Showing papers on "Point source published in 2010"

The AKARI/IRC mid-infrared all-sky survey

Abstract: Context. AKARI is the first Japanese astronomical satellite dedicated to infrared astronomy. One of the main purposes of AKARI is the all-sky survey performed with six infrared bands between 9 μ m and 200 μ m during the period from 2006 May 6 to 2007 August 28. In this paper, we present the mid-infrared part (9 μ m and 18 μ m bands) of the survey carried out with one of the on-board instruments, the infrared camera (IRC).Aims. We present unprecedented observational results of the 9 μ m and 18 μ m AKARI all-sky survey and detail the operation and data processing leading to the point source detection and measurements.Methods. The raw data are processed to produce small images for every scan, and the point sources candidates are derived above the 5σ noise level per single scan. The celestial coordinates and fluxes of the events are determined statistically and the reliability of their detections is secured through multiple detections of the same source within milli-seconds, hours, and months from each other.Results. The sky coverage is more than 90% for both bands. A total of 877 091 sources (851 189 for 9 μ m, 195 893 for 18 μ m) are confirmed and included in the current release of the point source catalog. The detection limit for point sources is 50 mJy and 90 mJy for the 9 μ m and 18 μ m bands, respectively. The position accuracy is estimated to be better than 2'' . Uncertainties in the in-flight absolute flux calibration are estimated to be 3% for the 9 μ m band and 4% for the 18 μ m band. The coordinates and fluxes of detected sources in this survey are also compared with those of the IRAS survey and are found to be statistically consistent.

Bright Source Subtraction Requirements for Redshifted 21 cm Measurements

Abstract: The H I 21 cm transition line is expected to be an important probe into the cosmic dark ages and epoch of reionization. Foreground source removal is one of the principal challenges for the detection of this signal. This paper investigates the extragalactic point source contamination and how accurately bright sources (≳ Jy) must be removed in order to detect 21 cm emission with upcoming radio telescopes such as the Murchison Widefield Array. We consider the residual contamination in 21 cm maps and power spectra due to position errors in the sky model for bright sources, as well as frequency-independent calibration errors. We find that a source position accuracy of 0.1 arcsec will suffice for detection of the H I power spectrum. For calibration errors, 0.05% accuracy in antenna gain amplitude is required in order to detect the cosmic signal. Both sources of subtraction error produce residuals that are localized to small angular scales, k⊥ ≳ 0.05 Mpc^(–1), in the two-dimensional power spectrum.

The intriguing nature of the high-energy gamma ray source XSS J12270-4859

Abstract: Context. The nature of the hard X-ray source XSS J12270-4859 is still unclear. It was claimed to be a possible magnetic cataclysmic variable of the Intermediate Polar type from its optical spectrum and a possible 860 s X-ray periodicity in RXTE data. However, recent observations do not support the latter variability, leaving this X-ray source still unclassified. Aims. To investigate its nature we present a broad-band X-ray and gamma ray study of this source based on a recent XMM-Newton observation and archival INTEGRAL and RXTE data. Using the Fermi/LAT 1-year point source catalogue, we tentatively associate XSS J12270-4859 with 1FGLJ1227.9-4852, a source of high-energy gamma rays with emission up to 10GeV. We further complement the study with UV photometry from XMM-Newton and ground-based optical and near-IR photometry. Methods. We have analysed both timing and spectral properties in the gamma rays, X-rays, UV and optical/near-IR bands of XSS J12270-4859. Results. The X-ray emission is highly variable, showing flares and intensity dips. The flares consist of flare-dip pairs. Flares are detected in both X-rays and the UV range, while the subsequent dips are present only in the X-ray band. Further aperiodic dipping behaviour is observed during X-ray quiescence, but not in the UV. The broad-band 0.2-100 keV X-ray/soft gamma ray spectrum is featureless and well described by a power law model with Gamma = 1.7. The high-energy spectrum from 100 MeV to 10 GeV is represented by a power law index of 2.45. The luminosity ratio between 0.1-100 GeV and 0.2-100 keV is similar to 0.8, indicating that the GeV emission is a significant component of the total energy output. Furthermore, the X-ray spectrum does not greatly change during flares, quiescence and the dips seen in quiescence. The X-ray spectrum however hardens during the post-flare dips, where a partial covering absorber is also required to fit the spectrum. Optical photometry acquired at different epochs reveals a period of 4.32 hr that could be ascribed to the binary orbital period. Near-IR, possibly ellipsoidal, variations are detected. Large amplitude variability on shorter (tens mins) timescales is found to be non-periodic. Conclusions. The observed variability at all wavelengths together with the spectral characteristics strongly favour a low-mass atypical low-luminosity X-ray binary and are against a magnetic cataclysmic variable nature. The association with a Fermi/LAT high-energy gamma ray source further strengths this interpretation.

Inflow-Outflow Model with Conduction and Self-Consistent Feeding for Sgr A*

Abstract: We propose a two-temperature radial inow-outow model near Sgr A* with self-consistent feeding and conduction. Stellar winds from individual stars are considered to nd the rates of mass injection and energy injection. These source terms help to partially eliminate the boundary conditions on the inow. Electron thermal conduction is crucial for inhibiting the accretion. Energy diuses out from several gravitational radii, unbinding more gas at several arcseconds and limiting the accretion rate to < 1% of Bondi rate. We successfully t the X-Ray surface brightness prole found from the extensive Chandra observations and reveal the X-Ray point source in the center. The super-resolution technique allows us to infer the presence and estimate the unabsorbed luminosity L 4 10 32 erg s 1 of the point source. The employed relativistic heat capacity and direct heating of electrons naturally lead to low electron temperature Te 4 10 10 K near the black hole. Within the same model we t 86 GHz optically thick emission and obtain the order of magnitude agreement of Faraday rotation measure, thus achieving a single accretion model suitable at all radii. Subject headings: accretion, accretion disks | conduction | Galaxy: center | stars: winds, outows

The intriguing nature of the high energy gamma ray source XSSJ12270-4859

Abstract: The nature of the hard X-ray source XSSJ12270-4859 is still unclear though it was claimed to be a magnetic Cataclysmic Variable. We here present a broad-band X-ray and gamma ray study based on a recent XMM-Newton observation and archival INTEGRAL and RXTE data. From the Fermi/LAT 1-year point source catalogue, we tentatively associate XSSJ12270-4859 with 1FGLJ1227.9-4852, a source of high energy gamma rays with emission up to 10GeV. We complement the study with UV photometry from XMM-Newton and ground-based optical and near-IR photometry. The X-ray emission is highly variable showing flares and intensity dips. The X-ray flares consist of flare-dip pairs. Flares are also detected in the UV range but not the dips. Aperiodic dipping behaviour is also observed during X-ray quiescence but not in the UV. The 0.2-100keV spectrum is featureless and described by a power law model with Gamma=1.7. The 100MeV-10GeV spectrum is instead represented by a power law index of 2.45. The luminosity ratio between 0.1-100GeV and 0.2--100keV is ~0.8, hence the GeV emission is a significant component of the total energy output. Furthermore, the X-ray spectrum does not greatly change during flares, quiescence and the dips seen in quiescence but it hardens during the post-flare dips. Optical photometry reveals a period of 4.32hr likely related to the binary orbit. Near-IR, possibly ellipsoidal, variations are detected. Large amplitude variability on shorter (tens mins) timescales are found to be non-periodic. The observed variability at all wavelengths and the spectral characteristics strongly favour a low-mass atypical low-luminosity X-ray binary and are against a Cataclysmic Variable nature. The association with a Fermi/LAT high energy gamma ray source further strengths this interpretation.

Seismic source mechanism of degassing bursts at Kilauea Volcano, Hawaii : results from waveform inversion in the 10–50 s band

Abstract: The current (March 2008 to February 2009) summit eruptive activity at Kilauea Volcano is characterized by explosive degassing bursts accompanied by very long period (VLP) seismic signals. We model the source mechanisms of VLP signals in the 10–50 s band using data recorded for 15 bursts with a 10‐station broadband network deployed in the summit caldera. To determine the source centroid location and source mechanism, we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account. The VLP signals associated with the bursts originate in a source region ∼1 km below the eastern perimeter of Halemaumau pit crater. The observed waveforms are well explained by the combination of a volumetric component and a vertical single force component. For the volumetric component, several source geometries are obtained which equally explain the observed waveforms. These geometries include (1) a pipe dipping 64° to the northeast; (2) two intersecting cracks including an east striking crack (dike) dipping 80° to the north, intersecting a north striking crack (another dike) dipping 65° to the east; (3) a pipe dipping 58° to the northeast, intersecting a crack dipping 48° to the west–southwest; and (4) a pipe dipping 57° to the northeast, intersecting a pipe dipping 58° to the west–southwest. Using the dual‐crack model as reference, the largest volume change obtained among the 15 bursts is ∼24,400 m3, and the maximum amplitude (peak to peak) of the force is ∼20 GN. Each burst is marked by a similar sequence of deflation and inflation, trailed by decaying oscillations of the volumetric source. The vertical force is initially upward, synchronous with source deflation, then downward, synchronous with source reinflation, followed by oscillations with polarity opposite to the volumetric oscillations. This combination of force and volume change is attributed to pressure and momentum changes induced during a fluid dynamic source mechanism involving the ascent, expansion, and burst of a large slug of gas within the upper ∼150 m of the magma conduit. As the slug expands upon approach to the surface and more liquid becomes wall supported by viscous shear forces, the pressure below the slug decreases, inducing conduit deflation and an upward force on the Earth. The final rapid slug expansion and burst stimulate VLP and LP oscillations of the conduit system, which slowly decay due to viscous dissipation and elastic radiation. Consideration of the fluid dynamic arguments leads us to prefer the dual‐crack VLP source model as it is the only candidate model capable of producing plausible values of length scales and pressure changes. The magnitudes of the vertical forces observed in the 15 bursts appear consistent with slug masses of 104 to 106 kg.

Automated procedure for point and kinematic source inversion at regional distances

Abstract: [1] The development of fast, automatic routines for the retrieval of point source parameters of medium to large earthquakes was convincingly established in the last years and decades, providing an increasing number of focal mechanism solutions. Original applications at teleseismic distances have been successively accompanied by specific routines for regional data sets. The majority of these methods are based on the fit of low-passed time traces. We present here a new technique for the automatic retrieval of point source parameters and highly parameterized kinematic rupture models at regional distances, assuming the recently proposed eikonal model to describe the extended source. In our approach we use a larger set of information to better constrain the source parameters, including the fit of amplitude spectra and displacements at different phases and frequency ranges. The time consumption of the inversion process is significantly improved, thanks to the implementation of Green's functions databases. We adopt a multistep inversion approach, finally providing the focal mechanism, magnitude, and centroid location of the point source. For events with magnitude higher than a threshold of Mw 5.5, source geometry, rupture extension, and average slip may be additionally retrieved. We discuss the methodology and the inversion stability, showing applications to significant earthquakes in two case areas. We focus on Germany and Greece, and their neighboring areas, considering major shallow earthquakes in the last 5 years. The proposed method is currently implemented for automatic data processing at the Seismological Observatory of the Federal Institute for Geosciences and Natural Resources in Germany.

High-frequency Radio Properties of Sources in the Fermi-LAT 1 year Point Source Catalog

Abstract: The high-frequency radio sky, like the gamma-ray sky surveyed by the Fermi satellite, is dominated by flat spectrum radio quasars and BL Lac objects at bright flux levels. To investigate the relationship between radio and gamma-ray emission in extragalactic sources, we have cross-matched the Australia Telescope 20 GHz survey catalog (AT20G) with the Fermi-LAT 1 year Point Source Catalog (1FGL). The 6.0 sr of sky covered by both catalogs ({delta} 1.{sup 0}5) contains 5890 AT20G radio sources and 604 1FGL gamma-ray sources. The AT20G source positions are accurate to within {approx}1 arcsec and, after excluding known Galactic sources, 43% of Fermi 1FGL sources have an AT20G source within the 95% Fermi confidence ellipse. Monte Carlo tests imply that at least 95% of these matches are genuine associations. Only five gamma-ray sources (1% of the Fermi catalog) have more than one AT20G counterpart in the Fermi error box. The AT20G matches also generally support the active galactic nucleus (AGN) associations in the First LAT AGN Catalog. We find a trend of increasing gamma-ray flux density with 20 GHz radio flux density. The Fermi detection rate of AT20G sources is close to 100% for the brightest 20 GHz sources,more » decreasing to 20% at 1 Jy, and to roughly 1% at 100 mJy. Eight of the matched AT20G sources have no association listed in 1FGL and are presented here as potential gamma-ray AGNs for the first time. We also identify an alternative AGN counterpart to one 1FGL source. The percentage of Fermi sources with AT20G detections decreases toward the Galactic plane, suggesting that the 1FGL catalog contains at least 50 Galactic gamma-ray sources in the southern hemisphere that are yet to be identified.« less

High-frequency radio properties of sources in the Fermi-LAT 1-year Point Source Catalogue

Abstract: The high-frequency radio sky, like the gamma-ray sky surveyed by the Fermi satellite, is dominated by flat spectrum radio quasars and BL Lac objects at bright flux levels. To investigate the relationship between radio and gamma-ray emission in extragalactic sources, we have cross-matched the Australia Telescope 20 GHz survey catalog (AT20G) with the Fermi-LAT 1 year Point Source Catalog (1FGL). The 6.0 sr of sky covered by both catalogs ({\delta} 1.\circ 5) contains 5890 AT20G radio sources and 604 1FGL gamma-ray sources. The AT20G source positions are accurate to within ~1 arcsec and, after excluding known Galactic sources, 43% of Fermi 1FGL sources have an AT20G source within the 95% Fermi confidence ellipse. Monte Carlo tests imply that at least 95% of these matches are genuine associations. Only five gamma-ray sources (1% of the Fermi catalog) have more than one AT20G counterpart in the Fermi error box. The AT20G matches also generally support the active galactic nucleus (AGN) associations in the First LAT AGN Catalog. We find a trend of increasing gamma-ray flux density with 20 GHz radio flux density. The Fermi detection rate of AT20G sources is close to 100% for the brightest 20 GHz sources, decreasing to 20% at 1 Jy, and to roughly 1% at 100 mJy. Eight of the matched AT20G sources have no association listed in 1FGL and are presented here as potential gamma-ray AGNs for the first time.We also identify an alternative AGN counterpart to one 1FGL source. The percentage of Fermi sources with AT20G detections decreases toward the Galactic plane, suggesting that the 1FGL catalog contains at least 50 Galactic gamma-ray sources in the southern hemisphere that are yet to be identified.

Localizing the VHE γ‐ray source at the Galactic Centre

Abstract: The inner 10 pc of our Galaxy contains many counterpart candidates of the very high energy (VHE; >100 GeV) γ-ray point source HESS J1745−290. Within the point spread function of the H.E.S.S. measurement, at least three objects are capable of accelerating particles to VHE and beyond and of providing the observed γ-ray flux. Previous attempts to address this source confusion were hampered by the fact that the projected distances between these objects were of the order of the error circle radius of the emission centroid (34 arcsec, dominated by the pointing uncertainty of the H.E.S.S. instrument). Here we present H.E.S.S. data of the Galactic Centre region, recorded with an improved control of the instrument pointing compared to H.E.S.S. standard pointing procedures. Stars observed during γ-ray observations by optical guiding cameras mounted on each H.E.S.S. telescope are used for off-line pointing calibration, thereby decreasing the systematic pointing uncertainties from 20 to 6 arcsec per axis. The position of HESS J1745−290 is obtained by fitting a multi-Gaussian profile to the background-subtracted γ-ray count map. A spatial comparison of the best-fitting position of HESS J1745−290 with the position and morphology of candidate counterparts is performed. The position is, within a total error circle radius of 13 arcsec, coincident with the position of the supermassive black hole Sgr A* and the recently discovered pulsar wind nebula candidate G359.95−0.04. It is significantly displaced from the centroid of the supernova remnant Sgr A East, excluding this object with high probability as the dominant source of the VHE γ-ray emission.

Search for an extended VHE gamma-ray emission from Mrk 421 and Mrk 501 with the MAGIC Telescope

Abstract: Context. Part of the very high energy -ray radiation coming from extragalactic sources is absorbed through the pair production process on the extragalactic background light photons. Extragalacti c magnetic fields alter the trajectories of these cascade pai rs and, in turn, convert cosmic background photons to gamma-ray energies by inverse Compton scattering. These secondary photons can form an extended halo around bright VHE sources. Aims. We searched for an extended emission around the bright blazars Mrk 421 and Mrk 501 using the MAGIC telescope data. Methods. If extended emission is present, the angular distribution o f reconstructed gamma-ray arrival directions around the source is broader than for a point-like source. In the analysis of a few tens of hours of observational data taken from Mrk 421 and Mrk 501 we used a newly developed method that provides better angular resolution. This method is based on the usage of multidimensional decision trees. Comparing the measured shapes of angular distributions with those expected from a point-like source one can detect or constrain possible exten ded emission around the source. We also studied the influence of di fferent types of systematic errors on the shape of the distribu tion of reconstructed gamma-ray arrival directions for a point source. Results. We present upper limits for an extended emission calculated for both sources for various source extensions and emission profiles. We obtain upper limits on the extended emission around the Mrk 421 (Mrk 501) on the level of < 5% (< 4% ) of the Crab Nebula flux above the energy threshold of 300 GeV. Using these results we discuss possible constraints on the extragalactic magnetic fields st rength around a few times 10 −15 G.

Very high-energy gamma-ray emission from IC 310

Abstract: We construct a systematic survey of extragalactic \gamma-ray sky at the energies above 100 GeV using the data of Fermi telescope. Such survey has not been previously done by the ground-based Cherenkov gamma-ray telescopes which have, contrary to Fermi, narrow field of view. We study a map of arrival directions of the highest energy photons detected by Fermi at Galactic latitudes |b| > 10 degrees and search for significant point source like excesses above the diffuse Galactic and extragalactic \gamma-ray backgrounds. We identify eight significant point source like excesses in this map. Seven of the eight sources are known TeV blazars. The previously unknown source is identified with a head-tail radio galaxy IC 310, situated in Perseus cluster of galaxies. The source is detected with significance 6 sigma above 30 GeV. We identify two possible scenaria for gamma-ray emission from this source. One possibility is that emission originates from the base of relativistic outflow from the active nucleus, as in the BL Lacs and FR I type radio galaxies. Otherwise gamma-ray photons could be produced at the bow shock formed in result of fast motion of the galaxy through the intracluster medium. The two models could be distinguished via the study of variability of the \gamma-ray signal.

Search for an extended VHE gamma-ray emission from Mrk 421 and Mrk 501 with the MAGIC Telescope

Abstract: Context: Part of the very high energy $\gamma$-ray radiation coming from extragalactic sources is absorbed through the pair production process on the extragalactic background light photons. Extragalactic magnetic fields alter the trajectories of these cascade pairs and, in turn, convert cosmic background photons to gamma-ray energies by inverse Compton scattering. These secondary photons can form an extended halo around bright VHE sources. Aims: We searched for an extended emission around the bright blazars Mrk 421 and Mrk 501 using the MAGIC telescope data. Methods: If extended emission is present, the angular distribution of reconstructed gamma-ray arrival directions around the source is broader than for a point-like source. In the analysis of a few tens of hours of observational data taken from Mrk 421 and Mrk 501 we used a newly developed method that provides better angular resolution. This method is based on the usage of multidimensional decision trees. Comparing the measured shapes of angular distributions with those expected from a point-like source one can detect or constrain possible extended emission around the source. We also studied the influence of different types of systematic errors on the shape of the distribution of reconstructed gamma-ray arrival directions for a point source. Results: We present upper limits for an extended emission calculated for both sources for various source extensions and emission profiles. We discuss possible constraints on the extragalactic magnetic fields strength. We obtain upper limits on the extended emission around the Mrk~421 (Mrk~501) on the level of < 5% (< 4%) of the Crab Nebula flux above the energy threshold of 300 GeV. Using these results we discuss possible constraints on the extragalactic magnetic fields strength around a few times $10^{-15}$~G.

Acoustic Scattering in the Time Domain Using an Equivalent Source Method

Abstract: A numerical method to solve acoustic scattering in the time domain is presented in the present paper. Equivalent sources are embedded within a scattering surface and their strengths are determined as a function of time by the pressure-gradient boundary condition on a scattering surface. Once the strengths are determined, the equivalent sources are used to predict the scattered pressure. Linear shape functions are used to discretize the strength of the equivalent sources in time, and singular value decomposition is used to find the least-squares solution and to overcome potential numerical instabilities. The predictions are found to be in excellent agreement with the exact solutions for sound from a point monopole source and band-passed broadband sound. The method works well even at the irregular frequencies at which internal resonance modes occur. Finally, the method is used to predict the scattering of sound from a moving source. It is shown that the method has the capability to capture aperiodic characteristics very well.

Statistical properties of polarized radio sources at high frequency and their impact on CMB polarization measurements

Abstract: We have studied the implications of high sensitivity polarization measurements of objects from the WMAP point source catalogue made using the VLA at 8.4, 22 and 43 GHz. The fractional polarization of sources is almost independent of frequency with a median of ~2 per cent and an average, for detected sources, of ~3.5 per cent. These values are also independent of the total intensity over the narrow range of intensity we sample. Using a contemporaneous sample of 105 sources detected at all 3 VLA frequencies, we have investigated the spectral behaviour as a function of frequency by means of a 2-colour diagram. Most sources have power-law spectra in total intensity, as expected. On the other hand they appear to be almost randomly distributed in the polarized intensity 2-colour diagram. This is compatible with the polarized spectra being much less smooth than those in intensity and we speculate on the physical origins of this. We have performed an analysis of the correlations between the fractional polarization and spectral indices including computation of the principal components. We find that there is little correlation between the fractional polarization and the intensity spectral indices. This is also the case when we include polarization measurements at 1.4 GHz from the NVSS. In addition we compute 45 rotation measures from polarization position angles which are compatible with a \lambda^2 law. We use our results to predict the level of point source confusion noise that contaminates CMB polarization measurements aimed at detecting primordial gravitational waves from inflation. We conclude that some level of source subtraction will be necessary to detect r~0.1 below 100 GHz and at all frequencies to detect r~0.01. We present estimates of the level of contamination expected and the number of sources which need to be subtracted as a function of the imposed cut flux density and frequency.

X-ray and radio variability of m31*, the andromeda galaxy nuclear supermassive black hole

Abstract: We confirm our earlier tentative detection of M31* in X-rays and measure its light curve and spectrum. Observations in 2004-2005 find M31* rather quiescent in the X-ray and radio. However, X-ray observations in 2006-2007 show M31* to be highly variable at times. A separate variable X-ray source is found near P1, the brighter of the two optical nuclei. The apparent angular Bondi radius of M31* is the largest of any black hole and large enough to be well resolved with Chandra. The diffuse emission within this Bondi radius is found to have an X-ray temperature ~0.3 keV and density 0.1 cm–3, indistinguishable from the hot gas in the surrounding regions of the bulge given the statistics allowed by the current observations. The X-ray source at the location of M31* is consistent with a point source and a power-law spectrum with energy slope 0.9 ± 0.2. Our identification of this X-ray source with M31* is based solely on positional coincidence.

The y-sky: diffuse spectral distortions of the cosmic microwave background

Abstract: The non-linear evolution of the energy density of the radiation induces spectral distortions of the cosmic microwave background both at recombination and during the reionization era. This distortion has the same spectral signature as the one produced by the re-scattering of photons by non-relativistic hot electrons, the thermal Sunyaev-Zeldovich effect, whose amplitude is quantified by a Compton y parameter. A diffuse y-sky is then expected to emerge from mode couplings in the non-linear evolution of the cosmological perturbations and to superimpose to the point source contributions of galaxy clusters. The equations describing the evolution of the y field and a hierarchy governing its angular multipoles are derived from the second order Boltzmann equation. These equations are then integrated numerically to obtain the first predicted power spectrum of the diffuse y-sky. It is found to be a remarkable tracer of the reionization history of the Universe.

On the single point resolution of on-axis digital holography.

Abstract: On-axis digital holography (DH) is becoming widely used for its time-resolved three-dimensional (3D) imaging capabilities. A 3D volume can be reconstructed from a single hologram. DH is applied as a metrological tool in experimental mechanics, biology, and fluid dynamics, and therefore the estimation and the improvement of the resolution are current challenges. However, the resolution depends on experimental parameters such as the recording distance, the sensor definition, the pixel size, and also on the location of the object in the field of view. This paper derives resolution bounds in DH by using estimation theory. The single point resolution expresses the standard deviations on the estimation of the spatial coordinates of a point source from its hologram. Cramer–Rao lower bounds give a lower limit for the resolution. The closed-form expressions of the Cramer–Rao lower bounds are obtained for a point source located on and out of the optical axis. The influences of the 3D location of the source, the numerical aperture, and the signal-to-noise ratio are studied.

Using the ROSAT catalogue to find counterparts for unidentified objects in the first Fermi/LAT catalogue

Abstract: There are a total of 1451 gamma-ray emitting objects in the Fermi Large Area Telescope First Source Catalogue. The point source location accuracy of typically a few arcmin has allowed the counterparts for many of these sources to be found at other wavelengths, but even so there are 630 which are described as having no plausible counterpart at 80 per cent confidence. In order to help identify the unknown objects, we have cross-correlated the positions of these sources with the ROSAT All Sky Survey Bright Source Catalogue. In this way, for Fermi sources which have a possible counterpart in soft X-rays, we can use the much smaller ROSAT error box to search for identifications. We find a strong correlation between the two samples and calculate that there are about 60 sources with a ROSAT counterpart. Using the ROSAT error boxes we provide tentative associations for half of them, demonstrate that the majority of these are either blazars or blazar candidates, and give evidence that most belong to the BL Lac class. Given that they are X-ray selected and most are high synchrotron peaked objects, which indicates the presence of high-energy electrons, these sources are also good candidates for TeV emission, and therefore good probes of the extragalactic background light.

Constraints on Small-Scale Structures of Dark Matter from Flux Anomalies in Quasar Gravitational Lenses

Abstract: We investigate the statistics of flux anomalies in gravitationally lensed QSOs as a function of dark matter halo properties such as substructure content and halo ellipticity. We do this by creating a very large number of simulated lenses with finite source sizes to compare with the data. After analyzing these simulations, our conclusions are: 1) The finite size of the source is important. The point source approximation commonly used can cause biased results. 2) The widely used R_cusp statistic is sensitive to halo ellipticity as well as the lens' substructure content. 3) For compact substructure, we find new upper bounds on the amount of substructure from the the fact that no simple single-galaxy lenses have been observed with a single source having more than four well separated images. 4) The frequency of image flux anomalies is largely dependent on the total surface mass density in substructures and the size--mass relation for the substructures, and not on the range of substructure masses. 5) Substructure models with the same size--mass relation produce similar numbers of flux anomalies even when their internal mass profiles are different. 6) The lack of high image multiplicity lenses puts a limit on a combination of the substructures' size--mass relation, surface density and mass. 7) Substructures with shallower mass profiles and/or larger sizes produce less extra images. 8) The constraints that we are able to measure here with current data are roughly consistent with \LambdaCDM Nbody simulations.

Positions and sizes of X-ray solar flare sources

Abstract: Aims: The positions and source sizes of X-ray sources taking into account Compton backscattering (albedo) are investigated. Methods: Using a Monte Carlo simulation of X-ray photon transport including photo-electric absorption and Compton scattering, we calculate the apparent source sizes and positions of X-ray sources at the solar disk for various source sizes, spectral indices and directivities of the primary source. Results: We show that the albedo effect can alter the true source positions and substantially increase the measured source sizes. The source positions are shifted by up to ~0.5” radially towards the disk centre and 5 arcsec source sizes can be two times larger even for an isotropic source (minimum albedo effect) at 1 Mm above the photosphere. The X-ray sources therefore should have minimum observed sizes, and thus their FWHM source size (2.35 times second-moment) will be as large as ~7” in the 20-50 keV range for a disk-centered point source at a height of 1 Mm (~1.4”) above the photosphere. The source size and position change is greater for flatter primary X-ray spectra, a stronger downward anisotropy, for sources closer to the solar disk centre, and between the energies of 30 and 50 keV. Conclusions: Albedo should be taken into account when X-ray footpoint positions, footpoint motions or source sizes from e.g. RHESSI or Yohkoh data are interpreted, and we suggest that footpoint sources should be larger in X-rays than in either optical or EUV ranges.

A near-IR study of the host galaxies of 2Jy radio sources at 0.03 < z < 0.5: I - the data

Abstract: We present the results of a program of K- and Ks-band imaging of a sample of 2Jy radio galaxies with redshifts 0.03 < z < 0.5, for which the host galaxy morphologies and structural parameters (effective radius, Sersic index and unresolved nuclear point source contribution) have been determined using GALFIT. Two-thirds of our sample are best modelled as being hosted by massive elliptical galaxies with Sersic indices of n=4-6, with the remainder being better suited either by a mixture of morphological components (usually a bulge plus a small, less luminous, disk component) or by more disky galaxy models with n=1-2. Our measured galaxy sizes are generally in very good agreement with other imaging programs, both space- and ground-based. We also determine a slightly higher average nuclear point source contribution than similar HST-based programs. This is due to our inability to separate the AGN emission from compact circum-nuclear stellar emission, but does not bias our modelling of the remainder of the host galaxies and our results remain robust. We also observe that roughly half of the objects in our sample are either undergoing major or minor merger activity or are clearly morphologically disturbed.

Perfect focusing of scalar wave fields in three dimensions

Abstract: A method to design isotropic inhomogeneous refractive index distribution is presented, in which the scalar wave field solutions propagate exactly on an eikonal function (i.e., remaining constant on the Geometrical Optics wavefronts). This method is applied to the design of "dipole lenses", which perfectly focus a scalar wave field emitted from a point source onto a point absorber, in both two and three dimensions. Also, the Maxwell fish-eye lens in two and three dimensions is analysed.

Using the Rosat Catalogue to find Counterparts for Unidentified Objects in the 1st Fermi/LAT Catalogue

Abstract: There are a total of 1451 gamma-ray emitting objects in the Fermi Large Area Telescope First Source Catalogue. The point source location accuracy of typically a few arcminutes has allowed the counterparts for many of these sources to be found at other wavelengths, but even so there are 630 which are described as having no plausible counterpart at 80% confidence. In order to help identify the unknown objects, we have cross-correlated the positions of these sources with the Rosat All Sky Survey Bright Source Catalogue. In this way, for Fermi sources which have a possible counterpart in soft X-rays, we can use the, much smaller, Rosat error box to search for identifications. We find a strong correlation between the two samples and calculate that there are about 60 sources with a Rosat counterpart. Using the Rosat error boxes we provide tentative associations for half of them, demonstrate that the majority of these are either blazars or blazar candidates and give evidence that most belong to the BL Lac class. Given that they are X-ray selected and most are high synchrotron peaked objects, which indicates the presence of high energy electrons, these sources are also good candidates for TeV emission, and therefore good probes of the extragalactic background light.

Evaluation of Thermal Radiation Models for Fire Spread Between Objects

Abstract: A current research initiative aims to produce a quantitative risk assessment tool, in the form of a probabilistic fire zone model for use in fire safety engineering design of buildings. In order to estimate if or when a remote object from a burning item will ignite, a radiation sub-model has been developed – part of which determines the thermal radiation received by the secondary object directly from the fire. There are a variety of methods presented in the literature that attempt to calculate the thermal radiation to a target from a flame. The performance of six of these methods: a spherical model, a simple correlation, three different cylindrical models and a planar model is investigated in this research. The predictions made by the models are compared with actual measurements of radiant heat flux around a propane gas burner. Different fire scenarios are represented by varying the burner geometry and heat release rate, with heat flux measurements being recorded in different locations around the fire. After comparing the measured data with predictions made by the theoretical radiation methods, the spherical (or point source) model was found to be the best performing method on average. This was unexpected given the relative simplicity of the model in comparison to some of its counterparts. Additionally, the point source model proved to be the most robust of the six methods investigated, being least affected by the experimental variables. Due to its performance and ease of implementation, the point source model has been recommended for use in the radiation submodel within the probabilistic fire zone model software.

Source location of the 19 February 2008 Oregon bolide using seismic networks and infrasound arrays

Abstract: [1] On 19 February 2008 a bolide traveled across the sky along a southern trajectory ending in a terminal burst above Oregon. The event was well recorded by the USArray, other seismic networks, four infrasound arrays, and several video cameras. We compare the results of locating the burst using these different sensor networks. Specifically, we reverse time migrate acoustic-to-seismic coupled signals recorded by the USArray out to 800 km range to image the source in 2-D space and time. We also apply a grid search over source altitude and time, minimizing the misfit between observed and predicted arrival times using 3-D ray tracing with a high-resolution atmospheric velocity model. Our seismic and video results suggest a point source rather than a line source associated with a hypersonic trajectory. We compare the seismic source locations to those obtained by using different combinations of observed infrasound array signal back azimuths and arrival times. We find that all locations are consistent. However, the seismic location is more accurate than the infrasound locations due to the larger number of seismic sensors, a more favorable seismic source-receiver geometry, and shorter ranges to the seismometers. For the infrasound array locations, correcting for the wind improved the accuracy, but implementing arrival times while increasing the precision reduced the accuracy presumably due to limitations of the source location method and/or atmospheric velocity model. We show that despite known complexities associated with acoustic-to-seismic coupling, aboveground infrasound sources can be located with dense seismic networks with remarkably high accuracy and precision.