F. Lewis - Faulkes Telescope Project, Univ. of Glamorgan, Open Univ.

F. Lewis
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F. Lewis
Faulkes Telescope Project, Univ. of Glamorgan, Open Univ.

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High Energy Astrophysical Phenomena (21)
Astrophysics (5)
Astrophysics of Galaxies (4)
Instrumentation and Methods for Astrophysics (3)
Solar and Stellar Astrophysics (3)
Earth and Planetary Astrophysics (2)
Statistics - Applications (1)
Mathematics - Optimization and Control (1)

Publications Authored By F. Lewis

Hypothesis tests based on linear models are widely accepted by organizations that regulate clinical trials. These tests are derived using strong assumptions about the data-generating process so that the resulting inference can be based on parametric distributions. Because these methods are well understood and robust, they are sometimes applied to data that depart from assumptions, such as ordinal integer scores. Read More

We present near-infrared polarimetric observations of the black hole X-ray binaries Swift J1357.2-0933 and A0620-00. In both sources, recent studies have demonstrated the presence of variable infrared synchrotron emission in quiescence, most likely from weak compact jets. Read More

We investigate the dust energy balance for the edge-on galaxy IC 2531, one of the seven galaxies in the HEROES sample. We perform a state-of-the-art radiative transfer modelling based, for the first time, on a set of optical and near-infrared galaxy images. We show that taking into account near-infrared imaging in the modelling significantly improves the constraints on the retrieved parameters of the dust content. Read More

We study in detail the evolution of the 2015 outburst of GS 1354-64 (BW Cir) at optical, UV and X-ray wavelengths using Faulkes Telescope South/LCOGT, SMARTS and Swift. The outburst was found to stay in the hard X-ray state, albeit being anomalously luminous with a peak luminosity of L$_{X} >$ 0.15 L$_{Edd}$, which could be the most luminous hard state observed in a black hole X-ray binary. Read More

On 2015 June 15 the burst alert telescope (BAT) on board {\em Swift} detected an X-ray outburst from the black hole transient V404 Cyg. We monitored V404 Cyg for the last 10 years with the 2-m Faulkes Telescope North in three optical bands (V, R, and i$^{'}$). We found that, one week prior to this outburst, the optical flux was 0. Read More

Galactic starburst clusters play a twin role in astrophysics, serving as laboratories for the study of stellar physics and also delineating the structure and recent star formation history of the Milky Way. In order to exploit these opportunities we have undertaken a multi-epoch spectroscopic survey of the red supergiant dominated young massive clusters thought to be present at both near and far ends of the Galactic Bar. Significant spectroscopic variability suggestive of radial pulsations was found for the yellow supergiant VdBH 222 #505. Read More

Affiliations: 1Sterrenkundig Observatorium, Universiteit Gent, 2Sterrenkundig Observatorium, Universiteit Gent, 3Sterrenkundig Observatorium, Universiteit Gent, 4Sterrenkundig Observatorium, Universiteit Gent, 5Sterrenkundig Observatorium, Universiteit Gent, 6Faulkes Telescope Project, Cardiff University, 7Osservatorio Astrofisico di Arcetri, INAF, 8Sterrenkundig Observatorium, Universiteit Gent, 9Centro de Radioastronomía y Astrofísica, CRyA, UNAM, 10University of Leiden, Sterrenwacht Leiden, 11Kapteyn Astronomical Institute, University of Groningen, 12Sterrenkundig Observatorium, Universiteit Gent

Context. Edge-on galaxies can offer important insights in galaxy evolution as they are the only systems where the distribution of the different components can be studied both radially and vertically. The HEROES project was designed to investigate the interplay between the gas, dust, stars and dark matter (DM) in a sample of 7 massive edge-on spiral galaxies. Read More

This is an extended version of a technical note accepted for publication in IEEE Transactions on Automatic Control. The note proposes an Input to State practically Stable (ISpS) formulation of distributed nonlinear model predictive controller (NMPC) for formation control of constrained autonomous vehicles in presence of communication bandwidth limitation and transmission delays. Planned trajectories are compressed using neural networks resulting in considerable reduction of data packet size, while being robust to propagation delays and uncertainty in neighbors' trajectories. Read More

We characterized the broad-band X-ray spectra of Swift J1745-26 during the decay of the 2013 outburst using INTEGRAL ISGRI, JEM-X and Swift XRT. The X-ray evolution is compared to the evolution in optical and radio. We fit the X- ray spectra with phenomenological and Comptonization models. Read More

This paper considers the distributed consensus problem of linear multi-agent systems subject to different matching uncertainties for both the cases without and with a leader of bounded unknown control input. Due to the existence of nonidentical uncertainties, the multi-agent systems discussed in this paper are essentially heterogeneous. For the case where the communication graph is undirected and connected, a distributed continuous static consensus protocol based on the relative state information is first designed, under which the consensus error is uniformly ultimately bounded and exponentially converges to a small adjustable residual set. Read More

We present contemporaneous X-ray, ultraviolet, optical and near-infrared observations of the black hole binary system, Swift J1753.5-0127, acquired in 2012 October. The UV observations, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope, are the first UV spectra of this system. Read More

We report striking changes in the broadband spectrum of the compact jet of the black hole transient MAXI J1836-194 over state transitions during its discovery outburst in 2011. A fading of the optical-infrared (IR) flux occurred as the source entered the hard-intermediate state, followed by a brightening as it returned to the hard state. The optical-IR spectrum was consistent with a power law from optically thin synchrotron emission, except when the X-ray spectrum was softest. Read More

We have discovered a \sim420d modulation, with associated X-ray dips, in RXTE-ASM/MAXI/Swift-BAT archival light-curves of the short-period (3.2h) black-hole X-ray transient, Swift J1753.5-0127. Read More

We present a 30-day monitoring campaign of the optical counterpart of the bright X-ray transient Swift J1745-26, starting only 19 minutes after the discovery of the source. We observe the system peaking at i' ~17.6 on day 6 (MJD 56192) to then decay at a rate of ~0. Read More

We report the result of a new Chandra observation of the black hole X-ray transient H 1705-250 in quiescence. H 1705-250 was barely detected in the new 50 ks Chandra observation. With 5 detected counts, we estimate the source quiescent luminosity to be Lx~9. Read More

The microquasar GX 339-4 experienced a new outburst in 2010: it was observed simultaneously at various wavelengths from radio up to soft gamma-rays. We focused on observations that are quasi-simultaneous with those made with the INTEGRAL and RXTE satellites: these were collected in 2010 March-April during our INTEGRAL Target of Opportunity program, and during some of the other INTEGRAL observing programs with GX 339-4 in the field-of-view. X-ray transients are extreme systems that often harbour a black hole, and are known to emit throughout the whole electromagnetic spectrum when in outburst. Read More

Many X-ray binaries remain undetected in the mid-infrared, a regime where emission from their compact jets is likely to dominate. Here, we report the detection of the black hole binary GX 339-4 with the Wide-field Infrared Survey Explorer (WISE) during a very bright, hard accretion state in 2010. Combined with a rich contemporaneous multiwavelength dataset, clear spectral curvature is found in the infrared, associated with the peak flux density expected from the compact jet. Read More

We present optical monitoring of the black hole candidate XTE J1752-223 during its 2009 - 2010 outburst and decay to quiescence. The optical light curve can be described by an exponential decay followed by a plateau, then a more rapid fade towards quiescence. The plateau appears to be due to an extra component of optical emission that brightens and then fades over ~ 40 days. Read More

Affiliations: 1Amsterdam, 2ICRAR - Curtin, 3Southampton, 4Amsterdam, 5Southampton, 6Faulkes Telescope Project, Univ. of Glamorgan, Open Univ.

We present ultradeep radio observations with the Expanded Very Large Array of 4U 1957+11, a Galactic black hole candidate X-ray binary known to exist in a persistent soft X-ray state. We derive a stringent upper limit of 11.4 micro-Jy beam^-1 (3 sigma) at 5-7 GHz, which provides the most rigorous upper limit to date on the presence of jets in a soft state black hole X-ray binary. Read More

Affiliations: 1Amsterdam, 2Southampton, 3Southampton, 4Groningen, 5ESO, 6Faulkes Telescope Project, 7Amsterdam

Time-resolved optical and infrared polarimetric observations of black hole and neutron star low-mass X-ray binaries are presented. Data were acquired with the VLT, UKIRT and HIPPO on the SAAO 1.9-m. Read More

We carried out observations of the small jovian satellite Amalthea (J5) as it was being eclipsed by the Galilean satellites near the 2009 equinox of Jupiter in order to apply the technique of mutual event photometry to the astrometric determination of this satellite's position. The observations were carried out during the period 06/2009-09/2009 from the island of Maui, Hawaii and Siding Spring, Australia with the 2m Faulkes Telescopes North and South respectively. We observed in the near-infrared part of the spectrum using a PanStarrs-Z filter with Jupiter near the edge of the field in order to mitigate against the glare from the planet. Read More

Dwarf novae in globular clusters seem to be rare with only 13 detections in the 157 known Galactic globular clusters. We report the identification of a new dwarf nova in M13, the 14th dwarf nova identified in a globular cluster to date. Using the 2m Faulkes Telescope North, we conducted a search for stars in M13 that show variability over a year (2005-2006) on timescales of days and months. Read More

We present the results of radio observations of the black hole binaries GRO J1655-40 and XTE J1550-564 in quiescence, with the upgraded Australia Telescope Compact Array. Neither system was detected. Radio flux density upper limits (3 sigma) of 26 micro Jy (at 5. Read More

In August 2008, the accreting milli-second X-ray pulsar (AMXP), IGR J00291+5934, underwent an outburst lasting ~ 100 days, the first since its discovery in 2004. We present data from the double-peaked outburst from Faulkes Telescope North, the INT, the Keck Telescope, PAIRITEL, the Westerbork Synthesis Radio Telescope and the Swift, XMM-Newton and RXTE X-ray missions. We study the outburst's evolution at various wavelengths. Read More

We present results from ongoing science projects conducted by members of the Faulkes Telescope (FT) team and Las Cumbres Observatory Global Telescope (LCOGT). Many of these projects incorporate observations carried out and analysed by FT users, comprising amateur astronomers and schools. We also discuss plans for the further development of the LCOGT network. Read More

Affiliations: 1University of Amsterdam, 2Faulkes Telescope Project, Cardiff University, 3Faulkes Telescope Project, Cardiff University, 4Open University, 5University of Southampton, 6University of Southampton

[abridged] Three years of optical monitoring of the low-mass X-ray binary (LMXB) 4U 1957+11 is presented. The source was observed in V, R and i-bands using the Faulkes Telescopes North and South. The light curve is dominated by long-term variations which are correlated (at the > 3 sigma level) with the RXTE ASM soft X-ray flux. Read More

The Faulkes Telescope (FT) Project is an educational and research arm of the Las Cumbres Observatory Global Telescope Network (LCOGTN). As well as producing spectacular images of galaxies, nebulae, supernovae remnants, star clusters, etc., the FT team is involved in several projects pursuing scientific goals. Read More

We carried out observations, with five different instruments ranging in aperture from 0.4m to 10m, of the satellites of Uranus during that planet's 2007 Equinox. Our observations covered specific intervals of time when mutual eclipses and occultations were predicted. Read More

We present phase resolved optical spectroscopy and photometry of V4580 Sagittarii, the optical counterpart to the accretion powered millisecond pulsar SAX J1808.4-3658, obtained during the 2008 September/October outburst. Doppler tomography of the N III 4640. Read More

Affiliations: 1University of Amsterdam, 2University of Amsterdam, 3University of Southampton, 4Las Cumbres Observatory Global Telescope Network
Category: Astrophysics

Synchrotron emission from jets produced by X-ray binaries can be detected at optical and infrared (IR) frequencies. I show that optical/IR colour-magnitude diagrams of the outbursts of nine X-ray binaries successfully separate thermal disc emission from non-thermal jet emission, in both black hole and neutron star sources. A heated single-temperature blackbody is able to reproduce the observed relations between colour and magnitude, except when excursions are made to a redder colour than expected, which is due to jet emission. Read More

The Faulkes Telescope Project is an educational and research arm of the Las Cumbres Observatory Global Telescope Network (LCOGTN). It has two 2-metre robotic telescopes, located at Haleakala on Maui (FT North) and Siding Spring in Australia (FT South). It is planned for these telescopes to be complemented by a research network of eighteen 1-metre telescopes, along with an educational network of twenty-eight 0. Read More

We have been undertaking a monitoring project of 13 low-mass X-ray binaries (LMXBs) using FT North since early 2006. The introduction of FT South has allowed us to extend this monitoring to include 15 southern hemisphere LMXBs. With new instrumentation, we also intend to expand this monitoring to include both infrared wavelengths and spectroscopy. Read More

The Faulkes Telescope Project is the educational arm of the Las Cumbres Observatory Global Telescope Network (LCOGT). It currently has two 2-metre robotic telescopes, located at Haleakala on Maui (FT North) and Siding Spring in Australia (FT South). It is planned to increase this to six 2-metre telescopes in the future, complemented by a network of 30-40 smaller (0. Read More

Affiliations: 1Department of Physics and Astronomy, University of Leicester, 2Department of Physics, University of Warwick, 3Department of Physics, University of Warwick, 4Department of Physics and Astronomy, University of Leicester, 5Department of Physics and Astronomy, University of Sheffield, Sheffield, UK, 6Department of Physics and Astronomy, University of Sheffield, Sheffield, UK, 7Oundle School, Northamptonshire, UK, 8Department of Physics and Astronomy, University of Leicester, 9Department of Physics and Astronomy, University of Leicester, 10Department of Physics and Astronomy, University of Leicester, 11Department of Physics and Astronomy, University of Leicester, 12Department of Physics and Astronomy, University of Leicester, 13Department of Physics and Astronomy, University of Leicester, 14Department of Physics and Astronomy, University of Leicester, 15Gemini Observatory, USA, 16Institute of Astronomy, University of Cambridge, UK, 17Institute of Astronomy, University of Cambridge, UK, 18Department of Physics and Astronomy, University of Wales, UK, 19Department of Physics and Astronomy, University of Wales, UK
Category: Astrophysics

Optical time series photometry of the short period magnetic white dwarf + probable brown dwarf binary SDSS 121209.31+013627.7 reveals pulse-like variability in all bands from i' to u', peaking at u'. Read More