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We present Low-Frequency Array (LOFAR) 143.5-MHz radio observations of flaring activity during 2019 May from the X-ray binary Cygnus X-3. Similar to radio observations of previous outbursts from Cygnus X-3, we find that this source was significantly variable at low frequencies, reaching a maximum flux density of about 5.8 Jy. We compare our LOFAR light curve with contemporaneous observations taken at 1.25 and 2.3 GHz with the RATAN-600 telescope, and at 15 GHz with the Arcminute Microkelvin Imager (AMI) Large Array. The initial 143.5-MHz flux density level, $\sim$2 Jy, is suggested to be the delayed and possibly blended emission from at least some of the flaring activity that had been detected at higher frequencies before our LOFAR observations had begun. There is also evidence of a delay of more than four days between a bright flare that initially peaked on May 6 at 2.3 and 15 GHz, and the corresponding peak ($\gtrsim$ 5.8 Jy) at 143.5 MHz. From the multi-frequency light curves, we estimate the minimum energy and magnetic field required to produce this flare to be roughly 10$^{44}$ erg and 40 mG, respectively, corresponding to a minimum mean power of $\sim$10$^{38}$ erg s$^{-1}$. Additionally, we show that the broadband radio spectrum evolved over the course of our observing campaign; in particular, the two-point spectral index between 143.5 MHz and 1.25 GHz transitioned from being optically thick to optically thin as the flare simultaneously brightened at 143.5 MHz and faded at GHz frequencies., 14 pages, 6 figures, 4 tables, accepted for publication in MNRAS

Thanks to recurrent observations of the black hole binary Cyg X-1 carried out over 15 years the INTEGRAL satellite has collected the largest data set in the hard X-ray band for this source. We have analyzed these data, complemented by data collected by other X-ray satellites and radio flux at 15 GHz. To characterize the spectral and variability properties of the system we have examined parameters such as the hard X-ray flux, photon index and fractional variability. Our main result is that the 2D distribution of the photon index and flux determined for the 22-100 keV band forms six clusters. This result, interpreted within the Comptonization scenario as the dominant process responsible for the hard X-ray emission, leads to a conclusion that the hot plasma in Cyg X-1 takes the form of six specific geometries. The distinct character of each of these plasma states is reinforced by their different X-ray and radio variability patterns. In particular, the hardest and softest plasma states show no short-term flux - photon index correlation typical for the four other states, implying a lack of interaction between the plasma and accretion disk. The system evolves between these two extreme states, with the spectral slope regulated by a variable cooling of the plasma by the disk photons., 21 pages, 11 figures, accepted for publication in ApJ

We study long-term radio/X-ray correlations in Cyg X-1. We find the persistent existence of a compact radio jet in its soft state. This represents a new phenomenon in black-hole binaries, in addition to compact jets in the hard state and episodic ejections of ballistic blobs in the intermediate state. While the radio emission in the hard state is strongly correlated with both the soft and hard X-rays, the radio flux in the soft state is not directly correlated with the flux of the dominant disk blackbody in soft X-rays, but instead it is lagged by about a hundred days. We interpret the lag as occurring in the process of advection of the magnetic flux from the donor through the accretion disk. On the other hand, the soft-state radio flux is very tightly correlated with the hard X-ray, 15--50 keV, flux without a measurable lag and at the same rms. This implies that the X-ray emitting disk corona and the soft-state jet are powered by the same process, probably magnetically., ApJL in press, 6 pages

The Arcminute Microkelvin Imager (AMI) carried out a blind survey for galaxy clusters via their Sunyaev-Zel'dovich effect decrements between 2008 and 2011. The first detection, known as AMI-CL J0300+2613, has been reobserved with AMI equipped with a new digital correlator with high dynamic range. The combination of the new AMI data and more recent high-resolution sub-mm and infra-red maps now shows the feature in fact to be a ring of positive dust-correlated Galactic emission, which is likely to be anomalous microwave emission (AME). If so, this is the first completely blind detection of AME at arcminute scales., 11 pages, 13 figures, 4 tables. Submitted to MNRAS

In an earlier paper (2007), we used follow-up observations of a sample of sources from the 9C survey at 15.2 GHz to derive a set of spectral-index distributions up to a frequency of 90 GHz. These were based on simultaneous measurements made at 15.2 GHz with the Ryle telescope and at 22 and 43 GHz with the Karl G. Jansky Very Large Array (VLA). We used these distributions to make empirical estimates of source counts at 22, 30, 43, 70 and 90 GHz. In a later paper (2013), we took data at 15.7 GHz from the Arcminute Microkelvin Imager (AMI) and data at 93.2 GHz from the Combined Array for Research in Millimetre-wave Astronomy (CARMA) and estimated the source count at 93.2 GHz. In this paper, we re-examine the data used in both papers and now believe that the VLA flux densities we measured at 43 GHz were significantly in error, being on average only about 70 per cent of their correct values. Here, we present strong evidence for this conclusion and discuss the effect on the source-count estimates made in the 2007 paper. The source-count prediction in the 2013 paper is also revised. We make comparisons with spectral-index distributions and source counts from other telescopes, in particular with a recent deep 95 GHz source count measured by the South Pole Telescope. We investigate reasons for the problem of the low VLA 43-GHz values and find a number of possible contributory factors, but none is sufficient on its own to account for such a large deficit., Comment: 9 pages, 5 figures

The Arcminute Microkelvin Imager (AMI) telescopes located at the Mullard Radio Astronomy Observatory near Cambridge have been significantly enhanced by the implementation of a new digital correlator with 1.2 MHz spectral resolution. This system has replaced a 750-MHz resolution analogue lag-based correlator, and was designed to mitigate the effects of radio frequency interference, particularly from geostationary satellites that contaminate observations at low declinations. The upgraded instrument consists of 18 ROACH2 Field Programmable Gate Array platforms used to implement a pair of real-time FX correlators -- one for each of AMI's two arrays. The new system separates the down-converted RF baseband signal from each AMI receiver into two 2.3 GHz-wide sub-bands which are each digitized at 5-Gsps with 8 bits of precision. These digital data streams are filtered into 2048 frequency channels and cross-correlated using FPGA hardware, with a commercial 10 Gb Ethernet switch providing high-speed data interconnect. Images formed using data from the new digital correlator show over an order of magnitude improvement in dynamic range over the previous system. The ability to observe at low declinations has also been significantly improved., Comment: 11 pages, 10 figures, accepted to MNRAS

We study high-energy $\gamma$-rays observed from Cyg X-3 by the Fermi Large Area Telescope and the 15-GHz emission observed by the Ryle Telescope and the Arcminute Microkelvin Imager. We measure the $\gamma$-ray spectrum averaged over strong flares much more accurately than before, and find it well modelled by Compton scattering of stellar radiation by relativistic electrons with the power law index of $\simeq$3.5 and a low-energy cutoff at the Lorentz factor of $\sim\!10^3$. We find a weaker spectrum in the soft spectral state, but only upper limits in the hard and intermediate states. We measure strong orbital modulation during the flaring state, well modelled by anisotropic Compton scattering of blackbody photons from the donor by jet relativistic electrons. We discover a weaker orbital modulation of the 15 GHz radio emission, which is well modelled by free-free absorption by the stellar wind. We then study cross-correlations between radio, $\gamma$-ray and X-ray emissions. We find the cross-correlation between the radio and $\gamma$-ray emissions peaks at a lag less than 1 d, while we detect a distinct radio lag of $\sim$50 d with respect to the soft X-rays in the soft spectral state., Comment: MNRAS, in press, 17 pages

Cygnus X-3 is a unique microquasar in the Galaxy hosting a Wolf-Rayet companion orbiting a compact object that most likely is a low-mass black hole. The unique source properties are likely due to the interaction of the compact object with the heavy stellar wind of the companion. In this paper, we concentrate on a very specific period of time prior to the massive outbursts observed from the source. During this period, Cygnus X-3 is in a so-called hypersoft state, where the radio and hard X-ray fluxes are found to be at their lowest values (or non-detected), the soft X-ray flux is at its highest values, and sporadic gamma-ray emission is observed. We will utilize multiwavelength observations in order to study the nature of the hypersoft state. We observed Cygnus X-3 during the hypersoft state with Swift and NuSTAR in the X-rays and SMA, AMI-LA, and RATAN-600 in the radio. We also considered X-ray monitoring data from MAXI and $\gamma$-ray monitoring data from AGILE and Fermi. We found that the spectra and timing properties of the multiwavelength observations can be explained by a scenario where the jet production is turned off or highly diminished in the hypersoft state and the missing jet pressure allows the wind to refill the region close to the black hole. The results provide proof of actual jet quenching in soft states of X-ray binaries., Comment: 15 pages, 13 figures. Accepted for publication in A&A

The microquasar Cygnus X-1 displays the two typical soft and hard X-ray states of a black hole transient. During the latter, Cygnus X-1 shows a one-sided relativistic radio-jet. Recent detection of the system in the high energy (HE; E greater than or similar to 60 MeV) gamma-ray range with FermiLAT associates this emission with the outflow. Former MAGIC observations revealed a hint of flaring activity in the very high-energy (VHE; E greater than or similar to 100 GeV) regime during this X-ray state. We analyse ~ to 97 h of Cygnus X-1 data taken with the MAGIC telescopes between July 2007 and October 2014. To shed light on the correlation between hard X-ray and VHE gamma rays as previously suggested, we study each main X-ray state separately. We perform an orbital phase-folded analysis to look for variability in the VHE band. Additionally, to place this variability behaviour in a multiwavelength context, we compare our results with Fermi-LAT, AGILE, Swift-BAT, MAXI, RXTE-ASM, AMI and RATAN-600 data. We do not detect Cygnus X-1 in the VHE regime. We establish upper limits for each X-ray state, assuming a power-law distribution with photon index Γ = 3.2. For steady emission in the hard and soft X-ray states, we set integral upper limits at 95 %per cent confidence level for energies above 200 GeV at 2.6 x 10⁻¹² photons cm⁻² s⁻¹ and 1.0 x 10⁻¹¹ photons cm⁻² s ⁻¹, respectively. We rule out steady VHE gamma-ray emission above this energy range, at the level of theMAGIC sensitivity, originating in the interaction between the relativistic jet and the surrounding medium, while the emission above this flux level produced inside the binary still remains a valid possibility.

Gamma-ray burst (GRB) 111215A was bright at X-ray and radio frequencies, but not detected in the optical or near-infrared (nIR) down to deep limits. We have observed the GRB afterglow with the Westerbork Synthesis Radio Telescope and Arcminute Microkelvin Imager at radio frequencies, with the William Herschel Telescope and Nordic Optical Telescope in the nIR/optical, and with the Chandra X-ray Observatory. We have combined our data with the Swift X-Ray Telescope monitoring, and radio and millimeter observations from the literature to perform broadband modeling, and determined the macro- and microphysical parameters of the GRB blast wave. By combining the broadband modeling results with our nIR upper limits we have put constraints on the extinction in the host galaxy. This is consistent with the optical extinction we have derived from the excess X-ray absorption, and higher than in other dark bursts for which similar modeling work has been performed. We also present deep imaging of the host galaxy with the Keck I telescope, Spitzer Space Telescope, and Hubble Space Telescope (HST), which resulted in a well-constrained photometric redshift, giving credence to the tentative spectroscopic redshift we obtained with the Keck II telescope, and estimates for the stellar mass and star formation rate of the host. Finally, our high resolution HST images of the host galaxy show that the GRB afterglow position is offset from the brightest regions of the host galaxy, in contrast to studies of optically bright GRBs., Comment: 11 pages, 4 figures, 4 tables; accepted for publication in MNRAS

We present model fits to the X-ray line spectrum of the well known High Mass X-ray binary Cyg X-3. The primary observational dataset is a spectrum taken with the $Chandra$ X-ray Observatory High Energy Transmission Grating (HETG) in 2006, though we compare it to all the other observations of this source taken so far by this instrument. We show that the density must be $\geq 10^{12}$ cm$^{-3}$ in the region responsible for most of the emission. We discuss the influence of the dust scattering halo on the broad band spectrum and we argue that dust scattering and extinction is not the most likely origin for the narrow featureseen near the Si K edge. We identify the features of a wind in the profiles of the strong resonance lines and we show that the wind is more apparent in the lines from the lighter elements. We argue that this wind is most likely associated with the companion star. We show that the intensities of most lines can be fitted, crudely, by a single component photoionized model. However, the iron K lines do not fit with this model. We show that the iron K line variability as a function of orbital phase is different from the lower energy lines, which indicates that the lines arise in physically distinct regions. We discuss the interpretation of these results in the context of what is known about the system and similar sys, ApJ Submitted

The ejection of a relativistic jet has been observed in the luminous Galactic low mass X-ray binary Cygnus X-2. Using high resolution radio observations, a directly resolved ejection event has been discovered while the source was on the Horizontal Branch of the Z-track. Contemporaneous radio and X-ray observations were made with the European VLBI Network at 6 cm and the Swift X-ray observatory in the 0.3 - 10 keV band. This has been difficult to achieve because of the previous inability to predict jet formation. Two sets of ~10 hr observations were spaced 12 hr apart, the jet apparently switching on during Day 1. The radio results show an unresolved core evolving into an extended jet. A preliminary value of jet velocity v/c of 0.33 +/- 0.12 was obtained, consistent with previous determinations in Galactic sources. Simultaneous radio and X-ray lightcurves are presented and the X-ray hardness ratio shows the source to be on the Horizontal Branch where jets are expected. The observations support our proposal that jet formation can in future be predicted based on X-ray intensity increases beyond a critical value., minor changes; accepted for publication in MNRAS (Letters)

We have obtained deep Sunyaev–Zel’dovich (SZ) observations towards 15 of the hottest XMM Cluster Survey (XCS) clusters that can be observed with the Arcminute Microkelvin Imager (AMI). We use a Bayesian analysis to quantify the significance of our SZ detections. We detect the SZ effect at high significance towards three of the clusters and at lower significance for a further two clusters. Towards the remaining 10 clusters, no clear SZ signal was measured. We derive cluster parameters using the XCS mass estimates as a prior in our Bayesian analysis. For all AMI-detected clusters, we calculate large-scale mass and temperature estimates while for all undetected clusters we determine upper limits on these parameters. We find that the large-scale mean temperatures derived from our AMI SZ measurements (and the upper limits from null detections) are substantially lower than the XCS-based core-temperature estimates. For clusters detected in the SZ, the mean temperature is, on average, a factor of 1.4 lower than temperatures from the XCS. Our upper limits on the cluster temperature of undetected systems are lower than the mean XCS derived temperature.

We present results from follow-up observations of a sample of 80 radio sources, originally detected as part of the 15.2-GHz Ninth Cambridge (9C) survey. The observations were carried out, close to simultaneously, at two frequencies: 15.7 GHz, using the Arcminute Microkelvin Imager (AMI) Large Array, and 93.2 GHz, using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). There is currently little direct information on the 90-GHz-band source count for S ≲ 1 Jy. However, we have used the measured 15.7-to-93.2-GHz spectral-index distribution and 9C source count to predict the differential source count at 93.2 GHz as 26 ± 4(S/Jy)^(−2.15) Jy^(−1) sr^(−1); our projection is estimated to be most accurate for 10 ≲ S ≲ 100 mJy. Our estimated differential count is more than twice the 90-GHz prediction made by Waldram et al.; we believe that this discrepancy is because the measured 43-GHz flux densities used in making their prediction were too low. Similarly, our prediction is significantly higher than that of Sadler et al. at 95 GHz. Since our spectral-index distribution is similar to the 20-to-95-GHz distribution measured by Sadler et al. and used in making their prediction, we believe that the difference is almost entirely attributable to the dissimilarity in the lower frequency counts used in making the estimates.

We have carried out extensive radio and optical follow-up of 176 sources from the 15 GHz 9th Cambridge survey. Optical identifications have been found for 155 of the radio sources; optical images are given with radio maps overlaid. The continuum radio spectrum of each source spanning the frequency range 1.4 - 43 GHz is also given. Two flux-limited samples are defined, one containing 124 sources complete to 25 mJy and one of 70 sources complete to 60 mJy. Between one fifth and one quarter of sources from these flux-limited samples display convex radio spectra, rising between 1.4 and 4.8 GHz. These rising-spectrum sources make up a much larger fraction of the radio source population at this high selection frequency than in lower frequency surveys. We find that by using non-simultaneous survey flux density measurements at 1.4 and 15 GHz to remove steep spectrum objects, the efficiency of selecting objects with spectra rising between 1.4 and 4.8 GHz (as seen in simultaneous measurements) can be raised to 49 percent without compromising the completeness of the rising spectrum sample., Comment: 40 pages, 223 figures. Accepted for publication in MNRAS. Version with full size images (A4 paper) avaliable at http://www.mrao.cam.ac.uk/publications/papers files ME777.ps and ME777.pdf

We estimate the bispectrum of the Very Small Array data from the compact and extended configuration observations released in December 2002, and compare our results to those obtained from Gaussian simulations. There is a slight excess of large bispectrum values for two individual fields, but this does not appear when the fields are combined. Given our expected level of residual point sources, we do not expect these to be the source of the discrepancy. Using the compact configuration data, we put an upper limit of 5400 on the value of f_NL, the non-linear coupling parameter, at 95 per cent confidence. We test our bispectrum estimator using non-Gaussian simulations with a known bispectrum, and recover the input values., Comment: 17 pages, 16 figures, replaced with version accepted by MNRAS. Primordial bispectrum recalculated and figure 11 changed

We have obtained a firm detection of Cyg X-1 during its hard and intermediate spectral states in the energy range of 40 MeV--60 GeV based on observations by the Fermi Large Area Telescope, confirming the independent results at $\geq$60MeV of a previous work. The detection significance is $\simeq\!8\sigma$ in the 0.1--10 GeV range. In the soft state, we have found only upper limits on the emission at energies $\gtrsim$0.1 MeV. However, we have found emission with a very soft spectrum in the 40--80 MeV range, not detected previously. This is likely to represent the high-energy cutoff of the high-energy power-law tail observed in the soft state. Similarly, we have detected a $\gamma$-ray soft excess in the hard state, which appears to be of similar origin. We have also confirmed the presence of an orbital modulation of the detected emission in the hard state, expected if the $\gamma$-rays are from Compton upscattering of stellar blackbody photons. However, the observed modulation is significantly weaker than that predicted if the blackbody upscattering were the dominant source of $\gamma$-rays. This argues for a significant contribution from $\gamma$-rays produced by the synchrotron-self-Compton process. We have found that such strong contribution is possible if the jet is strongly clumped. We reproduce the observed hard-state average broad-band spectrum using a self-consistent jet model, taking into account all the relevant emission processes, e$^\pm$ pair absorption, and clumping. This model also reproduces the amplitude of the observed orbital modulation., Comment: MNRAS, in press

We present 16-GHz AMI SZ observations of 19 clusters with L_X >7x10^37 W (h50=1) selected from the LoCuS survey (0.142

The spin of Cygnus X-1 is measured by fitting reflection models to Suzaku data covering the energy band 0.9-400 keV. The inner radius of the accretion disc is found to lie within 2 gravitational radii (r_g=GM/c^2) and a value for the dimensionless black hole spin is obtained of 0.97^{+0.014}_{-0.02}. This agrees with recent measurements using the continuum fitting method by Gou et al. and of the broad iron line by Duro et al. The disc inclination is measured at 23.7^{+6.7}_{-5.4} deg, which is consistent with the recent optical measurement of the binary system inclination by Orosz et al of 27+/-0.8 deg. We pay special attention to the emissivity profile caused by irradiation of the inner disc by the hard power-law source. The X-ray observations and simulations show that the index q of that profile deviates from the commonly used, Newtonian, value of 3 within 3r_g, steepening considerably within 2r_g, as expected in the strong gravity regime.

We present 16 GHz (1.9 cm) deep radio continuum observations made with the Arcminute Microkelvin Imager (AMI) of a sample of low-mass young stars driving jets. We combine these new data with archival information from an extensive literature search to examine spectral energy distributions (SEDs) for each source and calculate both the radio and sub-mm spectral indices in two different scenarios: (1) fixing the dust temperature (Td) according to evolutionary class; (2) allowing Td to vary. We use the results of this analysis to place constraints on the physical mechanisms responsible for the radio emission. From AMI data alone, as well as from model fitting to the full SED in both scenarios, we find that 80 per cent of the objects in this sample have spectral indices consistent with free-free emission. We find an average spectral index in both Td scenarios consistent with free-free emission. We examine correlations of the radio luminosity with bolometric luminosity, envelope mass, and outflow force and find that these data are consistent with the strong correlation with envelope mass seen in lower luminosity samples. We examine the errors associated with determining the radio luminosity and find that the dominant source of error is the uncertainty on the opacity index, beta. We examine the SEDs for variability in these young objects, and find evidence for possible radio flare events in the histories of L1551 IRS 5 and Serpens SMM 1.

We present an interesting Sunyaev-Zel'dovich (SZ) detection in the first of the Arcminute Microkelvin Imager (AMI) 'blind', degree-square fields to have been observed down to our target sensitivity of 100{\mu}Jy/beam. In follow-up deep pointed observations the SZ effect is detected with a maximum peak decrement greater than 8 \times the thermal noise. No corresponding emission is visible in the ROSAT all-sky X-ray survey and no cluster is evident in the Palomar all-sky optical survey. Compared with existing SZ images of distant clusters, the extent is large (\approx 10') and complex; our analysis favours a model containing two clusters rather than a single cluster. Our Bayesian analysis is currently limited to modelling each cluster with an ellipsoidal or spherical beta-model, which do not do justice to this decrement. Fitting an ellipsoid to the deeper candidate we find the following. (a) Assuming that the Evrard et al. (2002) approximation to Press & Schechter (1974) correctly gives the number density of clusters as a function of mass and redshift, then, in the search area, the formal Bayesian probability ratio of the AMI detection of this cluster is 7.9 \times 10^4:1; alternatively assuming Jenkins et al. (2001) as the true prior, the formal Bayesian probability ratio of detection is 2.1 \times 10^5:1. (b) The cluster mass is MT,200 = 5.5+1.2\times 10^14h-1M\odot. (c) Abandoning a physical model with num- -1.3 70 ber density prior and instead simply modelling the SZ decrement using a phenomenological {\beta}-model of temperature decrement as a function of angular distance, we find a central SZ temperature decrement of -295+36 {\mu}K - this allows for CMB primary anisotropies, receiver -15 noise and radio sources. We are unsure if the cluster system we observe is a merging system or two separate clusters.

The Planck Early Release Compact Source Catalogue includes 26 sources with no obvious matches in other radio catalogues (of predominantly extragalactic sources). Here we present observations made with the Arcminute Microkelvin Imager Small Array (AMI SA) at 15.75 GHz of the eight unmatched sources at δ > +10°. Of the eight, four are detected and are associated with known objects. The other four are not detected with the AMI SA, and are thought to be spurious.

With frequent flaring activity of its relativistic jets, Cygnus X-3 is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high energy Gamma-ray emission, thanks to detections by Fermi/LAT and AGILE. In 2011, Cygnus X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy Gamma-ray emission. We present the results of a multi-wavelength campaign covering a quenched state, when radio emission from Cygnus X-3 is at its weakest and the X-ray spectrum is very soft. A giant (~ 20 Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E >100 MeV) reveal renewed Gamma-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the Gamma-ray emission is not exclusively related to the rare giant radio flares. A 3-week period of Gamma-ray emission is also detected when Cygnus X-3 was weakly flaring in radio, right before transition to the radio quenched state. No Gamma rays are observed during the ~ one-month long quenched state, when the radio flux is weakest. Our results suggest transitions into and out of the ultrasoft X-ray (radio quenched) state trigger Gamma-ray emission, implying a connection to the accretion process, and also that the Gamma-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.

We present deep 1.8 cm (16 GHz) radio continuum imaging of seven young stellar objects in the Taurus molecular cloud. These objects have previously been extensively studied in the sub-mm to NIR range and their SEDs modelled to provide reliable physical and geometrical parametres.We use this new data to constrain the properties of the long-wavelength tail of the greybody spectrum, which is expected to be dominated by emission from large dust grains in the protostellar disk. We find spectra consistent with the opacity indices expected for such a population, with an average opacity index of beta = 0.26+/-0.22 indicating grain growth within the disks. We use spectra fitted jointly to radio and sub-mm data to separate the contributions from thermal dust and radio emission at 1.8 cm and derive disk masses directly from the cm-wave dust contribution. We find that disk masses derived from these flux densities under assumptions consistent with the literature are systematically higher than those calculated from sub-mm data, and meet the criteria for giant planet formation in a number of cases.

Most Sunyaev--Zel'dovich (SZ) and X-ray analyses of galaxy clusters try to constrain the cluster total mass and/or gas mass using parameterised models and assumptions of spherical symmetry and hydrostatic equilibrium. By numerically exploring the probability distributions of the cluster parameters given the simulated interferometric SZ data in the context of Bayesian methods, and assuming a beta-model for the electron number density we investigate the capability of this model and analysis to return the simulated cluster input quantities via three rameterisations. In parameterisation I we assume that the T is an input parameter. We find that parameterisation I can hardly constrain the cluster parameters. We then investigate parameterisations II and III in which fg(r200) replaces temperature as a main variable. In parameterisation II we relate M_T(r200) and T assuming hydrostatic equilibrium. We find that parameterisation II can constrain the cluster physical parameters but the temperature estimate is biased low. In parameterisation III, the virial theorem replaces the hydrostatic equilibrium assumption. We find that parameterisation III results in unbiased estimates of the cluster properties. We generate a second simulated cluster using a generalised NFW (GNFW) pressure profile and analyse it with an entropy based model to take into account the temperature gradient in our analysis and improve the cluster gas density distribution. This model also constrains the cluster physical parameters and the results show a radial decline in the gas temperature as expected. The mean cluster total mass estimates are also within 1 sigma from the simulated cluster true values. However, we find that for at least interferometric SZ analysis in practice at the present time, there is no differences in the AMI visibilities between the two models. This may of course change as the instruments improve.

We present deep radio continuum observations of the cores identified as deeply embedded young stellar objects in the Serpens molecular cloud by the Spitzer c2d programme at a wavelength of 1.8cm with the Arcminute Microkelvin Imager Large Array (AMI-LA). These observations have a resolution of ~30arcsec and an average sensitivity of 19microJy/beam. The targets are predominantly Class I sources, and we find the detection rate for Class I objects in this sample to be low (18%) compared to that of Class 0 objects (67%), consistent with previous works. For detected objects we examine correlations of radio luminosity with bolometric luminosity and envelope mass and find that these data support correlations found by previous samples, but do not show any indiction of the evolutionary divide hinted at by similar data from the Perseus molecular cloud when comparing radio luminosity with envelope mass. We conclude that envelope mass provides a better indicator for radio luminosity than bolometric luminosity, based on the distribution of deviations from the two correlations. Combining these new data with archival 3.6cm flux densities we also examine the spectral indices of these objects and find an average spectral index of 0.53+/-1.14, consistent with the canonical value for a partially optically thick spherical or collimated stellar wind. However, we caution that possible inter-epoch variability limits the usefulness of this value, and such variability is supported by our identification of a possible flare in the radio history of Serpens SMM 1.

We present an analysis of observations made with the Arcminute Microkelvin Imager (AMI) and the Canada-France-Hawaii Telescope (CFHT) of six galaxy clusters in a redshift range of 0.16--0.41. The cluster gas is modelled using the Sunyaev--Zel'dovich (SZ) data provided by AMI, while the total mass is modelled using the lensing data from the CFHT. In this paper, we: i) find very good agreement between SZ measurements (assuming large-scale virialisation and a gas-fraction prior) and lensing measurements of the total cluster masses out to r_200; ii) perform the first multiple-component weak-lensing analysis of A115; iii) confirm the unusual separation between the gas and mass components in A1914; iv) jointly analyse the SZ and lensing data for the relaxed cluster A611, confirming our use of a simulation-derived mass-temperature relation for parameterizing measurements of the SZ effect.

We present observations using the Small Array of the Arcminute Microkelvin Imager (AMI; 14-18 GHz) of four Abell and three MACS clusters spanning 0.171-0.686 in redshift. We detect Sunyaev-Zel'dovich (SZ) signals in five of these without any attempt at source subtraction, although strong source contamination is present. With radio-source measurements from high-resolution observations, and under the assumptions of spherical $\beta$-model, isothermality and hydrostatic equilibrium, a Bayesian analysis of the data in the visibility plane detects extended SZ decrements in all seven clusters over and above receiver noise, radio sources and primary CMB imprints. Bayesian evidence ratios range from 10^{11}:1 to 10^{43}:1 for six of the clusters and 3000:1 for one with substantially less data than the others. We present posterior probability distributions for, e.g., total mass and gas fraction averaged over radii internal to which the mean overdensity is 1000, 500 and 200, r_200 being the virial radius. Reaching r_200 involves some extrapolation for the nearer clusters but not for the more-distant ones. We find that our estimates of gas fraction are low (compared with most in the literature) and decrease with increasing radius. These results appear to be consistent with the notion that gas temperature in fact falls with distance (away from near the cluster centre) out to the virial radius.

We present evidence for the presence of a weak compact jet during a soft X-ray state of Cygnus X-1. Very-high-resolution radio observations were taken with the VLBA, EVN and MERLIN during a hard-to-soft spectral state change, showing the hard state jet to be suppressed by a factor of about 3-5 in radio flux and unresolved to direct imaging observations (i.e. < 1 mas at 4 cm). High time-resolution X-ray observations with the RXTE-PCA were also taken during the radio monitoring period, showing the source to make the transition from the hard state to a softer state (via an intermediate state), although the source may never have reached the canonical soft state. Using astrometric VLBI analysis and removing proper motion, parallax and orbital motion signatures, the residual positions show a scatter of ~0.2 mas (at 4 cm) and ~3 mas (at 13 cm) along the position angle of the known jet axis; these residuals suggest there is a weak unresolved outflow, with varying size or opacity, during intermediate and soft X-ray states. Furthermore, no evidence was found for extended knots or shocks forming within the jet during the state transition, suggesting the change in outflow rate may not be sufficiently high to produce superluminal knots.

We have studied the X-ray variability patterns and correlations of the radio and X-ray fluxes in all spectral states of Cyg X-1 using X-ray data from the All-Sky Monitor onboard the Rossi X-ray Timing Explorer, Burst And Transient Source Experiment onboard the Compton Gamma Ray Observatory and the Burst Alert Telescope onboard Swift. In the hard state, the dominant spectral variability is a changing of normalization with a fixed spectral shape, while in the intermediate state, the slope changes, with a pivot point around 10 keV. In the soft state, the low-energy X-ray emission dominates the bolometric flux which is only loosely correlated with the high-energy emission. In black hole binaries in the hard state, the radio flux is generally found to depend on a power of the X-ray flux, FR∝FpX. We confirm this for Cyg X-1. Our new finding is that this correlation extends to the intermediate and soft states, provided the broad-band X-ray flux in the Comptonization part of the spectrum (excluding the blackbody component) is considered instead of a narrow-band medium-energy X-ray flux. We find an index p≃ 1.7 ± 0.1 for 15-GHz radio emission, decreasing to p≃ 1.5 ± 0.1 at 2.25 GHz. We conclude that the higher value at 15 GHz is due to the effect of free–free absorption in the wind from the companion. The intrinsic correlation index remains uncertain. However, based on a theoretical model of the wind in Cyg X-1, it may to be close to ≃1.3, which, in the framework of accretion/jet models, would imply that the accretion flow in Cyg X-1 is radiatively efficient. The correlation with the flux due to Comptonization emission indicates that the radio jet is launched by the hot electrons in the accretion flow in all spectral states of Cyg X-1. On the other hand, we are able to rule out the X-ray jet model. Finally, we find that the index of the correlation, when measured using the X-ray flux in a narrow energy band, strongly depends on the band chosen and is, in general, different from that for either the bolometric flux or the flux in the hot-electron emission.

We have observed an area of approximatley 27 deg^2 to an rms noise level of less than 0.2 mJy at 15.7 GHz, using the Arcminute Microkelvin Imager Large Array. These observations constitute the most sensitive radio-source survey of any extent (greater than approximately 0.2 deg^2) above 1.4 GHz. This paper presents the techniques employed for observing, mapping and source extraction. We have used a systematic procedure for extracting information and producing source catalogues, from maps with varying noise and uv-coverage. We have performed simulations to test our mapping and source-extraction procedures, and developed methods for identifying extended, overlapping and spurious sources in noisy images. In an accompanying paper, AMI Consortium: Davies et al. 2010, the first results from the 10C survey, including the deep 15.7-GHz source count, are presented.

The first results from the Tenth Cambridge (10C) Survey of Radio Sources, carried out using the AMI Large Array (LA) at an observing frequency of 15.7 GHz, are presented. The survey fields cover an area of approximately 27 sq. degrees to a flux-density completeness of 1 mJy. Results for some deeper areas, covering approximately 12 sq. degrees, wholly contained within the total areas and complete to 0.5 mJy, are also presented. The completeness for both areas is estimated to be at least 93 per cent. The source catalogue contains 1897 entries and is available at www.mrao.cam.ac.uk/surveys/10C. It has been combined with that of the 9C Survey to calculate the 15.7-GHz source counts. A broken power law is found to provide a good parameterisation of the differential count between 0.5 mJy and 1 Jy. The measured count has been compared to that predicted by de Zotti et al. (2005). The model displays good agreement with the data at the highest flux densities but under-predicts the integrated count between 0.5 mJy and 1 Jy by about 30 per cent. Entries from the source catalogue have been matched to those contained in the catalogues of NVSS and FIRST (both of which have observing frequencies of 1.4 GHz). This matching provides evidence for a shift in the typical 1.4-to-15.7-GHz spectral index of the 15.7-GHz-selected source population with decreasing flux density towards sub-mJy levels - the spectra tend to become less steep. Automated methods for detecting extended sources have been applied to the data; approximately 5 per cent of the sources are found to be extended relative to the LA synthesised beam of approximately 30 arcsec. Investigations using higher-resolution data showed that most of the genuinely extended sources at 16 GHz are classical doubles, although some nearby galaxies and twin-jet sources were also identified.

We present deep radio continuum observations of the cores identified as deeply embedded young stellar objects in the Serpens molecular cloud by the Spitzer c2d programme at a wavelength of 1.8 cm with the Arcminute Microkelvin Imager Large Array (AMI-LA). These observations have a resolution of ≈30 arcsec and an average sensitivity of 19µJy beam −1 .T he targets are predominantly Class I sources, and we find the detection rate for Class I objects in this sample to be low (18 per cent) compared to that of Class 0 objects (67 per cent), consistent with previous works. For detected objects we examine correlations of radio luminosity with bolometric luminosity and envelope mass and find that these data support correlations found by previous samples, but do not show any indication of the evolutionary divide hinted at by similar data from the Perseus molecular cloud when comparing radio luminosity with envelope mass. We conclude that envelope mass provides a better indicator for radio luminosity than bolometric luminosity, based on the distribution of deviations from the two correlations. Combining these new data with archival 3.6 cm flux densities we also examine the spectral indices of these objects and find an average spectral index of ¯ α 1.8 3.5 = 0.53 ± 1.14, consistent with the canonical value for a partially optically thick spherical or collimated stellar wind. However, we caution that possible inter-epoch variability limits the usefulness of this value, and such variability is supported by our identification of a possible flare in the radio history of Serpens SMM 1.

We present 13.9-18.2 GHz observations of the Sunyaev-Zel'dovich (SZ) effect towards Abell 2146 using the Arcminute Microkelvin Imager (AMI). The cluster is detected with a peak SNR ratio of 13 sigma in the radio source subtracted map. Comparison of the SZ and X-ray images suggests that they both have extended regions which lie approximately perpendicular to one another, with their emission peaks significantly displaced. These features indicate non-uniformities in the distributions of the gas temperature and pressure, indicative of a cluster merger. We use a Bayesian cluster analysis to explore the high-dimensional parameter space of the cluster-plus-sources model to obtain cluster parameter estimates in the presence of radio point sources, receiver noise and primordial CMB anisotropy; the probability of SZ + CMB primordial structure + radio sources + receiver noise to CMB + radio sources + receiver noise is 3 x 10^{6}:1. We compare the results from three different cluster models. Our preferred model exploits the observation that the gas fractions do not appear to vary greatly between clusters. Given the relative masses of the two merging systems in Abell 2146, the mean gas temperature can be deduced from the virial theorem (assuming all of the kinetic energy is in the form of internal gas energy) without being affected significantly by the merger event, provided the primary cluster was virialized before the merger. In this model we fit a simple spherical isothermal beta-model, despite the inadequacy of this model for a merging system like Abell 2146, and assume the cluster follows the mass-temperature relation of a virialized, singular, isothermal sphere. We note that this model avoids inferring large-scale cluster parameters internal to r_200 under the widely used assumption of hydrostatic equilibrium. We find that at r_200 M_T= 4.1 \pm 0.5 x 10^{14} h^{-1}M_sun and T=4.5 \pm 0.5 keV.

We present follow-up observations of two galaxy clusters detected blindly via the Sunyaev-Zel'dovich (SZ) effect and released in the Planck Early Release Compact Source Catalogue. We use the Arcminute Microkelvin Imager, a dual-array 14-18 GHz radio interferometer. After radio source subtraction, we find a SZ decrement of integrated flux density -1.08+/-0.10 mJy toward PLCKESZ G121.11+57.01, and improve the position measurement of the cluster, finding the centre to be RA 12 59 36.4, Dec +60 04 46.8, to an accuracy of 20 arcseconds. The region of PLCKESZ G115.71+17.52 contains strong extended emission, so we are unable to confirm the presence of this cluster via the SZ effect.

We present ground-based and HST optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z = 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broadband spectral energy distributions (SEDs) of the OT resemble those of local type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB-supernova, and SN1994I, a typical type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly-available SWIFT -XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t-to > 0.5 days. We then compare the rest-frame, peak V -band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe.

We study properties of the superorbital modulation of the X-ray emission of Cyg X-1. We find that it has had a stable period of about 300 d in soft and hard X-rays and in radio since 2005 until at least 2010, which is about double the previously seen period. This new period, seen in the hard spectral state only, is detected not only in the light curves but also in soft X-ray hardness ratios and in the amplitude of the orbital modulation. On the other hand, the spectral slope in hard X-rays, >20 keV, averaged over superorbital bins is constant, and the soft and hard X-rays and the radio emission change in phase. This shows that the superorbital variability consists of changing the normalization of an intrinsic spectrum of a constant shape and of changes of the absorbing column density with the phase. The maximum column density is achieved at the superorbital minimum. The amplitude changes are likely to be caused by a changing viewing angle of an anisotropic emitter, most likely a precessing accretion disc. The constant shape of the intrinsic spectrum shows that this modulation is not caused by a changing accretion rate. The modulated absorbing column density shows the presence of a bulge around the disc centre, as proposed previously. We also find the change of the superorbital period from about 150 d to about 300 d to be associated with almost unchanged average X-ray fluxes, making the period change difficult to explain in the framework of disc-irradiation models. Finally, we find no correlation of the X-ray and radio properties with the reported detections in the GeV and TeV gamma-ray range.

We perform deep 1.8 cm radio continuum imaging towards thirteen protostellar regions selected from the Spitzer c2d small clouds and cores programme at high resolution (25") in order to detect and quantify the cm-wave emission from deeply embedded young protostars. Within these regions we detect fifteen compact radio sources which we identify as radio protostars including two probable new detections. The sample is in general of low bolometric luminosity and contains several of the newly detected VeLLO sources. We determine the 1.8 cm radio luminosity to bolometric luminosity correlation, L_rad -L_bol, for the sample and discuss the nature of the radio emission in terms of the available sources of ionized gas. We also investigate the L_rad-L_IR correlation and suggest that radio flux density may be used as a proxy for the internal luminosity of low luminosity protostars.

We use a sample of 19 gamma-ray bursts (GRBs) that exhibit single-peaked optical light curves to test the standard fireball model by investigating the relationship between the time of the onset of the afterglow and the temporal rising index. Our sample includes GRBs and X-ray flashes for which we derive a wide range of initial Lorentz factors (40 < Γ < 450). Using plausible model parameters, the typical frequency of the forward shock is expected to lie close to the optical band; within this low typical frequency framework, we use the optical data to constrain εe and show that values derived from the early time light-curve properties are consistent with published typical values derived from other afterglow studies. We produce expected radio light curves by predicting the temporal evolution of the expected radio emission from forward and reverse shock components, including synchrotron self-absorption effects at early time. Although a number of GRBs in this sample do not have published radio measurements, we demonstrate the effectiveness of thismethod in the case of Swift GRB 090313, for which millimetric and centimetric observations were available, and conclude that future detections of reverse-shock radio flares with newradio facilities such as the EVLA and ALMA will test the low-frequency model and provide constraints on magnetic models., A.M. acknowledges funding from the Particle Physics and Astronomy Research Council (PPARC). C.G.M. is grateful for financial support from the Royal Society and Research Councils (UK). A.G. acknowledges founding from the Slovenian Research Agency and from the Centre of Excellence for Space Sciences and Technologies SPACE-SI, an operation partly financed by the European Union, European Regional Development Fund and Republic of Slovenia, Ministry of Higher Education, Science and Technology. I.d.G.-M. is partially supported by Ministerio de Ciencia e Innovaci´on (Spain), grant AYA2008-06189-C03 (including FEDER funds), and by Consejer´ıa de Innovaci´on, Ciencia y Empresa of Junta deAndaluc´ıa (Spain). The Liverpool Telescope is operated by Liverpool John Moores University at the Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The Faulkes Telescopes, now owned by Las Cumbres Observatory, are operated with support from the Dill Faulkes Educational Trust. This work is partially based on observations carried out with the IRAM Plateau de Bure Interferometer and observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut f¨ur Astronomie Heidelberg and the Instituto de Astrof´ısica de Andaluc´ıa (CSIC). IRAM is supported by INSU/CNRS (France),MPG (Germany), and IGN (Spain). We thank Calar Alto Observatory for allocation of director’s discretionary time to this program. We also thank M.R Zapatero-Osorio for the acquisition and reduction of NOT data. The research of J.G. and A.J.C.T. is supported by the Spanish programmes AYA2007-63677, AYA2008-03467/ESP, and AYA2009-14000-C03-01. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.

Simultaneous multi-wavelength observations are crucial for understanding the physics of microquasars, especially the accretion disk/jet connection. The enigmatic microquasar Cygnus X-3 exhibits strong, relativistic jet ejection events producing radio flares up to 20 Jy. These events are preceded by a very soft X-ray state with quenched emission in the radio and hard X-ray bands. Recently, GeV flux was observed by the AGILE and Fermi γ-ray observatories during the newly-identified hypersoft state. By using an extensive database of simultaneous multi-wavelength observations gathered from Cygnus X-3 we can form a more unified picture of the nature of the source and show how the recent γ-ray observations fit into it.

Cygnus X-3 is one of the brightest X-ray and radio sources in the Galaxy, and is well known for its erratic behaviour in X-rays as well as in the radio, occasionally producing major radio flares associated with relativistic ejections. However, even after many years of observations in various wavelength bands Cyg X-3 still eludes clear physical understanding. Studying different emission bands simultaneously in microquasars has proved to be a fruitful approach towards understanding these systems, especially by shedding light on the accretion disc/jet connection. We continue this legacy by constructing a hardness-intensity diagram (HID) from archival Rossi X-ray Timing Explorer data and linking simultaneous radio observations to it. We find that surprisingly Cyg X-3 sketches a similar shape in the HID to that seen in other transient black hole X-ray binaries during outburst but with distinct differences. Together with the results of this analysis and previous studies of Cyg X-3 we conclude that the X-ray states can be assigned to six distinct states. This categorization relies heavily on the simultaneous radio observations and we identify one new X-ray state, the hypersoft state, similar to the ultrasoft state, which is associated to the quenched radio state during which there is no or very faint radio emission. Recent observations of GeV flux observed from Cyg X-3 (Tavani et al. 2009; Fermi LAT Collaboration et al. 2009) during a soft X-ray and/or radio quenched state at the onset of a major radio flare hint that a very energetic process is at work during this time, which is also when the hypersoft X-ray state is observed. In addition, Cyg X-3 shows flaring with a wide range of hardness.

The black hole X-ray transient, XTE J1118+480, has now twice been observed in outburst - 2000 and 2005 - and on both occasions remained in the low/hard X-ray spectral state. Here we present radio, infrared, optical, soft X-ray and hard X-ray observations of the more recent outburst. We find that the lightcurves have very different morphologies compared with the 2000 event and the optical decay is delayed relative to the X-ray/radio. We attribute this lesser degree of correlation to contributions of emission from multiple components, in particular the jet and accretion disc. Whereas the jet seemed to dominate the broadband spectrum in 2000, in 2005 the accretion disc seems to be more prominent and we use an analysis of the lightcurves and spectra to distinguish between the jet and disc emission. There also appears to be an optically thin component to the radio emission in the 2005 data, possibly associated with multiple ejection events and decaying as the outburst proceeds. These results add to the discussion that the term "low/hard state'" covers a wider range of properties than previously thought, if it is to account for XTE J1118+480 during these two outbursts.

In our first paper we described three regions of the 9C survey of radio sources with the Ryle telescope at 15.2 GHz, constituting a total area of 520 deg^2 to a completeness limit of approximately 25 mJy. Here we report on a series of deeper regions, amounting to an area of 115 deg^2 complete to approximately 10 mJy and of 29 deg^2 complete to approximately 5.5 mJy. We have investigated the source counts and the distributions of the 1.4 to 15.2 GHz spectral index (alpha) for these deeper samples. The whole catalogue of 643 sources is available online. Down to our lower limit of 5.5 mJy we detect no evidence for any change in the differential source count from the earlier fitted count above 25 mJy. We have matched both our new and earlier catalogues with the NRAO VLA Sky Survey (NVSS) catalogue at 1.4 GHz. For samples of sources selected at 15.2 GHz, in three flux density ranges, we detect a significant shift in the median value of alpha; samples with higher flux densities have higher proportions of sources with flat and rising spectra. We suggest that this observed shift is consistent with a model containing two distinct source populations having differently sloped source counts. Samples selected at 1.4 GHz contain significantly smaller proportions of sources with flat and rising spectra. Also, in our area complete to approximately 10 mJy, we find 5 sources between 10 to 15 mJy, amounting to 4.3 per cent of sources in this range, with no counterpart in the NVSS catalogue. These results illustrate the problems inherent in using a low frequency catalogue to characterise the source population at a much higher frequency and emphasise the value of our blind 15.2 GHz survey.

We present 25 arcsecond resolution radio images of five Lynds Dark Nebulae (L675, L944, L1103, L1111 & L1246) at 16 GHz made with the Arcminute Microkelvin Imager (AMI) Large Array. These objects were previously observed with the AMI Small Array to have an excess of emission at microwave frequencies relative to lower frequency radio data. In L675 we find a flat spectrum compact radio counterpart to the 850 micron emission seen with SCUBA and suggest that it is cm-wave emission from a previously unknown deeply embedded young protostar. In the case of L1246 the cm-wave emission is spatially correlated with 8 micron emission seen with Spitzer. Since the MIR emission is present only in Spitzer band 4 we suggest that it arises from a population of PAH molecules, which also give rise to the cm-wave emission through spinning dust emission., accepted MNRAS

We present simultaneous dual-frequency radio observations of Cygnus X-3 during a phase of low-level activity. We constrain the minimum variability timescale to be 20 minutes at 43 GHz and 30 minutes at 15 GHz, implying source sizes of 2 to 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 approximately 10 minutes 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 lightcurves 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 timescale and frequency at which this is attained. Brighter flares evolve on longer timescales 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 normalisation and magnetic field strength both playing a role in setting the strength of the outburst., Accepted for publication in MNRAS. 15 pages, 9 figures

We present interferometric imaging at 33 GHz, with the new superextended configuration of the Very Small Array (VSA), of a very deep decrement in the cosmic microwave background (CMB) temperature. This decrement is located in the direction of the Corona Borealis supercluster, at a position with no known galaxy clusters, and was discovered by a previous VSA survey (Genova-Santos et al.). A total area of 3 sq.deg. has now been imaged, with an angular resolution of 7 arcmin and a flux sensitivity of 5 mJy/beam. These observations confirm the presence of this strong and resolved negative spot at -41+/-5 mJy/beam (-258+/-29 muK), with a signal to noise level of 8. This structure is also present in the WMAP 5-year data. The temperature of the W-band (94 GHz) data at the position of the decrement agrees within 1.2-sigma with that observed by the VSA at 33 GHz, and within 0.2-sigma with the Sunyaev-Zel'dovich (SZ) spectrum. Our analyses show that it is a non-Gaussian feature in the CMB at a level of 4.8-sigma. The probability of finding such a deviation or larger in CMB Gaussian simulations is only 0.19 per cent. Therefore, an explanation other than primordial CMB is required. We have considered the possibility of an SZ effect generated in a diffuse, extended warm/hot gas distribution. This hypothesis is especially relevant, as the presence of such structures, if confirmed, could provide the location for a significant fraction of the missing baryons in the Local Universe.

We present observations between 14.2 and 17.9 GHz of sixteen Galactic HII regions made with the Arcminute Microkelvin Imager (AMI). In conjunction with data from the literature at lower radio frequencies we investigate the possibility of a spinning dust component in the spectra of these objects. We conclude that there is no significant evidence for spinning dust towards these sources and measure an average spectral index of 0.15+/-0.07 between 1.4 and 17.9 GHz for the sample., Comment: accepted MNRAS

(abridged) This is the second paper presenting the results of two years of monitoring of GRS 1915+105 with \integral and \rxte and the Ryle Telescope. We present the X-ray spectral and temporal analysis of four observations which showed strong radio to X-ray correlations. During one observation GRS 1915+105 was in a steady state, while during the three others it showed cycles of X-ray dips and spikes (followed by radio flares). We present the time-resolved spectroscopy of these cyclesand show that in all cases the hard X-ray component (the Comptonized emission from a coronal medium) is suppressed in coincidence with a soft X-ray spike that ends the cycle. We interpret these results as evidence that the soft X-ray spike is the trigger of the ejection, and that the ejected medium is the coronal material. In the steady state observation, the X-ray spectrum is indicative of the hard-intermediate state, with the presence of a relatively strong emission at 15 GHz. The X-ray spectra are the sum of a Comptonized component and an extra power law extending to energies >200 keV without any evidence for a cut-off. We observe a possible correlation of the radio flux with that of the power law component, which may indicate that we see direct emission from the jet at hard X-ray energies. We study the energy dependence of a ~4 Hz QPO during the hard-intermediate state observation. The QPO-``spectrum'' is well modeled by a power law with a cut-off at an energy about 11 keV that clearly differs from the relative contribution of the Comptonized component to the overall flux. This may rule out models of global oscillations of the Compton corona.

(Abridged) We report the results of monitoring observations of the Galactic microquasar GRS 1915+105 performed simultaneously with INTEGRAL and RXTE Ryle . We present the results of the whole \integral campaign, report the sources that are detected and their fluxes and identify the classes of variability in which GRS 1915+105 is found. The accretion ejection connections are studied in a model independent manner through the source light curves, hardness ratio, and color color diagrams. During a period of steady ``hard'' X-ray state (the so-called class chi) we observe a steady radio flux. We then turn to 3 particular observations during which we observe several types of soft X-ray dips and spikes cycles, followed by radio flares. During these observations GRS 1915+105 is in the so-called nu, lambda, and beta classes of variability. The observation of ejections during class lambda are the first ever reported. We generalize the fact that a (non-major) discrete ejection always occurs, in GRS 1915+105, as a response to an X-ray sequence composed of a spectrally hard X-ray dip terminated by an X-ray spike marking the disappearance of the hard X-ray emission above 18 keV. We also identify the trigger of the ejection as this X-ray spike. A possible correlation between the amplitude of the radio flare and the duration of the X-ray dip is found in our data. In this case the X-ray dips prior to ejections could be seen as the time during which the source accumulates energy and material that is ejected later.