Development of the adjoint of GEOS-Chem

International audienceWe present the adjoint of the global chemical transport model GEOS-Chem, focusing on the chemical and thermodynamic relationships between sulfate ? ammonium ? nitrate aerosols and their gas-phase precursors. The adjoint model is constructed from a combination of manually and automatically derived discrete adjoint algorithms and numerical solutions to continuous adjoint equations. Explicit inclusion of the processes that govern secondary formation of inorganic aerosol is shown to afford efficient calculation of model sensitivities such as the dependence of sulfate and nitrate aerosol concentrations on emissions of SOx, NOx, and NH3. The accuracy of the adjoint model is extensively verified by comparing adjoint to finite difference sensitivities, which are shown to agree within acceptable tolerances. We explore the robustness of these results, noting how discontinuities in the advection routine hinder, but do not entirely preclude, the use of such comparisons for validation of the adjoint model. The potential for inverse modeling using the adjoint of GEOS-Chem is assessed in a data assimilation framework using simulated observations, demonstrating the feasibility of exploiting gas- and aerosol-phase measurements for optimizing emission inventories of aerosol precursors

CXOM31 J004253.1+411422: The first ultra-luminous X-ray transient in M 31

We seek clarification of the nature of X-ray sources detected in M 31. Here we focus on CXOM31 J004253.1+411422, the brightness of which suggests that it belongs to the class of ultraluminous X-ray sources. We determine the X-ray properties of sources detected in the XMM-Newton Chandra monitoring program. We investigate spectral properties and search for periodic or quasi-periodic oscillations. A multi-component model is applied to the spectra obtained from XMM-Newton data to evaluate the relative contributions from thermal and non-thermal emission. The time dependence of this ratio is evaluated over a period of forty days. We simultaneously fit data from XMM-Newton EPIC-pn, MOS1 and MOS2 detectors with (non-thermal) powerlaw and (thermal) multicolored blackbody. The X-ray spectrum is best fit by the combination of a thermal component with kT ~ 1 keV and a powerlaw component with photon index approximately 2.6. From combined analysis of Chandra, Swift and XMM-Newton data, the unabsorbed total luminosity of this source decreases from ~ 3.8 x 10^{39} erg s^{-1} in the first observation to ~ 0.5 x 10^{39} ergs s^{-1} over a period of three months. The decay closely follows an exponential decline with a time constant of 32 days. The source spectrum evolves significantly, exhibiting a faster decline of the thermal component. We do not find evidence of any significant temporal features in the power density spectrum. The presence of a thermal component at kT ~ 1 keV in conjunction with a non-thermal high energy tail, is also consistent with spectral properties of other ULXs in the "high state". Our analysis indicates that the underlying source of this first ULX in M~31 is a black hole of mass, M > 13 M_{sun}, accreting near the Eddington limit, that underwent a transient outburst followed by an exponential decay reminiscent of transients associated with galactic X-ray novae.Comment: Accepted by Astronomy and Astrophysics. 6 pages, 8 figure

A Transiting Jupiter Analog

Decadal-long radial velocity surveys have recently started to discover analogs to the most influential planet of our solar system, Jupiter. Detecting and characterizing these worlds is expected to shape our understanding of our uniqueness in the cosmos. Despite the great successes of recent transit surveys, Jupiter analogs represent a terra incognita, owing to the strong intrinsic bias of this method against long orbital periods. We here report on the first validated transiting Jupiter analog, Kepler-167e (KOI-490.02), discovered using Kepler archival photometry orbiting the K4-dwarf KIC-3239945. With a radius of $(0.91\pm0.02)$ $R_{\mathrm{Jup}}$, a low orbital eccentricity ($0.06_{-0.04}^{+0.10}$) and an equilibrium temperature of $(131\pm3)$ K, Kepler-167e bears many of the basic hallmarks of Jupiter. Kepler-167e is accompanied by three Super-Earths on compact orbits, which we also validate, leaving a large cavity of transiting worlds around the habitable-zone. With two transits and continuous photometric coverage, we are able to uniquely and precisely measure the orbital period of this post snow-line planet ($1071.2323\pm0.0006$ d), paving the way for follow-up of this $K=11.8$ mag target.Comment: 14 pages, 10 figures. Accepted to ApJ. Posteriors available at https://github.com/CoolWorlds/Kepler-167-Posterior

J004457+4123 (Sharov 21): not a remarkable nova in M31 but a background quasar with a spectacular UV flare

We announce the discovery of a quasar behind the disk of M31, which was previously classified as a remarkable nova in our neighbour galaxy. The paper is primarily aimed at the outburst of J004457+4123 (Sharov 21), with the first part focussed on the optical spectroscopy and the improvement in the photometric database. Both the optical spectrum and the broad band spectral energy distribution of Sharov 21 are shown to be very similar to that of normal, radio-quiet type 1 quasars. We present photometric data covering more than a century and resulting in a long-term light curve that is densely sampled over the past five decades. The variability of the quasar is characterized by a ground state with typical fluctuation amplitudes of ~0.2 mag around B~20.5, superimposed by a singular flare of ~2 yr duration (observer frame) with the maximum at 1992.81 where the UV flux has increased by a factor of ~20. The total energy in the flare is at least three orders of magnitudes higher than the radiated energy of the most luminous supernovae, provided that it comes from an intrinsic process and the energy is radiated isotropically. The profile of the flare light curve appears to be in agreement with the standard predictions for a stellar tidal disruption event where a ~10 M_sun giant star was shredded in the tidal field of a ~2...5 10^8 M_sun black hole. The short fallback time derived from the light curve requires an ultra-close encounter where the pericentre of the stellar orbit is deep within the tidal disruption radius. Gravitational microlensing provides an alternative explanation, though the probability of such a high amplification event is very low.Comment: Accepted for publication in Astronomy and Astrophysics, 14 pages, 11 figure

Recent discoveries of supersoft X-ray sources in M 31

Classical novae (CNe) have recently been reported to represent the major class of supersoft X-ray sources (SSSs) in the central area of our neighbouring galaxy M 31. This paper presents a review of results from recent X-ray observations of M 31 with XMM-Newton and Chandra. We carried out a dedicated optical and X-ray monitoring program of CNe and SSSs in the central area of M 31. We discovered the first SSSs in M 31 globular clusters (GCs) and their connection to the very first discovered CN in a M 31 GC. This result may have an impact on the CN rate in GCs. Furthermore, in our optical and X-ray monitoring data we discovered the CN M31N 2007-11a, which shows a very short SSS phase of 29 - 52 days. Short SSS states (durations < 100 days) of CNe indicate massive white dwarfs (WDs) that are candidate progenitors of supernovae type Ia. In the case of M31N 2007-11a, the optical and X-ray light curves suggest a binary containing a WD with M_WD > 1.0 M_sun. Finally, we present the discovery of the SSS counterpart of the CN M31N 2006-04a. The X-ray light curve of M31N 2006-04a shows short-time variability, which might indicate an orbital period of about 2 hours.Comment: 4 pages, 1 figure; Proc. of workshop "Supersoft X-ray Sources - New Developments", ESAC, May 2009; accepted for publication in Astronomische Nachrichte

X-ray monitoring of classical novae in the central region of M 31. II. Autumn and winter 2007/2008 and 2008/2009

[Abridged] Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. We performed a dedicated monitoring of the M 31 central region with XMM-Newton and Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009 respectively, in order to find SSS counterparts of CNe, determine the duration of their SSS phase and derive physical outburst parameters. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and spectral properties. We detected in total 17 X-ray counterparts of CNe in M 31, only four of which were known previously. These latter sources are still active 12.5, 11.0, 7.4 and 4.8 years after the optical outburst. From the 17 X-ray counterparts 13 were classified as SSSs. Four novae displayed short SSS phases (< 100 d). Based on these results and previous studies we compiled a catalogue of all novae with SSS counterparts in M 31 known so far. We used this catalogue to derive correlations between the following X-ray and optical nova parameters: turn-on time, turn-off time, effective temperature (X-ray), t2 decay time and expansion velocity of the ejected envelope (optical). Furthermore, we found a first hint for the existence of a difference between SSS parameters of novae associated with the stellar populations of the M 31 bulge and disk. Additionally, we conducted a Monte Carlo Markov Chain simulation on the intrinsic fraction of novae with SSS phase. This simulation showed that the relatively high fraction of novae without detected SSS emission might be explained by the inevitably incomplete coverage with X-ray observations in combination with a large fraction of novae with short SSS states, as expected from the WD mass distribution. In order to verify our results with an increased sample further monitoring observations are needed.Comment: 31 pages, 23 figures, 10 tables; submitted to A&

Deep XMM-Newton observations of the northern disc of M31. I. Source catalogue

We carried out new observations of two fields in the northern ring of M31 with XMM-Newton with two exposures of 100 ks each and obtained a complete list of X-ray sources down to a sensitivity limit of ~7 x 10^34 erg s^-1 (0.5 - 2.0 keV). The major objective of the observing programme was the study of the hot phase of the ISM in M31. The analysis of the diffuse emission and the study of the ISM is presented in a separate paper. We analysed the spectral properties of all detected sources using hardness ratios and spectra if the statistics were high enough. We also checked for variability. We cross-correlated the source list with the source catalogue of a new survey of the northern disc of M31 carried out with Chandra and Hubble (Panchromatic Hubble Andromeda Treasury, PHAT) as well as with other existing catalogues. We detected a total of 389 sources, including 43 foreground stars and candidates and 50 background sources. Based on the comparison to the Chandra/PHAT survey, we classify 24 hard X-ray sources as new candidates for X-ray binaries (XRBs). In total, we identified 34 XRBs and candidates and 18 supernova remnants (SNRs) and candidates. Three of the four brightest SNRs show emission mainly below 2 keV, consistent with shocked ISM. The spectra of two of them also require an additional component with a higher temperature. The SNR [SPH11] 1535 has a harder spectrum and might suggest that there is a pulsar-wind nebula inside the SNR. We find five new sources showing clear time variability. We also studied the spectral properties of the transient source SWIFT J004420.1+413702, which shows significant variation in flux over a period of seven months (June 2015 to January 2016) and associated change in absorption. Based on the likely optical counterpart detected in the Chandra/PHAT survey, the source is classified as a low-mass X-ray binary.Comment: Accepted for publication in A&

Effect of epiretinal electrical stimulation on the glial cells in a rabbit retinal eyecup model

IntroductionWe examined how pulse train electrical stimulation of the inner surface of the rabbit retina effected the resident glial cells. We used a rabbit retinal eyecup preparation model, transparent stimulus electrodes, and optical coherence tomography (OCT). The endfeet of Müller glia processes line the inner limiting membrane (ILM).MethodsTo examine how epiretinal electrode stimulation affected the Müller glia, we labeled them post stimulation using antibodies against soluble glutamine synthetase (GS). After 5 min 50 Hz pulse train stimulation 30 μm from the surface, the retina was fixed, immunostained for Müller glia, and examined using confocal microscopic reconstruction. Stimulus pulse charge densities between 133–749 μC/cm2/ph were examined.ResultsHigh charge density stimulation (442–749 μC/cm2/ph) caused significant losses in the GS immunofluorescence of the Müller glia endfeet under the electrode. This loss of immunofluorescence was correlated with stimuli causing ILM detachment when measured using OCT. Müller cells show potassium conductances at rest that are blocked by barium ions. Using 30 msec 20 μA stimulus current pulses across the eyecup, the change in transretinal resistance was examined by adding barium to the Ringer. Barium caused little change in the transretinal resistance, suggesting under low charge density stimulus pulse conditions, the Müller cell radial conductance pathway for these stimulus currents was small. To examine how epiretinal electrode stimulation affected the microglia, we used lectin staining 0–4 h post stimulation. After stimulation at high charge densities 749 μC/cm2/ph, the microglia under the electrode appeared rounded, while the local microglia outside the electrode responded to the stimulated retina by process orientation inwards in a ring by 30 min post stimulation.DiscussionOur study of glial cells in a rabbit eyecup model using transparent electrode imaging suggests that epiretinal electrical stimulation at high pulse charge densities, can injure the Müller and microglia cells lining the inner retinal surface in addition to ganglion cells

Long-term palliation of right-sided congestive heart failure after stenting a recurrent cor triatriatum dexter in a 10½-year-old pug

A 10½-year-old, male neutered, pug presented with increasing ascites over two months. Echocardiography revealed cor triatriatum dexter with no concurrent cardiovascular anomalies, subsequently confirmed by computed tomography angiography. Balloon dilation of the perforated intra-atrial membrane under fluoroscopic guidance resulted in the transient resolution of all clinical abnormalities, but six months later stenosis and ascites recurred. After repeated balloon dilation, a stent was placed across the membrane. The dog remains asymptomatic fourteen months after the second procedure. One noteworthy feature of this case is the onset of congestive heart failure due to a congenital defect only at more than 10 years of age