2,307 research outputs found
Laboratory astrophysics : investigation of planetary and astrophysical maser emission
No full textThis paper describes a model for cyclotron maser emission applicable to planetary auroral radio emission, the stars UV Ceti and CU Virginus, blazar jets and astrophysical shocks. These emissions may be attributed to energetic electrons moving into convergent magnetic fields that are typically found in association with dipole like planetary magnetospheres or shocks. It is found that magnetic compression leads to the formation of a velocity distribution having a horseshoe shape as a result of conservation of the electron magnetic moment. Under certain plasma conditions where the local electron plasma frequency ωpe is much less than the cyclotron frequency ωce the distribution is found to be unstable to maser type radiation emission. We have established a laboratory-based facility that has verified many of the details of our original theoretical description and agrees well with numerical simulations. The experiment has demonstrated that the horseshoe distribution produces cyclotron emission at a frequency just below the local electron cyclotron frequency, with polarisation close to X-mode and propagating nearly perpendicularly to the electron beam motion. We discuss recent developments in the theory and simulation of the instability including addressing radiation escape problems, and relate these to the laboratory, space, and astrophysical observations. The experiments showed strong narrow band EM emissions at frequencies just below the cold-plasma cyclotron frequency as predicted by the theory. Measurements of the conversion efficiency, mode and spectral content were in close agreement with the predictions of numerical simulations undertaken using a particle-in-cell code and also with satellite observations confirming the horseshoe maser as an important emission mechanism in geophysical/astrophysical plasmas. In each case we address how the radiation can escape the plasma without suffering strong absorption at the second harmonic layer.Peer reviewe
Rapid time variations of water maser emission in W3(OH) and NGC 6334C
No full textWe report the observed results of a short time scale monitoring of the 22 GHz water maser emission in W3(OH) and NGC 6334C. Both sources were monitored daily for about a month. The aim of the observations is to investigate the possible presence of very short interval variations on time scales of hours or days. Our observations showed that the flux density of the component at -52.8 km s(-1) in W3(OH) decayed linearly with a timescale of about 19 days, and a maser in NGC 6334C flared rapidly, doubling the flux with a timescale of about 4 days. The rapid time variability of the observed water maser features may be caused by an external pumping event. The collision among dense clumps at sufficient relative velocities supplies the powerful energy required to excite H2O maser emission and then quenches the pump in the following days or longer period
DETECTION OF 36 GHz CLASS I METHANOL MASER EMISSION TOWARD NGC 253
No full textWe have used the Australia Telescope Compact Array to search for emission from the 4-1 -> 3(0)E transition of methanol (36.2 GHz) toward the center of the nearby starburst galaxy NGC 253. Two regions of emission were detected, offset from the nucleus along the same position angle as the inner spiral arms. The emission is largely unresolved on a scale of 5", has a FWHM line width of < 30 km s(-1), and an isotropic luminosity orders of a magnitude larger than that observed in any Galactic star formation region. These characteristics suggest that the 36.2 GHz methanol emission is most likely a maser, although observations with higher angular and spectral resolution are required to confirm this. If it is a maser, this represents the first detection of a class I methanol maser outside the Milky Way. The 36.2 GHz methanol emission in NGC 253 has more than an order of magnitude higher isotropic luminosity than the widespread emission recently detected toward the center of the Milky Way. If emission from this transition scales with the nuclear star formation rate, then it may be detectable in the central regions of many starburst galaxies. Detection of methanol emission in ultra-luminous infrared galaxies would open up a new tool for testing for variations in fundamental constants (particularly the proton-to-electron mass ratio) on cosmological scales
Numerical simulation of unconstrained cyclotron resonant maser emission
No full textWhen a mainly rectilinear electron beam is subject to significant magnetic compression, conservation of magnetic moment results in the formation of a horseshoe shaped velocity distribution. It has been shown that such a distribution is unstable to cyclotron emission and may be responsible for the generation of Auroral Kilometric Radiation (AKR) - an intense rf emission sourced at high altitudes in the terrestrial auroral magnetosphere. PiC code simulations have been undertaken to investigate the dynamics of the cyclotron emission process in the absence of cavity boundaries with particular consideration of the spatial growth rate, spectral output and rf conversion efficiency. Computations reveal that a well-defined cyclotron emission process occurs albeit with a low spatial growth rate compared to waveguide bounded simulations. The rf output is near perpendicular to the electron beam with a slight backward-wave character reflected in the spectral output with a well defined peak at 2.68GHz, just below the relativistic electron cyclotron frequency. The corresponding rf conversion efficiency of 1.1% is comparable to waveguide bounded simulations and consistent with the predictions of kinetic theory that suggest efficient, spectrally well defined radiation emission can be obtained from an electron horseshoe distribution in the absence of radiation boundaries
Discovery of two new class II methanol maser transitions in G 345.01+1.79
No full textWe have used the Swedish ESO Submillimetre Telescope (SEST) to search for new classII methanol maser transitions toward the southern source G345.01+1.79. Over a period of 5days, we observed 11 known or predicted classII methanol maser transitions. Emission with the narrow line width and characteristic velocity of classII methanol masers (in this source) was detected in eight of these transitions, two of which have not previously been reported as masers. The new classII methanol maser transitions are the 13-3-12-4 E transition at 104.1GHz and the 51-42 E transition at 216.9GHz. Both of these are from transition series for which there are no previous known classII methanol maser transitions. This takes the total number of known classII methanol maser series to 10, and the total number of transitions (or transition groups) to 18. The observed 104.1GHz maser suggests the presence of two or more regions of masing gas with similar line of sight velocities, but quite different physical conditions. Although these newly discovered transitions are likely to be relatively rare, where they are observed, combined studies using the Australia Telescope Compact Array and the Atacama Large Millimeter Array offer the prospect to be able to undertake multi-transition methanol maser studies with unprecedented detail. © 2012. The American Astronomical Society. All rights reserved
Hydrogen maser frequency standard
No full textThe fundamental theoretical limitations of the maser, systematic processes that cause instability, and some aspects of recently designed masers are described. A design for field use that has evolved from the development of the space borne maser is presented. The performance of this type of maser is close to theoretical limits imposed by thermal noise. Further developments of smaller masers for space and terrestrial use and recent work on masers operating at low temperatures is also discussed
Ultra-precise monitoring of a class I methanol maser
No full textWe report the results of a 7-year monitoring program using the Australia Telescope Compact Array (ATCA) for the 9.9 GHz class I methanol maser in G331.13-0.24 where a periodic class II methanol maser is present. The great deal of the project was to control systematics at an unprecedented level. Although no periodic flux variation was found, the maser shows a very stable decline of 166±7 Jy/day. The radial velocity of the maser is stable down to 1 m/s level. We also report a marginal periodic signal in radial velocity (comparable to the level of systematics) of about 20±7 cm/s with the period of 475±22 days, close to that of the 6.7-GHz maser in the source. No hyperfine split was detected which suggests preferential excitation of a single hyperfine transition. © The Author(s), 2024. Published by Cambridge University Press on behalf of International Astronomical Union
Maser Polarization with ALMA
No full textOnce ALMA full polarization capabilities are offered, (sub-)mm polarization studies will enter a new era. It will become possible to perform detailed studies of polarized maser emission towards for example massive star forming regions and late-type stars such as (post-) Asymptotic Giant Branch stars and young Planetary Nebulae. In these environments, SiO, H2O and HCN are molecules that can naturally generate polarized maser emission observable by ALMA. The maser polarization can then be used to derive the strength and morphology of the magnetic field in the masing regions. However, in order to derive, in particular, the magnetic field orientation from maser linear polarization, a number of conditions involving the rate of stimulated emission, molecular state decay and Zeeman splitting need to be satisfied. In this work, we discuss these conditions for the maser transitions in the ALMA frequency range and highlight the optimum transitions to further our understanding of star formation and evolved star magnetic fields
Jean-Antoine de Baif : Le Brave
No full textMaser Simone. Jean-Antoine de Baif : Le Brave. In: Bulletin de l'Association d'étude sur l'humanisme, la réforme et la renaissance, n°10, 1979. p. 100
Jean-Antoine de Baif : Le Brave
No full textMaser Simone. Jean-Antoine de Baif : Le Brave. In: Bulletin de l'Association d'étude sur l'humanisme, la réforme et la renaissance, n°10, 1979. p. 100
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