The Arcminute Microkelvin Imager Zwart, J. T. L.; Barker, R. W.; Biddulph, P. ...
Monthly notices of the Royal Astronomical Society,
12/2008, Letnik:
391, Številka:
4
Journal Article
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The Arcminute Microkelvin Imager is a pair of interferometer arrays operating with six frequency channels spanning 13.9–18.2 GHz, for observations on angular scales of 30 arcsec–10 arcmin and for ...declinations greater than −15°; the Small Array has a sensitivity of 30 mJy s−1/2 and the Large Array has a sensitivity of 3 mJy s−1/2. The telescope is aimed principally at Sunyaev–Zel'dovich imaging of clusters of galaxies. We discuss the design of the telescope and describe and explain its electronic and mechanical systems.
Transport policies to increase active and sustainable travel in Britain have focused mainly on persuading people of the health benefits of walking and cycling for short trips, and have assumed that ...if people can be persuaded that more active travel has personal benefits then behavioural change will follow. Research reported in this paper, based mainly on detailed qualitative research in four English towns, argues that the complexities and contingencies that most people encounter in everyday life often make such behavioural change difficult. Attention is focused on three sets of factors: perceptions of risk; constraints created by family and household responsibilities; and perceptions of normality. It is suggested that unless such factors are tackled directly then policies to increase levels of walking and cycling will have limited success. In particular, it is argued that there needs to be a much more integrated approach to transport policy that combines interventions to make walking and (especially) cycling as risk-free as possible with restrictions on car use and attitudinal shifts in the ways in which motorists view other road users. Such policies also need to be linked to wider social and economic change which, in combination, creates an environment in which walking or cycling for short trips in urban areas is perceived as the logical and normal means of travel and using the car is viewed as exceptional.
► Most British people find it hard to incorporate active travel into everyday routines. ► Perceptions of risk are a major deterrent especially for cycling. ► Family and household constraints frequently prevent walking and cycling. ► Walking and cycling is not seen as a normal way to travel. ► Transport policies need to recognise these constraints more explicitly.
We present 15-GHz follow-up radio observations of 11 Swift gamma-ray burst (GRB) sources, obtained with the Arcminute Microkelvin Imager Large Array (AMI-LA). The initial follow-up observation for ...each source was made in a fully automated fashion; as a result four observations were initiated within 5 min of the GRB alert time stamp. These observations provide the first millijansky-level constraints on prolonged radio emission from GRBs within the first hour post-burst. While no radio emission within the first six hours after the GRB is detected in this preliminary analysis, radio afterglow is detected from one of the GRBs (GRB 120326A) on a time-scale of days. The observations were made as part of an ongoing programme to use AMI-LA as a systematic follow-up tool for transients at radio frequencies. In addition to the preliminary results, we explain how we have created an easily extensible automated follow-up system, describing new software tools developed for astronomical transient alert distribution, automatic requesting of target-of-opportunity observations and robotic control of the observatory.
Context. Long gamma-ray bursts (GRBs) give us the chance to study both their extreme physics and the star-forming galaxies in which they form. Aims. GRB 100418A, at a redshift of z = 0.6239, had a ...bright optical and radio afterglow, and a luminous star-forming host galaxy. This allowed us to study the radiation of the explosion as well as the interstellar medium of the host both in absorption and emission. Methods. We collected photometric data from radio to X-ray wavelengths to study the evolution of the afterglow and the contribution of a possible supernova (SN) and three X-shooter spectra obtained during the first 60 h. Results. The light curve shows a very fast optical rebrightening, with an amplitude of ∼3 magnitudes, starting 2.4 h after the GRB onset. This cannot be explained by a standard external shock model and requires other contributions, such as late central-engine activity. Two weeks after the burst we detect an excess in the light curve consistent with a SN with peak absolute magnitude MV = −18.5 mag, among the faintest GRB-SNe detected to date. The host galaxy shows two components in emission, with velocities differing by 130 km s−1, but otherwise having similar properties. While some absorption and emission components coincide, the absorbing gas spans much higher velocities, indicating the presence of gas beyond the star-forming regions. The host has a star formation rate of SFR = 12.2 M⊙ yr−1, a metallicity of 12 + log(O/H) = 8.55, and a mass of 1.6 × 109 M⊙. Conclusions. GRB 100418A is a member of a class of afterglow light curves which show a steep rebrightening in the optical during the first day, which cannot be explained by traditional models. Its very faint associated SN shows that GRB-SNe can have a larger dispersion in luminosities than previously seen. Furthermore, we have obtained a complete view of the host of GRB 100418A owing to its spectrum, which contains a remarkable number of both emission and absorption lines.
We present 5-GHz Multi-Element Radio-Linked Interferometer Network (MERLIN) radio images of the microquasar GRS 1915+105 during two separate outbursts in 2001 March and July, following the evolution ...of the jet components as they move outwards from the core of the system. Proper motions constrain the intrinsic jet speed to be >0.57c, but the uncertainty in the source distance prevents an accurate determination of the jet speed. No deceleration is observed in the jet components out to an angular separation of ∼300 mas. Linear polarization is observed in the approaching jet component, with a gradual rotation in position angle and a decreasing fractional polarization with time. Our data lend support to the internal shock model whereby the jet velocity increases leading to internal shocks in the pre-existing outflow before the jet switches off. The compact nuclear jet is seen to reestablish itself within 2 d, and is visible as core emission at all epochs. The energetics of the source are calculated for the possible range of distances; a minimum power of 1–10 per cent of the Eddington luminosity (LEdd) is required to launch the jet.
Studies on glucocorticoid receptor (GR) action typically assess gene responses by long-term stimulation with synthetic hormones. As corticosteroids are released from adrenal glands in a circadian and ...high-frequency (ultradian) mode, such treatments may not provide an accurate assessment of physiological hormone action. Here we demonstrate that ultradian hormone stimulation induces cyclic GR-mediated transcriptional regulation, or gene pulsing, both in cultured cells and in animal models. Equilibrium receptor-occupancy of regulatory elements precisely tracks the ligand pulses. Nascent RNA transcripts from GR-regulated genes are released in distinct quanta, demonstrating a profound difference between the transcriptional programs induced by ultradian and constant stimulation. Gene pulsing is driven by rapid GR exchange with response elements and by GR recycling through the chaperone machinery, which promotes GR activation and reactivation in response to the ultradian hormone release, thus coupling promoter activity to the naturally occurring fluctuations in hormone levels. The GR signalling pathway has been optimized for a prompt and timely response to fluctuations in hormone levels, indicating that biologically accurate regulation of gene targets by GR requires an ultradian mode of hormone stimulation.
There is increasing focus on the role small-scale decentralised renewable energy developments could play in helping the UK meet its target of over 15% renewable energy by the year 2020 and alter ...energy behaviours through active community engagement. Upland areas are considered key areas where such community-based developments could occur due to their natural resources and range of community scales. This study uses GIS-based techniques to develop a methodology that assesses the regional-scale potential for community-based renewable electricity across Cumbria and whether a combination of these developments at the community-scale could make a significant contribution to local electricity consumption. This methodology looks at a range of technologies including hydro-power, wind-power, solar PV and bioenergy. The results suggest there is ample resource available for small communities by combining a mix of localised renewable electricity developments, which is highlighted through energy scenarios for a selected community. Further work will investigate whether this potential can be realised in reality by looking at resource resilience and community-level acceptability.
► A mix of wind, solar, bioenergy & hydro-power options are presented for Cumbria, UK. ► High resolution spatial analysis is conducted focussing on localised developments. ► Locations with sufficient renewable electricity potential were identified. ► Renewable options are explored further through a town case study. ► Scenarios consider different scales, mixes and contributions to local energy demand.
Context. Some recent observational results impose significant constraints on all the models that have been proposed to explain the Galactic black-hole X-ray sources in the hard state. In particular, ...it has been found that during the hard state of Cyg X-1 the power-law photon number spectral index, Γ, is correlated with the average time lag, $\langle t_{\rm lag}\rangle$, between hard and soft X-rays. Furthermore, the peak frequencies of the four Lorentzians that fit the observed power spectra are correlated with both Γ and $\langle t_{\rm lag}\rangle$. Aims. We have investigated whether our jet model can reproduce these correlations. Methods. We performed Monte Carlo simulations of Compton upscattering of soft, accretion-disk photons in the jet and computed the time lag between hard and soft photons and the power-law index Γ of the resulting photon number spectra. Results. We demonstrate that our jet model naturally explains the above correlations, with no additional requirements and no additional parameters.
Microquasars are accreting black holes or neutron stars in binary systems with associated relativistic jets. Despite their frequent outburst activity, they have never been unambiguously detected ...emitting high-energy gamma rays. The Fermi Large Area Telescope (LAT) has detected a variable high-energy source coinciding with the position of the x-ray binary and microquasar Cygnus X-3. Its identification with Cygnus X-3 is secured by the detection of its orbital period in gamma rays, as well as the correlation of the LAT flux with radio emission from the relativistic jets of Cygnus X-3. The gamma-ray emission probably originates from within the binary system, opening new areas in which to study the formation of relativistic jets.
Detecting gamma-rays from microquasars is a challenging but worthwhile endeavor for understanding particle acceleration and the jet mechanism and for constraining leptonic/hadronic emission models. ...We present results from a likelihood analysis on timescales of 1 day and 10 days of ~4 yr worth of gamma-ray observations (0.1-10 GeV) by Fermi-LAT of Cyg X-1, Cyg X-3, GRS 1915+105, and GX 339-4. Our analysis reproduced all but one of the previous gamma-ray outbursts of Cyg X-3 as reported with Fermi or AGILE, plus five new days on which Cyg X-3 is detected at a significance of ~5sigma that are not reported in the literature. In addition, Cyg X-3 is significantly detected on 10 day timescales outside of known gamma-ray flaring epochs, which suggests that persistent gamma-ray emission from Cyg X-3 has been detected for the first time. For Cyg X-1 we find three low-significance excesses (~3-4sigma) on daily timescales that are contemporaneous with gamma-ray flares reported (also at low significance) by AGILE. Two other microquasars, GRS 1915+105 and GX 339-4, are not detected, and we derive 3sigma upper limits of 2.3 x 10 super(-8) photons cm super(-2) s super(-1) and 1.6 x 10 super(-8) photons cm super(-2) s super(-1), respectively, on the persistent flux in the 0.1-10 GeV range. These results enable us to define a list of the general conditions that are necessary for the detection of gamma-rays from microquasars.
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