The emission regions in X-ray binaries: dipping as a diagnostic

X-ray dipping in the black hole binary Cygnus X-1, the Galactic jet source GRO J1655-40 and in low mass X-ray binaries is discussed. It is shown that spectral analysis strongly constrains emission models. Measurement of dip ingress/egress times allows the sizes of extended emission regions to be determined, notably for the Accretion Disk Corona which is responsible for Comptonization in X-ray binaries. In LMXB, the radius of the ADC is shown to be between ~ 10^9 and ~ 5x10^10 cm, an appreciable fraction of the accretion disk radius. This is inconsistent with Comptonization models requiring a localized Comptonizing region, for example, in the immediate neighbourhood of the neutron star. Results from a survey of LMXB using ASCA and BeppoSAX reveal an approximate equality between the height of the blackbody emission region on the neutron star and the height of the inner radiatively-supported disk, suggesting either that there is a direct causal link, such as a radial accretion flow between the inner disk edge and the star, or an indirect link, as in the case of accretion flow creep on the surface of the neutron star as suggested by Inogamov & Sunyaev. Finally, the survey shows that the blackbody cannot originate on the accretion disk as the required inner radii in many sources are substantially less than the neutron star radius.Comment: solicited review paper presented at COSPAR 2000 "X-ray and Gamma-ray Signatures of Black Holes and Weakly Magnetized Neutron Stars"; accepted for publication in Advances in Space Research (2nd affiliation added

Neutral absorber dips in the periodic burster LMXB XB 1323-619 from Suzaku

We present results of an observation with Suzaku of the dipping, periodic bursting low mass X-ray binary XB 1323-619. Using the energy band 0.8 - 70 keV, we show that the source spectrum is well-described as the emission of an extended accretion disk corona, plus a small contribution of blackbody emission from the neutron star. The dip spectrum is well-fitted by the progressive covering model in which the extended ADC is progressively overlapped by the absorbing bulge of low ionization state in the outer accretion disk and that dipping is basically due to photoelectric absorption in the bulge. An energy-independent decrease of flux at high energies (20 - 70 keV) is shown to be consistent with the level of Thomson scattering expected in the bulge. An absorption feature at 6.67 keV (Fe XXV) is detected in the non-dip spectrum and other possible weak features. In dipping, absorption lines of medium and highly ionized states are seen suggestive of absorption in the ADC but there is no evidence that the lines are stronger than in non-dip. We show that the luminosity of the source has changed substantially since the Exosat observation of 1985, increasing in luminosity between 1985 and 2003, then in 2003 - 2007 falling to the initial low value. X-ray bursting has again become periodic, which it ceased to do in its highest luminosity state, and we find that the X-ray bursts exhibit both the fast decay and later slow decay characteristic of the rp burning process. We present arguments against the recent proposal that the decrease of continuum flux in the dipping LMXB in general can be explained as absorption in an ionized absorber rather than in the bulge in the outer disk generally accepted to be the site of absorption.Comment: 12 pages, 6 figures, Astronomy and Astrophysics in pres

Results of a LMXB survey: variation in the height of the neutron star blackbody emission region

We present results of a survey of the spectra of Low Mass X-ray Binaries using ASCA. It is shown that all sources in the survey are well-fitted by the same two-component emission model that we have previously shown is able to describe both the non-dip and dip spectra of the dipping class of LMXB. This model consists of point-like blackbody emission from the neutron star plus Comptonized emission from a disk-like accretion disk corona of radius typically 50,000 km. Additional data from results published elsewhere by us from BeppoSAX and ASCA are added to the survey. The large variation in blackbody luminosity of survey sources is shown to be due primarily to major changes in blackbody emitting area. Fitting a multi-temperature disk blackbody plus Comptonization model to the survey spectra requires values of inner disk radius substantially less than the neutron star radius in many cases, making disk origin of the blackbody highly unlikely. Assuming that the emission is from an equatorial strip on the neutron star, it is shown that the half-height of the strip h agrees well with the half-height H of the radiatively-supported inner accretion disk, this agreement spanning three orders of magnitude in each parameter. Possible mechanisms for the agreement are discussed, including radial accretion flow between inner disk and star, and accretion flow ``creep' on the surface of the neutron star.Comment: 10 pages, 7 ps figures; accepted for publication in A&A Main Journa

Physical changes during Z-track movement in Sco X-1 on the flaring branch

We present results of a detailed study of X-ray flaring in the Z-track source Sco X-1 in a highly super-Eddington state made using high quality Rossi-XTE data from the PCA and HEXTE instruments. The emission model successfully used to explain the dipping LMXB, and other classes of LMXB in recent years, was applied to study the physical evolution along the Z-track which remains a major problem. This model consists of blackbody emission from the neutron star plus Comptonized emission from an extended accretion disk corona. As found in earlier work, major changes take place in the neutron star blackbody emission with kT increasing in flaring, and the blackbody radius R_BB increasing substantially to a maximum value of 9.4 +/- 0.6 km, consistent with the radius of the neutron star, after which R_BB decreases. Thus this result is a measurement of neutron star radius. The behaviour of Sco X-1 in flaring is compared with our previous results for the strong flaring that takes place in the bright dipping, flaring LMXB X 1624-490. Remarkably, during movement along the Normal Branch towards the apex with the Flaring Branch, the luminosities of both spectral components decrease, suggesting the possibility that Mdot may decrease on the Normal Branch, contrary to the widely-held view that Mdot increases monotonically along the Z-track. During flaring, we detect for the first time an increase of the Comptonization cut-off energy which may suggest heating of the ADC plasma by the neutron star flare. The energy of a broad Gaussian line at 6.4 keV does not change, but the intensity of the line increases in flaring suggesting either an increase in ADC size in flaring or the effects of irradiation by the neutron star.Comment: 12 pages including 8 figures, Astronomy and Astrophysics in press; reference list correcte

Measurements of accretion disc corona size in LMXB: consequences for Comptonization and LMXB models

We present results of measurements of the radial extent of the accretion disc corona in low mass X-ray binaries. These results prove conclusively the extended nature of the ADC, with radial extent varying from 20,000 km in the faintest sources to 700,000 km in the brightest, a substantial fraction of the accretion disc radius, typically 15%. This result rules out the Eastern model for LMXB which is extensively used, in which the Comptonizing region is a small central region. The ADC size depends strongly on the 1 - 30 keV source luminosity via a simple relationship r_ADC = L^{0.88 +/- 0.16} (99% confidence) close to a simple proportionality. We also present limited evidence that the ADC size agrees with the Compton radius r_C, or maximum radius for hydrostatic equilibrium. The results are consistent with models in which an extended ADC is formed by illumination of the disc by the central source. The dependence on luminosity may reflect the known decrease of coronal temperature as the source luminosity increases leading to an increase of r_C. The extended nature of the ADC means that the seed photons for Comptonization must consist of emission from the disc to the same radial extent as the corona, providing copious supplies of soft seed photons. We demonstrate the importance of the size of the ADC to the correct description of Comptonization, and derive the Comptonized spectrum of a LMXB based on thermal Comptonization of these seed photons and show that this differs fundamentally from that of the Eastern model which assumes a cut-off below 1 keV. Finally, we argue that our results are inconsistent with the assumption often made that the X-ray emission of accreting Black Holes and Neutron Stars has a common mechanism depending on the properties of the accretion flow only.Comment: 9 pages, 5 figures, MNRAS in press - final versio

Enforcing the climate change act

This paper examines the enforceability of the duties in the Climate Change Act 2008 which require the UK’s GHG emissions to be reduced over time. Section B highlights how the Act’s other provisions must be interpreted so as to give proper support to these duties. The paper goes on, in Section C, to dispute objections that have been made to the duties’ enforceability – on the grounds that they are ‘target duties’ or ‘non-justiciable’– and argues that the courts can enforce them provided they adopt the amplified role which this new kind of duty requires; by seeking to forge effective but appropriate remedies. Section D suggests what form these remedies might take. Final conclusions are described in Section E

Energy Prices Jump While Food Prices Show Modest Increases

The Consumer Price Index (CPI) is a measure of the average change over time in the prices paid by urban consumers for a market basket of consumer goods and services. Produced monthly by the Bureau of Labor Statistics (BLS), the CPI uses a “market basket,” or a sample of goods and services that consumers purchase for day-to-day living, and weighs each item on the basis of the amount of spending reported by a sample of families and individuals. Widely used as a measure of inflation, the CPI provides information about price changes in the nation’s economy and can be used by government, business, labor, and private individuals as a guide to making economic decisions. Over the last 12 months, the index for all items less food and energy has slowly accelerated. In contrast, the all-items index has decelerated since a 12-month increase of 3.9 percent in September 2011. The September 2011 increase capped a run of steady acceleration in the all-items index that began in December 2010. Despite the contrast, the all-items index increased at a higher rate than the index for all items less food and energy in the first quarter of 2012. This summary compares price changes in the CPI for detailed categories of goods and services over the first quarter of 2012 with those in 2011