Search

We showcase a tool suite that enables the fitting of soft X-ray spectra in active galactic nuclei (AGN), without the need for specialist software, allowing access to AGN physics for school students. While these standardised Python tools were useful for measuring velocities (Note I), they offered significantly fewer capabilities for radiative recombination continua (RRC), and R and G ratios, utilised to obtain the internal plasma properties within the out owing wind seen in NGC 4151. Although further work is required for these tools to be used in outreach projects, we present findings of the plasma temperature and density in NGC 4151 spanning a 15 year period., Comment: 3 pages, 1 figure

We present our analysis of the narrow emission lines produced in the plasma regions within the bright active galactic nucleus of NGC 4151, from an ORBYTS research-with-schools public engagement project. Our goal was to test whether the properties of these plasma regions changed between XMM- Newton observations spanning 15 years from 2000 to 2015, by measuring the outflow velocities and distances. From this study, we found that NGC 4151 has at least two to three plasma regions. There is no evidence of the outflowing wind properties changing as the velocities and distances are consistent throughout the observations., Comment: 1 Figure

Observations by the spacecraft Extreme Ultraviolet Explorer (EUVE), Far Ultraviolet Spectroscopic Explorer (FUSE), Chandra, and XMM-Newton of Capella (α Aurigae) have encountered problems with the relative intensities of the Fe xviii and Fe xix line emission in the soft-X-ray (XUV) and extreme-ultraviolet spectral ranges versus various model predictions based on theoretical atomic data. The reason may either lie in astrophysical phenomena, e.g., at emission or because of absorption by the interstellar medium, in the theoretical atomic data, in one or more spectrometer calibrations, or in the spectral modeling. By measurements using an electron beam ion trap we provide laboratory data obtained under conditions that are reasonably close to stellar emission regions. The laboratory data on Fe xviii and Fe xix show line ratios that are rather similar to the observations of Capella. The measurements, therefore, rule out astrophysical phenomena and calibration errors and point to issues with the modeling of the observed Capella emission.

The absorbed soft X-ray (N H = 1021−23 cm−2 may contain emission from star formation or scattered photons from the primary X-ray emission in Compton-thin circumnuclear gas extending out to ∼1 kpc, or leaky-absorbers along the line of sight allowing a part of the primary AGN emission to manifest in the soft X-rays. In a recent sample study of 20 Compton thin type-II AGN, Laha et al. detected variability in the soft X-ray spectra in 5 sources with timescales N H ∼ 0.7–1.3 × 1022 cm−2) in the sample.

The Dual-zone Aperture X-ray Solar Spectrometer (DAXSS) was flown on 2018 June18 on the NASA 36.336 sounding rocket flight and obtained the highest resolution to date for solar soft X-ray (SXR) spectra over a broad energy range. This observation was during a time with quiescent (non-flaring) small active regions on the solar disk and when the 10.7 cm radio flux (F10.7) was 75 solar flux units (1 sfu = 10-22 W/m^2/Hz). The DAXSS instrument consists of a LASP-developed dual-zone aperture and a commercial X-ray spectrometer from Amptek that measures solar full-disk irradiance from 0.5-20 keV with a resolving power of 20 near 1 keV. This paper discusses the novel design of the spectrometer and the instrument characterization techniques. Additionally,the solar measurements obtained from the 2018 sounding rocket flight are analyzed using CHIANTI spectral models to fit the temperatures, emission measures, and relative elemental abundances of the solar corona plasma. The abundance of iron was found to be 35 percent higher than expected in the quiescent sun's corona suggesting either that our spectral models require additional sophistication or that the underlying atomic database may require updates. Future long-term systematic observations of this spectral range are needed. DAXSS will fly on the INSPIRESat-1 CubeSat in late-2020, and its SXR spectral data could provide further insight into the sources of coronal heating through modeling the changes of relative elemental abundances during developments of active regions and solar flaring events., Comment: 21 pages, 12 figures, Submitted to The Astrophysical Journal

We report the discovery of soft X-ray pulsations from the nearby millisecond pulsar PSR J1231$-$1411 using NICER. The pulsed emission is characterized by a broad and asymmetric main pulse and a much fainter secondary interpulse, with a total pulsed count rate of 0.055 c s$^{-1}$ in the 0.35-1.5 keV band. We analyzed Fermi LAT data to update the pulse timing model covering 10 years of data and used that model to coherently combine NICER data over a year of observations. Spectral modeling suggests that the flux is dominated by thermal emission from a hot spot (or spots) on the neutron star surface. The phase relationship between the X-ray pulse and the radio and $\gamma$ rays provides insight into the geometry of the system., Comment: ApJ Letters, in press

It has long been shown that the extreme ultraviolet spectrum of the ionizing stars of H II regions can be estimated by comparing the observed line emission to detailed models. In the Galactic Center (GC), however, previous observations have shown that the ionizing spectral energy distribution (SED) of the local photon field is strange, producing both very low excitation ionized gas (indicative of ionization by late O stars) and also widespread diffuse emission from atoms too highly ionized to be found in normal H II regions. This paper describes the analysis of all the GC spectra taken by Spitzer's Infrared Spectrograph and downloaded from the Spitzer Heritage Archive. In it, H II region densities and abundances are described, and serendipitously discovered candidate planetary nebulae, compact shocks, and candidate young stellar objects are tabulated. Models were computed with Cloudy, using SEDs from Starburst99 plus additional X-rays, and compared to the observed mid-infrared forbidden and recombination lines. The ages inferred from the model fits do not agree with recent proposed star formation sequences (star formation in the GC occurring along streams of gas with density enhancements caused by close encounters with the black hole, Sgr A*), with Sgr~B1, Sgr~C, and the Arches Cluster being all about the same age, around 4.5 Myr old, with similar X-ray requirements. The fits for the Quintuplet Cluster appear to give a younger age, but that could be caused by higher-energy photons from shocks from stellar winds or from a supernova., 41 pages, 13 figures, 13 tables, published in The Astrophysical Journal. See the Erratum (2019, ApJ, 870, 140) for access to the data and revised tables

A time series of soft X-ray emission observed on 1974-2007 years (GOES) is analyzed. We show that in the periods of high solar activity 1977-1981, 1988-1992, 1999-2003 the energy statistics of soft X-ray solar flares for class M and C is well described by a FARIMA time series with Pareto innovations. The model is characterized by two effects. One of them is a long-range dependence (long-term memory), and another corresponds to heavy-tailed distributions. Their parameters are statistically stable enough during the periods. However, when the solar activity tends to minimum, they change essentially. We discuss possible causes of this evolution and suggest a statistical model for predicting the flare energy statistics., Comment: 21 pages, 7 figures

Coronal structure of active regions appearing in coronal holes is studied by using the data obtained with the Soft X-Ray Telescope (SXT) aboard {\it Yohkoh} from 1991 November to 1993 March. The following characteristics are found; Many of active regions appearing in coronal holes show a structure that looks like a ``sea-anemone''. Such active regions are called {\it anemone ARs}. About one-forth of all active regions that were observed with SXT from their births showed the anemone structure. For almost all the anemone ARs, the order of magnetic polarities is consistent with the Hale-Nicholson's polarity law. These anemone ARs also showed more or less east-west asymmetry in X-ray intensity distribution, such that the following (eastern) part of the ARs is brighter than its preceding (western) part. This, as well as the anemone shape itself, is consistent with the magnetic polarity distribution around the anemone ARs. These observations also suggest that an active region appearing in coronal holes has simpler (less sheared) and more preceding-spot-dominant magnetic structure than those appearing in other regions., Comment: 11 pages, 3 tables, 4 figures

It is been known for more than a decade that BALQSOs (broad absorption line quasars) are highly attenuated in the X-ray regime compared to other quasars, especially in the soft band ($< $ 1 keV). Using X-ray selection techniques we have found "soft X-ray loud" BALQSOs that, by definition, have soft X-ray (0.3 keV) to UV ($3000 ��$) flux density ratios that are higher than typical nonBAL radio quiet quasars. Our sample of 3 sources includes one LoBALQSO (low ionization BALQSO) which are generally considered to be the most highly attenuated in the X-rays. The three QSOs are the only known BALQSOs that have X-ray observations that are consistent with no intrinsic soft X-ray absorption. The existence of a large X-ray luminosity and the hard ionizing continuum that it presents to potential UV absorption gas is in conflict with the ionization states that are conducive to line driving forces within BAL winds (especially for the LoBALs)., To appear in ApJ Letters

Recent simulations of solar active regions have shown that it is possible to reproduce both the total intensity and the general morphology of the high temperature emission observed at soft X-ray wavelengths using static heating models. There is ample observational evidence, however, that the solar corona is highly variable, indicating a significant role for dynamical processes in coronal heating. Because they are computationally demanding, full hydrodynamic simulations of solar active regions have not been considered previously. In this paper we make first application of an impulsive heating model to the simulation of an entire active region, AR8156 observed on 1998 February 16. We model this region by coupling potential field extrapolations to full solutions of the time-dependent hydrodynamic loop equations. To make the problem more tractable we begin with a static heating model that reproduces the emission observed in 4 different \textit{Yohkoh} Soft X-Ray Telescope (SXT) filters and consider dynamical heating scenarios that yield time-averaged SXT intensities that are consistent with the static case. We find that it is possible to reproduce the total observed soft X-ray emission in all of the SXT filters with a dynamical heating model, indicating that nanoflare heating is consistent with the observational properties of the high temperature solar corona.

We report the results of Chandra and XMM-Newton observations of a new outburst of an ultra-luminous X-ray source in M101. During a Chandra monitoring observation of M101, M101 ULX-1 was found to be in outburst in 2004 December, the second outburst in 2004. The peak bolometric luminosity is about 3e40 erg/s (7e39 erg/s in 0.3-7 keV). The outburst spectra are very soft and can generally be fitted with a blackbody model with temperatures of 40-80 eV, similar to supersoft X-ray sources in the Milky Way and in the Magellanic Clouds. In one Chandra observation, the source spectrum appears to be harder with a temperature of 150 eV. Such a spectral state is rarely seen in M101 ULX-1 and no X-ray source in the Milky Way shows this kind of spectrum. However, such an unusual spectral state very likely belongs to a new class of X-ray sources, quasisoft X-ray sources, recently discovered in nearby galaxies. M101 ULX-1 returned to supersoft state in a subsequent XMM-Newton observation. Based on the two outbursts in 2004, the extremely high luminosity (L_bol=1e40-1e41 erg/s), very soft X-ray spectra (kT=40-150 eV), transient behavior, and state transition provide strong evidence that M101 ULX-1 harbors an intermediate-mass black hole., 4 pages, 2 figures, accepted for publication in ApJL

A technique for investigating the temporal relationship between Hα filament eruptions and soft X-ray flux is presented. The method is fast, simple, based on statistical measures, and requires no a priori knowledge regarding the location of the filaments on the solar disk. The method is used to study the filament eruption associated with a coronal mass ejection and the M-class flare that originated from NOAA Active Region 9163 on 2000 September 12. The technique provides a quantitative determination of the temporal relationship between changes in the Hα filament and soft X-ray flux. We conclude that the filament eruption begins 2 hr prior to the first detectable enhancement in soft X-ray flux.

Direct correlations and a Principal Component Analysis (PCA) are presented for a complete sample of 110 soft X-ray selected AGN of which about half are Narrow-Line Seyfert 1 galaxies (NLS1s). The direct correlation analyses show that narrower FWHM(H-beta) correlates with steeper X-ray spectrum, stronger optical FeII emission, weaker [OIII] emission and stronger short-term X-ray variability. This direct correlation analysis and the PCA confirm the Boroson & Green (1992) Eigenvector 1 relationship for AGN: FeII strength anti-correlates with [OIII] line strength. Eigenvector 1 is well-correlated with the Eddington luminosity ratio L/L_Edd while Eigenvector 2 shows a very good correlation with the mass of the central black hole and the mass accretion rate. The Eddington ratio L/L_Edd correlates with the X-ray spectral index alpha-X and the black home mass anti-correlates with the X-ray variability chi^2/nu. The Eddington ration L/L_Edd may be interpreted as the age of an AGN: AGN with steep X-ray spectra, strong FeII, and weak [OIII] are AGN in an early phase of their evolution. In this hypothesis NLS1s are young AGN., Accepted for publication in AJ (April 2004), 21 pages, 13 figures

As part of a larger project to complete a comprehensive catalog of astrophysically relevant emission lines in support of new-generation X-ray observatories using the Lawrence Livermore electron beam ion traps EBIT-I and EBIT-II, we present observations of argon lines in the extreme-ultraviolet region. Our database includes wavelength measurements with standard errors, relative intensities, and line assignments for Ar IX-Ar XVI between 20 and 50 A. The experimental data are complemented with a full set of calculations using the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Despite differences in calculated and measured wavelengths, we find the calculated lines to be of great utility in analyzing our laboratory spectra. The calculated line intensities are generally sufficient to identify the strongest transitions in each charge state. We note, however, an underestimation by theory of the strength of the 3s → 2p lines relative to the 3d → 2p lines in Ar IX, Ar X, and Ar XI. The laboratory data are compared with Chandra observations of Procyon, resulting in the identification of an Ar IX line that was previously thought to be from S IX.

Active region coronal loop observations with broadband X-ray instruments have often been found to be consistent with the predictions of static loop models. Recent observations in the EUV, however, have discovered a class of active region loops that are difficult to reconcile with static loop models. In this paper, we take a comprehensive look at how coronal loops compare with static models. We select 67 loops with a large range of apex temperatures and half-lengths observed with either the Transition Region and Coronal Explorer or the Soft X-Ray Telescope. We compare these observations to static loop models using both uniform and nonuniform heating. We find that only 2 of the 67 loops are fully consistent with static solutions with uniform heating and a filling factor of unity. We further find that long, cool ( 3 MK) loops are as much as 63 times underdense when compared to the static solutions with uniform heating. We then consider the possibility that the disparity in the density could be due to steady, nonuniform heating along the loop and find that footpoint heating can increase densities only by a factor of 3 over density solutions with uniform heating while loop-top heating results in density solutions that are, at most, a factor of 2.5 smaller than the density solutions with uniform heating. Only 19 of the 67 loops in this data set could be fully consistent with hydrodynamic solutions with steady heating. Hence, we conclude that static loop models are poor representations of most active region loops.

We present results on the spectroscopic analysis of XMM-Newton EPIC data of the central 0.5/h_50 Mpc regions of the clusters of galaxies Coma, A1795 and A3112. The temperature of the hot intracluster gas as determined by modeling the 2 - 7 keV PN and MOS data is consistent with that inferred from the FeXXV-FeXXVI line ratio. A significant warm emission component at a level above the systematic uncertainties is evident in the data and confirmed by ROSAT PSPC data for Coma and A1795. The non-thermal origin of the phenomenon cannot be ruled out at the current level of calibration accuracy, but the thermal model fits the data significantly better, with temperatures in the range of 0.6 -- 1.3 keV and electron densities of the order of 10^{-4} -- 10^{-3} cm^{-3}. In the outer parts of the clusters the properties of the warm component are marginally consistent with the results of recent cosmological simulations, which predict a large fraction of the current epoch's bayons located in a warm-hot intergalactic medium (WHIM). However, the derived densities are too high in the cluster cores, compared to WHIM simulations, and thus more theoretical work is needed to fully understand the origin of the observed soft X-ray excess., ApJ in press, 14 pages, 4 color figures WHIM discussion modified

We present a study of the X-ray properties of a volume-limited sample of optically selected emission-line galaxies. The sample is derived from a correlation between the KPNO International Spectroscopic Survey (KISS), an H-alpha-selected objective-prism survey of AGNs and starbursting galaxies, and the ROSAT All-Sky Survey (RASS). After elimination of all spurious matches, we identify 18 ROSAT-detected X-ray sources within the KISS sample in the 0.1-2.4 keV band. Due to soft X-ray selection effects, the majority of the ROSAT sources are Seyfert 1 galaxies. The majority (54%) of the ROSAT-KISS Seyferts are classified as narrow-line Seyfert 1 objects, a relatively high percentage compared to previous objective-prism-selected Seyfert galaxy samples. We estimate the X-ray luminosities of the ROSAT-detected KISS objects and derive volume emissivities of 6.63 x 10^38 ergs/s/Mpc^3 and 1.45 x 10^38 ergs/s/Mpc^3 for the 30 deg and 43 deg survey strips, respectively. For those KISS AGNs not detected by RASS, we use the median L_X/L_H-alpha ratio derived from a previous study to estimate L_X. The total 0.5-2 keV volume emissivity we predict for the overall KISS AGN sample is sufficient to account for 22.1 +/- 8.9% of the soft X-ray background (XRB), averaged over both survey strips. The KISS AGN sample is made up predominantly of intermediate-luminosity Seyfert 2's and LINERs, which tend to be weak soft X-ray sources. They may, however, represent a much more significant contribution to the hard XRB.

The study of soft X-ray emission of 38 X-ray selected galaxy clusters observed by ROSAT PSPC indicates that the soft excess phenomenon may be a common occurrence in galaxy clusters. Excess soft X-ray radiation, above the contribution from the hot intra-cluster medium, is evident in a large fraction of sources, and is clearly detected with large statistical significance in the deepest observations. The investigation relies on new, high resolution 21 cm HI observations. The sample selection also features analysis of infra-red images, to further ensure reliability of results with respect to the characteristics of Galactic absorption. The possibility of background or calibration effects as cause of the excess emission is likewise investigated; a detailed analysis of the distribution of the excess emission with respect to detector position and Galactic HI column density shows that the excess emission is a genuine celestial phenomenon. We find evidence for a preferential distribution of the soft excess emission at distances larger than ~150-200 kpc from the centers of clusters; this behavior may be naturally explained in the context of a non-thermal Inverse-Compton scenario. Alternatively, we propose that the phenomenon may be caused by thermal emission of very large-scale `warm' filaments seen in recent hydrodynamic simulations. This new interpretation relieves the very demanding requirements of either the traditional intra-cluster `warm' gas and the non-thermal scenarios. We also investigate the possibility of the soft excess originating from unresolved, X-ray faint cluster galaxies.

By combining Yohkoh soft X-ray images with high-resolution magnetograms simultaneously obtained at La Palma, we studied photospheric magnetic signatures responsible for soft X-ray microflares (active-region transient brightenings). In order to have a reliable correspondence between the photosphere and the corona, we studied 16 pointlike transient brightenings with X-ray source size less than 10'' occurring during periods when the seeing was excellent at La Palma, although a lot of transient brightenings were in forms of multiple- or single-loop structures. In half of the studied events, small-scale emergences of magnetic flux loops are found in the vicinity of the transient brightenings. Six events of that half show that a small-scale flux emergence accompanies the X-ray brightening 5-30 minutes prior to its onset. In the other half of the studied events, no apparent evolutionary change of magnetic flux elements is found associated with the transient brightenings. Many of these events are found in rather strong magnetic fields, such as sunspots and pores, implying that small-scale changes of magnetic flux are obscured or suppressed by strong magnetic fields. The horizontal plasma flows derived from local cross-correlation tracking of granules in continuum images are suppressed at the feet of some X-ray transient brightenings.

Using stellar luminosity functions derived from ROSAT data, the contributions of Galactic stars to the diffuse X-ray background are calculated for ROSAT PSPC energy bands. The model follows that of Guillout et al. (1996), but uses ROSAT rather than {\it Einstein} data to determine the intrinsic luminosity distributions. The model adequately predicts the numbers of stellar sources observed in deep ROSAT surveys. The contribution of unresolved stellar sources to the ROSAT All-Sky Survey at the Galactic poles is 6.85, 4.76, and 4.91 $\times$ counts s$^{-1}$ arcmin$^{-2}$ in bands R12 (1/4 keV), R45(3/4 keV), and R67(1.5 keV), respectively, which is equivalent to 4.66, 31.3 and 26.9 $\times10^{-14}$ ergs cm$^{-2}$ s$^{-1}$ deg$^{-2}$., 14 pages, 8 figures, accepted by ApJ

It is currently believed that the ``standard'' accretion disk theory under-predicts the observed X-ray luminosity from Soft X-ray Transients (SXT) in quiescence by as much as 4 to 6 orders of magnitude. This failure of the standard model is considered to be an important argument for the existence of the alternative mode of accretion -- Advection Dominated Accretion Flows (ADAF) in astrophysics, since these flows allow a much higher level of X-ray emission in quiescence, in agreement with the observations. Here we point out that, in stark contrast to steady-state standard disks, such disks in quiescence (being non-steady) produce most of the X-ray emission very far from the last stable orbit. Taking this into account, these disks can accommodate the observed X-ray luminosities of SXTs rather naturally. Our theory predicts that Fe K-alpha lines from standard accretion disks in quiescence should be narrow even though the cold disk goes all the way down to the last stable orbit., Version accepted by ApJ Letters. Please note the change in the Authors from the previous version: Prof. Svensson made a very substantial contribution to the paper through discussions and changes to the text [made after SN submitted the first version of the paper to ApJ and astro-ph]

Using observations from the Yohkoh Bragg Crystal Spectrometer (BCS), the Soft X-Ray Telescope, and the Hard X-Ray Telescope, we have examined the properties of 45 limb flares. Twenty-eight of the flares appear to have most or all of their footpoints occulted by the solar limb, leaving only soft X-ray emission from a looptop source visible. The remaining 17 flares have exposed footpoints. In most observational characteristics, occulted limb flares are indistinguishable from nonocculted limb flares. There does appear to be some evidence that the peak temperature observed in the BCS Ca XIX channel is lower by 2-3 MK in the occulted flares. We also see some tendency for the hard X-ray spectra averaged over the entire event to exhibit a softer spectral index in the occulted limb flares. Most of the flares for which it is possible to measure a peak in the Ca XIX nonthermal broadening velocity as a function of time show that the peak in the nonthermal broadening velocity occurs after the first significant hard X-ray peak.

We present ROSAT PSPC and HRI images of eight galaxies selected from a distance-limited sample of 22 edge-on Seyfert galaxies. Kiloparsec-scale soft X-ray nebulae extend along the galaxy minor axes in three galaxies (NGC 2992, NGC 4388 and NGC 5506). The extended X-ray emission has 0.2-2.4 keV X-ray luminosities of $0.4-3.5 \times 10^{40} erg s^{-1}$. The X-ray nebulae are roughly co-spatial with the large-scale radio emission, suggesting that both are produced by large-scale galactic outflows. Assuming pressure balance between the radio and X-ray plasmas, the X-ray filling factor is $\gapprox 10^4$ times larger than the radio plasma filling factor, suggesting that large-scale outflows in Seyfert galaxies are predominantly winds of thermal X-ray emitting gas. We favor an interpretation in which large-scale outflows originate as AGN-driven jets that entrain and heat gas on kpc scales as they make their way out of the galaxy. AGN- and starburst-driven winds are also possible explanations in cases where the winds are oriented along the rotation axis of the galaxy disk., Comment: 24 pages, 7 ps figures, AASTEX 4.0, accepted for ApJ April 1, 1998

The X-ray emission from the faintest X-ray elliptical and S0 galaxies is characterized by a hard ~5 keV component, and a very soft ~0.2 keV component. The hard component has generally been regarded as the integrated emission from low mass X-ray binaries (LMXBs), but the origin of the soft component is unknown. We present evidence which suggests that LMXBs also exhibit a soft component, which is responsible for the very soft X-ray emission in the faintest early-type galaxies. This soft component is present in two Galactic LMXBs which lie in directions of low Galactic hydrogen column densities, and in LMXBs in the bulge of M31, which comprise a majority of the X-ray emission in the bulge of that galaxy. The X-ray spectral characteristics and X-ray-to-blue luminosity ratios of the bulges of M31 and the Sa galaxy NGC 1291 are very similar to those of the X-ray faintest early-type galaxies, indicating that LMXBs are responsible for both soft and hard components in the latter. In addition, a low temperature interstellar medium might be present in some X-ray faint galaxies., (ApJ Letters, in press, 4 pages with 2 imbedded figures, Latex in the emulateapj style)

Recent X-ray studies have shown that supernova shock models are unable to satisfactorily explain X-ray emission in the rim of the Cygnus Loop. In an attempt to account for this anomalously enhanced X-ray flux, we fit the region with a model including theoretical charge exchange (CX) data along with shock and background X-ray models. The model includes the CX collisions of $O^{8+}$, $O{7+}$, $N^{7+}$, $N^{6+}$, $C^{6+}$, and $C^{5+}$ with H with an energy of 1 keV/u (438 km/s). The observations reveal a strong emission feature near 0.7 keV that cannot fully be accounted for by a shock model, nor the current CX data. Inclusion of CX, specifically $O^{7+} + H$, does provide for a statistically significant improvement over a pure shock model., Accepted for publication in ApJL, 5 pages, 4 figures, 1 table

The X-ray spectra of many active galactic nuclei (AGN) exhibit a `soft excess' below 1keV, whose physical origin remains unclear. Diverse models have been suggested to account for it, including ionised reflection of X-rays from the inner part of the accretion disc, ionised winds/absorbers, and Comptonisation. The ionised reflection model suggests a natural link between the prominence of the soft excess and the Compton reflection hump strength above 10keV, but it has not been clear what hard X-ray signatures, if any, are expected from the other soft X-ray candidate models. Additionally, it has not been possible up until recently to obtain high-quality simultaneous measurements of both soft and hard X-ray emission necessary to distinguish these models, but upcoming joint XMM-NuSTAR programmes provide precisely this opportunity. In this paper, we present an extensive analysis of simulations of XMM+NuSTAR observations, using two candidate soft excess models as inputs, to determine whether such campaigns can disambiguate between them by using hard and soft X-ray observations in tandem. The simulated spectra are fit with the simplest "observer's model" of a black body and neutral reflection to characterise the strength of the soft and hard excesses. A plot of the strength of the hard excess against the soft excess strength provides a diagnostic plot which allows the soft excess production mechanism to be determined in individual sources and samples using current state-of-the-art and next generation hard X-ray enabled observatories. This approach can be straightforwardly extended to other candidate models for the soft excess., 12 pages, 11 figures, accepted for publication in ApJ. Added references

We have discovered a bright (V ~ 14.5) cataclysmic variable during observations of the soft X-ray sources in the list of Singh et al. The optical source, which is coincident with the X-ray position of WGA J1802.1+1804, shows all the characteristics of a magnetic AM Herculis-type system: circular polarization, He II strength greater than Hβ, multiple line components, and a consistent photometric, polarimetric, spectroscopic, and X-ray period of 113 minutes. The X-ray spectrum shows a dominant soft blackbody (kT = 20-45 eV) and a weaker bremsstrahlung component (kT > 1 keV), while the circular polarization is relatively low (4% in the red).

The GOES M2-class solar flare, SOL2010-06-12T00:57, was modest in many respects yet exhibited remarkable acceleration of energetic particles. The flare produced an ~50 s impulsive burst of hard X- and \gamma-ray emission up to at least 400 MeV observed by the Fermi GBM and LAT experiments. The remarkably similar hard X-ray and high-energy \gamma-ray time profiles suggest that most of the particles were accelerated to energies >300 MeV with a delay of ~10 s from mildly relativistic electrons, but some reached these energies in as little as ~3 s. The \gamma-ray line fluence from this flare was about ten times higher than that typically observed from this modest GOES class of X-ray flare. There is no evidence for time-extended >100 MeV emission as has been found for other flares with high-energy \gamma rays., Comment: 27 pages, 7 figures. Corresponding Authors: M. S. Briggs, michael.briggs@nasa.gov; D. Gruber, dgruber@mpe.mpg.de; F. Longo, francesco.longo@trieste.infn.it; N. Omodei, nicola.omodei@gmail.com; G. H. Share, gerald.share@nrl.navy.mil

Nova GQ Muscae 1983 was detected by ROSAT as a luminous 'supersoft' X-ray source in 1992, nearly a decade after outburst. Further, this is the only classical postnova known to have maintained constant luminosity on a timescale predicted by theoretical models. Follow-up observations were made with the ROSAT position-sensitive proportional counter in 1993 January and September, and complemented with B-band photometry taken in 1993 January. By 1993 January, the X-ray count rate had declined by a factor of 17, while there was neither an appreciable decrease in the optical magnitude nor a change in the amplitude of modulation. In 1993 September the soft X-ray flux was below the ROSAT threshold limit, implying a decrease of a factor greater than or equal to 30 in the count rate. This decline can be interpreted by the turnoff of nuclear processes due to the complete consumption of the residual hydrogen-rich envelope. However, the optical luminosity of the system is not simply coupled to the X-ray luminosity (e.g., through reprocessing).