Radio wave scattering by circumgalactic cool gas clumps

We consider the effects of radio wave scattering by cool ionized clumps (T ∼ 10^4 K) in circumgalactic media (CGMs). The existence of such clumps is inferred from intervening quasar absorption systems, but has long been something of a theoretical mystery. We consider the implications for compact radio sources of the ‘fog-like’ two-phase model of the CGM recently proposed by McCourt et al. In this model, the CGM consists of a diffuse coronal gas (T ≳ 10^6 K) in pressure equilibrium with numerous ≲1 pc scale cool clumps or ‘cloudlets’ formed by shattering in a cooling instability. The areal filling factor of the cloudlets is expected to exceed unity in ≳10^(11.5) M⊙ haloes, and the ensuing radio wave scattering is akin to that caused by turbulence in the Galactic warm ionized medium. If 30 per cent of cosmic baryons are in the CGM, we show that for a cool-gas volume fraction of fv ∼ 10^(−3), sources at z_s ∼ 1 suffer angular broadening by ∼15μ as and temporal broadening by ∼1 ms at λ = 30 cm, due to scattering by the clumps in intervening CGM. The former prediction will be difficult to test (the angular broadening will suppress Galactic scintillation only for <10μ Jy compact synchrotron sources). However the latter prediction, of temporal broadening of localized fast radio bursts, can constrain the size and mass fraction of cool ionized gas clumps as a function of halo mass and redshift, and thus provides a test of the model proposed by McCourt et al

On associating Fast Radio Bursts with afterglows

A radio source that faded over six days, with a redshift of $z\approx0.5$ host, has been identified by Keane et al. (2016) as the transient afterglow to a fast radio burst (FRB 150418). We report follow-up radio and optical observations of the afterglow candidate and find a source that is consistent with an active galactic nucleus. If the afterglow candidate is nonetheless a prototypical FRB afterglow, existing slow-transient surveys limit the fraction of FRBs that produce afterglows to 0.25 for afterglows with fractional variation, $m=2|S_1-S_2|/(S_1+S_2)\geq0.7$, and 0.07 for $m\geq1$, at 95% confidence. In anticipation of a barrage of bursts expected from future FRB surveys, we provide a simple framework for statistical association of FRBs with afterglows. Our framework properly accounts for statistical uncertainties, and ensures consistency with limits set by slow-transient surveys.Comment: Accepted version (ApJL

Radio wave scattering by circumgalactic cool gas clumps

We consider the effects of radio-wave scattering by cool ionized clumps ($T\sim 10^4\,$K) in circumgalactic media (CGM). The existence of such clumps are inferred from intervening quasar absorption systems, but have long been something of a theoretical mystery. We consider the implications for compact radio sources of the `fog-like' two-phase model of the circumgalactic medium recently proposed by McCourt et al.(2018). In this model, the CGM consists of a diffuse coronal gas ($T\gtrsim 10^6\,$K) in pressure equilibrium with numerous $\lesssim 1\,$pc scale cool clumps or `cloudlets' formed by shattering in a cooling instability. The areal filling factor of the cloudlets is expected to exceed unity in $\gtrsim 10^{11.5} M_\odot$ haloes, and the ensuing radio-wave scattering is akin to that caused by turbulence in the Galactic warm ionized medium (WIM). If $30\,$per-cent of cosmic baryons are in the CGM, we show that for a cool-gas volume fraction of $f_{\rm v}\sim 10^{-3}$, sources at $z_{\rm s}\sim 1$ suffer angular broadening by $\sim 15\,\mu$as and temporal broadening by $\sim 1\,$ms at $\lambda = 30\,$cm, due to scattering by the clumps in intervening CGM. The former prediction will be difficult to test (the angular broadening will suppress Galactic scintillation only for $<10\,\mu$Jy compact synchrotron sources). However the latter prediction, of temporal broadening of localized fast radio bursts, can constrain the size and mass fraction of cool ionized gas clumps as function of halo mass and redshift, and thus provides a test of the model proposed by McCourt et al.(2018).Comment: In press MNRA

Guidance for the prevention and treatment of the post-thrombotic syndrome

The post-thrombotic syndrome (PTS) is a frequent, potentially disabling complication of deep vein thrombosis (DVT) that reduces quality of life and is costly. Clinical manifestations include symptoms and signs such as leg pain and heaviness, edema, redness, telangiectasia, new varicose veins, hyperpigmentation, skin thickening and in severe cases, leg ulcers. The best way to prevent PTS is to prevent DVT with pharmacologic or mechanical thromboprophylaxis used in high risk patients and settings. In patients whose DVT is treated with a vitamin K antagonist, subtherapeutic INRs should be avoided. We do not suggest routine use of elastic compression stockings (ECS) after DVT to prevent PTS, but in patients with acute DVT-related leg swelling that is bothersome, a trial of ECS is reasonable. We suggest that selecting patients for catheter-directed thrombolytic techniques be done on a case-by-case basis, with a focus on patients with extensive thrombosis, recent symptoms onset, and low bleeding risk, who are seen at experienced hospital centers. For patients with established PTS, we suggest prescribing 20–30 mm Hg knee-length ECS to be worn daily. If ineffective, a stronger pressure stocking can be tried. We suggest that intermittent compression devices or pneumatic compression sleeve units be tried in patients with moderate-to-severe PTS whose symptoms are inadequately controlled with ECS alone. We suggest that a supervised exercise training program for 6 months or more is reasonable for PTS patients who can tolerate it. We suggest that management of post-thrombotic ulcers should involve a multidisciplinary approach. We briefly discuss upper extremity PTS and PTS in children

Stellar Systems at Low Radio Frequencies:The Discovery of Radio Exoplanets

For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf — the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star, and our follow-up radial-velocity (RV) observations with Harps-N to confirm the exoplanet's presence. Our study highlights the powerful new and developing synergy between low-frequency radio astronomy and RV observations, with radio emission providing a strong prior on the presence of a short-period planet. I will conclude the talk detailing how the radio detection of an star-exoplanet interaction provides unique information for exoplanet climate and habitability studies, and the extension of our survey to other stellar systems

Neurobiological findings in posttraumatic stress disorder: a review

Since posttraumatic stress disorder (PTSD) was first recognized as a psychiatric disorder, it has generated a great deal of scientific interest. Recent studies on the neurobiology of PTSD provide evidence that PTSD is biologically distinct from other types of traumatic and nontraumatic stress responses. This paper reviews three important directions of neurobiological research in PTSD: noradrenergic axis changes and associated alterations in autonomic responsivity neuroendocrine changes involving the hypothalamic-pituitary-adrenocortical (HPA) axis, and neuroanatomy changes involving the hippocampus. Each section reviews the salient aspects of preclinical research on the biology of stress and their bearing on the understanding of PTSD, and summarizes prominent findings from clinical biological studies of PTSD, Tentative models that integrate current findings from the clinical study of PTSD are reviewed. To conclude, the important methodological and empirical issues that need to be addressed by future studies are indicated

Radio wave scattering by circumgalactic cool gas clumps

We consider the effects of radio wave scattering by cool ionized clumps (T ∼ 10^4 K) in circumgalactic media (CGMs). The existence of such clumps is inferred from intervening quasar absorption systems, but has long been something of a theoretical mystery. We consider the implications for compact radio sources of the ‘fog-like’ two-phase model of the CGM recently proposed by McCourt et al. In this model, the CGM consists of a diffuse coronal gas (T ≳ 10^6 K) in pressure equilibrium with numerous ≲1 pc scale cool clumps or ‘cloudlets’ formed by shattering in a cooling instability. The areal filling factor of the cloudlets is expected to exceed unity in ≳10^(11.5) M⊙ haloes, and the ensuing radio wave scattering is akin to that caused by turbulence in the Galactic warm ionized medium. If 30 per cent of cosmic baryons are in the CGM, we show that for a cool-gas volume fraction of fv ∼ 10^(−3), sources at z_s ∼ 1 suffer angular broadening by ∼15μ as and temporal broadening by ∼1 ms at λ = 30 cm, due to scattering by the clumps in intervening CGM. The former prediction will be difficult to test (the angular broadening will suppress Galactic scintillation only for <10μ Jy compact synchrotron sources). However the latter prediction, of temporal broadening of localized fast radio bursts, can constrain the size and mass fraction of cool ionized gas clumps as a function of halo mass and redshift, and thus provides a test of the model proposed by McCourt et al

Prospects for detecting the 21cm forest from the diffuse intergalactic medium with LOFAR

We discuss the feasibility of the detection of the 21cm forest in the diffuse IGM with the radio telescope LOFAR. The optical depth to the 21cm line has been derived using simulations of reionization which include detailed radiative transfer of ionizing photons. We find that the spectra from reionization models with similar total comoving hydrogen ionizing emissivity but different frequency distribution look remarkably similar. Thus, unless the reionization histories are very different from each other (e.g. a predominance of UV vs. x-ray heating) we do not expect to distinguish them by means of observations of the 21cm forest. Because the presence of a strong x-ray background would make the detection of 21cm line absorption impossible, the lack of absorption could be used as a probe of the presence/intensity of the x-ray background and the thermal history of the universe. Along a random line of sight LOFAR could detect a global suppression of the spectrum from z>12, when the IGM is still mostly neutral and cold, in contrast with the more well-defined, albeit broad, absorption features visible at lower redshift. Sharp, strong absorption features associated with rare, high density pockets of gas could be detected also at z~7 along preferential lines of sight.Comment: 12 pages, 13 figures. MNRAS, in pres