He-like ions as practical astrophysical plasma diagnostics: From stellar coronae to active galactic nuclei

We review X-ray plasma diagnostics based on the line ratios of He-like ions. Triplet/singlet line intensities can be used to determine electronic temperature and density, and were first developed for the study of the solar corona. Since the launches of the X-ray satellites Chandra and XMM-Newton, these diagnostics have been extended and used (from CV to Si XIII) for a wide variety of astrophysical plasmas such as stellar coronae, supernova remnants, solar system objects, active galactic nuclei, and X-ray binaries. Moreover, the intensities of He-like ions can be used to determine the ionization process(es) at work, as well as the distance between the X-ray plasma and the UV emission source for example in hot stars. In the near future thanks to the next generation of X-ray satellites (e.g., Astro-H and IXO), higher-Z He-like lines (e.g., iron) will be resolved, allowing plasmas with higher temperatures and densities to be probed. Moreover, the so-called satellite lines that are formed closed to parent He-like lines, will provide additional valuable diagnostics to determine electronic temperature, ionic fraction, departure from ionization equilibrium and/or from Maxwellian electron distribution.Comment: 36 pages, 16 figures. Invited Review talk at the "High-resolution X-ray spectroscopy: past, present, and future" conference, Utrecht, March 15-17 2010. Accepted for publication in Space Science Reviews (2010); the final publication is available at http://www.springerlink.co

Study of the X-ray activity of Sgr A* during the 2011 XMM-Newton campaign

In Spring 2011 we observed Sgr A*, the supermassive black hole at the center of our Galaxy, with XMM-Newton with a total exposure of ~226 ks in coordination with the 1.3 mm VLBI. We have performed timing analysis of the X-ray emission from Sgr A* using Bayesian blocks algorithm to detect X-ray flares observed with XMM-Newton. Furthermore, we computed X-ray smoothed light curves observed in this campaign in order to have better accuracy on the position and the amplitude of the flares. We detected 2 X-ray flares on the 2011 March 30 and April 3 which have for comparison a peak detection level of 6.8 and 5.9 sigma in the XMM-Newton/EPIC light curve in the 2-10 keV energy range with a 300 s bin. The former is characterized by 2 sub-flares: the first one is very short (~458 s) with a peak luminosity of ~9.4E34 erg/s whereas the second one is longer (~1542 s) with a lower peak luminosity of ~6.8E34 erg/s. The comparison with the sample of X-ray flares detected during the 2012 Chandra XVP campaign favors the hypothesis that the 2011 March 30 flare is a single flare rather than 2 distinct sub-flares. We model the light curve of this flare with the gravitational lensing of a simple hotspot-like structure but we can not satisfactorily reproduce the large decay of the light curve between the 2 sub-flares with this model. From magnetic energy heating during the rise phase of the first sub-flare and assuming an X-ray photons production efficiency of 1 and a magnetic field of 100 G at 2 r_g, we derive an upper limit to the radial distance of the first sub-flare of 100 r_g. We estimate using the decay phase of the first sub-flare a lower limit to the radial distance of 4 r_g from synchrotron cooling in the infrared. The X-ray emitting region of the first sub-flare is located at a radial position of 4-100 and has a corresponding radius of 1.8-2.87 in r_g unit for a magnetic field of 100 G at 2 r_g.Comment: Version published in A&A + corrigendum published in A&

Caractérisation du rôle non ciliaire de la Kinésine-2 dans l'établissement de l'axe droite/gauche chez Drosophila melanogaster

In nature most of the bilateralia are left/right (L/R) asymmetric. In Drosophila, asymmetry is apparent in the directional looping of gut and terminalia. Dextral orientation of organs is controlled by the activity of a single gene myosin ID (myoID) whose mutation induces a fully inverted L/R axis. To date little is known of how the initial L/R cue induced by MyoID is propagated and maintained through the rest of the architecture of the L/R organizer. Here we present the identification of klp64D and klp68D as new myoID interacting genes. These genes encodes the two motor sub-units of the Drosophila Kinesin-2 motor complex. Interestingly, this microtubule-based motor plays a ciliary function in vertebrate L/R morphogenesis. However, we show that in Drosophila cilia are not involved in L/R asymmetry. We demonstrate that Kinesin-2 acts during L/R determination in the dextral pathway. Furthermore Kinesin-2 is required for proper L/R patterning both of male genitalia and of adult hindgut. L/R activity of Kinesin-2 is restricted to cells that do not express MyoID suggesting a role for this motor in propagation of the L/R cue. Our findings show for the first time a non ciliary role for Kinesin-2 in L/R axis determination. Thus, these results shed light on an evolutionary conservation between Drosophila and vertebrate L/R determination.Chez Drosophila melanogaster, l’orientation horaire (dextrale) des organes est déterminée par un gène unique codant la Myosine non conventionnelle de type ID (MyoID). Un crible génétique modificateur en contexte sensibilisé pour myoID nous a permis d’identifier klp64D comme un gène interagissant génétiquement avec myoID. Celui-ci code l’une des sous-unités motrices du complexe moteur hétérotrimérique Kinésine-2 (Kin-2) constitué d’une autre sous-unité motrice Klp68D et d’une sous-unité adaptatrice Kap3. Nous montrons que klp68D interagit génétiquement avec myoID lors de la mise en place de l’axe D/G. Ceci suggère donc un rôle de l’ensemble du complexe Kin-2 dans l’asymétrie D/G. Chez les vertébrés, Kin-2 participe à l’assemblage des cils impliqués dans la détermination D/G lors de la gastrulation. Or, chez la drosophile, les cils ne sont pas requis dans la détermination D/G. MyoID et Kin-2 sont requis de manière synchrone dans la voie dextrale lors de la détermination D/G. En outre, Kin-2 joue un rôle important dans la rotation horaire du génitalia et l’enroulement dextral de l’intestin postérieur adulte (hindgut). Kin-2 est requise dans l’organisateur D/G de l’hindgut adulte pour l’orientation biaisée des cellules qui n’expriment pas MyoID. Par ailleurs, nos résultats suggèrent que l’activité de Kin-2 n’est pas requise dans le sous-ensemble de cellules qui exprime MyoID. Enfin, le rôle joué par Kin-2 dans l’asymétrie D/G semble indépendant de la polarité apico-basale et des jonctions adhérentes. Kin-2 pourrait donc jouer un rôle non ciliaire dans la phase de propagation de l’information directionnelle induite par MyoID

Étude de l'implication de la E-sélectine et de son récepteur, le Death receptor 3, dans le processus métastatique

La E-sélectine, un récepteur d'adhérence spécifique des cellules endothéliales interagit avec le Death Receptor 3 (DR3), exprimé par les cellules du cancer du côlon. Dans cette étude, nous nous sommes intéressés plus particulièrement aux mécanismes par lesquels les voies activées en aval de DR3 confèrent des avantages de survie aux cellules cancéreuses du côlon. Dans un premier temps, nous avons montré que DR3 est exprimé par les cellules HT29 sous une version potentiellement sécrétée et sous une forme membranaire toutes deux tronquées. Ces versions dépourvues de Death Domain n’induisent pas l'apoptose. Secondairement, nous avons constaté que la E-sélectine déclenche la phosphorylation sur tyrosine du récepteur via un membre de la famille des Src kinases. Nous avons finalement obtenu des preuves indiquant que la E-sélectine comme le TL1A activent l’axe de survie PI3K/Akt/ NFB.E-selectin, a specific endothelial adhesion receptor, interacts with Death Receptor 3 (DR3) expressed by colon cancer cells. In this study, we investigated further the mechanisms by which the E-selectin-activated pathways downstream of DR3 confer a survival advantage to colon cancer cells. We found that DR3 exists under both transmembrane and secreted versions in HT29 cells. These Death Domain deleted isoforms hamper apoptosis. Additionally, we found that E-selectin could trigger the tyrosine phosphorylation Tyr285 of DR3 in a Src family member-dependent manner. We also obtained evidence indicating that E-selectin and TL1A induce the PI3K/Akt/NFκB p65 survival axis

Modelling the X-ray polarimetric signatures of complex geometry: the case study of the "changing look" AGN NGC 1365

"Changing look" Active Galactic Nuclei (AGN) are a subset of Seyfert galaxies characterized by rapid transitions between Compton-thin and Compton-thick regimes. In their Compton-thin state, the central engine is less obscured, hence spectroscopy or timing observations can probe their innermost structures. However, it is not clear if the observed emission features and the Compton hump are associated with relativistic reflection onto the accretion disc, or complex absorption by distant, absorbing gas clouds passing by the observer's line-of-sight. Here, we investigate these two scenarios under the scope of X-ray polarimetry, providing the first polarisation predictions for an archetypal "changing look" AGN: NGC 1365. We explore the resulting polarisation emerging from lamp-post emission and scattering off an accretion disc in the immediate vicinity of a supermassive black hole. The computed polarisation signatures are compared to the results of an absorption-dominated model, where high column density gas partially covers the central source. While the shape of the polarisation spectrum is similar, the two models differ in net polarisation percentage, with the relativistic reflection scenario producing significantly stronger polarisation. Additionally, the variation of the polarisation position angle is distinctly different between both scenarios: the reflection-dominated model produces smooth rotations of the polarisation angle with photon energy whereas circumnuclear absorption causes an orthogonal switch of the polarisation angle between the soft and the hard X-ray bands. By comparing the predicted polarisation of NGC 1365 to the detectability levels of X-ray polarimetry mission concepts proposed in the past, we demonstrate that with a large, soft X-ray observatory or a medium-sized mission equipped with a hard (6 - 35 keV) polarimeter, the correct interpretation would be unambiguous.Comment: 6 pages, 4 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Societ

Repeated X-ray Flaring Activity in Sagittarius A*

Investigating the spectral and temporal characteristics of the X-rays coming from Sagittarius A* (Sgr A*) is essential to our development of a more complete understanding of the emission mechanisms in this supermassive black hole located at the center of our Galaxy. Several X-ray flares with varying durations and spectral features have already been observed from this object. Here we present the results of two long XMM-Newton observations of the Galactic nucleus carried out in 2004, for a total exposure time of nearly 500 ks. During these observations we detected two flares from Sgr A* with peak 2-10 keV luminosities about 40 times (L ~ 9x10^34 erg s−1) above the quiescent luminosity: one on 2004 March 31 and another on 2004 August 31. The first flare lasted about 2.5 ks and the second about 5 ks. The combined fit on the Epic spectra yield photon indeces of about 1.5 and 1.9 for the first and second flare respectively. This hard photon index strongly suggests the presence of an important population of non-thermal electrons during the event and supports the view that the majority of flaring events tend to be hard and not very luminous.Comment: 8 pages, 7 figures, Accepted for publication in the Astrophysical Journa

Probing the face-on disc-corona system of the bare AGN Mrk 110 from UV to hard X-rays: a moderate changing-state AGN?

[Abridged] The X-ray broadband spectra of the bare AGN Mrk 110, obtained by simultaneous XMM-Newton and NuSTAR observations (Nov 2019 and April 2020), are characterised by the presence of a prominent and absorption-free smooth soft X-ray excess, moderately broad OVII and Fe Kalpha emission lines, and a lack of a strong Compton hump. While relativistic reflection as the sole emission is ruled out, a simplified combination of soft and hard Comptonisation from a warm and a hot coronae, plus mild relativistic disc reflection reproduces the data very well. We aim to confirm the physical origin of the soft X-ray excess of Mrk 110 and to determine its disc-corona system properties from its energetics using two new sophisticated models: reXcor and relagn, respectively. At both epochs, the inferred high-values of the warm-corona heating from the X-ray broadband spectral analysis using reXcor confirm that the soft X-ray excess originates mainly from a warm corona rather than relativistic reflection. The intrinsic best-fit SED determined at both epochs using relagn show a high X-ray contribution relative to the UV and are very well reproduced by a warm and hot coronae plus mild relativistic reflection. The outer radii of the hot and warm coronae are located at a few 10s and ~100 Rg, respectively. Moreover, combining the inferred low Eddington ratio (~ a few %) from this work, and previous multi-wavelength spectral and timing studies suggests that Mrk 110 could be classified as a moderate changing-state AGN. Our analysis confirms the existence of a warm corona as a significant contribution to the soft X-ray excess and UV emission in Mrk 110, adding to growing evidence that AGN accretion deviates from standard disc theory. This strengthens the importance of long-term multi-wavelength monitoring on both single targets and large AGN surveys to reveal the real nature of disc-corona system in AGN.Comment: 12 pages, 7 figures, accepted for publication in A&

Sixteen years of X-ray monitoring of Sagittarius A*: Evidence for a decay of the faint flaring rate from 2013 August, 13 months before a rise in the bright flaring rate

Recently, in a study the X-ray flaring activity of Sgr A* with Chandra and XMM-Newton public observations from 1999 to 2014 and 2014 Swift data, it has been argued that the "bright and very bright" flaring rate raised from 2014 Aug. 31. Thanks to 482ks of observations performed in 2015 with Chandra, XMM-Newton and Swift, we test the significance of this rise of flaring rate and determine the threshold of unabsorbed flare flux or fluence leading to any flaring-rate change. The mean unabsorbed fluxes of the 107 flares detected in the 1999-2015 observations are consistently computed from the extracted spectra and calibration files, assuming the same spectral parameters. We construct the observed flare fluxes and durations distribution for the XMM-Newton and Chandra flares and correct it from the detection biases to estimate the intrinsic distribution from which we determine the average flare detection efficiency for each observation. We apply the BB algorithm on the flare arrival times corrected from the corresponding efficiency. We confirm a constant overall flaring rate in 1999-2015 and a rise in the flaring rate for the most luminous/energetic flares from 2014 Aug. 31 (4 months after the passage of the DSO/G2 close to Sgr A*). We also identify a decay of the flaring rate for the less luminous and less energetic flares from 2013 Aug. and Nov., respectively (10 and 7 months before the pericenter of the DSO/G2). The decay of the faint flaring rate is difficult to explain by the tidal disruption of the DSO/G2, whose stellar nature is now well established, since it occurred well before its pericenter. Moreover, a mass transfer from the DSO/G2 to Sgr A* is not required to produce the rise in the bright flaring rate since the energy saved by the decay of the number of faint flares during a long time period may be later released by several bright flares during a shorter time period. (abridged)Comment: Accepted in A&A in 2017 April 2

XIPE: the X-ray Imaging Polarimetry Explorer

X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017 but not selected. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus and two additional GPDs filled with pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 % at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil).Comment: 49 pages, 14 figures, 6 tables. Paper published in Experimental Astronomy http://link.springer.com/journal/1068

Survival advantages conferred to colon cancer cells by E-selectin-induced activation of the PI3K-NFκB survival axis downstream of Death receptor-3

International audienceABSTRACT: BACKGROUND: Extravasation of circulating cancer cells is a key event of metastatic dissemination that is initiated by the adhesion of cancer cells to endothelial cells. It requires interactions between adhesion receptors on endothelial cells and their counter-receptors on cancer cells. Notably, E-selectin, a major endothelial adhesion receptor, interacts with Death receptor-3 present on metastatic colon carcinoma cells. This interaction confers metastatic properties to colon cancer cells by promoting the adhesion of cancer cells to endothelial cells and triggering the activation of the pro-migratory p38 and pro-survival ERK pathways in the cancer cells. In the present study, we investigated further the mechanisms by which the E-selectin-activated pathways downstream of DR3 confer a survival advantage to colon cancer cells. METHODS: Cell survival has been ascertained by using the WST-1 assay and by evaluating the activation of the PI3 kinase/NFκB survival axis. Apoptosis has been assayed by determining DNA fragmentation by Hoechst staining and by measuring cleavage of caspases-8 and -3. DR3 isoforms have been identified by PCR. For more precise quantification, targeted PCR reactions were carried out, and the amplified products were analyzed by automated chip-based microcapillary electrophoresis on an Agilent 2100 Bioanalyzer instrument. RESULTS: Interaction between DR3-expressing HT29 colon carcinoma cells and E-selectin induces the activation of the PI3K/Akt pathway. Moreover, p65/RelA, the anti-apoptotic subunit of NFκB, is rapidly translocated to the nucleus in response to E-selectin. This translocation is impaired by the PI3K inhibitor LY294002. Furthermore, inhibition of the PI3K/Akt pathway increases the cleavage of caspase 8 in colon cancer cells treated with E-selectin and this effect is still further increased when both ERK and PI3K pathways are concomitantly inhibited. Intriguingly, metastatic colon cancer cell lines such as HT29 and SW620 express higher levels of a splice variant of DR3 that has no trans-membrane domain and no death domain. CONCLUSION: Colon cancer cells acquire an increased capacity to survive via the activation of the PI3K/NFκB pathway following the stimulation of DR3 by E-selectin. Generation of a DR3 splice variant devoid of death domain can further contribute to protect against apoptosis