The TeV gamma-ray point source HESS J1832−093 remains unidentified despite extensive multiwavelength studies. The gamma-ray emission could originate in a very compact pulsar wind nebula or an X-ray ...binary system composed of the X-ray source XMMU J183245−0921539, and a companion star (2MASS J18324516−0921545). To unveil the nature of XMMU J183245−0921539 and its relation to HESS J1832−093, we performed deeper follow-up observations in X-rays with Chandra and Swift to improve source localization and to investigate time variability. We observed an increase of the X-ray flux by a factor of ∼6 in the Chandra data compared to previous observations. The source is point-like for Chandra and its updated position is only 0.3 arcsec offset from 2MASS J18324516−0921545, confirming the association with this infrared source. Subsequent Swift target of opportunity observations resulted in a lower flux, again compatible with the one previously measured with XMM–Newton, indicating a variability time-scale of the order of two months or shorter. The now-established association of XMMU J183245−0921539 and 2MASS J18324516−0921545, and the observed variability in X-rays are strong evidence for binary nature of HESS J1832−093. Furthermore, observations to characterize the optical counterpart as well as to search for orbital periodicity are needed to confirm this scenario.
Terzan 5 is the only Galactic globular cluster that has plausibly been detected at very high energies by the High Energy Stereoscopic System. It has an unexpectedly asymmetric very high energy ...morphology that is offset from the cluster center, in addition to a large-scale, offset radio structure and compact diffuse X-ray emission associated with this cluster. We present new data from the Fermi Large Area Telescope on this source. We model the updated broadband spectral energy distribution, attributing this to cumulative pulsed emission from a population of embedded millisecond pulsars, as well as unpulsed emission from the interaction of their leptonic winds with the ambient magnetic and soft-photon fields. In particular, our model invokes unpulsed synchrotron and inverse Compton components to model the radio and TeV data and cumulative pulsed curvature radiation to fit the Fermi data, and it explains the hard Chandra X-ray spectrum via a "new" cumulative synchrotron component from electron-positron pairs within the pulsar magnetospheres that has not been implemented before. We find reasonable spectral fits for plausible model parameters. We also derive constraints on the millisecond pulsar luminosity function using the diffuse X-ray data and the Chandra sensitivity. Future higher-quality spectral and spatial data will help discriminate between competing scenarios (such as dark matter annihilation, white dwarf winds, or hadronic interactions) proposed for the broadband emission, as well as constraining degenerate model parameters.
Context. Recently, diffuse and extended sources in TeV γ-rays as well as in X-rays have been detected in the direction of the Galactic globular cluster (GC) Terzan 5. Remarkably, this is among the ...brightest GCs detected in the GeV regime. The nature of either the TeV or the diffuse X-ray signal from Terzan 5 is not yet settled. These emissions most likely indicate the presence of several non-thermal radiation processes in addition to those that give rise to the GeV signal. Aims. The aim of this work is to search for diffuse X-ray emission from all GeV-detected GCs where appropriate X-ray observations are available, and to compare the obtained results with the signal detected from Terzan 5. This study will help to determine whether Terzan 5 stands out among other GC or whether a whole population of globular clusters feature similar properties. Methods. After assessing all archival X-ray observations of GeV detected GCs, we analyzed the data of six Chandra observations pointed toward M 62, NGC 6388, NGC 6541, M 28, M 80, and NGC 6139. For each GC we characterized the diffuse X-ray emission using the same analysis techniques as for Terzan 5. To study the emission on the same relative scales we used the half-mass radius as a scale parameter to determine the extent of the potential emission region. Results. None of the six GCs show significant diffuse X-ray emission above the particle and diffuse Galactic X-ray background components. The derived upper limits allow to assess the validity of different models that were discussed in the interpretation of the multi-wavelength data of Terzan 5. A scenario based on synchrotron emission from relativistic leptons provided by the millisecond pulsar population cannot be securely rejected if a comparable magnetic field strength as in Terzan 5 is assumed for every GC. However, such a scenario seems to be unlikely for NGC 6388, and M 62. An inverse-Compton scenario relying on the presence of a putative GRB remnant with the same properties as proposed for Terzan 5 can be ruled out for all six GCs. Finally, the assumption that each GC hosts a source with the same luminosity as in Terzan 5 is ruled out for all GCs but NGC 6139.
Aims. We analysed eight XMM-Newton observations toward the Small Magellanic Cloud (SMC), performed between October 2006 and June 2007, to investigate high mass X-ray binary systems. Methods. We ...produced images from the European Photon Imaging Cameras (EPIC) and extracted X-ray spectra and light curves in different energy bands from sources that yielded a sufficiently high number of counts for a detailed temporal and spectral analysis. To search for periodicity we applied Fourier transformations and folding techniques and determined pulse periods using a Bayesian approach. To identify optical counterparts we produced X-ray source lists for each observation using maximum likelihood source detection techniques and correlated them with optical catalogues. The correlations were also used for astrometric boresight corrections of the X-ray source positions. Results. We found new X-ray binary pulsars with periods of 202 s (XMMU J005929.0-723703), 342 s (XMMU J005403.8-722632), 645 s (XMMU J005535.2-722906) and 325 s (XMMU J005252.1-721715), in the latter case confirming the independent discovery in Chandra data. In addition we detected sixteen known Be/X-ray binary pulsars and six ROSAT-classified candidate high mass X-ray binaries. From one of the candidates, RX J0058.2-7231, we discovered X-ray pulsations with a period of 291 s which makes it the likely counterpart of XTE J0051-727. From the known pulsars, we revise the pulse period of CXOU J010206.6-714115 to 967 s, and we detected the 18.37 s pulsar XTE J0055-727 (=XMM J004911.4-724939) in outburst, which allowed us to localise the source. The pulse profiles of the X-ray pulsars show a wide variety of shapes from smooth to highly structured patterns and differing energy dependence. For all the candidate high mass X-ray binaries, optical counterparts can be identified with magnitudes and colours consistent with Be stars. Twenty of the Be/X-ray binaries were detected with X-ray luminosities in the range 1.5 $\times$ 1035–5.5 $\times$ 1036 erg s-1. The majority of the spectra is well represented by an absorbed power-law with an average power-law index of 0.93. The absorption (in addition to the Galactic foreground value) varies over a wide range between a few 1020 cm-2 and several 1022 cm-2. An overall correlation of the absorption with the total SMC H I column density suggests that the absorption seen in the X-ray spectra is often largely caused by interstellar gas.
Aims. Terzan 5 , a globular cluster (GC) prominent in mass and population of compact objects, is searched for diffuse X-ray emission, as proposed by several models. Methods. We analyzed the data of ...an archival Chandra observation of Terzan 5 to search for extended diffuse X-ray emission outside the half-mass radius of the GC. We removed detected point sources from the data to extract spectra from diffuse regions around Terzan 5. The Galactic background emission was modeled by a 2-temperature thermal component, which is typical for Galactic diffuse emission. Results. We detected significant diffuse excess emission above the particle background level from the whole field-of-view. The surface brightness appears to be peaked at the GC center and decreases smoothly outwards. After the subtraction of particle and Galactic background, the excess spectrum of the diffuse emission between the half-mass radius and 3' can be described by a power-law model with photon index Γ = 0.9 ± 0.5 and a surface flux of Fx = (1.17±0.16) × 10-7 erg cm-2 s-1 sr-1 in the 1–7 keV band. We estimated the contribution from unresolved point sources to the observed excess to be negligible. The observations suggest that a purely thermal origin of the emission is less likely than a non-thermal scenario. However, from simple modeling we cannot identify a clearly preferred scenario.
The unidentified very high energy (VHE, E > 100 GeV) gamma-ray source HESS J1507-622 seems to not fit into standard models for sources related to young supernova remnants, pulsar wind nebulae, or ...young stellar populations in general. This is due to its intrinsically extended, but yet compact morphology, coupled with a relative large offset ( similar to 3.5 degree ) from the Galactic plane. Therefore, it has been suggested that this object may be the first representative of a new distinct class of extended off-plane gamma-ray sources. The distance to HESS J1507-622 is the key parameter to constrain the source's most important properties, such as age and energetics of the relativistic particle population. In this paper, we report on results of follow-up observations of the potential X-ray counterpart with Suzaku. We present detailed measurements of its spectral parameters and find a high-absorbing hydrogen column density, compatible with the total amount of Galactic gas in this direction. In comparisons to measurements and models of the Galactic 3D gas distribution, we show that the potential X-ray counterpart of HESS J1507-622 may be located at the far end of the Galaxy. If the gamma-ray source is indeed physically connected to this extended X-ray source, this in turn would place the object outside of the usual distribution of Galactic VHE gamma-ray emitters.
Pyruvic acid (CH3C(O)C(O)OH, 2-oxopropanoic acid) is an organic acid of
biogenic origin that plays a crucial role in plant metabolism, is present in
tropospheric air in both gas-phase and ...aerosol-phase, and is implicated in
the formation of secondary organic aerosols (SOAs). Up to now, only a few
field studies have reported mixing ratios of gas-phase pyruvic acid, and its
tropospheric sources and sinks are poorly constrained. We present the first
measurements of gas-phase pyruvic acid in the boreal forest as part of the
IBAIRN (Influence of Biosphere–Atmosphere Interactions on the
Reactive Nitrogen budget) field campaign in Hyytiälä, Finland, in
September 2016. The mean pyruvic acid mixing ratio during IBAIRN was 96 pptv, with a maximum value of 327 pptv. From our measurements we estimated
the overall pyruvic acid source strength and quantified the contributions of
isoprene oxidation and direct emissions from vegetation in this
monoterpene-dominated forested environment. Further, we discuss the
relevance of gas-phase pyruvic acid for atmospheric chemistry by
investigating the impact of its photolysis on acetaldehyde and peroxy
radical production rates. Our results show that, based on our present
understanding of its photochemistry, pyruvic acid is an important source of
acetaldehyde in the boreal environment, exceeding ethane and propane oxidation
by factors of ∼10 and ∼20.
Aims. We performed a spatially resolved spectral X-ray study of the pulsar wind nebula (PWN) in the supernova remnant G0.9+0.1. Furthermore, we modeled its nonthermal emission in the X-ray and very ...high-energy (VHE, E > 100 GeV) γ-ray regime. Methods. Using Chandra ACIS-S3 data, we investigated the east-west dependence of the spectral properties of G0.9+0.1 by calculating hardness ratios. We analyzed the EPIC-MOS and EPIC-pn data of two on-axis observations of the XMM-Newton telescope and extracted spectra of four annulus-shaped regions, centered on the region of brightest emission of the source. A radially symmetric leptonic model was applied in order to reproduce the observed X-ray emission of the inner part of the PWN. Using the optimized model parameter values obtained from the X-ray analysis, we then compared the modeled inverse Compton (IC) radiation with the published H.E.S.S. γ-ray data. Results. The spectral index within the four annuli increases with growing distance to the pulsar, whereas the surface brightness drops. With the adopted model we are able to reproduce the characteristics of the X-ray spectra. The model results for the VHE γ radiation, however, strongly deviate from the H.E.S.S. data.
Aims. To follow the long term evolution of Be/X-ray binaries in the Small Magellanic Cloud (SMC) we analyzed twenty-two XMM-Newton observations towards the calibration target 1E 0102.2-7218 and ...seven observations towards the neighboring region around the eclipsing binary HD 5980. Methods. The data from the European Photon Imaging Cameras (EPIC) were used to produce images, X-ray spectra and light curves in different energy bands. We performed a detailed spectral and temporal analysis on the data of all known Be/X-ray binary pulsars that have been detected with a sufficiently high number of counts. Fast Fourier Transformation (FFT) power spectra were produced to search for X-ray pulsations and to determine their significance. To derive accurate values for the pulse periods we utilized the Bayesian method. To identify or confirm the optical counterparts we derived the X-ray positions of the pulsars using maximum likelihood source detection techniques and correlated them with optical catalogues. Results. There are ten known Be/X-ray binaries located in the observed fields. In addition to the previously published results for three of these sources, we present long term X-ray light curves and pulse period histories for the following six pulsars: CXOU J005736.2-721934 (565 s), RX J0057.8-7207 (152 s), RX J0059.3-7223 (201 s), CXOU J010102.7-720658 (304 s), RX J0101.3-7211 (455 s), SAX J0103.2-7209 (345 s) and RX J0103.6-7201 (1323 s). We do not agree with the identification of the ROSAT source RX J0105.1-7211 = XMMU J010509.7-721146 as the 3.34 s ASCA pulsar AX J0105-722 and suggest that RX J0105.1-7211 is more likely a background AGN. We find soft excess emission around 1 keV in the X-ray spectra of two pulsars (SAX J0103.2-7209 and RX J0103.6-7201). The spin history in combination with the long term X-ray light-curve indicate a type II outburst of CXOU J010102.7-720658 at the end of 2005 and a reversal in the accretion disc torque in SAX J0103.2-7209 in May 2002. An X-ray ephemeris for the binary orbit was only available in the literature for CXOU J005736.2-721934 and is in good agreement with the observed XMM-Newton light-curve.
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