arXiv subjects

R. Mignani

Publications and source records attributed to R. Mignani.

At least 37 records · Page 2Linked to original sources

arXiv2008

The Second-Generation Guide Star Catalog: Description and Properties

The GSC-II is an all-sky database of objects derived from the uncompressed DSS that the STScI has created from the Palomar and UK Schmidt survey plates and made available to the community. Like its predecessor (GSC-I), the GSC-II was primarily created to provide guide star information and observation planning support for HST. This version, however, is already employed at some of the ground-based new-technology telescopes such as GEMINI, VLT, and TNG, and will also be used to provide support for the JWST and Gaia space missions as well as LAMOST, one of the major ongoing scientific projects in China. Two catalogs have already been extracted from the GSC-II database and released to the astronomical community. A magnitude-limited (R=18.0) version, GSC2.2, was distributed soon after its production in 2001, while the GSC2.3 release has been available for general access since 2007. The GSC2.3 catalog described in this paper contains astrometry, photometry, and classification for 945,592,683 objects down to the magnitude limit of the plates. Positions are tied to the ICRS; for stellar sources, the all-sky average absolute error per coordinate ranges from 0.2" to 0.28" depending on magnitude. When dealing with extended objects, astrometric errors are 20% worse in the case of galaxies and approximately a factor of 2 worse for blended images. Stellar photometry is determined to 0.13-0.22 mag as a function of magnitude and photographic passbands (B,R,I). Outside of the galactic plane, stellar classification is reliable to at least 90% confidence for magnitudes brighter than R=19.5, and the catalog is complete to R=20.

astro-ph↗

arXiv2008

An Optical Counterpart Candidate for the Isolated Neutron Star RBS1774

Multiwavelength studies of the seven identified X-ray dim isolated neutron stars (XDINSs) offer a unique opportunity to investigate their surface thermal and magnetic structure and the matter-radiation interaction in presence of strong gravitational and magnetic fields. As a part of an ongoing campaign aimed at a complete identification and spectral characterization of XDINSs in the optical band, we performed deep imaging with the ESO Very Large Telescope (VLT) of the field of the XDINS RBS1774 (1RXS J214303.7 +065419). The recently upgraded FORS1 instrument mounted on the VLT provided the very first detection of a candidate optical counterpart in the B band. The identification is based on a very good positional coincidence with the X-ray source (chance probability ~2E-3). The source has B=27.4 +/- 0.2 (1 sigma confidence level), and the optical flux exceeds the extrapolation of the X-ray blackbody at optical wavelengths by a factor ~35 (+/- 20 at 3sigma confidence level). This is barely compatible with thermal emission from the neutron star surface, unless the source distance is d~200-300 pc, and the star is an almost aligned rotator or its spin axis is nearly aligned with the line of sight. At the same time, such a large optical excess appears difficult to reconcile with rotation-powered magnetospheric emission, unless the source has an extremely large optical emission efficiency. The implications and possible similarities with the optical spectra of other isolated NSs are discussed.

astro-ph↗

arXiv2007

Speeding-up Thorium decay

We show that cavitation of a solution of thorium-228 in water induces its transformation at a rate 10000 times faster than the natural radioactive decay would do. This result agrees with the alteration of the secular equilibrium of thorium-234 obtained by a Russian team via explosion of titanium foils in water and solutions. These evidences further support some preliminary clues for the possibility of piezonuclear reactions (namely nuclear reactions induced by pressure waves) obtained in the last ten years.

physics.gen-ph↗

arXiv2007

The shadow of light: evidences of photon behaviour contradicting known electrodynamics

We report the results of a double-slit-like experiment in the infrared range, which evidence an anomalous behaviour of photon systems under particular (energy and space) constraints. The statistical analysis of these outcomes (independently confirmed by crossing photon beam experiments in both the optical and the microwave range) shows a significant departure from the predictions of both classical and quantum electrodynamics.

physics.gen-ph↗

arXiv2007

Accurate X-ray position and multiwavelength observations of the isolated neutron star RBS 1774

We report on X-ray, optical, infrared and radio observations of the X-ray dim isolated neutron star (XDINS) 1RXS J214303.7+065419 (also known as RBS 1774). The X-ray observation was performed with the High Resolution Camera on board of the Chandra X-ray Observatory, allowing us to derive the most accurate position for this source (alpha = 21h43m3.38s, delta= +6deg54'17".53; 90% uncertainty of 0."6). Furthermore, we confirmed with a higher spatial accuracy the point-like nature of this X-ray source. Optical and infrared observations were taken in B, V, r', i', J, H and Ks filters using the Keck, VLT, Blanco and Magellan telescopes, while radio observations were obtained from the ATNF Parkes single dish at 2.9GHz and 708MHz. No plausible optical and/or infrared counterpart for RBS 1774 was detected within the refined sub-arsecond Chandra X-ray error circle. Present upper limits to the optical and infrared magnitudes are r'>25.7 and J>22.6 (5 sigma confidence level). Radio observations did not show evidence for radio pulsations down to a luminosity at 1.4 GHz of L < 0.02 mJy kpc^2, the deepest limit up to date for any XDINS, and lower than what expected for the majority of radio pulsars. We can hence conclude that, if RBS 1774 is active as radio pulsar, its non detection is more probably due to a geometrical bias rather than to a luminosity bias. Furthermore, no convincing evidence for RRAT-like radio bursts have been found. Our results on RBS 1774 are discussed and compared with the known properties of other thermally emitting neutron stars and of the radio pulsar population.

astro-ph↗

arXiv2005

The shadow of light: further experimental evidences

We report the results of a double-slit-like experiment in the infrared range, which confirm those of a previous one by evidencing an anomalous behaviour of photon systems under particular (energy and space) constraints. These outcomes (independently confirmed by crossing photon beam experiments in both the optical and the microwave range) apparently rule out the Copenhagen interpretation of the quantum wave, i.e. the probability wave, by admitting an interpretation in terms of the Einstein-de Broglie-Bohm hollow wave for photons. Moreover, this second experiment further supports the interpretation of the hollow wave as a deformation of the Minkowski space-time geometry.

physics.gen-ph↗

arXiv2005

The shadow of light: Lorentz invariance and complementarity principle in anomalous photon behaviour

We review the results of two double-slit-like experiments in the infrared range, which evidence an anomalous behaviour of photon systems under particular (energy and space) constraints. These outcomes (independently confirmed by crossing photon beam experiments in both the optical and the microwave range) apparently rule out the Copenhagen interpretation of the quantum wave, i.e. the probability wave, by admitting an interpretation in terms of the Einstein-de Broglie-Bohm hollow wave for photons. Moreover, these experiments support the interpretation of the hollow wave as a deformation of the Minkowski space-time geometry. We stress the implications of these experimental results and of their interpretation for the concept of action-at-a-distance, the Einstein relativistic correlation and the Bohr principle of complementarity.

physics.gen-ph↗

arXiv2004

Infrared and X-ray variability of the transient Anomalous X-ray Pulsar XTE J1810-197

We report on observations aimed at searching for flux variations from the proposed IR counterpart of the Anomalous X-ray Pulsar XTE J1810-197. These data, obtained in March 2004 with the adaptive optics camera NAOS-CONICA at the ESO VLT, show that the candidate proposed by Israel et al. (2004) was fainter by Delta H=0.7+/-0.2 and Delta Ks=0.5+/-0.1 with respect to October 2003, confirming it as the IR counterpart of XTE J1810-197. We also report on an XMM-Newton observation carried out the day before the VLT observations. The 0.5-10 keV absorbed flux of the source was 2.2x10^-11 erg/s/cm^2, which is less by a factor of about two compared to the previous XMM-Newton observation on September 2003. Therefore, we conclude that a similar flux decrease took place in the X-ray and IR bands. We briefly discuss these results in the framework of the proposed mechanism(s) responsible for the IR variable emission of Anomalous X-ray Pulsars.

astro-ph↗

arXiv2004

X-ray and optical coverage of 3EG J0616-3310 and 3EG J1249-8330

The limited angular resolution of gamma-ray telescopes prevents the straight identification of the majority of the sources detected so far. This is particularly true for the low latitude, probably galactic ones, only 10 % of which has been identified. Most of the counterparts are Isolated Neutron Stars, both radio-loud and radio-quiet, characterised by an extremely high value of X-ray-to-optical flux ratio. The best way to search for INSs in the error boxes of unidentified EGRET sources is to perform the X-ray coverage of the gamma-ray field, followed by the optical characterization of each X-ray source. We applied this procedure to two EGRET sources, which could belong to a local galactic population: 3EG J0616-3310 and 3EG J1249-8330. Here we report on the analysis of about 300 X-ray objects, as well as on their optical study.

astro-ph↗

arXiv2004

Accurate X-ray position of the Anomalous X-ray Pulsar XTE J1810-197 and identification of its likely IR counterpart

We report the accurate sub-arcsec X-ray position of the new Anomalous X-ray Pulsar (AXP) XTE J1810-197, derived with a Chndra-HRC Target of Opportunity observation carried out in November 2003. We also report the discovery of a likely IR counterpart based on a VLT (IR band) Target of Opportunity observation carried out in October 2003. Our proposed counterpart is the only IR source (Ks=20.8) in the X-ray error circle. Its IR colors as well as the X-ray/IR flux ratio, are consistent with those of the counterparts of all other AXPs (at variance with field star colors). Deep Gunn-i band images obtained at the 3.6m ESO telescope detected no sources down to a limiting magnitude of 24.3. Moreover, we find that the pulsed fraction and count rates of XTE J1810-197 remained nearly unchanged since the previous Chandra and XMM-Newton observations (2003 August 27th and September 8th, respectively). We briefly discuss the implications of these results. In particular, we note that the transient (or at least highly variable) nature of this AXP might imply a relatively large number of hidden members of this class.

astro-ph↗

arXiv2003

Out of the Chorus Line : What Makes 1E1207.4-5209 a Unique Object?

The discovery of deep spectral features in the X-ray spectrum of 1E1207.4-5209 has pushed this Isolated Neutron Star (INS) out of the chorus line, since no other INS has shown significant features in its X-ray continuum. On August 2002, XMM-Newton devoted a two-orbit TOO observation to this target with the aim to better understand the nature of such spectral features, using much improved statistics. Indeed, the 260 ksec observation yielded 360,000 photons from 1E1207.4-5209, allowing for a very sensitive study of the temporal and spectral behaviour of this object.

astro-ph↗

arXiv2003

Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar B1821-24

We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). 46 X-ray sources are detected, of which 12 lie within one core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources for which we determine the X-ray luminosity function down to a limit of about 6xE30 erg/s. For the first time the unconfused phase-averaged X-ray spectrum of the 3.05-ms pulsar B1821--24 is measured and found to be best described by a power law with photon index ~ 1.2. Marginal evidence of an emission line centered at 3.3 keV in the pulsar spectrum is found, which could be interpreted as cyclotron emission from a corona above the pulsar's polar cap if the the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.5--8.0 keV band is ~3.5xE-13 ergs/s/cm^2. Spectral analysis of the 5 brightest unidentified sources is presented. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature T_eff^\infty = 90^{+30}_{-10} eV and the radius R_NS^\infty = 14.5^{+6.9}_{-3.8} km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core of M28. Using the Chandra-derived positions, we also report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.

astro-ph↗

arXiv2003

The IR counterpart to the Anomalouos X-ray Pulsar 1RXS J1708-4009

We report the discovery of the likely IR counterpart to the Anomalous X-ray Pulsar (AXP) 1RXS J1708-4009, based on the combination of Chandra HRC-I X-ray position, and deep optical/IR observations carried out from ESO telescopes and the Canada France Hawaii Telescope (CFHT) during 1999-2002. Within the narrow uncertainty region we found two relatively faint (K'=20.0 and K'=17.53) IR objects. Based on their color and position in the J-K' versus J-H diagram only the brighter object is consistent with the known IR properties of the counterparts to other AXPs. No variability was detected for this source, similarly to what is observed in the case of 4U 0142+614. Like in other AXPs, we found that the IR flux of 1RXSJ1708-4009 is higher then expected for a simple blackbody component extrapolated from the X-ray data. If confirmed, this object would be the fourth IR counterpart to a source of the AXP class, and would make the IR excess a likely new characteristic of AXPs.

astro-ph↗

arXiv2002

The runaway black hole GRO J1655-40

We have used the Hubble Space Telescope to measure the motion in the sky and compute the galactocentric orbit of the black hole X-ray binary GRO J1655-40. The system moves with a runaway space velocity of $112\pm 18$ km s$^{-1}$ in a highly eccentric ($e = 0.34\pm 0.05$) orbit. The black hole was formed in the disk at a distance greater than 3 kpc from the Galactic centre and must have been shot to such an eccentric orbit by the explosion of the progenitor star. The runaway linear momentum and kinetic energy of this black hole binary are comparable to those of solitary neutron stars and millisecond pulsars. GRO J1655-40 is the first black hole for which there is evidence for a runaway motion imparted by a natal kick in a supernova explosion.

astro-ph↗

arXiv2002

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.

astro-ph↗

arXiv2002

Pulse phase variations of the X-ray spectral features in the radio-quiet neutron star 1E 1207-5209

We present the results of an XMM-Newton observation of the radio-quiet X-ray pulsar 1E 1207-5209 located at the center of the shell-like supernova remnant G296.5+10.0. The X-ray spectrum is characterized by the presence of two phase-dependent absorption lines at energies ~0.7 keV and ~1.4 keV. Moreover, these broad spectral features have significant substructure, suggesting that they are due to the blending of several narrower lines. We interpret such features as evidence for an atmosphere containing metals and a magnetic field value of a few 10^12 G, consistent with the observed spin-down rate P_dot=(1.98+/-0.83)*10^(-14) s/s. Since 1E 1207-5209 is the only X-ray emitting pulsar showing evidence of such features, we tentatively link them to the unique combination of age and energetics that characterize this object. We suggest that a young age and a low level of magnetospheric activity are favorable conditions for the detection of atomic spectral features from metals in neutron star atmospheres, which would be either blanketed by a thin layer of accreted hydrogen in older objects or masked by non-thermal processes in young energetic pulsars.

astro-ph↗

arXiv2002

XMM-Newton and Wide Field Optical Imaging to crack the mystery of unidentified gamma-ray sources

The limited angular resolution of gamma-ray telescopes prevents the straight identification of the majority of the sources detected so far. While the only certified galactic gamma-ray emitters are associated with pulsars, more than 90% of the nearly 100 low latitude sources detected by EGRET on the GRO lack an identification. The best identification strategy devised over the years relies on the use of X-ray and optical data to single out possible counterparts, rating them on the basis of their extreme F_x/F_opt. Here we describe our multiwavelength programme based on the EPIC mapping of selected EGRET sources complemented by the optical coverage of the same fields obtained through the Wide Field Imager (WFI) of the ESO 2.2 m telescope. The field of view of the WFI, comparable to that of EPIC, will allow to directly cross-correlate X and optical data speeding up significantly the selection of interesting candidates worth follow-up optical (and X-ray) studies.

astro-ph↗

arXiv2001

BMW: a ROSAT-HRI source catalogue obtained with a wavelet transform detection algorithm

In collaboration with the Observatories of Palermo and Rome and the SAX-SDC we are constructing a multi-site interactive archive system featuring specific analysis tools. In this context we developed a detection algorithm based on the Wavelet Transform (WT) and performed a systematic analysis of all ROSAT-HRI public data (~3100 observations +1000 to come). The WT is specifically suited to detect and characterize extended sources while properly detecting point sources in very crowded fields. Moreover, the good angular resolution of HRI images allows the source extension and position to be accurately determined. This effort has produced the BMW (Brera Multiscale Wavelet) catalogue, with more than 19,000 sources detected at the ~4.2sigma level. For each source detection we have information on the position, X-ray flux and extension. This allows for instance to select complete samples of extended X-ray sources such as candidate clusters of galaxies or SNR's. Details about the detection algorithm and the catalogue can be found in Lazzati et al. (1999), Campana et al. (1999) and Panzera et al. (2001). Here we shall present an overview of first results from several undergoing projects which make use of the BMW catalogue.

astro-ph↗