81 research outputs found
Multiwavelength observations of the Be/X-ray binary 4U1145-619
We report optical and infrared observations of the massive X-ray binary
system 4U1145-619 (V801 Cen) which show that the circumstellar disc of the Be
star component is in decline. Infrared J,H,K,L magnitudes of V801Cen have been
monitored from 1993 March to 1996 April. H alpha spectra have been obtained
throughout the same period. We find that both the infrared excess and the
Balmer emission have been in decline throughout the period of observations. A
13 year optical and X-ray history of the source has been collated, revealing a
possible correlation between the optical and X-ray activity. In addition, we
have used u,v,b,y,beta indices, corrected for both circumstellar and
interstellar effects, to calculate the physical parameters of the underlying B
star.Comment: 8 pages postscript. Accepted by MNRA
Optical Polarimetry of the May 2022 Lunar Eclipse
The sunlight reflected from the Moon during a total lunar eclipse has been
transmitted through the Earth's atmosphere on the way to the Moon. The
combination of multiple scattering and inhomogeneous atmospheric
characteristics during that transmission can potentially polarize that light. A
similar (although much smaller) effect should also be observable from the
atmosphere of a transiting exoplanet. We present the results of polarization
observations during the first 15 minutes of totality of the lunar eclipse of
2022 May 16. We find degrees of polarization of 2.1 +/- 0.4 per cent in B, 1.2
+/- 0.3 per cent in V, 0.5 +/- 0.2 per cent in R and 0.2 +/- 0.2 per cent in I.
Our polarization values lie in the middle of the range of those reported for
previous eclipses, providing further evidence that the induced polarization can
change from event to event. We found no significant polarization difference
(<0.02 per cent) between a region of dark Mare and nearby bright uplands or
between the lunar limb and regions closer to the disk centre due to the
different angle of incidence. This further strengthens the interpretation of
the polarization's origin being due to scattering in the Earth's atmosphere
rather than by the lunar regolith.Comment: Accepted for publication in MNRA
MOPTOP: Multi-colour Optimised Optical Polarimeter
Polarimetric measurements are essential for the study of jetted sources associated with black holes, such as γ-ray bursts and blazars. The relativistic jets launched from regions close to the black hole are threaded with magnetic fields, which produce synchrotron emission, and can be studied with polarimetric measurements. The multi-colour, optimised, optical polarimeter (MOPTOP) is a multi-band imaging instrument designed for use on the Liverpool Telescope. By replacing the rotating polaroid with a half wave plate and beam splitter, the instrument utilises twice as much of the incoming beam of light from the telescope compared to its predecessor, Ringo3. MOPTOP also builds on the successful introduction of dichroic mirrors to perform simultaneous multi-waveband polarimetric and photometric analysis in Ringo3, and enhances the sensitivity of the instrument with sCMOS cameras to use all photons as efficiently as possible
A flash of polarized optical light points to an aspherical ‘cow’
The astronomical transient AT2018cow is the closest example of the new class of luminous, fast blue optical transients (FBOTs). Liverpool telescope RINGO3 observations of AT 2018cow are reported here, which constitute the earliest polarimetric observations of an FBOT. At 5.7 days post-explosion, the optical emission of AT2018cow exhibited a chromatic polarization spike that reached ∼ 7% at red wavelengths. This is the highest intrinsic polarization recorded for a non-relativistic explosive transient and is observed in multiple bands and at multiple epochs over the first night of observations, before rapidly declining. The apparent wavelength dependence of the polarization may arise through depolarization or dilution of the polarized flux, due to conditions in AT 2018cow at early times. A second 'bump' in the polarization is observed at blue wavelengths at ∼ 12 days. Such a high polarization requires an extremely aspherical geometry that is only apparent for a brief period (<1 d), such as shock breakout through an optically thick disk. For a disk-like configuration, the ratio of the thickness to radial extent must be ∼ 10%.</p
The Liverpool Telescope: Rapid follow-up observation of Targets of opportunity with a 2 m robotic telescope
The Liverpool Telescope, situated at Roque de los Muchachos Observatory, La
Palma, Canaries, is the first 2-m, fully instrumented robotic telescope. It
recently began observations. Among Liverpool Telescope's primary scientific
goals is to monitor variable objects on all timescales from seconds to years.
An additional benefit of its robotic operation is rapid reaction to
unpredictable phenomena and their systematic follow up, simultaneous or
coordinated with other facilities. The Target of Opportunity Programme of the
Liverpool Telescope includes the prompt search for and observation of GRB and
XRF counterparts. A special over-ride mode implemented for GRB/XRF follow-up
enables observations commencing less than a minute after the alert, including
optical and near infrared imaging and spectroscopy. In particular, the moderate
aperture and rapid automated response make the Liverpool Telescope excellently
suited to help solving the mystery of optically dark GRBs and for the
investigation of currently unstudied short bursts and XRFs.Comment: 4 pages, 1 figure. To appear in the Proceedings of The Restless
High-Energy Universe, 5-8 May 2003, Amsterdam, E.P.J. van den Heuvel, J.J.M.
in 't Zand, and R.A.M.J. Wijers (eds.
Two Decades in the Life of EXO 2030+375
EXO 2030+375, a 42-s accreting pulsar in a 46-day orbit around a Be star, has undergone a detected outburst at nearly every periastron passage since 1991. It has been monitored with BATSE, RXTE, and Fermi/GBM. We will present preliminary results of long-term monitoring, including a long-term frequency history, long-term pulsed flux measurements, and available long ]term optical/ir monitoring results
All-Sky Monitoring of Variable Sources with Fermi GBM
Using the Gamma ray Burst Monitor (GBM) on Fermi, we monitor the transient hard X-ray/soft gamma ray sky. The twelve GBM NaI detectors span 8 keV to 1 MeV, while the two BGO detectors span 150 keV to 40 MeV. We use the Earth occultation technique to monitor a number of sources, including X-ray binaries, AGN, and solar flaring activity. Our monitoring reveals predictable and unpredictable phenomena such as transient outbursts and state changes. With GBM we also track the pulsed flux and spin frequency of accretion powered pulsars using epoch-folding techniques. Searches for quasi-periodic oscillations and X-ray bursts are also possible with GBM all-sky monitoring. Highlights from the Earth Occultation and Pulsar projects will be presented including our recent surprising discovery of variations in the total flux from the Crab. Inclusion of an all-sky monitor is crucial for a successful future X-ray timing mission
The perihelion activity of comet 67P/Churyumov-Gerasimenko as seen by robotic telescopes
Around the time of its perihelion passage the observability of 67P/Churyumov-Gerasimenko from Earth was limited to very short windows each morning from any given site, due to the low solar elongation of the comet. The peak in the comet's activity was therefore difficult to observe with conventionally scheduled telescopes, but was possible where service/queue scheduled mode was possible, and with robotic telescopes. We describe the robotic observations that allowed us to measure the total activity of the comet around perihelion, via photometry (dust) and spectroscopy (gas), and compare these results with the measurements at this time by Rosetta's instruments. The peak of activity occurred approximately two weeks after perihelion. The total brightness (dust) largely followed the predictions from Snodgrass et al. (2013), with no significant change in total activity levels from previous apparitions. The CN gas production rate matched previous orbits near perihelion, but appeared to be relatively low later in the year
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