Examinando por Autor "Bramich D.M."

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    MiNDSTEp differential photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756: Microlensing and a new time delay
    (EDP Sciences, 2017) Giannini E.; Schmidt R.W.; Wambsganss J.; Alsubai K.; Andersen J.M.; Anguita T.; Bozza V.; Bramich D.M.; Browne P.; Calchi Novati S.; Damerdji Y.; Diehl C.; Dodds P.; Dominik M.; Elyiv A.; Fang X.; Figuera Jaimes R.; Finet F.; Gerner T.; Gu S.; Hardis S.; Harpsøe K.; Hinse T.C.; Hornstrup A.; Hundertmark M.; Jessen-Hansen J.; Jørgensen U.G.; Juncher D.; Kains N.; Kerins E.; Korhonen H.; Liebig C.; Lund M.N.; Lundkvist M.S.; Maier G.; Mancini L.; Masi G.; Mathiasen M.; Penny M.; Proft S.; Rabus M.; Rahvar S.; Ricci D.; Scarpetta G.; Sahu K.; Schäfer S.; Schönebeck F.; Skottfelt J.; Snodgrass C.; Southworth J.; Surdej J.; Tregloan-Reed J.; Vilela C.; Wertz O.; Zimmer F.
    Aims. We present V and R photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756. The data were taken by the MiNDSTEp collaboration with the 1.54 m Danish telescope at the ESO La Silla observatory from 2008 to 2012. Methods. Differential photometry has been carried out using the image subtraction method as implemented in the HOTPAnTS package, additionally using GALFIT for quasar photometry. Results. The quasar WFI 2033-4723 showed brightness variations of order 0.5 mag in V and R during the campaign. The two lensed components of quasar HE 0047-1756 varied by 0.2-0.3 mag within five years. We provide, for the first time, an estimate of the time delay of component B with respect to A of Δt = (7.6 ± 1.8) days for this object. We also find evidence for a secular evolution of the magnitude difference between components A and B in both filters, which we explain as due to a long-duration microlensing event. Finally we find that both quasars WFI 2033-4723 and HE 0047-1756 become bluer when brighter, which is consistent with previous studies. © ESO, 2016.
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    Probing Jet Launching in Neutron Star X-Ray Binaries: The Variable and Polarized Jet of SAX J1808.4-3658
    (IOP Publishing Ltd., 2020-12) Baglio M.C.; Russell D.M.; Crespi S.; Covino S.; Johar A.; Homan J.; Bramich D.M.; Saikia P.; Campana S.; D'Avanzo P.; Fender R.P.; Goldoni P.; Goodwin A.J.; Lewis F.; Masetti N.; Zanon A.M.; Motta S.E.; Munoz-Darias T.; Shahbaz T.
    We report on an optical photometric and polarimetric campaign on the accreting millisecond X-ray pulsar (AMXP) x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">SAX x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">4-x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">J1808.x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">4-x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">3658 during its 2019 outburst. The emergence of a low-frequency excess x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">in the spectral energy distribution x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">in the form of a red excess above the disk spectrum (seen most prominently x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">in the z, i, and R bands) is observed as the outburst evolves. This is indicative of optically thin synchrotron emission due to a jet, as seen previously x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">in this source and x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">in other AMXPs during outburst. At the end of the outburst decay, the source enters a reflaring state. The low-frequency excess is still observed during the reflares. Our optical (BVRI) polarimetric campaign shows variable linear polarization (LP) throughout the outburst. We show that this is intrinsic to the source, with low-level but significant detections (0.2%-2%) x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">in all bands. The LP spectrum is red during both the main outburst and the reflaring state, favoring a jet origin for this variable polarization over other interpretations, such as Thomson scattering with free electrons from the disk or the propelled matter. During the reflaring state, a few episodes with stronger LP levels (1%-2%) are observed. The low-level, variable LP is suggestive of strongly tangled magnetic fields near the base of the jet. These results clearly demonstrate how polarimetry is a powerful tool for x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">probing the magnetic field structure x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">in X-ray binary jets, as for active galactic nuclei jets. © 2020. The American Astronomical Society. All rights reserved..