Hintze Centre for Astrophysical Surveys

Abstract:

We derive accretion rate functions (ARFs) and kinetic luminosity functions (KLFs) for jet-launching supermassive black holes. The accretion rate as well as the kinetic power of an active galaxy is estimated from the radio emission of the jet. For compact low-power jets, we use the core radio emission while the jet power of high-power radio-loud quasars is estimated using the extended low-frequency emission to avoid beaming effects. We find that at low luminosities the ARF derived from the radio emission is in agreement with the measured bolometric luminosity function (BLF) of active galactic nucleus (AGN), i.e. all low-luminosity AGN launch strong jets. We present a simple model, inspired by the analogy between X-ray binaries (XRBs) and AGN, that can reproduce both the measured ARF of jet-emitting sources as well as the BLF. The model suggests that the break in power-law slope of the BLF is due to the inefficient accretion of strongly sub-Eddington sources. As our accretion measure is based on the jet power it also allows us to calculate the KLF and therefore the total kinetic power injected by jets into the ambient medium. We compare this with the kinetic power output from supernova remnants (SNRs) and XRBs, and determine its cosmological evolution. © 2007 The Authors.

Abstract:

We present deep optical and infrared (IR) observations of the short-duration GRB 050906. Although no X-ray or optical/IR afterglow was discovered to deep limits, the error circle of the gamma-ray burst (GRB) (as derived from the Swift Burst Alert Telescope, or BAT) is unusual in containing the relatively local starburst galaxy IC328. This makes GRB 050906 a candidate burst from a soft gamma-ray repeater (SGR), similar to the giant flare from SGR 1806-20. The probability of chance alignment of a given BAT position with such a galaxy is small (≲1 per cent), although the size of the error circle (2.6 arcmin radius) is such that a higher z origin cannot be ruled out. Indeed, the error circle also includes a moderately rich galaxy cluster at z = 0.43, which is a plausible location for the burst given the apparent preference that short-duration GRBs have for regions of high mass density. No residual optical or IR emission has been observed, in the form of either an afterglow or a later time emission from any associated supernova-like event. We discuss the constraints these limits place on the progenitor of GRB 050906 based on the expected optical signatures from both SGRs and merging compact object systems. © 2008 RAS.

Abstract:

Near-infrared (NIR) and optical polarimetric observations of a selection of X-ray binaries are presented. The targets were observed using the Very Large Telescope and the United Kingdom Infrared Telescope. We detect a significant level (3σ) of linear polarization in four sources. The polarization is found to be intrinsic (at the >3σ level) in two sources; GRO J1655-40 (∼4-7 per cent in the H and Ks bands during an outburst) and Sco X-1 (∼0.1-0.9 per cent in the H and K bands), which is stronger at lower frequencies. This is likely to be the signature of optically thin synchrotron emission from the collimated jets in these systems, whose presence indicates that a partially ordered magnetic field is present at the inner regions of the jets. In Sco X-1, the intrinsic polarization is variable (and sometimes absent) in the H and K bands. In the J band (i.e. at higher frequencies), the polarization is not significantly variable and is consistent with an interstellar origin. The optical light from GX 339-4 is also polarized, but at a level and position angle consistent with scattering by interstellar dust. The other polarized source is SS 433, which has a low level (0.5-0.8 per cent) of J-band polarization, likely due to local scattering. The NIR counterparts of GRO J0422+32, XTE J1118+480, 4U 0614+09 and Aql X-1 (which were all in or near quiescence) have a linear polarization level of <16 per cent (3σ upper limit, some are <6 per cent). We discuss how such observations may be used to constrain the ordering of the magnetic field close to the base of the jet in such systems. © 2008 The Authors.

Abstract:

We report on a comprehensive and consistent investigation into the X-ray emission from GX 339-4. All public observations in the 11 year RXTE archive were analysed. Three different types of model - single power law, broken power law and a disc + power law - were fitted to investigate the evolution of the disc, along with a fixed Gaussian component at 6.4 keV to investigate any iron line in the spectrum. We show that the relative variation in flux and X-ray colour between the two best sampled outbursts are very similar. The decay of the disc temperature during the outburst is clearly seen in the soft state. The expected decay is SDisc ∝ T4; we measure T 4.75±0.23. This implies that the inner disc radius is approximately constant in the soft state. We also show a significant anticorrelation between the iron line equivalent width (EW) and the X-ray flux in the soft state while in the hard state the EW is independent of the flux. This results in hysteresis in the relation between X-ray flux and both line flux and EW. To compare the X-ray binary outburst to the behaviour seen in active galactic nuclei (AGN), we construct a disc fraction luminosity diagram for GX 339-4, the first for an X-ray binary. The shape qualitatively matches that produced for AGN. Linking this with the radio emission from GX 339-4 the change in radio spectrum between the disc and power-law-dominated states is clearly visible. © 2008 The Authors.

Abstract:

We analysed two-dimensional maps of 48 early-type galaxies obtained with the SAURON and OASIS integral-field spectrographs using kinemetry, a generalization of surface photometry to the higher order moments of the line-of-sight velocity distribution (LOSVD). The maps analysed include: reconstructed image, mean velocity, velocity dispersion, h3 and h4 Gauss-Hermite moments. Kinemetry is a good method to recognize structures otherwise missed by using surface photometry, such as embedded discs and kinematic subcomponents. In the SAURON sample, we find that 31 per cent of early-type galaxies are single component systems. 91 per cent of the multicomponents systems have two kinematic subcomponents, the rest having three. In addition, 29 per cent of galaxies have kinematically decoupled components, nuclear components with significant kinematic twists. We differentiate between slow and fast rotators using velocity maps only and find that fast-rotating galaxies contain discs with a large range in mass fractions to the main body. Specifically, we find that the velocity maps of fast rotators closely resemble those of inclined discs, except in the transition regions between kinematic subcomponents. This deviation is measured with the kinemetric k 5/k1 ratio, which is large and noisy in slow rotators and about 2 per cent in fast rotators. In terms of E/S0 classification, this means that 74 per cent of Es and 92 per cent of S0s have components with disc-like kinematics. We suggest that differences in k5/k1 values for the fast and slow rotators arise from their different intrinsic structure which is reflected on the velocity maps. For the majority of fast rotators, the kinematic axial ratios are equal to or less than their photometric axial ratios, contrary to what is predicted with isotropic Jeans models viewed at different inclinations. The position angles of fast rotators are constant, while they vary abruptly in slow rotators. Velocity dispersion maps of face-on galaxies have shapes similar to the distribution of light. Velocity dispersion maps of the edge-on fast rotators and all slow rotators show differences which can only be partially explained with isotropic models and, in the case of fast rotators, often require additional cold components. We constructed local (bin-by-bin) h3-V/σ and h4-V/σ diagrams from SAURON observations. We confirm the classical anticorrelation of h3 and V/σ, but we also find that h3 is almost zero in some objects or even weakly correlated with V/σ. The distribution of h4 for fast and slow rotators is mildly positive on average. In general, fast rotators contain flattened components characterized by a disc-like rotation. The difference between slow and fast rotators is traceable throughout all moments of the LOSVD, with evidence for different intrinsic shapes and orbital contents and, hence, likely different evolutionary paths. © 2008 RAS.