The swansong in context: long-timescale X-ray variability of NGC 4051

On 9-11 May 1998, the highly-variable, low luminosity Seyfert 1 galaxy NGC4051 was observed in an unusual low flux state by BeppoSAX (Guainazzi et al. 1998) RXTE and EUVE. We present fits of the 4-15 keV RXTE spectrum and BeppoSAX MECS spectrum obtained during this observation, which are consistent with the interpretation that the source had switched off, leaving only the spectrum of pure reflection from distant cold matter. We place this result in context by showing the X-ray lightcurve of NGC4051 obtained by our RXTE monitoring campaign over the past two and a half years, which shows that the low state lasted for ~150 days before the May observations (implying that the reflecting material is > 10^17 cm from the continuum source) and forms part of a lightcurve showing distinct variations in long-term average flux over timescales > months. We show that the long-timescale component to X-ray variability is intrinsic to the primary continuum and is probably distinct from the variability at shorter timescales, possibly associated with variations in the accretion flow of matter onto the central black hole. As the source approaches the low state, the variability process becomes non-linear. NGC4051 may represent a microcosm of all X-ray variability in radio quiet active galactic nuclei (AGNs), displaying in a few years a variety of flux states and variability properties which more luminous AGNs may pass through on timescales of decades to thousands of years.Comment: 5 pages, accepted for publication in MNRA

Measuring the broadband power spectra of active galactic nuclei with RXTE

We have developed a Monte Carlo technique to test models for the true power spectra of intermittently sampled lightcurves against the noisy, observed power spectra, and produce a reliable estimate of the goodness of fit of the given model. We apply this technique to constrain the broadband power spectra of a sample of four Seyfert galaxies monitored by the Rossi X-ray Timing Explorer (RXTE) over three years. We show that the power spectra of three of the AGN in our sample (MCG-6-30-15, NGC5506 and NGC3516) flatten significantly towards low frequencies, while the power spectrum of NGC5548 shows no evidence of flattening. We fit two models for the flattening, a `knee' model, analogous to the low-frequency break seen in the power spectra of BHXRBs in the low state (where the power-spectral slope flattens to \alpha=0) and a `high-frequency break' model (where the power-spectral slope flattens to \alpha=1), analogous to the high-frequency break seen in the high and low-state power spectra of the classic BHXRB Cyg X-1. Both models provide good fits to the power spectra of all four AGN. For both models, the characteristic frequency for flattening is significantly higher in MCG-6-30-15 than in NGC 3516 (by factor ~10) although both sources have similar X-ray luminosities, suggesting that MCG-6-30-15 has a lower black hole mass and is accreting at a higher rate than NGC 3516. Assuming linear scaling of characteristic frequencies with black hole mass, the high accretion rate implied for MCG-6-30-15 favours the high-frequency break model for this source and further suggests that MCG-6-30-15 and possibly NGC 5506, may be analogues of Cyg X-1 in the high state [ABRIDGED].Comment: 23 pages, accepted for publication in MNRA

Complex Optical-X-ray Correlations in the Narrow-Line Seyfert 1 Galaxy NGC 4051

This paper presents the results of a dense and intensive X-ray and optical monitoring of the narrow-line Seyfert 1 galaxy NGC 4051 carried out in 2000. Results of the optical analysis are consistent with previous measurements. The amplitude of optical emission line variability is a factor of two larger than that of the underlying optical continuum, but part or all of the difference can be due to host-galaxy starlight contamination or due to the lines being driven by the unseen UV continuum, which is more variable than the optical continuum. We measured the lag between optical lines and continuum and found a lower, more accurate broad line region size of 3.0+-1.5 light days in this object. The implied black hole mass is M_BH=5(+6,-3)x10^5 M_sun; this is the lowest mass found, so far, for an active nucleus. We find significant evidence for an X-ray-optical (XO) correlation with a peak lag of about <1 day, although the centroid of the asymmetric correlation function reveals that part of the optical flux varies in advance of the X-ray flux by 2.4+-1.0 days. This complex XO correlation is explained as a possible combination of X-ray reprocessing and perturbations propagating from the outer (optically emitting) parts of the accretion disc into its inner (X-ray emitting) region.Comment: 8 pages, 4 figures included, LaTeX mn.sty, accepted for publication in MNRA

Discovery of multiple Lorentzian components in the X-ray timing properties of the Narrow Line Seyfert 1 Ark 564

We present a power spectral analysis of a 100 ksec XMM-Newton observation of the narrow line Seyfert 1 galaxy Ark~564. When combined with earlier RXTE and ASCA observations, these data produce a power spectrum covering seven decades of frequency which is well described by a power law with two very clear breaks. This shape is unlike the power spectra of almost all other AGN observed so far, which have only one detected break, and resemble Galactic binary systems in a soft state. The power spectrum can also be well described by the sum of two Lorentzian-shaped components, the one at higher frequencies having a hard spectrum, similar to those seen in Galactic binary systems. Previously we have demonstrated that the lag of the hard band variations relative to the soft band in Ark 564 is dependent on variability time-scale, as seen in Galactic binary sources. Here we show that the time-scale dependence of the lags can be described well using the same two-Lorentzian model which describes the power spectrum, assuming that each Lorentzian component has a distinct time lag. Thus all X-ray timing evidence points strongly to two discrete, localised, regions as the origin of most of the variability. Similar behaviour is seen in Galactic X-ray binary systems in most states other than the soft state, i.e. in the low-hard and intermediate/very high states. Given the very high accretion rate of Ark 564 the closest analogy is with the very high (intermediate) state rather than the low-hard state. We therefore strengthen the comparison between AGN and Galactic binary sources beyond previous studies by extending it to the previously poorly studied very high accretion rate regime.Comment: 11 pages, 11 figures, accepted for publication in MNRA

Neutral Hydrogen 21cm Absorption at Redshift 0.673 towards 1504+377

We detect the 21 cm line of neutral hydrogen in absorption at a redshift of 0.673 towards the 1 Jy radio source 1504+377. The 1504+377 radio source is located toward the center of what appears to be an inclined disk galaxy at z = 0.674. The 21 cm absorption line shows multiple velocity components over a velocity range of about 100 km sec$^{-1}$, with a total HI column density: N(HI) = $3.8\times10^{19}\times({{T_s}\over{f}})$ cm$^{-2}$. The velocity-integrated optical depth of this system is the largest yet seen for redshifted HI 21 cm absorption line systems (Carilli 1995). The 21 cm absorption line is coincident in redshift with a previously detected broad molecular absorption line system (Wiklind and Combes 1996). We do not detect HI 21 cm absorption associated with the narrow molecular absorption line system at z = 0.67150, nor do we detect absorption at these redshifts by the 18 cm lines of OH, nor by the 2 cm transition of H$_2$CO. There is no evidence for a bright optical AGN in 1504+377, suggesting significant obscuration through the disk -- a hypothesis supported by the strong absorption observed. The 1504+377 system resembles the ``red quasar'' PKS 1413+135, which has been modeled as a optically obscured AGN with a very young radio jet in the center of a gas rich disk galaxy (Perlman et al. 1996). The presence of very bright radio jets at the centers of these two disk galaxies presents a challenge to unification schemes for extragalactic radio sources and to models for the formation of radio loud AGN.Comment: 17 pages, postscrip

An absorption event in the X-ray lightcurve of NGC 3227

We have monitored the Seyfert galaxy NGC 3227 with the Rossi X-ray Timing Explorer (RXTE) since January 1999. During late 2000 and early 2001 we observed an unusual hardening of the 2-10 keV X-ray spectrum which lasted several months. The spectral hardening was not accompanied by any correlated variation in flux above 8 keV. We therefore interpret the spectral change as transient absorption by a gas cloud of column density 2.6 10^23 cm^-2 crossing the line of sight to the X-ray source. A spectrum obtained by XMM-Newton during an early phase of the hard-spectrum event confirms the obscuration model and shows that the absorbing cloud is only weakly ionised. The XMM-Newton spectrum also shows that ~10% of the X-ray flux is not obscured, but this unabsorbed component is not significantly variable and may be scattered radiation from a large-scale scattering medium. Applying the spectral constraints on cloud ionisation parameter and assuming that the cloud follows a Keplerian orbit, we constrain the location of the cloud to be R~10-100 light-days from the central X-ray source, and its density to be n_H~10^8cm^-3, implying that we have witnessed the eclipse of the X-ray source by a broad line region cloud.Comment: 5 pages, 6 figures, accepted for publication in MNRAS letter

Golf and upper limb injuries: a summary and review of the literature

BACKGROUND: Golf is a popular past time that provides exercise with social interaction. However, as with all sports and activities, injury may occur. Many golf-related injuries occur in the upper limb, yet little research on the potential mechanisms of these injuries has been conducted. OBJECTIVE: To review the current literature on golf-related upper limb injuries and report on potential causes of injury as it relates to the golf swing. DISCUSSION: An overview of the golf swing is described in terms of its potential to cause the frequently noted injuries. Most injuries occur at impact when the golf club hits the ball. This paper concludes that more research into golf-related upper limb injuries is required to develop a thorough understanding of how injuries occur. Types of research include epidemiology studies, kinematic swing analysis and electromyographic studies of the upper limb during golf. By conducting such research, preventative measures maybe developed to reduce golf related injury

Simultaneous EUV and X-ray variability of NGC 4051

We present a flux variability study of simultaneous RXTE and EUVE observations of the highly variable Seyfert galaxy NGC4051. We find a strong correlation between variability in the EUV and medium energy X-ray bands,indicating that both are sampling the same power-law continuum. The lag between the two bands is less than 20 ks and, depending on model assumptions, may be <1 ks. We examine the consequences of such a small lag in the context of simple Comptonisation models for the production of the power-law continuum. A lag of <1 ks implies that the size of the Comptonising region is less than 20 Schwarzschild radii for a black hole of mass >1E6 solar masses.Comment: 8 pages, accepted for publication in MNRA