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BL Lacertae (BL Lac) is categorized as TeV blazar and considered as a possible source of astrophysical neutrinos. In 2020, the brightest X-ray flare ever detected from it. A detailed study can answer many puzzling questions related to multiband emissions and fast-flux variability often seen in this kind of source. We have performed the temporal and spectral analysis of the brightest flare. The variability is characterized by the fractional variability amplitude and the variability time. We found that the source has crossed all its previous limits of flux and reached the maximum ever seen from it in optical and X-rays. It is highly variable in X-rays with fractional variability above 100$\%$ (1.8397$\pm$0.0181) and the fastest variability time of 11.28 hours within a day. The broadband light curves correlation with X-ray suggest a time lag of one day. A broadband SED modeling is pursued to understand the possible physical mechanisms responsible for broadband emission. Modeling requires two emission regions located at two different sites to explain the low and high flux states. A significant spectral change is observed in the optical-UV and X-ray spectrum during the high state, which eventually leads to shifts in the location of the synchrotron peak towards higher energy, suggesting an emergence of a new HBL component., Comment: 13 pages, 11 figures, 3 tables, Accepted in MNRAS

Octopus cells in the posteroventral cochlear nucleus exhibit characteristic onset responses to broad band transients but are little investigated in response to more complex sound stimuli. In this paper, we propose a phenomenological, but biophysically motivated, modeling approach that allows to simulate responses of large populations of octopus cells to arbitrary sound pressure waves. The model depends on only few parameters and reproduces basic physiological characteristics like onset firing and phase locking to amplitude modulations. Simulated responses to speech stimuli suggest that octopus cells are particularly sensitive to high-frequency transients in natural sounds and their sustained firing to phonemes provides a population code for sound level.

We present broadband X-ray spectral-timing analysis of the new Galactic X-ray transient MAXI~J1348--630 using five simultaneous {\it AstroSat} and {\it NICER} observations. Spectral analysis using {\it AstroSat} data identify the source to be in the soft state for the first three observations and in a faint and bright hard state for the next two. Quasi-periodic oscillations at $\sim 0.9$ and $\sim 6.9$\,Hz, belonging to the type-C and type-A class are detected. In the soft state, the power density spectra are substantially lower (by a factor $> 5$) for the {\it NICER} (0.5--12 keV) band compared to the {\it AstroSat}/LAXPC (3--80 keV) one, confirming that the disk is significantly less variable than the Comptonization component. For the first time, energy-dependent fractional rms and time lag in the 0.5--80 keV energy band was measured at different Fourier frequencies, using the bright hard state observation. Hard time lag is detected for the bright hard state, while the faint one shows evidence for soft lag. A single-zone propagation model fits the LAXPC results in the energy band 3--80 keV with parameters similar to those obtained for Cygnus X--1 and MAXI J1820+070. Extending the model to lower energies, reveals qualitative similarities but having quantitative differences with the {\it NICER} results. These discrepancies could be because the {\it NICER} and {\it AstroSat} data are not strictly simultaneous and because the simple propagation model does not take into account disk emission. The results highlight the need for more joint coordinated observations of such systems by {\it NICER} and {\it AstroSat}., 14 Pages, 13 Figures, 3 Tables. Accepted for publication in MNRAS

ELF/VLF waves have been registered in the outer polar cusps simultaneously with high energy electrons fluxes by the satellites Magion 4 (subsatellite to Interball 1), Polar and CLUSTER. Further, we discuss similar observations in the different regions of the ionosphere, where DEMETER registered energetic electrons. The DEMETER satellite operating on the nearly polar orbit at the altitude 650 km crossed different regions in the ionosphere. Registrations of ELF/VLF/HF waves together with the energetic electrons in the polar cusp, in the ionospheric trough and over thunderstorm areas are presented in this paper. The three satellites of ESA’s Swarm mission provide additional information on the ELF waves in the mentioned areas together with electron density and temperature. A brief discussion of the generation of these emissions by the so-called “fan instability” (FI) and beam instability is presented.

We have extensively studied the broadband X-ray spectra of the source ESO~141--G055 using all available \xmm{} and \nustar{} observations. We detect a prominent soft excess below 2 keV, a narrow Fe line and a Compton hump (>10 keV). The origin of the soft excess is still debated. We used two models to describe the soft excess: the blurred reflection from the ionized accretion disk and the intrinsic thermal Comptonisation model. We find that both of these models explain the soft excess equally well. We confirm that we do not detect any broad Fe line in the X-ray spectra of this source, although both the physical models prefer a maximally spinning black hole scenario (a$>$0.96). This may mean that either the broad Fe line is absent or blurred beyond detection. The Eddington rate of the source is estimated to be $\lambda_{Edd} \sim 0.31$. In the reflection model, the Compton hump has a contribution from both ionized and neutral reflection components. The neutral reflector which simultaneously describes the narrow Fe K$\alpha$ and the Compton hump has a column density of $\rm N_{H} \geq 7\times 10^{24} \rm cm^{-2} $. In addition, we detect a partially covering ionized absorption with ionization parameter $\log \xi/\rm erg cm s^{-1}$ = $0.1^{+0.1}_{-0.1}$ and column density $\rm N_{H} =20.6^{+1.0}_{-1.0}\times 10^{22} \rm cm^{-2}$ with a covering factor of $0.21^{+0.01}_{-0.01}$., Comment: 10 pages, 4 tables and 4 figures. Accepted in MNRAS

This review is dedicated to the Effective Medium Theory of two-component metamaterials in the broad frequency range from microwaves to visible region. The metamaterials are unbounded periodic 2-D l...

We present the results of multi-wavelength optical observations, using B, V, R and I band filters, of a sample of 61 active geostationary communications satellites, on 2015 July 9–11. These observations were done outside the glinting season, with a longitudinal solar angle smaller than 6 ° and a latitudinal solar phase angle of ~ 16.5 ° . This approach enabled us to determine the distribution of quiescent magnitudes and colors of these targets during a period of the night when they are expected to be the brightest. We present the distribution of magnitudes and colors of the sample. We find that the colors of these satellites are in general redder than the Solar spectrum, with a wide distribution of values ( 0.62 B - V 1.49 , 1.00 B - R 2.28 , 1.31 B - I 3.07 , 0.34 V - R 0.90 , 0.63 V - I 1.69 , 0.27 R - I 0.79 ). Satellites from different manufacturers are found to cluster around specific colors in color-color plots, indicating that this information can be used to identify different satellites and resolve cross tagging issues. We also investigate whether the colors of satellites change with time and find that in most cases there is no significant change to these properties as the satellites age.

The amplitude–frequency characteristics of hydraulic bearings under the action of broad-band random vibrations with different input root-mean-square acceleration are investigated. The damping of the vibrational signals by the hydraulic bearings is studied experimentally.

During November 2017, an active source seismic survey was performed in Andaman sea to study the acoustic propagation characteristics. High power low frequency acoustic signals generated by 20-air gun array onboard ORV Samudra Ratnagar were recorded from INS Sagardhwani at four different depths within 8 km ranges in shallow and deep waters. Low frequency sound levels were estimated using root mean square and power spectral values. Amplitude levels were analysed with respect to arrival time variation with frequency and is presented.

An in-plane hybrid design is proposed to achieve broadband radar cross section (RCS) reduction based on the integration of a diffusion scattering electromagnetic band-gap (EBG) metasurface and a magnetic absorbing material (MAM) at a thin thickness (d). A scattering field calculation formula is derived for the hybrid design, in which the MAM and EBG metasurface have complementary dominant working bands. Moreover, they are able to achieve strong RCS reduction in broad band by working together. As a result, the as-designed hybrid metasurface show in both simulation and experiment an unprecedented broadband RCS reduction of 6 dB in the frequency range of 5–34 GHz with d of only 2 mm. The design strategy proposed here provides a feasible and extendable approach to broaden the bandwidth of RCS reduction by multiple mechanisms and hybrid materials based on the concept of metasurface. Keywords: Microwave absorber, Scattering redirection, Metasurface, Radar cross section reduction

This paper deals with the asymptotic efficiency estimation of mismatched electrically small antennas in the receiving or transmitting mode. It is often necessary to work with mismatched electrically small antennas in modern communication systems. This situation may occur when an antenna is matched on a single frequency, while the whole system operates in a broad band. Expressions are given for electrically small loop and dipole antennas. Frequency dependences of the efficiency for various geometries of the considered antennas are revealed.

SummaryPerception and cognition require the integration of feed-forward sensory information with feedback signals. Feed-forward and feedback signals have been associated with specific cortical laminae and specific oscillatory frequencies. We used stimuli of different sizes to isolate spectral signatures of feedforward and feedback signals, and their effect on communication between layers in primary visual cortex of male macaque monkeys. Small stimuli, centered on the neurons’ receptive fields elicited broad band gamma frequency oscillations predominantly in the superficial layers. These Granger causal originated in upper layer 4 and lower supragranular layers, in line with existing feed-forward models of oscillatory responses. However, large stimuli extending into the far surround of neurons’ receptive fields, generated strong narrow band gamma oscillatory activity across cortical layers. They Granger causal arose in layer 5, were conveyed through layer 6 to superficial layers, and violated existing models of feedback spectral signatures. Equally surprising, with large stimuli, alpha band oscillatory activity arose predominantly in granular and supragranular layers, and communicated in a feed-forward direction. This shows that oscillations in specific frequency bands can be dynamically modulated to serve feedback and feed-forward communication and are not restricted to specific cortical layers in V1

For broad-band synthetic aperture radar applications, a compact waveguide array antenna with broad operating frequency band is investigated in this paper. Ridged waveguide and square horn are used for broadband operating, and the size of the antenna element is much smaller than the traditional horn. The phased array providing more than 28% bandwidth with VSWR better than 2 in Ka band. The better angle scan performance of the array antenna can be obtained. The radiation patterns of the phased array are presented.

We present the first release of GTC OSIRIS broad-band data archive. This is an effort conducted in the framework of the Spanish Virtual Observatory to help optimize science from the Gran Telescopio Canarias Archive. Data Release 1 includes 6788 broad-band images in the Sloan griz filters obtained between 2009 April and 2014 January and the associated catalogue with roughly 6.23 million detections of more than 630 000 unique sources. The catalogue contains standard PSF and Kron aperture photometry with a mean accuracy better than 0.09 and 0.15 mag, respectively. The relative astrometric residuals are always better than 30 mas and better than 15 mas in most cases. The absolute astrometric uncertainty of the catalogue is of 0.12 arcsec. In this paper we describe the procedure followed to build the image archive and the associated catalogue, as well as the quality tests carried out for validation. To illustrate some of the scientific potential of the catalogue, we also provide two examples of its scientific exploitation: discovery and identification of asteroids and cool dwarfs. HB acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 682903, P.I. H. Bouy), and from the French State in the framework of the 'Investments for the future' Program, IdEx Bordeaux, reference ANR-10-IDEX-03-02. This research has been financed by ASTERICS, a project supported by the European Commission Framework Programme Horizon 2020 Research and Innovation action under grant agreement no. 653477. This research has been partially funded by the Spanish State Research Agency (AEI) Project No. ESP2017-87676-C5-1-R and No. MDM-2017-0737 Unidad de Excelencia 'Maria de Maeztu'-Centro de Astrobiologia (CSIC-INTA). This publication makes use of VOSA, developed under the Spanish Virtual Observatory project supported by the Spanish MINECO through grant AyA2017-84089. This research has made use of the SVO Filter Profile Service (http://svo2.cab.inta-csic.es/theory/fps/) supported from the Spanish MINECO through grant AYA2017-84089. This research made use of the cross-match service, the SIMBAD data base (Wenger et al. 2000), VizieR catalogue access tool (Ochsenbein, Bauer & Marcout 2000), 'Aladin sky atlas' (Bonnarel et al. 2000; Boch & Fernique 2014) provided by CDS, Strasbourg, France. This research has also made use of the TOPCAT (Taylor 2005) and STILTS (Taylor 2006). This research has made use of IMCCE's SkyBoT VO tool (Berthier et al. 2006). MCC and FJE acknowledge financial support from the Tec2Space-CM project (P2018/NMT-4291). MM is funded by the European Space Agency under the research contract C4000122918 ; With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737). Peer review

We present the first results of extragalactic black hole X-ray binaries LMC X-1 and LMC X-3 using all the archival and legacy observations by AstroSat during the period of $2016-2020$. Broadband energy spectra ($0.5-20$ keV) of both sources obtained from the SXT and LAXPC on-board AstroSat are characterized by strong thermal disc blackbody component ($kT_{in}\sim1$keV, $f_{disc}>79\%$) along with a steep power-law ($\Gamma\sim2.4-3.2$). Bolometric luminosity of LMC X-1 varies from $7-10\%$ of Eddington luminosity ($L_{Edd}$) and for LMC X-3 is in the range $7-13\%$ of $L_{Edd}$. We study the long-term variation of the light curve using MAXI data and find the fractional variance to be $\sim25\%$ for LMC X-1 and $\sim53\%$ for LMC X-3. We examine the temporal properties of both sources and obtain fractional rms variability of PDS in the frequency range $0.002-10$ Hz to be $\sim9\%-17\%$ for LMC X-1, and $\sim7\%-11\%$ for LMC X-3. The `spectro-temporal' properties indicate both sources are in thermally dominated soft state. By modelling the spectra with relativistic accretion disc model, we determine the mass of LMC X-1 and LMC X-3 in the range $7.64-10.00$ $M_{\odot}$ and $5.35-6.22$ $M_{\odot}$ respectively. We also constrain the spin of LMC X-1 to be in the range $0.82-0.92$ and that of LMC X-3 in $0.22-0.41$ with 90\% confidence. We discuss the implications of our results in the context of accretion dynamics around the black hole binaries and compare it with the previous findings of both sources., Comment: Accepted for publication in MNRAS, 11 pages, 5 figures

We present joint \textit{XMM-Newton} and \textit{NuSTAR} observations of the `bare' narrow line Seyfert 1 Ton S180 ($z=0.062$), carried out in 2016 and providing the first hard X-ray view of this luminous galaxy. We find that the 0.4--30 keV band cannot be self-consistently reproduced by relativistic reflection models, which fail to account simultaneously for the soft and hard X-ray emission. The smooth soft excess prefers extreme blurring parameters, confirmed by the nearly featureless nature of the RGS spectrum, while the moderately broad Fe K line and the modest hard excess above 10 keV appear to arise in a milder gravity regime. By allowing a different origin of the soft excess, the broadband X-ray spectrum and overall spectral energy distribution (SED) are well explained by a combination of: (a) direct thermal emission from the accretion disc, dominating from the optical to the far/extreme UV; (b) Comptonization of seed disc photons by a warm ($kT_{\rm e}\sim0.3$ keV) and optically thick ($\tau\sim10$) corona, mostly contributing to the soft X-rays; (c) Comptonization by a standard hot ($kT_{\rm e} \gtrsim 100$ keV) and optically thin ($\tau, Comment: 20 pages, 12 figures. Accepted for publication MNRAS

We present results from the major coordinated X-ray observing program on the ULX NGC 1313 X-1 performed in 2017, combining $XMM$-$Newton$, $Chandra$ and $NuSTAR$, focusing on the evolution of the broadband ($\sim$0.3-30.0 keV) continuum emission. Clear and unusual spectral variability is observed, but this is markedly suppressed above $\sim$10-15 keV, qualitatively similar to the ULX Holmberg IX X-1. We model the multi-epoch data with two-component accretion disc models designed to approximate super-Eddington accretion, allowing for both a black hole and a neutron star accretor. With regards to the hotter disc component, the data trace out two distinct tracks in the luminosity-temperature plane, with larger emitting radii and lower temperatures seen at higher observed fluxes. Despite this apparent anti-correlation, each of these tracks individually shows a positive luminosity-temperature relation. Both are broadly consistent with $L\propto{T}^{4}$, as expected for blackbody emission with a constant area, and also with $L\propto{T}^{2}$, as may be expected for an advection-dominated disc around a black hole. We consider a variety of possibilities for this unusual behaviour. Scenarios in which the innermost flow is suddenly blocked from view by outer regions of the super-Eddington disc/wind can explain the luminosity-temperature behaviour, but are difficult to reconcile with the lack of strong variability at higher energies, assuming this emission arises from the most compact regions. Instead, we may be seeing evidence for further radial stratification of the accretion flow than is included in the simple models considered, with a combination of winds and advection resulting in the suppressed high-energy variability., Comment: 18 pages, 7 figures, accepted for publication in MNRAS

A compact circularly polarized (CP) rectenna based on wide-slot antenna is designed at 5.8 GHz. The feedback wide-slot antenna is used for its broad band, easy-to-integrate circuitry, simple structure, and low sidelobes. The designed receiving antenna has a bandwidth of 31.8%. In order to minimize the profile of the rectenna, the rectifier is integrated on the back side of the substrate with a matching circuit and a dc-pass filter. It features stable conversion efficiency on three azimuthal planes. The maximum efficiency of 66.2% and an output dc voltage of 6.33 V have been measured with a 900 Ω load at the power density of 11.4 mW/cm2. A 5 × 5 rectenna array is built for large physical aperture and increased output power. The maximum conversion efficiency of 62% is observed with the array. Taking the advantage of immunity to misalignment of the CP antenna, the proposed rectenna and array are suitable to be used in mobile applications for wireless power transfer.

We have undertaken a comprehensive search for both Lyman Alpha Emitters (LAEs) and Lyman Break Galaxies (LBGs) in the SHARDS Survey of the GOODS-N field. SHARDS is a deep imaging survey, made with the 10.4 m Gran Telescopio Canarias (GTC), employing 25 medium band filters in the range from 500 to 941 nm. This is the first time that both LAEs and LBGs are surveyed simultaneously in a systematic way in a large field. We draw a sample of 1558 sources; 528 of them are LAEs. Most of the sources (1434) show rest-frame UV continua. A minority of them (124) are pure LAEs with virtually no continuum detected in SHARDS. We study these sources from $z\sim3.35$ up to $z\sim6.8$, well into the epoch of reionization. Note that surveys done with just one or two narrow band filters lack the possibility to spot the rest-frame UV continuum present in most of our LAEs. We derive redshifts, Star Formation Rates (SFRs), Ly$\alpha$ Equivalent Widths (EWs) and Luminosity Functions (LFs). Grouping within our sample is also studied, finding 92 pairs or small groups of galaxies at the same redshift separated by less than 60 comoving kpc. In addition, we relate 87 and 55 UV-selected objects with two known overdensities at $z=4.05$ and $z=5.198$, respectively. Finally, we show that surveys made with broad band filters are prone to introduce many unwanted sources ($\sim20$% interlopers), which means that previous studies may be overestimating the calculated LFs, specially at the faint end., Comment: Accepted for publication in MNRAS. 18 pages, 19 figures

A novel compact planar UHF RFID tag with broadband operation and enhanced read range characteristics are presented. The structure of the tag consists of a T- matched dipole antenna whose arms are orthogonally loaded with Triangular SRR arrays. Triangular SRR arms loaded in the structure produce compactness and good impedance matching which is needed for maximizing the read range. The measured results shows that the projected tag shows a highest read range of 9.6 meter in the European UHF RFID band of 866 MHz and significantly better read range in the other UHF RFID bands in the 860-930 MHz range . Measured read range differences over the azimuth and elevation angular ranges are also suggested.

In the present study a partial mass isolation (PMI) technique is proposed. This approach, through isolating different portions of masses at different stories, can provide a building with multiple inherent vibration suppressors without the need to add extra masses. Optimization of the PMI system’s parameters is conducted for reference structural models with 6, 12, and 20 stories to minimize root-mean-square inter-story drift responses under Kanai-Tajimi filtered Gaussian white noise excitations, while parameter constraints are specified to control isolated components’ (ICs) responses. The seismic performance of the PMI technique under excitations with different frequency contents (representing different soil profiles) is compared to that of conventional tuned mass damper (TMD) and base-isolation (BI) systems as baseline configurations. Simulation results indicate that the PMI system with extreme isolated mass ratios of 5% or 90% exhibits dynamic behaviors equivalent to those of an equivalent TMD or an ideal BI systems, respectively. Meanwhile, this technique can resolve some of the inherent difficulties associated with the implementation of TMD (e.g., weight restriction) and BI (e.g., problems due to the superstructure flexibility, overturning moments, and heavy loads) in high-rise buildings.

The feasibility of the determination of the physical conditions in star’s atmosphere and the parameters of interstellar extinction from broad-band photometric observations in the 300–3000 nm wavelength interval is studied using SDSS and 2MASS data. The photometric accuracy of these surveys is shown to be insufficient for achieving in practice the theoretical possibility of estimating the atmospheric parameters of stars based on ugriz and JHKs photometry exclusively because such determinations result in correlations between the temperature and extinction estimates. The uncertainty of interstellar extinction estimates can be reduced if prior data about the temperature are available. The surveys considered can nevertheless be potentially valuable sources of information about both stellar atmospheric parameters and the interstellar medium.

The transient radial shearing interferometry technique based on fast Fourier transform (FFT) provides a means for the measurement of the wavefront phase of transient light field. However, which factors affect the spatial bandwidth of the wavefront phase measurement of this technology and how to achieve high-precision measurement of the broad-band transient wavefront phase are problems that need to be studied further. To this end, a theoretical model of phase-retrieved bandwidth of radial shearing interferometry is established in this paper. The influence of the spatial carrier frequency and the calculation window on phase-retrieved bandwidth is analyzed, and the optimal carrier frequency and calculation window are obtained. On this basis, a broad-band transient radial shearing interference phase-retrieval method based on chirp Z transform (CZT) is proposed, and the corresponding algorithm is given. Through theoretical simulation, a known phase is used to generate the interferogram and it is retrieved by the traditional method and the proposed method respectively. The residual wavefront RMS of the traditional method is 0.146λ, and it is 0.037λ for the proposed method, which manifests an improvement of accuracy by an order of magnitude. At the same time, different levels of signal-to-noise ratios (SNRs) from 50 dB to 10 dB of the interferogram are simulated, and the RMS of the residual wavefront is from 0.040λ to 0.066λ. In terms of experiments, an experimental verification device based on a phase-only spatial light modulator is built, and the known phase on the modulator is retrieved from the actual interferogram. The RMS of the residual wavefront retrieved through FFT is 0.112λ, and it decreases to 0.035λ through CZT. The experimental results verify the effectiveness of the method proposed in this paper. Furthermore, the method can be used in other types of spatial carrier frequency interference, such as lateral shearing interference, rotational shearing interference, flipping shearing interference, and four-wave shearing interference.

Linear acoustic metamaterials (LAMs) are widely used to manipulate sound; however, it is challenging to obtain bandgaps with a generalized width (ratio of the bandgap width to its start frequency) >1 through linear mechanisms. Here we adopt both theoretical and experimental approaches to describe the nonlinear chaotic mechanism in both one-dimensional (1D) and two-dimensional (2D) nonlinear acoustic metamaterials (NAMs). This mechanism enables NAMs to reduce wave transmissions by as much as 20–40 dB in an ultra-low and ultra-broad band that consists of bandgaps and chaotic bands. With subwavelength cells, the generalized width reaches 21 in a 1D NAM and it goes up to 39 in a 2D NAM, which overcomes the bandwidth limit for wave suppression in current LAMs. This work enables further progress in elucidating the dynamics of NAMs and opens new avenues in double-ultra acoustic manipulation., Linear acoustic metamaterials based on resonances are generally tunable but limited by their narrow bands. Here, Fang et al. fabricate one- and two-dimensional nonlinear acoustic metamaterials with a broadband, low-frequency, response—greatly suppressing low frequency noise.

We present results from a coordinated $XMM$-$Newton$+$NuSTAR$ observation of the type 1.8 Seyfert galaxy IRAS 13197-1627. This is a highly complex source, with strong contributions from relativistic reflection from the inner accretion disk, neutral absorption and further reprocessing by more distant material, and ionised absorption from an outflow. We undertake a detailed spectral analysis combining the broadband coverage provided by $XMM$-$Newton$+$NuSTAR$ with a multi-epoch approach incorporating archival observations performed by $XMM$-$Newton$ and $Suzaku$. Our focus is on characterising the reflection from the inner accretion disk, which previous works have suggested may dominate the AGN emission, and constraining the black hole spin. Using lamppost disk reflection models, we find that the results for the inner disk are largely insensitive to assumptions regarding the geometry of the distant reprocessor and the precise form of the illuminating X-ray continuum. However, these results do depend on the treatment of the iron abundance of the distant absorber/reprocessor. The multi-epoch data favour a scenario in which the AGN is chemically homogeneous, and we find that a rapidly rotating black hole is preferred, with $a^* \geq 0.7$, but a slowly-rotating black hole is not strongly excluded. In addition to the results for the inner disk, we also find that both the neutral and ionised absorbers vary from epoch to epoch, implying that both have some degree of inhomogeneity in their structure., 15 pages, 7 figures, accepted for publication in MNRAS

In this letter, an efficient approach for broadband radar cross-section (RCS) reduction is proposed. By coding eight types of linear-phase gradients in a spiral pattern, the reflected wave was uniformly diffused, and thus, the backscatter RCS reduction was achieved within an ultrabroadband. For verification, a spiral-coded metasurface composed of $8\times 8$ subarrays is designed, fabricated, and measured. Numerical and experimental results both show that the thin metasurface enables a 10 dB RCS reduction over an ultrabroadband ranging from 12.2 to 23.4 GHz. Moreover, the good merit of our approach is further demonstrated by comparing the scattering behavior to the steering beam of a regular sequential layout pattern. Our approach features broad band, polarization insensitivity, wide incident angles, and easy design without any optimization, promising great potential in real-world low-scattering stealth applications.

We present magnetic field induced modulation of the optical response of slit plasmonic metasurfaces fabricated out of giant magnetoresistance/spintronic materials in the 2–17 μm spectral range of the spectrum. The modulation of the slit plasmonic modes is due to the modification of the electrical resistivity (and, in turn, of the optical constants) induced by the application of an external magnetic field. This modulation is found to continuously increase both with the slit concentration and with the slit resonance wavelength, with a prospective further increase for wavelengths of up to 60–80 μm. The direct fabrication and implementation of the modulation setup opens a competitive route for the development of active plasmonic metasurfaces in a wide spectral range., We acknowledge financial support from MINECO through projects AMES (MAT2014-58860-P), Quantum Spin Plasmonics (FIS2015-72035-EXP), PlasmoQuanta (FIS2016-80174-P), MIRRAS (MAT2017-84009-R), and Comunidad de Madrid through project SINOXPHOSCM (S2018/BAA-4403). LB, NZ, and JA acknowledge support from the Department of Education of the Basque Government under project IT1164-19, and the Department of Industry of the Basque Government under Elkartek project KK-2018/00001. We acknowledge the service from the MiNa Laboratory at IMN and funding from MINECO under project CSIC13-4E-1794 and from CM under project S2018/NMT-4291 TEC2SPACE, both with support from EU (FEDER, FSE).

For terahertz integrated systems, an intersection between waveguides is inevitable and is often accompanied by considerable crosstalk and loss. Here, we propose and experimentally demonstrate a novel type of crossing with a footprint less than $0.2\times 0.2$ mm2 for terahertz surface plasmon polariton waveguiding. The crossing loss is estimated by investigating a sequence of waveguides with one, two and three crossings. By optimizing the crossover structure to suppress crosstalk, the measured loss is as low as -3.86 dB and the crosstalk is less than -19.06 dB/crossing at 0.55 THz. The proposed crossing structure is compact and has low loss and crosstalk within a broad band, which will pave the way for a wide range of new applications for THz integrated systems.

In this paper a broad band circularly polarized antenna is presented which can operate over 300MHz bandwidth. Investigation for the design parameter is performed and improvement in axial ratio for the proposed design is also shown. The fabricated antenna is tested and measured results are given for comparison. The prototype is used as a transmitter and receiver antenna in a FMCW radar system. Also the range profile for a moving target is recorded and presented with experimental setup.

The NRAO VLA Sky Survey (NVSS) Rotation Measure (RM) catalogue has enabled numerous studies in cosmic magnetism, and will continue being a unique dataset complementing future polarisation surveys. Robust comparisons with these new surveys will however require further understandings in the systematic effects present in the NVSS RM catalogue. In this paper, we make careful comparisons between our new on-axis broadband observations with the Karl G. Jansky Very Large Array and the NVSS RM results for 23 sources. We found that two unpolarised sources were reported as polarised at about 0.5% level in the RM catalogue, and noted significant differences between our newly derived RM values and the catalogue values for the remaining 21 sources. These discrepancies are attributed to off-axis instrumental polarisation in the NVSS RM catalogue. By adopting the 0.5% above as the typical off-axis instrumental polarisation amplitude, we quantified its effect on the reported RMs with a simulation, and found that on average the RM uncertainties in the catalogue have to be increased by $\approx$ 10% to account for the off-axis instrumental polarisation effect. This effect is more substantial for sources with lower fractional polarisation, and is a function of the source's true RM. Moreover, the distribution of the resulting RM uncertainty is highly non-Gaussian. With the extra RM uncertainty incorporated, we found that the RM values from the two observations for most (18 out of 21) of our polarised targets can be reconciled. The remaining three are interpreted as showing hints of time variabilities in RM., 16 pages, MNRAS accepted

We present the results of Target of Opportunity (ToO) observations made with AstroSat of the newly discovered black hole binary MAXI J1535-571. We detect prominent C-type Quasi-periodic Oscillations (QPOs) of frequencies varying from 1.85 Hz to 2.88 Hz, along with distinct harmonics in all the AstroSat observations. We note that while the fundamental QPO is seen in the 3 - 50 keV energy band, the harmonic is not significant above ~ 35 keV. The AstroSat observations were made in the hard intermediate state, as seen from state transitions observed by MAXI and Swift. We attempt spectral modelling of the broadband data (0.7-80 keV) provided by AstroSat using phenomenological and physical models. The spectral modelling using nthComp gives a photon index in the range between 2.18-2.37 and electron temperature ranging from 21 to 63 keV. The seed photon temperature is within 0.19 to 0.29 keV. The high flux in 0.3 - 80 keV band corresponds to a luminosity varying from 0.7 to 1.07 L_Edd assuming the source to be at a distance of 8 kpc and hosting a black hole with a mass of 6 M$_{\odot}$. The physical model based on the two-component accretion flow gives disc accretion rates as high as ~ 1 $\dot{m}_{Edd}$ and halo rate ~ 0.2 $\dot{m}_{Edd}$ respectively. The near Eddington accretion rate seems to be the main reason for the unprecedented high flux observed from this source. The two-component spectral fitting of AstroSat data also provides an estimate of a black hole mass between 5.14 to 7.83 M$_{\odot}$., 15 pages, 9 figures, MNRAS (Accepted on 2019 May 10)

In this paper, the design of a broadband circular waveguide $\mathbf{TE}^{\circ}_{\pmb{21}}$ mode generator for gyro-TWT cold test is presented. The proposed mode generator is constituted by a rectangular waveguide $\mathbf{TE}_{\pmb{10}}^{\square }$ to rectangular waveguide $\mathbf{TE}^{\square} _{ \pmb{20}}$ mode converter, a rectangular waveguide $\mathbf{TE}^{\square} _{\pmb{20}}$ to crossing waveguide $\mathbf{TE}^{\pmb{+}}_{\pmb{22}}$ mode converter and the converter from $\mathbf{TE}^{\pmb+}_{\pmb22}$ to $\mathbf{TE}^{\pmb\circ}_{\pmb{21}}$ mode. The linear gradient structure is adopted in each convert for easy fabricating. Simulation results reveal that the $\mathbf{S}_{\pmb{21}}$ parameter of the proposed $\mathbf{TE}^{\pmb{\circ}}_{\pmb{21}}$ mode converter is better than −0.037dB and the $\mathbf{S}_{\pmb{11}}$ parameter is below −28dB in whole Q-band. Cold test shows that the designed generator realizes high conversion efficiency $\pmb{(> 96.6\%)}$ in whole Q-band.

Vector vortex waveplates offer distinct advantages compared to conventional light blocking components for coronagraphs due to their continuous structure, thinness, and transparency. They allow high contrast over a broad band in any spectral region for which the available anisotropic optical materials are transparent. We present opportunities of reducing in-band leakage of vector vortex waveplates to

We review the current status of the understanding how the accretion onto the central black hole proceeds in Active Galaxies. Standard accretion disk is a key element in all relatively bright active galaxies like Seyferts and quasars, although it is not present in very low luminosity sources, like Sgr A*. However, the standard disk does not explain the broad band spectrum, so the disk has to be supplemented with a number of additional components, and our deeper understanding of these components is still far from being complete. These additional elements are: compact hard X-ray corona, inner hot flow, warm corona, disk wind and the Broad Line Region, and finally dusty/molecular torus. All these elements seem to be needed in various proportions, depending predominantly on the Eddington ratio of a given source. These elements also interact with each other which is not yet fully taken into account., 17 pages, 7 figures, Accepted for publication on PoS Proceedings, Contribution "PoS(APCS2018)006" to the Conference on "Accretion Processes in Cosmic Sources", Saint Petersburg, Russia

International audience; We numerically investigate the modulation instability generated in a dispersion oscillating fiber pumped by a chirped pulse with a broad bandwidth. We highlight that the side bands are wide, not symmetric in frequency about the pump and several instantaneous side bands can spectrally overlap with each other in one side while they are well located in the other side. We also show that the spectral distribution can be intuitively explained with an analogy in which the fiber is pumped by a tuneable continuous wave.

Over the past 20 years, a consistent phenomenology has been established to describe the variability properties of black hole X-ray binaries. However, the physics behind the observational data is still poorly understood. The recently proposed model PROPFLUC assumes a truncated disc/hot inner flow geometry, with mass accretion rate fluctuations propagating through a precessing inner flow. These two processes give rise respectively to broad band variability and a quasi-periodic oscillation (QPO) on the precession frequency. We recently applied systematically for the first time PROPFLUC on a black hole candidate (MAXI J1543-564) in order to compare the results of phenomenological and physical modeling of the source power spectrum and to give a physical interpretation of the rising phase of the source outburst. Here we resume the results of our study on MAXI J1543-564 and we discuss future PROPFLUC implementations. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present the broad band UBVI CCD photometry in the region of two open star clusters Teutsch 1 and Riddle 4 located in the second Galactic quadrant. The optical CCD data for these clusters are obtained for the first time. Radii of the clusters are estimated as 3′.5 for both the clusters. Using two color ( U − B ) versus ( B − V ) diagram we determined the reddening as E ( B − V ) = 0.40 ± 0.05 mag for Teutsch 1 and 1.10 ± 0.05 mag for Riddle 4. Using 2MASS JHK and optical data, we estimated E ( J − K ) = 0.24 ± 0.05 mag and E ( V − K ) = 1.40 ± 0.05 mag for Teutsch 1 and E ( J − K ) = 0.47 ± 0.06 mag and E ( V − K ) = 2.80 ± 0.06 mag for Riddle 4. Color-excess ratio indicates normal interstellar extinction law in the direction of both the clusters. We estimated distance as 4.3 ± 0.5 Kpc for Teutsch 1 and 2.8 ± 0.2 Kpc for Riddle 4 by comparing the color-magnitude diagram of the clusters with theoretical isochrones. The age of the clusters has been estimated as 200 ± 20 Myr for Teutsch 1 and 40 ± 10 Myr for Riddle 4 using the stellar isochrones of metallicity Z = 0.02 . The Mass function slope has been derived 1.89 ± 0.43 and 1.41 ± 0.70 for Teutsch 1 and Riddle 4 respectively. Our analysis indicates that both the clusters are dynamically relaxed. A slight bend of Galactic disc towards the southern latitude is found in the longitude range l = 130–180°.

The Lund Broad-band Neutron Facility provides access to a variety of neutron sources together with a well-established user infrastructure. Neutrons from radioactive sources have been successfully employed for the research and development of both detectors and materials for the European Spallation Source. A recently procured d-t neutron generator delivers higher neutron fluxes than those provided by the radioactive sources, and further allows for pulsed operation. With the currently on-going construction of a dedicated neutron beam-line at our 3 MeV Pelletron accelerator, the facility is anticipated to produce approximately 1010 n/s. Cost-effective access to neutrons as well as a platform for educational purposes are the ultimate goals of the project.

We report on the 2016 outburst of the transient Galactic Black Hole candidate IGR J17091-3624 based on the observation campaign carried out with SWIFT and NuSTAR. The outburst profile, as observed with SWIFT-XRT, shows a typical `q'-shape in the Hardness Intensity Diagram (HID). Based on the spectral and temporal evolution of the different parameters, we are able to identify all the spectral states in the q-profile of HID and the Hardness-RMS diagram (HRD). Both XRT and NuSTAR observations show an evolution of low frequency Quasi periodic oscillations (QPOs) during the low hard and hard intermediate states of the outburst rising phase. We also find mHz QPOs along- with distinct coherent class variabilities (heartbeat oscillations) with different timescales, similar to the $\rho$-class (observed in GRS 1915+105). Phenomenological modelling of the broad-band XRT and NuSTAR spectra also reveals the evolution of high energy cut-off and presence of reflection from ionized material during the rising phase of the outburst. Further, we conduct the modelling of X-ray spectra of SWIFT and NuSTAR in 0.5 - 79 keV to understand the accretion flow dynamics based on two component flow model. From this modelling, we constrain the mass of the source to be in the range of 10.62 - 12.33 Msun with 90% confidence, which is consistent with earlier findings., Comment: Accepted for publication in Astrophysics & Space science

International audience

Suppressing or manipulating elastic waves over a broad band is a dream for applications in fields such as mechanics, acoustics, metamaterials, and dynamics. The recently reported ``chaotic band'' mechanism offers possibilities for achieving this goal, but the physics of generating and controlling the chaotic band is not understood. This work reports an interesting remote-interaction regime, $b\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}d\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}g$ $c\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}g$ $o\phantom{\rule{0}{0ex}}f$ $b\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}d$ $g\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}s$, in which the gaps behave as piers of a bridge that support the bridge floor, $i.e.$ the chaotic band. This result also provides a solution for designing nonlinear acoustic metamaterials.

The radio emission during 201 X-ray selected solar flares was surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zurich. The selection includes all RHESSI flares larger than C5.0 jointly observed from launch until June 30, 2003. Detailed association rates of radio emission during X-ray flares are reported. In the decimeter wavelength range, type III bursts and the genuinely decimetric emissions (pulsations, continua, and narrowband spikes) were found equally frequently. Both occur predominantly in the peak phase of hard X-ray (HXR) emission, but are less in tune with HXRs than the high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron radiation. In 10% of the HXR flares, an intense radiation of the above genuine decimetric types followed in the decay phase or later. Classic meter-wave type III bursts are associated in 33% of all HXR flares, but only in 4% they are the exclusive radio emission. Noise storms were the only radio emission in 5% of the HXR flares, some of them with extended duration. Despite the spatial association (same active region), the noise storm variations are found to be only loosely correlated in time with the X-ray flux. In a surprising 17% of the HXR flares, no coherent radio emission was found in the extremely broad band surveyed. The association but loose correlation between HXR and coherent radio emission is interpreted by multiple reconnection sites connected by common field lines., Solar Physics, in press