Multiple relativistic outbursts of GRS 1915+105: radio emission and internal shocks     

J. C. A. Miller-Jones  D. G. McCormick  R. P. Fender  R. E. Spencer  T. W. B. Muxlow  G. G. Pooley 《Monthly notices of the Royal Astronomical Society》2005,363(3):867-881

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  >0.57 c   , 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 ( L _Edd) is required to launch the jet.  相似文献   

Initial low/hard state, multiple jet ejections and X-ray/radio correlations during the outburst of XTE J1859+226   总被引：1，自引：0，他引：1  

C.Brocksopp  R. P.Fender  M.McCollough  G. G.Pooley  M. P.Rupen  R. M.Hjellming  C. J.de la Force  R. E.Spencer  T. W. B.Muxlow  S. T.Garrington  S.Trushkin 《Monthly notices of the Royal Astronomical Society》2002,331(3):765-775

We have studied the 1999 soft X-ray transient outburst of XTE J1859+226 at radio and X-ray wavelengths. The event was characterized by strong variability in the disc, corona and jet – in particular, a number of radio flares (ejections) took place and seemed well-correlated with hard X-ray events. Apparently unusual for the canonical 'soft' X-ray transient, there was an initial period of low/hard state behaviour during the rise from quiescence but prior to the peak of the main outburst – we show that not only could this initial low/hard state be a ubiquitous feature of soft X-ray transient outbursts, but also it could be extremely important in our study of outburst mechanisms.  相似文献   

5-GHz MERLIN and VLBA observations of compact 9C sources     

R. C. Bolton  C. J. Chandler  G. Cotter  T. J. Pearson  G. G. Pooley  A. C. S. Readhead  J. M. Riley  E. M. Waldram 《Monthly notices of the Royal Astronomical Society》2006,367(1):323-330

In this paper, we present subarcsecond resolution observations of 36 compact sources from the 15^h region of the 15-GHz 9th Cambridge survey. These sources all have previously measured simultaneous continuum radio spectra spanning 1.4–43 GHz and we classify each source by fitting a quadratic function to its spectrum. Using the Multi-Element Radio-Linked Interferometer Network and the Very Long Baseline Array, both at 5 GHz, we resolve all six steep-spectrum objects and four of the 13 flat-spectrum objects. However, none of the 16 objects with convex spectra peaking above 2.5 GHz is resolved even at <3-mas resolution. These results, in combination with the findings of a 15-GHz variability study, suggest that emission from the high-frequency peaking objects is affected by relativistic beaming, and that these objects are not necessarily as young as the synchrotron self-absorption interpretation of their peak frequencies would imply.  相似文献   

Opacity effects and shock-in-jet modelling of low-level activity in Cygnus X-3     

James C. A. Miller-Jones  Michael P. Rupen  Marc Türler  Elina J. Lindfors  Katherine M. Blundell  Guy G. Pooley 《Monthly notices of the Royal Astronomical Society》2009,394(1):309-322

We present simultaneous dual-frequency radio observations of Cygnus X-3 during a phase of low-level activity. We constrain the minimum variability time-scale to be 20 min at 43 GHz and 30 min at 15 GHz, implying source sizes of 2–4 au. We detect polarized emission at a level of a few per cent at 43 GHz which varies with the total intensity. The delay of ∼10 min between the peaks of the flares at the two frequencies is seen to decrease with time, and we find that synchrotron self-absorption and free–free absorption by entrained thermal material play a larger role in determining the opacity than absorption in the stellar wind of the companion. A shock-in-jet model gives a good fit to the light curves at all frequencies, demonstrating that this mechanism, which has previously been used to explain the brighter, longer lived giant outbursts in this source, is also applicable to these low-level flaring events. Assembling the data from outbursts spanning over two orders of magnitude in flux density shows evidence for a strong correlation between the peak brightness of an event, and the time-scale and frequency at which this is attained. Brighter flares evolve on longer time-scales and peak at lower frequencies. Analysis of the fitted model parameters suggests that brighter outbursts are due to shocks forming further downstream in the jet, with an increased electron normalization and magnetic field strength both playing a role in setting the strength of the outburst.  相似文献   

The great British earthquake of 1984 seen from afar     

H. Trodd  P. Warburton  C. I. Pooley 《Geophysical Journal International》1985,83(3):809-812

Summary. The Lleyn Peninsular earthquake which occurred at 0656 on 1984 July 19 was recorded at three medium aperture seismological array stations located at teleseismic distances. From these recordings an estimate is made of the hypocentre, origin time, magnitude and fault-plane solution of the earthquake. The fault-plane solution was determined using the Pearce algorithm and indicates that the focal mechanism is predominantly strike-slip. The fault-plane solution was used to generate synthetic seismograms for comparison with the observed to confirm the nature of the source and in particular the depth of focus which was estimated to be 20.5 km. It is concluded that the determination of the earthquake parameters using only three teleseismic seismograms is in good agreement with the results obtained from an analysis of 45 local and regional seismological stations.  相似文献   

SEM/microprobe study of some symplectic intergrowths replacing cordierite     

R.H. Vernon  G.D. Pooley 《Lithos》1981,14(1):75-82

Scanning electron microscopy (SEM), involving images produced by back-scattered electrons, reveals the microstructures of symplectic intergrowths replacing cordierite, which generally are too fine-grained and/or intricately intergrown for investigation using an optical microscope. Microprobe analysis, combined with the SEM technique, enables accurate identification of the intergrown minerals, and permits inference of equations for the local chemical changes involved in the formation of the intergrowths. Generally, the local replacement appears to have involved partial reactions taking place in a larger reactive system. Intergrowths forming partial pseudomorphs of cordierite in three metamorphic complexes consists of up to three minerals, only two of which comprise the intergrowth in any one domain. The following intergrown pairs of minerals have been identified: quartz-Al₂SiO₃, quartz-biotite, biotite-oligoclase, biotite-K-feldspar, muscovite-oligoclase, oligoclase-andalusite, K-feldspar-andalusite, aluminous orthopyroxene-Al₂SiO₃, and aluminous anthophylite-Al₂SiO₃.  相似文献   

Cosmic ray propagation and the star formation history of NGC 1961     

U. Lisenfeld  P. Alexander  G. G. Pooley  & T. Wilding 《Monthly notices of the Royal Astronomical Society》1998,300(1):30-38

We present new radio continuum data at four frequencies for the supermassive, peculiar galaxy NGC 1961. These observations allow us to separate the thermal and non-thermal radio emission and to determine the non-thermal spectral index distribution. This spectral index distribution in the galactic disc is unusual: at the maxima of the radio emission the synchrotron spectrum is very steep, indicating aged cosmic ray electrons. Away from the maxima the spectrum is much flatter. The steep spectrum of the synchrotron emission at the maxima indicates that a strong decline of the star formation rate has taken place at these sites. The extended radio emission is a sign of recent cosmic ray acceleration, probably by recent star formation. We suggest that a violent event in the past, most likely a merger or a collision with an intergalactic gas cloud, has caused the various unusual features of the galaxy.  相似文献   

Variability of the extreme z = 4.72 blazar, GB 1428+4217     

A. C. Fabian  A. Celotti  G. Pooley  K. Iwasawa  W. N. Brandt  R. G. McMahon  M. D. Hoenig 《Monthly notices of the Royal Astronomical Society》1999,308(1):L6-L10

On 1998 May 9–11, the highly variable, low-luminosity Seyfert 1 galaxy NGC 4051 was observed in an unusual low-flux state by BeppoSAX , RXTE and EUVE . We present fits of the 4–15 keV RXTE spectrum and BeppoSAX MECS spectrum obtained during this observation, which are consistent with the interpretation that the source had switched off, leaving only the spectrum of pure reflection from distant cold matter. We place this result in context by showing the X-ray light curve of NGC 4051 obtained by our RXTE monitoring campaign over the past two and a half years, which shows that the low state lasted for ∼150 d before the May observations (implying that the reflecting material is >10¹⁷ cm from the continuum source) and forms part of a light curve showing distinct variations in long-term average flux over time-scales > months. We show that the long-time-scale component to X-ray variability is intrinsic to the primary continuum and is probably distinct from the variability at shorter time-scales. The long-time-scale component to variability maybe associated with variations in the accretion flow of matter on to the central black hole . As the source approaches the low state, the variability process becomes non-linear. NGC 4051 may represent a microcosm of all X-ray variability in radio-quiet active galactic nuclei (AGNs), displaying in a few years a variety of flux states and variability properties which more luminous AGNs may pass through on time-scales of decades to thousands of years.  相似文献   

H ₀ from an orientation-unbiased sample of Sunyaev–Zel'dovich and X-ray clusters     

Michael E. Jones  Alastair C. Edge  Keith Grainge  William F. Grainger  Rüdiger Kneissl  G. G. Pooley  Richard Saunders  Shigeru J. Miyoshi  Taisuke Tsuruta  Koujun Yamashita  Yuzuru Tawara  Akihiro Furuzawa  Akihiro Harada  Isamu Hatsukade 《Monthly notices of the Royal Astronomical Society》2005,357(2):518-526

We have observed the Sunyaev–Zel'dovich (SZ) effect in a sample of five moderate-redshift clusters with the Ryle Telescope, and used them in conjunction with X-ray imaging and spectral data from ROSAT and ASCA to measure the Hubble constant. This sample was chosen with a strict X-ray flux limit using both the Bright Cluster Sample and the Northern ROSAT All-Sky Survey (RASS) cluster catalogues to be well above the surface brightness limit of the RASS, and hence to be unbiased with respect to the orientation of the cluster. This controls a major potential systematic effect in the SZ/X-ray method of measuring H ₀. Taking the weighted geometric mean of the results and including the main sources of error, namely the noise in the SZ measurement, the uncertainty in the X-ray temperatures and the unknown ellipticity and substructure of the clusters, we find   H ₀= 59⁺¹⁰₋₉ (random)⁺⁸₋₇(systematic) km s⁻¹ Mpc⁻¹  assuming a standard cold dark matter model with  Ω_M= 1.0, Ω_Λ= 0.0  or   H ₀= 66⁺¹¹₋₁₀ ⁺⁹₋₈ km  s⁻¹ Mpc⁻¹  if  Ω_M= 0.3, Ω_Λ= 0.7  .  相似文献   

Radio and X-ray observations of an exceptional radio flare in the extreme z= 4.72 blazar GB B1428+4217     

M. A. Worsley  A. C. Fabian  G. G. Pooley  C. J. Chandler 《Monthly notices of the Royal Astronomical Society》2006,368(2):844-850

We report on the extreme behaviour of the high-redshift blazar GB B1428+4217 at   z = 4.72  . A continued programme of radio measurements has revealed an exceptional flare in the light curve, with the 15.2-GHz flux density rising by a factor of ∼3 from ∼140 to ∼430  mJy in a rest-frame time-scale of only ∼4 months – much larger than any previous flares observed in this source. In addition to new measurements of the 1.4–43  GHz radio spectrum, we also present the analysis and results of a target-of-opportunity X-ray observation using XMM–Newton , made close to the peak in radio flux. Although the X-ray data do not show a flare in the high-energy light curve, we are able to confirm the X-ray spectral variability hinted at in previous observations. GB B1428+4217 is one of several high-redshift radio-loud quasars that display a low-energy break in the X-ray spectrum, probably due to the presence of excess absorption in the source. X-ray spectral analysis of the latest XMM–Newton data is shown to be consistent with the warm-absorption scenario which we have hypothesized previously. Warm absorption is also consistent with the observed X-ray spectral variability of the source, in which the spectral changes can be successfully accounted-for with a fixed column density of material in which the ionization state is correlated with hardness of the underlying power-law emission.  相似文献