The Response of Black Hole Spark Gaps to External Changes: A Production Mechanism of Rapid TeV Flares?

We study the response of a starved Kerr black hole magnetosphere to abrupt changes in the intensity of disk emission and in the global magnetospheric current, by means of one-dimensional general relativistic particle-in-cell simulations. Such changes likely arise from the intermittency of the accretion process. We find that in cases where the pair-production opacity contributed by the soft disk photons is modest, as in, e.g., M87, such changes can give rise to delayed, strong teraelectronvolt (TeV) flares, dominated by curvature emission of particles accelerated in the gap. The flare rise time, and the delay between the external variation and the onset of the flare emitted from the outer gap boundary, are of the order of the light-crossing time of the gap. The rapid, large-amplitude TeV flares observed in M87, and perhaps, other active galactic nuclei may be produced by such a mechanism.

Single-Level Cervical Arthroplasty with a Keel-less Prosthesis: Results in a Series of 35 Patients Operated on for Soft Disk Herniation with a Minimum of 3 Years of Follow-Up

Background Cervical arthroplasty with artificial cervical disks has gained popularity as an alternative to anterior discectomy and fusion. The main advantages of disk arthroplasty include maintenance of the range of movement, restitution of disk height and spinal alignment, and reduction of adjacent segment degeneration (ASD). In this article, we aimed to assess the outcomes of the use of a keel-less prosthesis. Material and Methods We included all the patients who underwent single-level cervical arthroplasties with the Discocerv Cervidisc Evolution for “soft” disk herniation. Clinical assessment included Neck Disability Index (NDI) and visual analog scale (VAS) for neck and arm pain. Radiologic studies investigated the occurrence of ASD and system failure or subsidence. The reoperation rate was also recorded. Results The study included 35 patients (14 men and 21 women; mean age: 42.5 years; mean follow-up: 57.8 months). There was a significant decrease in VAS neck and VAS arm scores, which went from 7.2 and 6.9 preoperatively to 2.2 and 1.7 postoperatively, 2.2 and 1.6 at 6 months, 2.0 and 1.8 at 1 year, and 2.1 and 1.3 at the last follow-up, respectively. The mean NDI score was 58.0 preoperatively, 19.4 postoperatively, 17.0 at 6 months, 16.1 at 1 year, and 16.2 at the last follow-up. Radiologic studies revealed a preserved range of motion in 33 of 35 patients. No ASD occurred and no reoperation was required. Conclusions Cervical disk arthroplasty with a keel-less prosthesis can be a safe and effective alternative to fusion for degenerative disk disease in selected patients, with a possible reduction of ASD.

Posterior Endoscope-Assisted Diskectomy Is an Effective Technique for Cervical Soft Disk Herniation

Objective To evaluate the clinicoradiologic conditions of patients with a herniated cervical disk who were treated with percutaneous endoscope-assisted cervical diskectomy. Materials and Methods The medical data of 27 patients (16 men and 11 women; mean age: 40.9 years) who were operated on with the posterior endoscope-assisted cervical diskectomy method were reviewed retrospectively. The mean follow-up was 35.1 months, and the patients were assessed with combined preoperative and postoperative visual analog scale (VAS), Prolo Functional Economic Outcome Rating scale, MacNab scale, and clinical imaging. Results The mean preoperative VAS level was 8.6 (range: 7–10), and mean Prolo score was 2.5 (range: 2–5). A postoperative assessment performed 1 week postsurgery found a mean VAS level of 2.1 (range: 0–4). At the final examination, the mean VAS level was 0.81 (range: 0–3), and the mean Prolo score was 4.5 (range: 3–5). The final MacNab scale scores were 62.9%, excellent; 25.9%, good; 7.4%, moderate; and 3.7%, poor. Conclusion Percutaneous endoscope-assisted cervical diskectomy is a suitable and effective treatment method for soft cervical disk herniation.

XMM-Newton detection of the 2.1 ms coherent pulsations from IGR J17379–3747

We report the detection of X-ray pulsations at 2.1 ms from the known X-ray burster IGR J17379–3747 using XMM-Newton. The coherent signal shows a clear Doppler modulation from which we estimate an orbital period of ~1.9 h and a projected semi-major axis of ~8 lt-ms. Taking into account the lack of eclipses (inclination angle of <75°) and assuming a neutron star mass of 1.4 M⊙, we have estimated a minimum companion star of ~0.06 M⊙. Considerations on the probability distribution of the binary inclination angle make the hypothesis of a main-sequence companion star less likely. On the other hand, the close correspondence with the orbital parameters of the accreting millisecond pulsar SAX J1808.4–3658 suggests the presence of a bloated brown dwarf. The energy spectrum of the source is well described by a soft disk black-body component (kT ~ 0.45 keV) plus a Comptonisation spectrum with photon index ~1.9. No sign of emission lines or reflection components are significantly detected. Finally, combining the source ephemerides estimated from the observed outbursts, we obtained a first constraint on the long-term orbital evolution of the order of Ṗorb = (−2.5 ± 2.3) × 10−12 s s−1.

Correlation of time lag and photon index in GX 339-4

Context. Black hole transients, as a class, exhibit during their outbursts a correlation between the time lag of hard photons with respect to softer ones and the photon index of the hard X-ray power law. The correlation is not very tight and therefore it is necessary to examine it source by source. Aims. The objective of the present work is to investigate in detail the correlation between the time lag and the photon index in GX 339-4, which is the best studied black hole transient. Methods. We have obtained RXTE energy spectra and light curves and have computed the photon index and the time lag of the 9–15 keV photons with respect to the 2–6 keV photons. The observations cover the first stages of the hard state, the pure hard state, and the hard-intermediate state. Results. We have found a tight correlation between time lag and photon index Γ in the hard and hard-intermediate states. At low Γ, the correlation is positive; it becomes negative at high Γ By assuming that the hard X-ray power-law index Γ is produced by inverse Compton scattering of soft disk photons in the jet, we have reproduced the entire correlation by varying two parameters in the jet: the radius of the jet at its base R0 and the Thomson optical depth along the jet τ∥. We have found that as the luminosity of the source increases, R0 initially increases and then decreases. This behavior is expected in the context of the Cosmic Battery. Conclusions. Our jet model nicely explains the correlation with reasonable values of the parameters R0 and τ∥ These parameters also correlate between themselves. As a further test of our model, we predict the break frequency in the radio spectrum as a function of the photon index during the rising part of an outburst.

Could GRB170817A be really correlated to an NS–NS merging?

The exciting development of gravitational wave (GW) astronomy in the correlation of LIGO and VIRGO detection of GW signals makes possible to expect registration of effects of not only binary black hole (BH) coalescence but also binary neutron star (NS) merging accompanied by electromagnetic (gamma ray burst; GRB) signal. Here we consider the possibility that an NS, merging in an NS–NS or NS–BH system might be (soon) observed in correlation with any LIGO–VIRGO GWs detection. We analyze as an example the recent case of the short GRB170817A observed by Fermi and integral. The associated optical transient (OT) source in NGC4993 implies a rare near source, a consequent averaged large rate of such events (almost) compatible with expected NS–NS merging rate. However the expected beamed GRB (or short GRB) may be mostly aligned to a different direction than ours. Therefore, even soft GRB photons, spread more than hard ones, might be hardly able to shower to us. Nevertheless, a prompt spiraling electron turbine jet in largest magnetic fields, at the base of the NS–NS collapse, might shine by its tangential synchrotron radiation in spread way with its skimming photons shining in large open disk. The consequent solid angle for such soft disk gamma radiation may be large enough to be nevertheless often observed.

Ultrasensitive detection enabled by nonlinear magnetization of nanomagnetic labels

The magnetically soft, disk-shaped particles reveal a strong nonlinearity of the magnetization process due to irreversible transitions from the spin vortex to single-domain configuration, enabling their ultrasensitive detection in high-background environments.

Transforaminal Percutaneous Endoscopic Lumbar Diskectomy for Downmigrated Disk Herniations: Lever-Up, Rotate, and Tilt Technique

Background and Study Aims Although transforaminal percutaneous endoscopic lumbar diskectomy (PELD) offers certain advantages in the treatment of disk herniations, it used to be limited to nonmigrated or low-migrated herniations. With improvements in endoscopic spinal surgery, the range of indications for PELD has expanded. Various techniques including transforaminal and interlaminar approaches for migrated disk herniations are described in the literature. This study describes a transforaminal PELD approach to address downmigrated intracanal soft disk herniations effectively using the lever-up, rotate, and tilt technique. Patients and Methods We performed a retrospective review of 18 patients who had been operated on with the described technique between October 2012 and December 2015. We assessed clinical outcomes using the visual analog scale (VAS) for back and leg pain and the Oswestry Disability Index (ODI) preoperatively at their respective clinical visits and postoperatively at the patients' final follow-up examinations. Results The mean preoperative VAS scores for back and leg pain were 3.75 + 1.34 (range: 2–6) and 8.3 + 0.6 (range: 8–10), respectively. The mean preoperative ODI was 67.3 + 15.3 (range: 48–90). The mean VAS scores for back and leg pain improved to 1.38 + 1.58 (range: 0–6) and 1.19 + 0.75 (range: 0–3), respectively, at the last follow-up. The mean ODI also improved to 14.1 + 6.2 (range: 8–30) at the last follow-up. All differences between the preoperative and last follow-up scores were statistically significant (p < 0.05), Two surgeries failed because of a remnant disk fragment. Conclusions The lever-up, rotate, and tilt technique for transforaminal PELD is an effective maneuver to treat downmigrated disk herniations in selected patients by experienced surgeons.