Quasi-steady Emission Research Articles

Radio Emission from the Exoplanetary System ϵ Eridani

Abstract As part of a wider search for radio emission from nearby systems known or suspected to contain extrasolar planets, ϵ Eridani was observed by the Jansky Very Large Array (VLA) in the 2–4 GHz and 4–8 GHz frequency bands. In addition, as part of a separate survey of thermal emission from solar-like stars, ϵ Eri was observed in the 8–12 GHz and the 12–18 GHz bands of the VLA. Quasi-steady continuum radio emission from ϵ Eri was detected in the three high-frequency bands at levels ranging from 67 to 83 μJy. No significant variability is seen in the quasi-steady emission. The emission in the 2–4 GHz emission, however, is shown to be the result of a circularly polarized (up to 50%) radio pulse or flare of a few minutes in duration that occurred at the beginning of the observation. We consider the astrometric position of the radio source in each frequency band relative to the expected position of the K2V star and the purported planet. The quasi-steady radio emission at frequencies ≥8 GHz is consistent with a stellar origin. The quality of the 4–8 GHz astrometry provides no meaningful constraint on the origin of the emission. The location of the 2–4 GHz radio pulse is >2.5σ from the star; however, based on the ephemeris of Benedict et al., it is not consistent with the expected location of the planet either. If the radio pulse has a planetary origin, then either the planetary ephemeris is incorrect or the emission originates from another planet.

XMM-Newtonand the Pleiades - I. Bright coronal sources and the X-ray emission from intermediate-type stars

We perform X-ray spectral and timing analyses of solar-like (spectral types F5--K8) and intermediate-type (B4--F4) Pleiads observed in a 40-ks XMM-Newton EPIC exposure. All 8 solar-like members have ``quasi-steady'' \lx $\ga 10^{29}$ erg/s and 4 exhibit flares. Using a hydrodynamic modelling technique we derive loop half-lengths ${\cal L} \la 0.5 R_{\star}$ for the two strongest flares, on HII 1032 and HII 1100. HII 1100's lightcurve suggests a total occultation of the flaring loop. Eclipse by a substellar companion in a close orbit is possible but would seem a highly fortuitous event; absorption by a fast-moving cloud of cool material requires \nh at least two orders of magnitude greater than any solar or stellar prominence. An occultation may have been mimicked by the coincidence of two flares, though the first, its decay time shorter than its rise time and suggestive of ${\cal L} \sim 0.02 R_{\star}$, would be unusual. Spectral modelling of the quasi-steady emission shows a rising trend in coronal temperature from F and slowly-rotating G stars through K stars to fast-rotating G stars, and a preference for low coronal metallicity: features consistent with those of nearby solar-like stars, although none of the three stars showing ``saturated'' emission bears the significant component at 2 keV seen in the saturated coronae of AB Dor and 47 Cas. Of 5 intermediate-type stars, 2 are undetected (\lx$ < 4 \times 10^{27}$ erg/s) and 3 show X-ray emission with a spectrum and \lx consistent with origin from an active solar-like companion.

Disk‐Jet Connection in the Microquasar GRS 1915+105 and Infrared and Radio Emission

We present evidence of a direct accretion disk-jet connection in the Galactic microquasar GRS 1915+105 based on our analysis of RXTE/PCA data with a "spike" in X-ray light curves. We find that the radio emission increases as the hardness ratio increases during the low hard state. We suggest that the "spike," which separates the dips with hard and soft spectra, marks the beginning of the burst phase when the luminosity of the soft X-rays (5-15 keV) increases by a large factor (~10). This produces a major ejection episode of the synchrotron-emitting plasma termed as "baby jets," which are associated with infrared (IR) and radio flares of about half an hour period widely reported in the literature. Subsequent short but frequent soft dips produce overlapping faint flares which result in an enhanced level of quasi-steady emission. We discuss the differences between "baby jets" and relativistic radio jets and especially investigate their signatures in X-rays.

Analytic and numerical solutions of rate equations for multilevel chemical and molecular lasers in quasisteady approximation. I. Analytic treatment

An analysis is made of kinetics of a multilevel laser utilizing vibration-rotational transitions in molecules. A solution is obtained of the rate equations for quasisteady emission. This solution is used in the derivation of an analytic expression describing the dependence of the output power of a laser on its principal parameters.