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IMBOSS is an experiment based on X-ray microcalorimeters and aimed to perform a high spectral resolution all-sky survey. One of the primary scientific goals is the observation of the baryon “missing” matter at z<2. This is expected to be in the form of a warm-hot medium emitting in soft X-rays. We aim to detect and study the WHIM via X-ray emission lines. Another key goal is the detection of X-ray features in the prompt emission of GRBs, ultimately leading to a measurement of z for those class of GRBs still embedded in the mystery. Finally, a high-resolution spectroscopy survey will clarify the origin of the many components thought to make up the diffuse galactic X-ray emission. [Copyright &y& Elsevier]

We report on a systematic investigation of the cold and mildly ionized gaseous baryonic metal components of our Galaxy, through the analysis of high-resolution Chandra andXMM-Newton spectra of two samples of Galactic and extragalactic sources. The comparison between lines of sight towards sources located in the disc of our Galaxy and extragalactic sources allows us for the first time to clearly distinguish between gaseous metal components in the disc and halo of our Galaxy. We find that a warm ionized metal medium (WIMM) permeates a large volume above and below the Galaxy's disc, perhaps up to the circum-galactic space. This halo WIMM imprints virtually the totality of the OIand OII absorption seen in the spectra of our extragalactic targets, has a temperature of THalo WIMM = 2900 ± 900 K, a density (nH)Halo WIMM = 0.023 ± 0.009 cm-3 and a metallicity ZHalo WIMM = (0.4 ± 0.1) Z☉. Consistently with previous works, we also confirm that the disc of the Galaxy contains at least two distinct gaseous metal components, one cold and neutral (the CNMM: cold neutral metal medium) and onewarm and mildly ionized, with the same temperature of the halo WIMM, but higher density ((nH)DiscWIMM= 0.09 ± 0.03 cm-3) and metallicity (ZDiscWIMM = 0.8 ± 0.1 Z☉). By adopting a simple disc+sphere geometry for the Galaxy, we estimate masses of the CNMM and the total (disc + halo) WIMM of MCNMM ≲ 8 × 108 M☉ and MWIMM ≃ 8.2 × 109 M☉. [ABSTRACT FROM AUTHOR]

Context. Observations in the X-ray energy band are often limited by the background because of the low fluxes of typical sources. The background can easily be higher than the signal itself, and thus any mission with the scientific goal of observing faint and/or extended sources in the X-ray band must deal with the background problem. ESA has recently selected "the hot and energetic universe" as science theme for the second large-class mission in the Cosmic Vision science program, to be pursued with an advanced X-ray observatory to be launched in 2028, and at present ATHENA is the proposal that is most likely to be selected for this slot. The mission is aimed to place an X-ray telescope in the L2 orbit equipped with an X-ray Integral Field Unit (X-IFU) based on high spectral resolution transition-edge microcalorimeters, and has among its goals the detection and characterization of high-redshift active galactic nuclei (AGNs), cluster of galaxies and their outskirts, which is why great care must be taken to reduce the background impact on the detection/characterization of these sources. Aims. The background is composed of a diffuse component and an internal particle component for any satellite operating in the X-ray band. We take as reference the X-ray IFU instrument that will be placed onboard the ATHENA mission to analyze both these components and their variability for different orbits, observational conditions and/or design choices.We also show how different background levels affect the instrumental performance, and the scientific results obtainable with the instrument in the best configuration. The X-IFU is a cryogenic X-ray spectrometer, based on a large array of 3840 transition-edge sensors (TES) of 250 μm side, with a spectral energy resolution of 2.5 eV in the 0.2-10 keV energy band, over a field of view of 5 × 5 arcmin2, high count rate capability and a 5 arcsec angular resolution. Methods. There are no experimental data about the background experienced by microcalorimeters in the L2 orbit, and thus the particle background levels were calculated by means of Monte Carlo simulations: we considered the original design configuration and an improved configuration aimed to reduce the unrejected background, and tested them in the L2 orbit and in the low Earth orbit, comparing the results with experimental data reported by other X-ray instruments. For the diffuse component, we used the background levels measured from a 1 sr region representative of typical high galactic latitude pointings and analyzed the variations expected with the different orbital conditions. To show the results obtainable with the improved configuration we simulated the observation of a faint, high-redshift, point source (F[0.5-10 keV] ∼ 6.4 × 10-16 erg cm-2 s-1, z = 3.7), and of a hot galaxy cluster at R200 (Sb [0.5-2 keV] = 8.61 × 1016 erg cm-2 s-1 arcmin-2, T = 6.6 keV). Results. First we confirm that implementing an active cryogenic anticoincidence reduces the particle background by an order of magnitude and brings it close to the required level. The implementation and test of several design solutions can reduce the particle background level by a further factor of 6 with respect to the original configuration. The residual background is dominated by secondary particles, and this component can be decreased by design solutions such as passive shielding with appropriate materials. The best background level achievable in the L2 orbit with the implementation of ad-hoc passive shielding for secondary particles is similar to that measured in the more favorable LEO environment without the passive shielding, allowing us to exploit the advantages of the L2 orbit. We define a reference model for the diffuse background and collect all the available information on its variation with epoch and pointing direction. With this background level the ATHENA mission with the X-IFU instrument is able to detect ∼4100 new obscured AGNs with F > 6.4 × 1016 erg cm-2 s-1 during three years, to characterize cluster of galaxies with S b(0.5-2 keV) > 9.4 × 1016 erg cm-2 s-1 sr-1 on timescales of 50 ks (500 ks) with errors <∼40% (<∼12%) on metallicity, <∼16% (∼4.8%) on temperature, ∼2.6% (∼0.72%) on the gas density, and several single-element abundances. Conclusions. With respect to the original design the background level obtained significantly enhances the performance of the X-IFU. It allows us to improve the times needed for the detection and the characterization of high-redshift and/or faint Compton-thick AGNs and to reduce the limit flux of X-IFU, and thus to have a significant measurement of the fraction of these objects where current surveys are missing data. Moreover, the reduced background allows an improved characterization of diffuse and/or faint sources in terms of relative errors on the physical properties of the sources and observational times needed to obtain them. [ABSTRACT FROM AUTHOR]

BSTRACT [ABSTRACT FROM AUTHOR]

In this letter we present analysis of BeppoSAX data from a long look at the Seyfert 1 galaxy NGC 7469. The presence of a soft excess below 0.8 keV is confirmed by our analysis and no warm absorber component is required to fit the spectrum. A complex iron emission line and the Compton reflection hump are clearly detected. The profile of the line is too broad to associate this feature with distant matter. In addition, the observed soft excess and the energy of the iron line E[sub Fe] = 6.8 keV strongly support a scenario in which the hard X-rays are reprocessed by a photoionized accretion disc. This hypothesis was tested by fitting the BeppoSAX spectrum with the ionized disc reflection model of Ross & Fabian. A second narrow line component, in addition to that produced in the disc, is also required to fit the observed iron line profile. A high energy cut-off around 150 keV is clearly detected in the spectrum. [ABSTRACT FROM AUTHOR]

The results of a BeppoSAX target of opportunity (TOO) observation of the BL Lac object Mrk 421 during a high-intensity state are reported and compared with monitoring X-ray data collected with the BeppoSAX Wide Field Cameras (WFC) and the RXTE All Sky Monitor (ASM). The 0.1-100 keV spectmm of Mrk 421 shows continuous convex curvature that can be interpreted as the high-energy end of the synchrotron emission. The source shows significant short-term temporal and spectral variability, which can be interpreted in terms of synchrotron cooling. The comparison of our results with those of previous observations when the source was a factor 3-5 fainter shows evidence for strong spectral variability, with the maximum of the synchrotron power shifting to higher energy during high states. This behaviour suggests an increase in the number of energetic electrons during high states. [ABSTRACT FROM AUTHOR]

ABSTRACT Preliminary results from a BeppoSAX NFI observation of Mkn421 in a very bright state are reported together with monitoring data collected with the BeppoSAX-WFC and the RXTE-ASM. The BeppoSAX observation was carried out as part of a Target Of Opportunity program aimed at the study of AGN near record level intensity states. The comparison of our results with those of previous observations of Mkn421 shows clear evidence for strong spectral evolution. [ABSTRACT FROM AUTHOR]

ABSTRACT We present BeppoSAX broad band (0.1-200 keV) spectral results on a sample of bright Seyfert 1 galaxies, chosen to be representative of the class as a whole. The objects discussed ill this paper are: Fairall 9, NGC 5506, NGC 4593 and IC 4329A. In all of them a (broad) iron line and the Compton reflection continuum are clearly detected. In one of them (IC 4329A) a high energy cut-off with e-folding energy of 350 keV is also present. [ABSTRACT FROM AUTHOR]