The corona contracts in a black-hole transient

The geometry of the accretion flow around stellar-mass black holes can change on timescales of days to months^1-3. When a black hole emerges from quiescence (that is, it 'turns on' after accreting material from its companion) it has a very hard (high-energy) X-ray spectrum produced by a hot corona^4,5 positioned above its accretion disk, and then transitions to a soft (lower-energy) spectrum dominated by emission from the geometrically thin accretion disk, which extends to the innermost stable circular orbit^6,7. Much debate persists over how this transition occurs and whether it is driven largely by a reduction in the truncation radius of the disk^8,9 or by a reduction in the spatial extent of the corona^10,11. Observations of X-ray reverberation lags in supermassive black-hole systems^12,13 suggest that the corona is compact and that the disk extends nearly to the central black hole^14,15. Observations of stellar-mass black holes, however, reveal equivalent (mass-scaled) reverberation lags that are much larger¹⁶, leading to the suggestion that the accretion disk in the hard-X-ray state of stellar-mass black holes is truncated at a few hundreds of gravitational radii from the black hole^17,18. Here we report X-ray observations of the black-hole transient MAXI J1820+070^19,20. We find that the reverberation time lags between the continuum-emitting corona and the irradiated accretion disk are 6 to 20 times shorter than previously seen. The timescale of the reverberation lags shortens by an order of magnitude over a period of weeks, whereas the shape of the broadened iron K emission line remains remarkably constant. This suggests a reduction in the spatial extent of the corona, rather than a change in the inner edge of the accretion disk.

Aqueous humor analysis after Nd:YAG laser capsulotomy with the laser flare-cell meter

Using the laser flare-cell meter (Kowa FC-1000), we conducted a prospective study analyzing the effect of Nd:YAG posterior capsulotomy on the quantity of aqueous particles, aqueous flare, and intraocular pressure in 65 eyes (58 patients). Aqueous particles increased at six hours, followed by flare rise which was significant at 18 hours after capsulotomy. Only 22 eyes (34%) had a significant flare rise over prelaser values. Anti-inflammatory therapy was necessary in only one patient. The mean intraocular pressure value did not rise significantly after capsulotomy. Acute intraocular hypertension (AIOHT) (> 7 mm Hg increase) occurred between three and six hours after laser therapy in 12 patients (19%), was related in time to particle rise, and always responded to a single dose of acetazolamide. Acute intraocular hypertension was strongly correlated with elevated aqueous particles (P < .0001) and somewhat correlated with flare rise (P < .036), but was not correlated with the intraocular lens position (bag or sulcus fixation). Our findings strongly suggest that trabecular meshwork clogging by debris generated by the capsulotomy is the mechanism at the origin of AIOHT.

[Complications of posterior capsulotomy with the Nd:YAG laser. Study of 226 cases]

BACKGROUND

Severe complications are classically described after capsulotomy: ocular hypertension, cystoid macular edema and secondary retinal detachment.

PATIENTS AND METHODS

A series of 226 patients having sustained Nd:YAG laser (PC). Posterior capsulotomy has been studied retrospectively in order to determine the rate of early complications (24 hours after PC) and late complications (up to 6 months after the PC).

RESULTS

Fifteen patients (6.6%) presented acute temporary intraocular hypertension, 2 patients (0.9%) a retinal detachment, 2 patients (0.9%) a cystoid macular edema (CME). A total number of complications of 8.4% was observed, 1.8% were heavy.

CONCLUSIONS

Transient rise of intraocular pressure is seen. Prophylactic treatment with acetazolamide 500 mg (Diamox) and timolol (Timoptic) is necessary.

A persistent ultraviolet outflow from an accreting neutron star binary transient

All disc-accreting astrophysical objects produce powerful disc winds. In compact binaries containing neutron stars or black holes, accretion often takes place during violent outbursts. The main disc wind signatures during these eruptions are blue-shifted X-ray absorption lines, which are preferentially seen in disc-dominated 'soft states'^1,2. By contrast, optical wind-formed lines have recently been detected in 'hard states', when a hot corona dominates the luminosity³. The relationship between these signatures is unknown, and no erupting system has as yet revealed wind-formed lines between the X-ray and optical bands, despite the many strong resonance transitions in this ultraviolet (UV) region⁴. Here we report that the transient neutron star binary Swift J1858.6-0814 exhibits wind-formed, blue-shifted absorption lines associated with C IV, N V and He II in time-resolved UV spectroscopy during a luminous hard state, which we interpret as a warm, moderately ionized outflow component in this state. Simultaneously observed optical lines also display transient blue-shifted absorption. Decomposing the UV data into constant and variable components, the blue-shifted absorption is associated with the former. This implies that the outflow is not associated with the luminous flares in the data. The joint presence of UV and optical wind features reveals a multi-phase and/or spatially stratified evaporative outflow from the outer disc⁵. This type of persistent mass loss across all accretion states has been predicted by radiation-hydrodynamic simulations⁶ and helps to explain the shorter-than-expected duration of outbursts⁷.

Acute retinal necrosis: a result of immune dysfunction? Report of a case with subacute evolution and relapses in a patient with impaired cellular immunity

We report an atypical case of acute retinal necrosis (ARN) with a subacute course and relapses lasting for more than 4 years in an apparently immunocompetent 71-year-old female who had been followed for 4.5 years for recurrent retinochoroidal lesions with transient exudative retinal detachments and areas of consecutive chorioretinal atrophy. The diagnosis of varicella-zoster virus (VZV)-induced ARN was finally made on the basis of anterior granulomatous uveitis, typical retinal necrosis and the detection of anti-VZV antibodies in the aqueous humor. A widespread lumbar zoster dermatitis, cutaneous anergy and depressed in vitro lymphocyte activation indicated depressed cellular immunity. Absolute and relative numbers of B lymphocytes were increased. It is suspected that depressed cellular immunity and maintained B cell function might possibly be at the origin of ARN. The protracted course of ARN in this patient also suggests that the dysregulation of the immune system has probably existed for a long time.

[Prospective study of 163 retinal detachments operated by episcleral technique (preoperative examination)]

The predominance of retinal breaks in the superior temporal quadrant is well known. This predominance was found to be related to age and refraction (p < 0.01). The distribution of breaks plotted across the 12 meridians shows a predilection for the superior temporal quadrant and half of the inferior temporal and superior nasal one. However, in this area the distribution is irregular (p >> 0.001) with a predominance in the 10-11 and 12-1 o'clock section (if we consider the right eye). The H/T ratio (holes/tears for each case) is positive for patients under 40 years of age and becomes negative after 50 years.

A shared accretion instability for black holes and neutron stars

Accretion disks around compact objects are expected to enter an unstable phase at high luminosity1. One instability may occur when the radiation pressure generated by accretion modifies the disk viscosity, resulting in the cyclic depletion and refilling of the inner disk on short timescales2. Such a scenario, however, has only been quantitatively verified for a single stellar-mass black hole3-5. Although there are hints of these cycles in a few isolated cases6-10, their apparent absence in the variable emission of most bright accreting neutron stars and black holes has been a continuing puzzle11. Here we report the presence of the same multiwavelength instability around an accreting neutron star. Moreover, we show that the variability across the electromagnetic spectrum-from radio to X-ray-of both black holes and neutron stars at high accretion rates can be explained consistently if the accretion disks are unstable, producing relativistic ejections during transitions that deplete or refill the inner disk. Such a new association allows us to identify the main physical components responsible for the fast multiwavelength variability of highly accreting compact objects.

[Re-evaluation of the role of argon laser trabeculoplasty in therapy of glaucoma]

BACKGROUND

The pressure lowering effect of Argon laser trabeculoplasty (ALT) has been well demonstrated in the past. Today some clinicians tend to avoid ALT perhaps because it has been used in erroneous indications. The aim of this study was to re-evaluate the usefulness of ALT and to define its indication in the treatment of glaucoma.

PATIENTS AND METHODS

A collective of 81 patients treated by ALT entered in a data bank between 1989 and 1991 were analysed retrospectively, focussing on: the percentage of patients requiring trabeculectomy (TE) after ALT, the mean time from ALT to TE, the stage of disease progression at which the decision for ALT was taken and the post-ALT evolution of ocular pressure (IOP), visual field and optic disc.

RESULTS

After a mean follow-up of 28 +/- 10.5 months a TE was performed in 25% of cases. It was found that in our clinical practice the decision for ALT tended to be taken at a rather late stage of disease. For the patients that did not need a TE, the mean decrease of IOP at the end of follow-up was 5.4 mm Hg and the analysis of glaucoma parameters showed that there was no significant worsening of disease. The disease progression in the group of patients that were operated was already significantly worse than the total collective before ATL was performed.

CONCLUSIONS

ALT is useful in the treatment of glaucoma, as long as it is not considered as an alternative to TE and as long as the patients benefit from a strict follow-up. Advanced cases should however be operated without delay.