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Tracking the motions of transient jets launched by low-mass X-ray binaries (LMXBs) is critical for determining the moment of jet ejection, and identifying any corresponding signatures in the accretion flow. However, these jets are often highly variable and can travel across the resolution element of an image within a single observation, violating a fundamental assumption of aperture synthesis. We present a novel approach in which we directly fit a single time-dependent model to the full set of interferometer visibilities, where we explicitly parameterise the motion and flux density variability of the emission components, to minimise the number of free parameters in the fit, while leveraging information from the full observation. This technique allows us to detect and characterize faint, fast-moving sources, for which the standard time binning technique is inadequate. We validate our technique with synthetic observations, before applying it to three Very Long Baseline Array (VLBA) observations of the black hole candidate LMXB MAXI J1803-298 during its 2021 outburst. We measured the proper motion of a discrete jet component to be $1.37\pm0.14$ mas/hr, and thus we infer an ejection date of MJD $59348.08_{-0.06}^{+0.05}$, which occurs just after the peak of a radio flare observed by the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/Sub-Millimeter Array (ALMA), while MAXI J1803-298 was in the intermediate state. Further development of these new VLBI analysis techniques will lead to more precise measurements of jet ejection dates, which, combined with dense, simultaneous multi-wavelength monitoring, will allow for clearer identification of jet ejection signatures in the accretion flow., 15 pages, 9 figures, 4 tables; Accepted for publication in MNRAS

We present a high time resolution, multi-frequency linear polarization analysis of Very Large Array (VLA) radio observations during some of the brightest radio flaring (~1 Jy) activity of the 2015 outburst of V404 Cygni. The VLA simultaneously captured the radio evolution in two bands (each with two 1 GHz base-bands), recorded at 5/7 GHz and 21/26 GHz, allowing for a broadband polarimetric analysis. Given the source's high flux densities, we were able to measure polarization on timescales of ~13 minutes, constituting one of the highest temporal resolution radio polarimetric studies of a black hole X-ray binary (BHXB) outburst to date. Across all base-bands, we detect variable, weakly linearly polarized emission (, 24 pages, 9 figures, accepted by MNRAS

We present a technique to measure the time-resolved velocity and ion sound speed in magnetized, supersonic high-energy-density plasmas. We place an inductive (“b-dot”) probe in a supersonic pulsed-power-driven plasma flow and measure the magnetic field advected by the plasma. As the magnetic Reynolds number is large ( R M > 10), the plasma flow advects a magnetic field proportional to the current at the load. This enables us to estimate the flow velocity as a function of time from the delay between the current at the load and the signal at the probe. The supersonic flow also generates a hydrodynamic bow shock around the probe, the structure of which depends on the upstream sonic Mach number. By imaging the shock around the probe with a Mach–Zehnder interferometer, we determine the upstream Mach number from the shock Mach angle, which we then use to determine the ion sound speed from the known upstream velocity. We use the sound speed to infer the value of [Formula: see text], where [Formula: see text] is the average ionization and T e is the electron temperature. We use this diagnostic to measure the time-resolved velocity and sound speed of a supersonic ( M S ∼ 8), super-Alfvénic ( M A ∼ 2) aluminum plasma generated during the ablation stage of an exploding wire array on the Magpie generator (1.4 MA, 250 ns). The velocity and [Formula: see text] measurements agree well with the optical Thompson scattering measurements reported in the literature and with 3D resistive magnetohydrodynamic simulations in GORGON.

During a 2018 outburst, the black hole X-ray binary MAXI J1820+070 was comprehensively monitored at multiple wavelengths as it underwent a hard to soft state transition. During this transition a rapid evolution in X-ray timing properties and a short-lived radio flare were observed, both of which were linked to the launching of bi-polar, long-lived relativistic ejecta. We provide detailed analysis of two Very Long Baseline Array observations, using both time binning and a new dynamic phase centre tracking technique to mitigate the effects of smearing when observing fast-moving ejecta at high angular resolution. We identify a second, earlier ejection, with a lower proper motion of $18.0\pm1.1$ mas day$^{-1}$. This new jet knot was ejected $4\pm1$ hours before the beginning of the rise of the radio flare, and $2\pm1$ hours before a switch from type-C to type-B X-ray quasi-periodic oscillations (QPOs). We show that this jet was ejected over a period of $\sim6$ hours and thus its ejection was contemporaneous with the QPO transition. Our new technique locates the original, faster ejection in an observation in which it was previously undetected. With this detection we revised the fits to the proper motions of the ejecta and calculated a jet inclination angle of $(64\pm5)^\circ$, and jet velocities of $0.97_{-0.09}^{+0.03}c$ for the fast-moving ejecta ($\Gamma>2.1$) and $(0.30\pm0.05)c$ for the newly-identified slow-moving ejection ($\Gamma=1.05\pm0.02$). We show that the approaching slow-moving component is predominantly responsible for the radio flare, and is likely linked to the switch from type-C to type-B QPOs, while no definitive signature of ejection was identified for the fast-moving ejecta., Comment: 11 pages including 5 figures. Accepted for publication in MNRAS

We present results from six epochs of quasi-simultaneous radio, (sub-)millimetre, infrared, optical, and X-ray observations of the black hole X-ray binary MAXI~J1535$-$571. These observations show that as the source transitioned through the hard-intermediate X-ray state towards the soft intermediate X-ray state, the jet underwent dramatic and rapid changes. We observed the frequency of the jet spectral break, which corresponds to the most compact region in the jet where particle acceleration begins (higher frequencies indicate closer to the black hole), evolve from the IR band into the radio band (decreasing by $\approx$3 orders of magnitude) in less than a day. During one observational epoch, we found evidence of the jet spectral break evolving in frequency through the radio band. Estimating the magnetic field and size of the particle acceleration region shows that the rapid fading of the high-energy jet emission was not consistent with radiative cooling; instead the particle acceleration region seems to be moving away from the black hole on approximately dynamical timescales. This result suggests that the compact jet quenching is not caused by local changes to the particle acceleration, rather we are observing the acceleration region of the jet travelling away from the black hole with the jet flow. Spectral analysis of the X-ray emission show a gradual softening in the few days before the dramatic jet changes, followed by a more rapid softening $\sim$1--2\,days after the onset of the jet quenching., 17 pages, 6 figures, data provided in the appendices. Accepted for publication in MNRAS

Swift J1858.6-0814 is a transient neutron star X-ray binary discovered in October 2018. Multi-wavelength follow-up observations across the electromagnetic spectrum revealed many interesting properties, such as erratic flaring on minute timescales and evidence for wind outflows at both X-ray and optical wavelengths, strong and variable local absorption, and an anomalously hard X-ray spectrum. Here, we report on a detailed radio observing campaign consisting of one observation at 5.5/9 GHz with the Australia Telescope Compact Array, and nine observations at 4.5/7.5 GHz with the Karl G. Jansky Very Large Array. A radio counterpart with a flat to inverted radio spectrum is detected in all observations, consistent with a compact jet being launched from the system. Swift J1858.6-0814 is highly variable at radio wavelengths in most observations, showing significant variability when imaged on 3-to-5-minute timescales and changing up to factors of 8 within 20 minutes. The periods of brightest radio emission are not associated with steep radio spectra, implying they do not originate from the launching of discrete ejecta. We find that the radio variability is similarly unlikely to have a geometric origin, be due to scintillation, or be causally related to the observed X-ray flaring. Instead, we find that it is consistent with being driven by variations in the accretion flow propagating down the compact jet. We compare the radio properties of Swift J1858.6-0814 with those of Eddington-limited X-ray binaries with similar X-ray and optical characteristics, but fail to find a match in radio variability, spectrum, and luminosity., Comment: 14 pages, 8 figures, 3 tables; accepted for publication in MNRAS

We present a study of perpendicular subcritical shocks in a collisional laboratory plasma. Shocks are produced by placing obstacles into the super-magnetosonic outflow from an inverse wire array z-pinch. We demonstrate the existence of subcritical shocks in this regime and find that secondary shocks form in the downstream. Detailed measurements of the subcritical shock structure confirm the absence of a hydrodynamic jump. We calculate the classical (Spitzer) resistive diffusion length and show that it is approximately equal to the shock width. We measure little heating across the shock (< 10 % of the ion kinetic energy) which is consistent with an absence of viscous dissipation., 6 pages, 5 figures

We present results from pulsed-power driven differentially rotating plasma experiments designed to simulate physics relevant to astrophysical disks and jets. In these experiments, angular momentum is injected by the ram pressure of the ablation flows from a wire array Z pinch. In contrast to previous liquid metal and plasma experiments, rotation is not driven by boundary forces. Axial pressure gradients launch a rotating plasma jet upwards, which is confined by a combination of ram, thermal, and magnetic pressure of a surrounding plasma halo. The jet has subsonic rotation, with a maximum rotation velocity $23 \pm 3$ km/s. The rotational velocity profile is quasi-Keplerian with a positive Rayleigh discriminant $\kappa^2 \propto r^{-2.8\pm0.8}$ rad$^2$/s$^2$. The plasma completes $0.5 - 2$ full rotations in the experimental time frame ($\sim 150$ ns)., Comment: 4 figures

Supplemental Digital Content is available in the text, Objective: To investigate whether [18F]fluorothymidine (FLT) and/or [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) can differentiate growth in neurofibromatosis 2 (NF2) related vestibular schwannomas (VS) and to evaluate the importance of PET scanner spatial resolution on measured tumor uptake. Methods: Six NF2 patients with 11 VS (4 rapidly growing, 7 indolent), were scanned with FLT and FDG using a high-resolution research tomograph (HRRT, Siemens) and a Siemens Biograph TrueV PET-CT, with and without resolution modeling image reconstruction. Mean, maximum, and peak standardised uptake values (SUV) for each tumor were derived and the intertumor correlation between FDG and FLT uptake was compared. The ability of FDG and FLT SUV values to discriminate between rapidly growing and slow growing (indolent) tumors was assessed using receiver operator characteristic (ROC) analysis. Results: Tumor uptake was seen with both tracers, using both scanners, with and without resolution modeling. FDG and FLT uptake was correlated (R2 = 0.67–0.86, p

Supersonic interacting flows occurring in phenomena, such as protostellar jets, give rise to strong shocks and have been demonstrated in several laboratory experiments. To study such colliding flows, we use the AstroBEAR AMR code to conduct hydrodynamic simulations in three dimensions. We introduce variations in the flow parameters of density, velocity, and cross-sectional radius of the colliding flows in order to study the propagation and conical shape of the bow shock formed by collisions between two, not necessarily symmetric, hypersonic flows. We find that the motion of the interaction region is driven by imbalances in ram pressure between the two flows, while the conical structure of the bow shock is a result of shocked lateral outflows being deflected from the horizontal when the flows are of differing cross sections.

We report new radio observations of a sample of thirty-six neutron star (NS) X-ray binaries, more than doubling the sample in the literature observed at current-day sensitivities. These sources include thirteen weakly-magnetised ($B, Accepted for publication in MNRAS; 31 pages, 8 figures, 8 tables (including online supplementary materials)

We report on a long-term optical monitoring of the neutron star X-ray binary Centaurus X-4 performed during the last 13.5 years. This source has been in quiescence since its outburst in 1979. Our monitoring reveals the overall evolution of the accretion disc; we detect short-duration flares, likely originating also in the disc, superimposed with a small-amplitude (< 0.1 mag) ellipsoidal modulation from the companion star due to geometrical effects. A long-term (~2300 days) downward trend, followed by a shorter (~1000 days) upward one, is observed in the disc light curve. Such a rise in the optical has been observed for other X-ray binaries preceding outbursts, as predicted by the disc instability model. For Cen X-4, the rise of the optical flux proceeded for ~3 years, and culminated in a flux increase at all wavelengths (optical-UV-X-rays) at the end of 2020. This increase faded after ~2 weeks, without giving rise to a full outburst. We suggest that the propagation of an inside-out heating front was ignited due to a partial ionization of hydrogen in the inner disc. The propagation might have stalled soon after the ignition due to the increasing surface density in the disc that the front encountered while propagating outwards. The stall was likely eased by the low level irradiation of the outer regions of the large accretion disc, as shown by the slope of the optical/X-ray correlation, suggesting that irradiation does not play a strong role in the optical, compared to other sources of emission., 18 pages, 10 figures, accepted for publication in ApJ

Background: Feminizing hormone therapy with estradiol is used to align an individual’s physical characteristics with their gender identity. Australian expert consensus guidelines (1) recommend targeting estradiol concentrations of 250-600 pmol/L (68-163 pg/mL) based on local cross-sectional data (2). We aimed to establish the proportion of individuals achieving estradiol concentrations in consensus guidelines. Methods: A retrospective cross-sectional analysis was performed of transfeminine individuals attending a primary or secondary care clinic in Melbourne, Australia who were prescribed oral estradiol valerate for at least 6 months and had estradiol dose and concentration available. Estradiol concentration was measured by immunoassay. Outcomes were (1) proportion of individuals achieving target estradiol concentrations and (2) influence of estradiol dose and BMI on estradiol concentrations. Results: 259 individuals (median age 25.8(IQR 21.9,33.5) years)) had data available for analysis. Median duration of estradiol therapy was 24(15,33) months. Median estradiol concentration was 328(238,434) pmol/L (89(65,118) pg/mL) on 6(4,8) mg estradiol valerate. 172 (66%) individuals had estradiol concentrations within the target range recommended in consensus guidelines. 70 (27%) individuals had estradiol concentrations below target, and 17 (7%) above target. There was a weak positive correlation between estradiol dose and estradiol concentration (r=0.156, p=0.012). There was no correlation between BMI and estradiol concentration achieved (r=-0.063, p=0.413). Conclusions: 66% of individuals achieved estradiol concentration recommended in consensus guidelines with a relatively high oral estradiol dose. There was significant interindividual variability. Estradiol concentration should be interpreted in conjunction with clinical features of feminization and weighed against potential risks of escalating estradiol dose. References 1. Cheung AS, Wynne K, Erasmus J, Murray S, Zajac JD. Position statement on the hormonal management of adult transgender and gender diverse individuals. Med J Aust 2019; 211:127-133 2. Angus L, Leemaqz SY, Ooi O, Cundill P, Silberstein N, Locke P, Zajac JD, Cheung AS. Cyproterone acetate or spironolactone in lowering testosterone concentrations for transgender individuals receiving estradiol therapy. Endocr Connect 2019

The 2D scrape-off-layer turbulence code (nSOLT) includes 1D Boltzmann neutral–plasma interactions, a model of divertor recycling (introduced here), and a fixed source of plasma concentrated at the core-side boundary. Three fueling methods are considered herein: (1) neutral injection in the far-SOL is accomplished by specifying the density of Franck–Condon distributed neutrals streaming in from the boundary. (2) Divertor recycling is modeled by injecting a fraction of the particle parallel flux in the scrape-off layer (SOL) back into the edge region as a source of plasma. (3) A constant source fuels the edge plasma from the core-side boundary to model pellet injection. For machine parameters (B, Rm, and L//) illustrative of the MAST-U device, and for a deuterium plasma, turbulent equilibria are obtained that share the same plasma fueling rate for each of the three fueling methods, with only one of the sources on in each case. In the presence of self-consistent turbulence, quasi-steady plasma and neutral (deuterium) profiles, fueling efficiencies, SOL transparencies, and heat flux widths are compared. Characteristics of the turbulent fluctuations, including skewness, cross-phases, and power spectra, are described. The calculated fueling efficiencies, SOL transparencies to neutral penetration, and many of the turbulent properties are remarkably similar for all three fueling methods despite significant differences in the plasma profiles. The nonlinear states of the three cases are dominated by separatrix-spanning vortex cells that control particle and heat losses into the SOL.

Whilst astronomy as a science is historically founded on observations at optical wavelengths, studying the Universe in other bands has yielded remarkable discoveries, from pulsars in the radio, signatures of the Big Bang at submm wavelengths, through to high energy emission from accreting, gravitationally-compact objects and the discovery of gamma-ray bursts. Unsurprisingly, the result of combining multiple wavebands leads to an enormous increase in diagnostic power, but powerful insights can be lost when the sources studied vary on timescales shorter than the temporal separation between observations in different bands. In July 2015, the workshop "Paving the way to simultaneous multi-wavelength astronomy" was held as a concerted effort to address this at the Lorentz Center, Leiden. It was attended by 50 astronomers from diverse fields as well as the directors and staff of observatories and spaced-based missions. This community white paper has been written with the goal of disseminating the findings of that workshop by providing a concise review of the field of multi-wavelength astronomy covering a wide range of important source classes, the problems associated with their study and the solutions we believe need to be implemented for the future of observational astronomy. We hope that this paper will both stimulate further discussion and raise overall awareness within the community of the issues faced in a developing, important field., Comment: 52 pages, 15 figures, accepted, invited review (to appear in New Astronomy Reviews), v3: updated figure and text

Summary A 19-year-old Quarter Horse gelding was evaluated for respiratory distress and a rapidly enlarging retropharyngeal mass. Initial evaluation revealed severe respiratory distress, and a large, firm mass, visibly appreciable as 12 × 12 cm, in the left retropharyngeal and perilaryngeal region, with surrounding left and right retropharyngeal swelling. No significant abnormalities were present on complete blood count and serum biochemistry analyses. Endoscopy revealed severe pharyngeal collapse restricting airflow without gross abnormalities of the pharyngeal mucosa other than inflammation and irritation. A multilobular retropharyngeal mass, diffusely heterogeneous in echogenicity, was present adjacent to, but not occluding, the carotid artery as assessed by ultrasonography. Initial needle aspirate suggested lymphoma. Tissue biopsy and histopathology confirmed a round cell tumour. A temporary tracheotomy was performed to provide respiratory relief, and the horse was managed on oral antibiotics and anti-inflammatory medications while awaiting histopathological results. The decision was made to humanely euthanise the horse after biopsy results indicated lymphoma. Definitive diagnosis of T cell rich, large B cell lymphoma was made by combination of cytology, immunohistochemistry and molecular clonality PCR (PARR) testing. Lymphoma should be considered in horses with focal masses of the retropharyngeal region. Although treatment was not pursued, PARR testing was successful in this case and may be helpful for accurate characterisation of lymphoma in horses to more precisely determine prognosis and the most effective treatment plans, as it has been in human patients and small animals.

We present simultaneous radio through sub-mm observations of the black hole X-ray binary (BHXB) V404 Cygni during the most active phase of its June 2015 outburst. Our $4$ hour long set of overlapping observations with the Very Large Array, the Sub-millimeter Array, and the James Clerk Maxwell Telescope (SCUBA-2), covers 8 different frequency bands (including the first detection of a BHXB jet at $666 \,{\rm GHz}/450\mu m$), providing an unprecedented multi-frequency view of the extraordinary flaring activity seen during this period of the outburst. In particular, we detect multiple rapidly evolving flares, which reach Jy-level fluxes across all of our frequency bands. With this rich data set we performed detailed MCMC modeling of the repeated flaring events. Our custom model adapts the van der Laan synchrotron bubble model to include twin bi-polar ejections, propagating away from the black hole at bulk relativistic velocities, along a jet axis that is inclined to the line of sight. The emission predicted by our model accounts for projection effects, relativistic beaming, and the geometric time delay between the approaching and receding ejecta in each ejection event. We find that a total of 8 bi-polar, discrete jet ejection events can reproduce the emission that we observe in all of our frequency bands remarkably well. With our best fit model, we provide detailed probes of jet speed, structure, energetics, and geometry. Our analysis demonstrates the paramount importance of the mm/sub-mm bands, which offer a unique, more detailed view of the jet than can be provided by radio frequencies alone., Comment: 25 pages, 11 figures, Accepted to MNRAS

X-ray transients, such as accreting neutron stars, periodically undergo outbursts, thought to be caused by a thermal-viscous instability in the accretion disk. Usually outbursts of accreting neutron stars are identified when the accretion disk has undergone an instability, and the persistent X-ray flux has risen to a threshold detectable by all sky monitors on X-ray space observatories. Here we present the earliest known combined optical, UV, and X-ray monitoring observations of the outburst onset of an accreting neutron star low mass X-ray binary system. We observed a significant, continuing increase in the optical i'-band magnitude starting on July 25, 12 days before the first X-ray detection with Swift/XRT and NICER (August 6), during the onset of the 2019 outburst of SAX J1808.4-3658. We also observed a 4 day optical to X-ray rise delay, and a 2 day UV to X-ray delay, at the onset of the outburst. We present the multiwavelength observations that were obtained, discussing the theory of outbursts in X-ray transients, including the disk instability model, and the implications of the delay. This work is an important confirmation of the delay in optical to X-ray emission during the onset of outbursts in low mass X-ray binaries, which has only previously been measured with less sensitive all sky monitors. We find observational evidence that the outburst is triggered by ionisation of hydrogen in the disk., 12 pages, 5 figures, accepted by MNRAS

The black hole binary, V404 Cygni, went into outburst in 2015 June, after 26 years of X-ray quiescence. We observed the outburst with the Neil Gehrels Swift observatory. We present optical/UV observations taken with the Swift Ultra-violet Optical Telescope, and compare them with the X-ray observations obtained with the Swift X-ray Telescope. We find that dust extinction affecting the optical/UV does not correlate with absorption due to neutral hydrogen that affects the X-ray emission. We suggest there is a small inhomogeneous high-density absorber containing a negligible amount of dust, close to the black hole. Overall, temporal variations in the optical/UV appear to trace those in the X-rays. During some epochs we observe an optical time-lag of (15–35) s. For both the optical/UV and X-rays, the amplitude of the variations correlates with flux, but this correlation is less significant in the optical/UV. The variability in the light curves may be produced by a complex combination of processes. Some of the X-ray variability may be due to the presence of a local, inhomogeneous and dust-free absorber, while variability visible in both the X-ray and optical/UV may instead be driven by the accretion flow: the X-rays are produced in the inner accretion disc, some of which are reprocessed to the optical/UV; and/or the X-ray and optical/UV emission is produced within the jet. © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society, SRO gratefully acknowledges the support of the Leverhulme Trust Early Career Fellowship. AJCT and SRO acknowledge support from the Spanish Ministry, Project Number AYA2012-39727-C03-01. SEM acknowledges the Violette and Samuel Glasstone Research Fellowship program and the UK Science and Technology Facilities Council (STFC) for financial support. PG thanks STFC and UKIERI for support. This work was also supported by the UK Space Agency.

We present optical, UV and X-ray monitoring of the short orbital period black hole X-ray binary candidate Swift J1753.5-0127, focusing on the final stages of its 12$-$year long outburst that started in 2005. From September 2016 onward, the source started to fade and within three months, the optical flux almost reached the quiescent level. Soon after that, using a new proposed rebrightening classification method we recorded a mini-outburst and a reflare in the optical light curves, peaking in February (V$\rm\sim$17.0) and May (V$\rm\sim$17.9) 2017, respectively. Remarkably, the mini-outburst has a peak flux consistent with the extrapolation of the slow decay before the fading phase preceding it. The following reflare was fainter and shorter. We found from optical colors that the temperature of the outer disk was $\sim 11$,000 K when the source started to fade rapidly. According to the disk instability model, this is close to the critical temperature when a cooling wave is expected to form in the disk, shutting down the outburst. The optical color could be a useful tool to predict decay rates in some X-ray transients. We notice that all X-ray binaries that show mini-outbursts following a main outburst are short orbital period systems ($, Comment: 12 pages, 4 figures, accepted for publication in ApJ

Optical collective Thomson scattering (TS) is used to diagnose magnetized high energy density physics experiments at the Magpie pulsed-power generator at Imperial College London. The system uses an amplified pulse from the second harmonic of a Nd:YAG laser (3 J, 8 ns, 532 nm) to probe a wide diversity of high-temperature plasma objects, with densities in the range of 1017–1019 cm−3 and temperatures between 10 eV and a few keV. The scattered light is collected from 100 μm-scale volumes within the plasmas, which are imaged onto optical fiber arrays. Multiple collection systems observe these volumes from different directions, providing simultaneous probing with different scattering K-vectors (and different associated α-parameters, typically in the range of 0.5–3), allowing independent measurements of separate velocity components of the bulk plasma flow. The fiber arrays are coupled to an imaging spectrometer with a gated intensified charge coupled device. The spectrometer is configured to view the ion-acoustic waves of the collective Thomson scattered spectrum. Fits to the spectra with the theoretical spectral density function S(K, ω) yield measurements of the local plasma temperatures and velocities. Fitting is constrained by independent measurements of the electron density from laser interferometry and the corresponding spectra for different scattering vectors. This TS diagnostic has been successfully implemented on a wide range of experiments, revealing temperature and flow velocity transitions across magnetized shocks, inside rotating plasma jets and imploding wire arrays, as well as providing direct measurements of drift velocities inside a magnetic reconnection current sheet.