Multiwavelength study of 20 jets that emanate from the periphery of active regions

We present a multiwavelength analysis of 20 EUV jets which occurred at the periphery of active regions close to sunspots. We discuss the physical parameters of the jets and their relation with other phenomena such as H alpha surges, nonthermal type III radio bursts and hard X-ray emission. Using AIA wavelength channels sensitive to coronal temperatures, we studied the temperature distribution in the jets using the line-of-sight Differential Emission Measure technique. We also investigated the role of the photospheric magnetic field using the LOS magnetogram data from the HMI. The lifetime of jets range from 5 to 39 minutes with an average of 18 minutes and their velocities range from 87 to 532 km/s with an average of 271 km/s. Most of the jets are co-temporal with nonthermal type III radio bursts observed by the Wind/WAVES spacecraft. We confirm the source region of these bursts using the Potential Field Source Surface technique. 10 out of 20 events showed that the jets originated in a region of flux cancellation and 6 jets in a region of flux emergence. 4 events showed flux emergence and then cancellation during the jet evolution. DEM analyses showed that for most of the spires of the jets, the DEM peaked at around log T [K] = 6.2/6.3. In addition, we derived an emission measure and a lower limit of electron density at the location of the spire and the footpoint. These results are in agreement with those obtained earlier by studying individual active region jets. The observation of flux cancellation, the association with HXR emission and emission of nonthermal type III radio bursts, suggest that the initiation and therefore, heating is taking place at the base of the jet. This is also supported by the high temperature plasma revealed by the DEM analysis in the jet footpoint. Our results provide substantial constraints for theoretical modeling of the jets and their thermodynamic nature.Part of the work was done when one of the authors (SMM) was a Junior Research Fellow at Inter-University Centre of Astronomy and Astrophysics (IUCAA), India. S.M.M. and D.T. acknowledge support from DST under the Fast Track Scheme (SERB/F/3369/2012/2013). S.M.M. also ackowledges support from the Cambridge Trust, University of Cambridge, UK. H.E.M. and G.D.Z. acknowledge the support of STFC. AIA data are courtesy of SDO (NASA) and the AIA consortium. RHESSI work is supported by NASA contract NAS 5-98033. The authors thank the open data policy of WIND/WAVES instrument team. This work utilizes data obtained by the Global Oscillation Network Group (GONG) Program, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de AstrofÃŋsica de Canarias, and Cerro Tololo Interamerican Observatory.This is the final version of the article. It first appeared from EDP Sciences via http://dx.doi.org/10.1051/0004-6361/20152747

Cool and hot emission in a recurring active region jet

Aims. We present a thorough investigation of the cool and hot temperature components in four recurring active region jets observed on July 10, 2015 using the Atmospheric Imaging Assembly (AIA), X-ray Telescope (XRT), and Interface Region Imaging Spectrograph (IRIS) instruments. Methods. A Differential Emission Measure (DEM) analysis was performed on areas in the jet spire and footpoint regions by combining the IRIS spectra and the AIA observations. This procedure better constrains the low temperature DEM values by adding IRIS spectral lines. Plasma parameters, such as doppler velocities, electron densities, nonthermal velocities and a filling factor were also derived from the IRIS spectra. Results. In the DEM analysis, significant cool emission was found in the spire and the footpoint regions. The hot emission was peaked at log T [K] = 5.6-5.9 and 6.5 respectively. The DEM curves show the presence of hot plasma (T = 3 MK) in the footpoint region. We confirmed this result by estimating the Fe XVIII emission from the AIA 94 Å channel which was formed at an effective temperature of log T [K] = 6.5. The average XRT temperatures were also found to be in agreement with log T [K] = 6.5. The emission measure (EM) was found to be three orders of magnitude higher in the AIA-IRIS DEM compared with that obtained using only AIA. The O IV (1399/1401 Å) electron densities were found to be close to those obtained by Cheung et al. (2015). Different threads along the spire show different plane-of-sky velocities both in the lower corona and transition region. Doppler velocities of 32 km/s (blueshifted) and 13 km/s (redshifted) were obtained in the spire and footpoint, respectively from the Si IV 1402.77 Å spectral line. Nonthermal velocities of 69 and 53 km/s were recorded in the spire and footpoint region, respectively. We obtained a filling factor of 0.1 in the spire at log T [K] = 5. Conclusions. The recurrent jet observations confirmed the presence of significant cool emission co-spatial with the coronal emission.SMM acknowledges support from the Cambridge Trust, University of Cambridge, UK. HEM and GDZ acknowledge the support of STFC

Slipping magnetic reconnection, chromospheric evaporation, implosion, and precursors in the 2014 September 10 X1.6-class solar flare

© 2016. The American Astronomical Society. All rights reserved.. We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. Slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions toward both ends of the ribbons. Velocities of 20-40 km s-1 are found within time windows where the slipping is well resolved. The warm coronal loops exhibit expanding and contracting motions that are interpreted as displacements due to the growing flux rope that subsequently erupts. This flux rope existed and erupted before the onset of apparent coronal implosion. This indicates that the energy release proceeds by slipping reconnection and not via coronal implosion. The slipping reconnection leads to changes in the geometry of the observed structures at the Interface Region Imaging Spectrograph slit position, from flare loop top to the footpoints in the ribbons. This results in variations of the observed velocities of chromospheric evaporation in the early flare phase. Finally, it is found that the precursor signatures, including localized EUV brightenings as well as nonthermal X-ray emission, are signatures of the flare itself, progressing from the early phase toward the impulsive phase, with the tether-cutting being provided by the slipping reconnection. The dynamics of both the flare and outlying coronal loops is found to be consistent with the predictions of the standard solar flare model in three dimensions

Borrelia burgdorferi Requires the Alternative Sigma Factor RpoS for Dissemination within the Vector during Tick-to-Mammal Transmission

While the roles of rpoSBb and RpoS-dependent genes have been studied extensively within the mammal, the contribution of the RpoS regulon to the tick-phase of the Borrelia burgdorferi enzootic cycle has not been examined. Herein, we demonstrate that RpoS-dependent gene expression is prerequisite for the transmission of spirochetes by feeding nymphs. RpoS-deficient organisms are confined to the midgut lumen where they transform into an unusual morphotype (round bodies) during the later stages of the blood meal. We show that round body formation is rapidly reversible, and in vitro appears to be attributable, in part, to reduced levels of Coenzyme A disulfide reductase, which among other functions, provides NAD+ for glycolysis. Our data suggest that spirochetes default to an RpoS-independent program for round body formation upon sensing that the energetics for transmission are unfavorable

Blood pressure and TNF-α act synergistically to increase leucocyte CD11b adhesion molecule expression in the BELFAST study: implications for better blood pressure control in ageing

Hypertension, a key risk factor for stroke, cardiovascular disease and dementia, is associated with chronic vascular inflammation, and although poorly understood, putative mechanisms include pro-inflammatory responses induced by mechanical stretching, with cytokine release and associated up-regulated expression of adhesion molecules. Because blood pressure increases with age, we measured baseline and tumour necrosis alpha (TNF-α)-stimulated CD11b/CD18 adhesion molecule expression on leucocytes to assess any association between the two. In 38 subjects (mean age 85 years), consecutively enrolled from Belfast Elderly Longitudinal Free-Living Aging Study (BELFAST), baseline and TNF-α-stimulated CD11b/CD18 expression on separated monocytes and neutrophils increased with systolic blood pressure >120 mmHg (p = 0.05) and for lymphocytes, with diastolic blood pressure >80 mmHg (p < 0.05).These findings show increased potential stickiness of intravascular cells with increasing blood pressure which is accentuated by TNF-α, and suggest mechanistic reasons why better hypertension control is important