comment: 21 pages, 25 figures, accepted for publication on the Astrophysical Journal Supplement Series - pre-proof versio

Discovery of a Cyclotron Resonance Scattering Feature in the X-ray Spectrum of XTE J1946+274

Observations of the transient accreting pulsar XTE J1946+274 made with the Rossi X-ray Timing Explorer during the course of the 1998 September-November outburst, reveal a cyclotron resonance scattering feature (or "cyclotron line") in the hard X-ray spectrum near 35 keV. We determine a centroid energy of 36.2 +0.5/-0.7 keV, which implies a magnetic field strength of 3.1(1+z)x10^12 G, where z is the gravitational redshift of the scattering region. The optical depth, Tau = 0.33 +0.07/-0.06, and width, sigma = 3.37 +0.92/-0.75 keV, are typical of known cyclotron lines in other pulsars. This discovery makes XTE J1946+274 one of thirteen pulsars with securely detected cyclotron lines resulting in direct magnetic field measurements.Comment: Five pages including four postscript figures and two tables. Uses emulateapj5. Published in ApJ Letters: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...563L..35

Quiescent Thermal Emission from the Neutron Star in Aql X-1

We report on the quiescent spectrum measured with Chandra/ACIS-S of the transient, type-I X-ray bursting neutron star Aql X-1, immediately following an accretion outburst. The neutron star radius, assuming a pure hydrogen atmosphere and hard power-law spectrum, is $R_\infty$=13.4{+5}{-4} (d/5 \kpc) km. Based on the historical outburst record of RXTE/ASM, the quiescent luminosity is consistent with that predicted by Brown, Bildsten and Rutledge from deep crustal heating, lending support to this theory for providing a minimum quiescent luminosity of transient neutron stars. While not required by the data, the hard power-law component can account for 18+/-8% of the 0.5-10 keV thermal flux. Short-timescale intensity variability during this observation is less than 15% rms (3 sigma; 0.0001-1 Hz, 0.2-8 keV). Comparison between the Chandra spectrum and three X-ray spectral observations made between Oct 1992 and Oct 1996 find all spectra consistent with a pure H atmosphere, but with temperatures ranging from 145--168 eV, spanning a factor of 1.87+/-0.21 in observed flux. The source of variability in the quiescent luminosity on long timescales (greater than years) remains a puzzle. If from accretion, then it remains to be explained why the quiescent accretion rate provides a luminosity so nearly equal to that from deep crustal heating.Comment: 15 pages, 1 figure, 2 tables; ApJ, accepte

The BMW Deep X-ray Cluster Survey

We briefly describe the main features of the Brera Multi-Wavelet (BMW) survey of serendipitous X-ray clusters, based on the still unexploited ROSAT-HRI archival observations. Cluster candidates are selected from the general BMW catalogue of 20,000 sources based exclusively on their X-ray extension. Contrary to common wisdom, a clever selection of the HRI energy channels allows us to significantly reduce the background noise, thus greatly improving the ability to detect low surface-brightness sources as clusters. The resulting sample of ~250 candidates shows a very good sky coverage down to a flux \~3x10^-14 erg/s/cm^2 ([0.5-2.0] keV band), i.e comparable to existing PSPC-based deep survey, with a particularly interesting area of ~100 sq.deg. around fluxes ~10^-13 erg/s/cm^2, i.e. where highly-luminous, rare systems at z~0.6-1 can be detected. At the same time, the superior angular resolution of the instrument should avoid biases against intrinsically small systems, while easing the identification process (e.g. by spotting blends and AGN contaminants). While about 20% of the candidates are already identified with groups/clusters at z<0.3 on the DSS2 images, we have started a deep CCD imaging campaign to observe all sources associated to "blank fields". First results from these observations reveal a distant (z>0.5) bonafide cluster counterpart for ~80% of the targets.Comment: 3 pages, 2 figures; to appear in Proc. of the ESO/ECF/STSCI workshop on "Deep Fields", Garching Oct 2000, (Publ: Springer

On the "spin-freezing" mechanism in underdoped superconducting cuprates

The letter deals with the spin-freezing process observed by means of NMR-NQR relaxation or by muon spin rotation in underdoped cuprate superconductors. This phenomenon, sometimes referred as coexistence of antiferromagnetic and superconducting order parameters, is generally thought to result from randomly distributed magnetic moments related to charge inhomogeneities (possibly stripes) which exhibit slowing down of their fluctuations on cooling below T$_c$ . Instead, we describe the experimental findings as due to fluctuating, vortex-antivortex, orbital currents state coexisting with d-wave superconducting state. A direct explanation of the experimental results, in underdoped Y$_{1-x}$Ca$_x$Ba$_2$Cu$_3$O$_{6.1}$ and La$_{2-x}$Sr$$CuO$_4$, is thus given in terms of freezing of orbital current fluctuations

The Quiescent Optical and Infrared Counterpart to EXO 0748-676 = UY Vol

We present optical and infrared photometry of the low-mass X-ray binary EXO 0748-676 in quiescence for the first time in 24 years since it became X-ray active in 1985. We find the counterpart at average magnitudes of R=22.4 and J=21.3. We monitored the source approximately nightly through 2008 November to 2009 January. During this time there was considerable night-to-night optical variability but no long term trends were apparent. The night-to-night variability reveals a periodicity of P=0.159331+/-0.000012d, consistent with the X-ray orbital period to within 0.01%. This indicates that the quiescent optical modulation is indeed orbital in nature rather than a superhump. Interestingly, the modulation remains single-peaked with a deep minimum coincident with the times of X-ray eclipse, and there is no indication of a double-peaked ellipsoidal modulation. This indicates that even in `quiescence' emission from the accretion disk and/or X-ray heated inner face of the companion star dominate the optical emission, and implies that obtaining an accurate dynamical mass estimate in quiescence will be challenging.Comment: Accepted for publication by the Astrophysical Journal Letter

Lagrangian fibrations of holomorphic-symplectic varieties of K3^[n]-type

Let X be a compact Kahler holomorphic-symplectic manifold, which is deformation equivalent to the Hilbert scheme of length n subschemes of a K3 surface. Let L be a nef line-bundle on X, such that the 2n-th power of c_1(L) vanishes and c_1(L) is primitive. Assume that the two dimensional subspace H^{2,0}(X) + H^{0,2}(X), of the second cohomology of X with complex coefficients, intersects trivially the integral cohomology. We prove that the linear system of L is base point free and it induces a Lagrangian fibration on X. In particular, the line-bundle L is effective. A determination of the semi-group of effective divisor classes on X follows, when X is projective. For a generic such pair (X,L), not necessarily projective, we show that X is bimeromorphic to a Tate-Shafarevich twist of a moduli space of stable torsion sheaves, each with pure one dimensional support, on a projective K3 surface.Comment: 34 pages. v3: Reference [Mat5] and Remark 1.8 added. Incorporated improvement to the exposition and corrected typos according to the referees suggestions. To appear in the proceedings of the conference Algebraic and Complex Geometry, Hannover 201

IVF treatment of moderate male factor infertility: a comparison of mini-Percoll, partial zona dissection and sub-zonal sperm insertion techniques

In this study we examined various techniques of in-vitro fertilization (IVF) for treating couples in whom the male had subnormal semen parameters. We compared two sperm preparation methods (mini-Percoll and conventional swim-up) for efficiency of recovery after preparation and for fertilization rates after IVF, and compared the suitability of partial zona dissection (PZD) and sub-zonal sperm insertion (SUZI) to patients with different types of male factor infertility. The mini-Percoll technique allowed the recovery of significantly more motile spermatozoa from the same semen sample compared to the swim-up method. More oocytes were fertilized after spermatozoa were prepared by the mini-Percoll technique. An increased number of spermatozoa recovered from an ejaculate led to an improvement in the quality of spermatozoa in the insemination droplet. Subsequently, when using the PZD technique, the fertilization rate increased when there was a higher number of spermatozoa in the patient's ejaculate. When comparing the two micromanipulation techniques, SUZI provided patients with oligoasthenzoo-spermia (i.e. < 10 × 106 spermatozoa/ml and 40% motility) with a higher chance of obtaining 2-pronculeate egg

The detection of variability from the candidate IR counterpart to the Anomalous X-ray Pulsar 1E1048.1-5937

We report on the detection of variability from the proposed IR counterpart to the Anomalous X-ray Pulsar (AXP) 1E1048.1-5937 based on Chandra and ESO optical/IR deep observations carried out in 2001-2002. Within the narrow Chandra uncertainty region for 1E1048.1-5937 we found only one relatively faint (J=22.1+/-0.3, J-Ks=2.4) source, while the recently proposed IR counterpart was not detected down to a limiting Ks magnitude of about 20.7 (3sigma confidence level). This implies a remarkable IR brightening of this object, Delta Ks>1.3, on a timescale of about 50 days. Although our knowledge of the IR properties of AXPs is rather limited (there is only another source, 1E2259+586, for which IR variability has been detected), the observed IR variability of the proposed counterpart strengthens its association with 1E1048.1-5937. Our results make the IR (and presumably optical) variability a likely common characteristic of AXPs, and provide new constraints on this class of objects.Comment: 4 pages. Accepted for publication on ApJ Letters. emulateapj5.sty macro use