We present continued radio observations of the tidal disruption event Swift J164449.3+573451 extending to delta t approx = 216 days after discovery. The data were obtained with the EVLA, AMI Large ...Array, CARMA, the SMA, and the VLBA+Effelsberg as part of a long-term program to monitor the expansion and energy scale of the relativistic outflow, and to trace the parsec-scale environment around a previously dormant supermassive black hole (SMBH). The new observations reveal a significant change in the radio evolution starting at delta t approx = 1 month, with a brightening at all frequencies that requires an increase in the energy by about an order of magnitude, and an overall density profile around the SMBH of rho is proportional tor super(-3/2) (0.1-1.2 pc) with a significant flattening at r approx = 0.4-0.6 pc. The increase in energy cannot be explained with continuous injection from an L is proportional tot super(-5/3) tail, which is observed in the X-rays. Instead, we conclude that the relativistic jet was launched with a wide range of Lorentz factors, obeying E(> Gammaj)is proportional toGamma super(-2.5)j. The similar ratios of duration to dynamical timescale for Sw 1644+57 and gamma-ray bursts (GRBs) suggest that this result may be applicable to GRB jets as well. The radial density profile may be indicative of Bondi accretion, with the inferred flattening at r ~ 0.5 pc in good agreement with the Bondi radius for a ~few x 10 super(6) M black hole. The density at ~0.5 pc is about a factor of 30 times lower than inferred for the Milky Way Galactic Center, potentially due to a smaller number of mass-shedding massive stars. From our latest observations ( delta t approx = 216 days) we find that the jet energy is E sub(j, iso) approx = 5 x 10 super(53) erg (E sub(j) approx = 2.4 x 10 super(51) erg or thetaj = 0.1), the radius is r approx = 1.2 pc, the Lorentz factor is Gammaj approx = 2.2, the ambient density is n approx = 0.2 cm super(-3), and the projected angular size is r sub(proj) approx = 25 mu as, below the resolution of the VLBA+Effelsberg. Assuming no future changes in the observed evolution and a final integrated total energy of E sub(j) approx = 10 super(52) erg, we predict that the radio emission from Sw 1644+57 should be detectable with the EVLA for several decades and will be resolvable with very long baseline interferometry in a few years.
We present continued multi-frequency radio observations of the relativistic tidal disruption event Swift J164449.3+573451 extending to t approximate 600 days. The data were obtained with the JVLA and ...AMI Large Array as part of our on-going study of the jet energetics and the density structure of the parsec-scale environment around the disrupting super-massive black hole. We combine these data with public Swift/XRT and Chandra X-ray observations over the same time-frame to show that the jet has undergone a dramatic transition starting at approximate 500 days, with a sharp decline in the X-ray flux by about a factor of 170 on a timescale of delta t/t < or = 0.2. On the other hand, our radio data uniquely demonstrate that the low X-ray flux measured by Chandra at approximate 610 days is consistent with emission from the forward shock. Projecting forward, we predict that the emission in the radio and X-ray bands will evolve in tandem with similar decline rates.
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 of
is obtained for the dimensionless black hole spin. 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
, which is consistent with the recent optical measurement of the binary system inclination by Orosz et al. of 27°± 0°.8. 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 study high-energy γ-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 γ-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 ≃3.5 and a low-energy cutoff at the Lorentz factor of ∼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, γ-ray, and X-ray emissions. We find the cross-correlation between the radio and γ-ray emission peaks at a lag less than 1 d, while we detect a distinct radio lag of ∼50 d with respect to the soft X-rays in the soft spectral state.
Active galactic nuclei, which are powered by long-term accretion onto central supermassive black holes, produce relativistic jets with lifetimes of at least one million years, and the observation of ...the birth of such a jet is therefore unlikely. Transient accretion onto a supermassive black hole, for example through the tidal disruption of a stray star, thus offers a rare opportunity to study the birth of a relativistic jet. On 25 March 2011, an unusual transient source (Swift J164449.3+573451) was found, potentially representing such an accretion event. Here we report observations spanning centimetre to millimetre wavelengths and covering the first month of evolution of a luminous radio transient associated with Swift J164449.3+573451. The radio transient coincides with the nucleus of an inactive galaxy. We conclude that we are seeing a newly formed relativistic outflow, launched by transient accretion onto a million-solar-mass black hole. A relativistic outflow is not predicted in this situation, but we show that the tidal disruption of a star naturally explains the observed high-energy properties and radio luminosity and the inferred rate of such events. The weaker beaming in the radio-frequency spectrum relative to γ-rays or X-rays suggests that radio searches may uncover similar events out to redshifts of z ≈ 6.
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Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Several independent lines of evidence now point to a connection between the physical processes that govern radio (i.e. jet) and X-ray emission from accreting X-ray binaries. We present a ...comprehensive study of (quasi-)simultaneous radio–X-ray observations of stellar black hole binaries during the spectrally hard X-ray state, finding evidence for a strong correlation between these two bands over more than three orders of magnitude in X-ray luminosity. The correlation extends from the quiescent regime up to close to the soft state transition, where radio emission starts to decline, sometimes below detectable levels, probably corresponding to the physical disappearance of the jet. The X-ray transient V404 Cygni is found to display the same functional relationship already reported for GX 339−4 between radio and X-ray flux, namely Sradio∝S+0.7X. In fact, the data for all low/hard state black holes is consistent with a universal relation between the radio and X-ray luminosity of the form Lradio∝L+0.7X. Under the hypothesis of common physics driving the disc–jet coupling in different sources, the observed spread to the best-fitting relation can be interpreted in terms of a distribution in Doppler factors and hence used to constrain the bulk Lorentz factors of both the radio- and X-ray-emitting regions. Monte Carlo simulations show that, assuming little or no X-ray beaming, the measured scatter in radio power is consistent with Lorentz factors ≲ 2 for the outflows in the low/hard state, significantly less relativistic than the jets associated with X-ray transients. When combined radio and X-ray beaming is considered, the range of possible jet bulk velocities significantly broadens, allowing highly relativistic outflows, but therefore implying severe X-ray selection effects. If the radio luminosity scales as the total jet power raised to x > 0.7, then there exists an X-ray luminosity below which most of the accretion power will be channelled into the jet, rather than into X-rays. For x= 1.4, as in several optically thick jet models, the power output of ‘quiescent’ black holes may be jet-dominated below LX≃ 4 × 10−5LEdd.
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 data set is a spectrum taken with the Chandra X-ray Observatory High ...Energy Transmission Grating 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 ≥1012 cm−3 in the region responsible for most of the emission. We discuss the influence of the dust scattering halo on the broadband spectrum, and we argue that dust scattering and extinction is not the most likely origin for the narrow feature seen near the Si K edge. We identify the features of a wind in the profiles of the strong resonance lines and 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 systems.
Continuing the observational campaign initiated by our group, we present the long term spectral evolution of the Galactic black hole candidate Cygnus X-1 in the X-rays and at 15 GHz. We present 6200 ...pointed observations taken between early 1999 and late 2004 with the Rossi X-ray Timing Explorer and the Ryle radio telescope. The X-ray spectra are remarkably well described by a simple broken power law spectrum with an exponential cutoff. Physically motivated Comptonization models, e.g., by Titarchuk (1994, ApJ, 434, 570, compTT) and by Coppi (1999, in High Energy Processes in Accreting Black Holes, ed. J. Poutanen, & R. Svensson (San Francisco: ASP), ASP Conf. Ser., 161, 375, eqpair), can reproduce this simplicity; however, the success of the phenomenological broken power law models cautions against "overparameterizing" the more physical models. Broken power law models reveal a significant linear correlation between the photon index of the lower energy power law and the hardening of the power law at 610keV. This phenomenological soft/hard power law correlation is partly attributable to correlations of broad band continuum components, rather than being dominated by the weak hardness/reflection fraction correlation present in the Comptonization model. Specifically, the Comptonization models show that the bolometric flux of a soft excess (e.g., disk component) is strongly correlated with the compactness ratio of the Comptonizing medium, with Ldisk 8 (lh/ls)-0.19. Over the course of our campaign, Cyg X-1 transited several times into the soft state, and exhibited a large number of "failed state transitions". The fraction of the time spent in such low radio emission/soft X-ray spectral states has increased from 610% in 1996-2000 to 634% since early 2000. We find that radio flares typically occur during state transitions and failed state transitions (at lh/ls 6 3), and that there is a strong correlation between the 10-50 keV X-ray flux and the radio luminosity of the source. We demonstrate that rather than there being distinctly separated states, in contrast to the timing properties the spectrum of Cyg X-1 shows variations between extremes of properties, with clear cut examples of spectra at every intermediate point in the observed spectral correlations.
The culture of insurgents in early modern Europe was primarily an oral one; memories of social conflicts in the communities affected were passed on through oral forms such as songs and legends. This ...popular history continued to influence political choices and actions through and after the early modern period. The chapters in this book examine numerous examples from across Europe of how memories of revolt were perpetuated in oral cultures, and they analyse how traditions were used. From the German Peasants’ War of 1525 to the counter-revolutionary guerrillas of the 1790s, oral traditions can offer radically different interpretations of familiar events. This is a ‘history from below’, and a history from song, which challenges existing historiographies of early modern revolts.
Over the past decade, long-duration γ-ray bursts (GRBs)-including the subclass of X-ray flashes (XRFs)-have been revealed to be a rare variety of type Ibc supernova. Although all these events result ...from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary type Ibc supernovae by many orders of magnitude. The essential physical process that causes a dying star to produce a GRB or XRF, and not just a supernova, is still unknown. Here we report radio and X-ray observations of XRF 060218 (associated with supernova SN 2006aj), the second-nearest GRB identified until now. We show that this event is a hundred times less energetic but ten times more common than cosmological GRBs. Moreover, it is distinguished from ordinary type Ibc supernovae by the presence of 1048 erg coupled to mildly relativistic ejecta, along with a central engine (an accretion-fed, rapidly rotating compact source) that produces X-rays for weeks after the explosion. This suggests that the production of relativistic ejecta is the key physical distinction between GRBs or XRFs and ordinary supernovae, while the nature of the central engine (black hole or magnetar) may distinguish typical bursts from low-luminosity, spherical events like XRF 060218.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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