Discovery of pulsations in the X-ray transient 4U 1901+03

We describe observations of the 2003 outburst of the hard-spectrum X-ray transient 4U 1901+03 with the Rossi X-ray Timing Explorer. The outburst was first detected in 2003 February by the All-Sky Monitor, and reached a peak 2.5-25 keV flux of 8x10^-9 ergs/cm^2/s (around 240 mCrab). The only other known outburst occurred 32.2 yr earlier, likely the longest presently known recurrence time for any X-ray transient. Proportional Counter Array (PCA) observations over the 5-month duration of the 2003 outburst revealed a 2.763 s pulsar in a 22.58 d orbit. The detection of pulsations down to a flux of 3x10^-11 ergs/cm^2/s (2.5-25 keV), along with the inferred long-term accretion rate of 8.1x10^-11 M_sun/yr (assuming a distance of 10 kpc) suggests that the surface magnetic field strength is below ~5x10^11 G. The corresponding cyclotron energy is thus below 4 keV, consistent with the non-detection of resonance features at high energies. Although we could not unambiguously identify the optical counterpart, the lack of a bright IR candidate within the 1' RXTE error circle rules out a supergiant mass donor. The neutron star in 4U 1901+03 probably accretes from the wind of a main-sequence O-B star, like most other high-mass binary X-ray pulsars. The almost circular orbit e=0.036 confirms the system's membership in a growing class of wide, low-eccentricity systems in which the neutron stars may have received much smaller kicks as a result of their natal supernova explosions.Comment: 7 pages, 6 figures, accepted by ApJ. Very minor addition in response to referee's comment; updated author affiliatio

Soliton Solutions to the Einstein Equations in Five Dimensions

We present a new class of solutions in odd dimensions to Einstein's equations containing either a positive or negative cosmological constant. These solutions resemble the even-dimensional Eguchi-Hanson--(anti)-de Sitter ((A)dS) metrics, with the added feature of having Lorentzian signatures. They provide an affirmative answer to the open question as to whether or not there exist solutions with negative cosmological constant that asymptotically approach AdS$_{5}/\Gamma$, but have less energy than AdS$_{5}/\Gamma$. We present evidence that these solutions are the lowest-energy states within their asymptotic class.Comment: 9 pages, Latex; Final version that appeared in Phys. Rev. Lett; title changed by journal from original title "Eguchi-Hanson Solitons

On the Gannon-Lee Singularity Theorem in Higher Dimensions

The Gannon-Lee singularity theorems give well-known restrictions on the spatial topology of singularity-free (i.e., nonspacelike geodesically complete), globally hyperbolic spacetimes. In this paper, we revisit these classic results in the light of recent developments, especially the failure in higher dimensions of a celebrated theorem by Hawking on the topology of black hole horizons. The global hyperbolicity requirement is weakened, and we expand the scope of the main results to allow for the richer variety of spatial topologies which are likely to occur in higher-dimensional spacetimes.Comment: 13 pages, no figures, to appear in Class. Quantum Gra

Thermonuclear burst physics with RXTE

Recently we have made measurements of thermonuclear burst energetics and recurrence times which are unprecedented in their precision, largely thanks to the sensitivity of the Rossi X-ray Timing Explorer. In the "Clocked Burster", GS 1826-24, hydrogen burns during the burst via the rapid-proton (rp) process, which has received particular attention in recent years through theoretical and modelling studies. The burst energies and the measured variation of alpha (the ratio of persistent to burst flux) with accretion rate strongly suggests solar metallicity in the neutron star atmosphere, although this is not consistent with the corresponding variation of the recurrence time. Possible explanations include extra heating between the bursts, or a change in the fraction of the neutron star over which accretion takes place. I also present results from 4U 1746-37, which exhibits regular burst trains which are interrupted by "out of phase" bursts.Comment: 4 pages, 2 figures, AIP conference proceedings format. To appear in the proceedings of the "X-ray Timing 2003: Rossi and Beyond" meeting held in Cambridge, MA, November, 200

The Cosmic Censor Forbids Naked Topology

For any asymptotically flat spacetime with a suitable causal structure obeying (a weak form of) Penrose's cosmic censorship conjecture and satisfying conditions guaranteeing focusing of complete null geodesics, we prove that active topological censorship holds. We do not assume global hyperbolicity, and therefore make no use of Cauchy surfaces and their topology. Instead, we replace this with two underlying assumptions concerning the causal structure: that no compact set can signal to arbitrarily small neighbourhoods of spatial infinity (``$i^0$-avoidance''), and that no future incomplete null geodesic is visible from future null infinity. We show that these and the focusing condition together imply that the domain of outer communications is simply connected. Furthermore, we prove lemmas which have as a consequence that if a future incomplete null geodesic were visible from infinity, then given our $i^0$-avoidance assumption, it would also be visible from points of spacetime that can communicate with infinity, and so would signify a true naked singularity.Comment: To appear in CQG, this improved version contains minor revisions to incorporate referee's suggestions. Two revised references. Plain TeX, 12 page

Angular Momentum Transfer in the Binary X-ray Pulsar GX 1+4

We describe three presentations relating to the X-ray pulsar GX 1+4 at a workshop on magnetic fields and accretion at the Astrophysical Theory Centre, Australian National University on 1998, November 12-13. Optical and X-ray spectroscopy indicate that GX 1+4 is seen through a cloud of gravitationaly bound matter. We discuss an unstable negative feedback mechanism (originally proposed by Kotani et al, 1999), based on X-ray heating of this matter which controls the accretion rate when the source is in a low X-ray luminosity state. A deep minimum lasting ~6 hours occurred during observations with the RXTE satellite over 1996, July 19-21. The shape of the X-ray pulses changed remarkably from before to after the minimum. These changes may be related to the transition from neutron star spin-down to spin-up which occurred at about the same time. Smoothed particle hydrodynamic simulations of the effect of adding matter with opposite angular momentum to an existing disc, show that it is possible for a number of concentric rings with alternating senses of rotation to co-exist in a disc. This could provide an explanation for the step-like changes in Pdot which are observed in GX 1+4. Changes at the inner boundary of the disc occur at the same timescale as that imposed at the outer boundary. Reversals of material torque on the neutron star occur at a minimum in L_X.Comment: 10 pages, 5 figures; accepted for publication by PAS

Non-Existence of Black Holes in Certain Λ<0\Lambda<0 Spacetimes

Assuming certain asymptotic conditions, we prove a general theorem on the non-existence of static regular (i.e., nondegenerate) black holes in spacetimes with a negative cosmological constant, given that the fundamental group of space is infinite. We use this to rule out the existence of regular negative mass AdS black holes with Ricci flat scri. For any mass, we also rule out a class of conformally compactifiable static black holes whose conformal infinity has positive scalar curvature and infinite fundamental group, subject to our asymptotic conditions. In a limited, but important, special case our result adds new support to the AdS/CFT inspired positive mass conjecture of Horowitz and Myers.Comment: 17 pages, Latex. Typos corrected, minor changes to the text. Accepted for publication in Classical and Quantum Gravit

A population study of type II bursts in the Rapid Burster

Type II bursts are thought to arise from instabilities in the accretion flow onto a neutron star in an X-ray binary. Despite having been known for almost 40 years, no model can yet satisfactorily account for all their properties. To shed light on the nature of this phenomenon and provide a reference for future theoretical work, we study the entire sample of Rossi X-ray Timing Explorer data of type II bursts from the Rapid Burster (MXB 1730-335). We find that type II bursts are Eddington-limited in flux, that a larger amount of energy goes in the bursts than in the persistent emission, that type II bursts can be as short as 0.130 s, and that the distribution of recurrence times drops abruptly below 15-18 s. We highlight the complicated feedback between type II bursts and the NS surface thermonuclear explosions known as type I bursts, and between type II bursts and the persistent emission. We review a number of models for type II bursts. While no model can reproduce all the observed burst properties and explain the source uniqueness, models involving a gating role for the magnetic field come closest to matching the properties of our sample. The uniqueness of the source may be explained by a special combination of magnetic field strength, stellar spin period and alignment between the magnetic field and the spin axis.Comment: Accepted 2015 February 12. Received 2015 February 10; in original form 2014 December 1

Evidence for a parsec scale X-ray jet from the accreting neutron star Circinus X-1

We analyzed the zero-order image of a 50 ks Chandra gratings observation of Circinus X-1, taken in 2005 during the source's low-flux state. Circinus X-1 is an accreting neutron star that exhibits ultra-relativistic arcsecond-scale radio jets and diffuse arcminute-scale radio jets and lobes. The image shows a clear excess along the general direction of the north-western counter-jet, coincident with the radio emission, suggesting that it originates either in the jet itself or in the shock the jet is driving into its environment. This makes Circinus X-1 the first neutron star for which an extended X-ray jet has been detected. The kinetic jet power we infer is significantly larger than the minimum power required for the jet to inflate the large scale radio nebula.Comment: Added journal reference, corrected on reference and typo in labels for Fig. 1; 5 pages, 3 figures, ApJ Letter, in pres

The efficacy of randomised controlled trials of cognitive behaviour therapy for perfectionism: a systematic review and meta-analysis

Perfectionism is a transdiagnostic process across anxiety, depression, and eating disorders. The aim of this systematic review was to examine the efficacy of self-help and face to face CBT for perfectionism in reducing perfectionism and anxiety, depression, and eating disorders. A total of 15 randomised controlled trials of CBT for perfectionism were identified (N = 912 participants; mean pooled age = 23 years) which met inclusion criteria. There were medium or large effect sizes found on perfectionism measures; personal standards (g = 0.57, 95% CI = 0.43–0.72), concern over mistakes (g = 0.89, 95% CI = 0.71–1.08) and clinical perfectionism (g = 0.87, 95% CI = 0.70–1.04). There were medium effects for symptoms of eating disorders (g = 0.61, 95% CI = 0.36–0.87) and depression (g = 0.60, 95% CI = 0.28–0.91), and a small-medium effect on anxiety (g = 0.42, 95% CI = 0.21–0.62). There was no publication bias found. Limitations included the small number of trials included and lack of active treatment comparisons. Results suggested that CBT for perfectionism is efficacious in reducing perfectionism and symptoms of depression, anxiety and eating disorders. Future research should examine comparisons of CBT for perfectionism with other psychological treatments