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  • Sasaki, M.  (7)
  • 2020-2024  (7)
  • 1
    Online Resource
    Online Resource
    SRG/eROSITA X-ray shadowing study of giant molecular clouds
    EDP Sciences ; 2023
    In:  Astronomy & Astrophysics Vol. 676 ( 2023-8), p. A3-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 676 ( 2023-8), p. A3-
    Abstract: Context. SRG/eROSITA is situated in a halo orbit around L2 where the highly variable solar wind charge exchange (SWCX) emission from Earth’s magnetosheath is expected to be negligible. The soft X-ray foreground emissions from the local hot bubble (LHB) and the remaining heliospheric SWCX emissions could be studied in unprecedented detail with eROSITA All-Sky Survey (eRASS) data in a 6-month cadence and better spectral resolution than ROSAT. Aims. We aim to use eRASS data of the sight lines towards three giant molecular clouds away from the Galactic plane to isolate and study the soft X-ray diffuse foreground emission. These X-ray shadows will serve as calibration baselines for the future three-dimensional structural study of the LHB. Methods. We conducted spectral analysis on the diffuse X-ray spectra of these clouds from the first four eRASSs to estimate and separate the heliospheric SWCX contribution from the LHB emission. Results. We find the density of the LHB to be independent of the sight line with n e ~ 4 × 10 −3 cm −3 , but not the temperature. We report a lower temperature of kT LHB = 0.084 ± 0.004 keV towards Chamaeleon II & III (Cha II & III) than Ophiuchus (Oph) and Corona Australis (CrA), in which we measured 0.102 ± 0.006 and 0.112 ± 0.009 keV, respectively. We measured the emission measure of the LHB to be ~2 × 10 −3 cm −6 pc at medium Galactic latitudes (| b | ~ 20°). A monotonic increase in the SWCX contribution has been observed since the start of 2020, coincidental with the beginning of solar cycle 25. For Oph, SWCX has dominated the LHB in the 0.3−0.7 keV band intensity since eRASS2. We observed lower SWCX contributions in Cha II & III and CrA, consistent with the expected decreasing solar wind ion density at high heliographic latitudes.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202345867
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 2
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    Abundance and temperature of the outer hot circumgalactic medium : The SRG/eROSITA view of the soft X-ray background in the eFEDS field
    EDP Sciences ; 2023
    In:  Astronomy & Astrophysics Vol. 674 ( 2023-6), p. A195-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 674 ( 2023-6), p. A195-
    Abstract: Context. Despite their vital importance to understanding galaxy evolution and our own Galactic ecosystem, our knowledge of the physical properties of the hot X-ray emitting phase of the Milky Way is still inadequate. However, sensitive SRG/eROSITA large area surveys are now providing us with the long-sought data needed to mend this state of affairs. Aims. Our aim is to constrain the properties of the Milky Way hot halo emission toward intermediate Galactic latitudes close to the Galactic anti-center. Methods. We analyzed the spectral properties of the integrated soft X-ray emission observed by eROSITA in the relatively deep eFEDS field. Results. We observe a flux of 12.6 and 5.1 × 10 −12 erg cm −2 s −1 deg −2 in the total (0.3–2) and soft (0.3–0.6 keV) band. We measure the temperature and metal (oxygen) abundance of the hot circumgalactic medium (CGM) to be within kT CGM = 0.153–0.178 keV and Z CGM = 0.052–0.072 Z ⊙ , depending on the contribution of solar wind charge exchange (SWCX). Slightly higher CGM abundances Z CGM = 0.05–0.10 Z ⊙ are possible, considering the uncertain extrapolation of the extragalactic cosmic X-ray background (CXB) emission below ~1 keV. To recover CGM abundances as high as Z CGM = 0.3 Z ⊙ , the presence of an additional component must be postulated, likely associated with the warm-hot intergalactic medium, providing ~15–20% of the flux in the soft X-ray band. We observe line widths of the CGM plasma smaller than Δ υ ≤ 500 km s −1 . The emission in the soft band is dominated (~47%) by the circumgalactic medium (CGM), whose contribution reduces to ~30% if heliospheric SWCX contributes at the level of ~15% also during solar minimum. The remaining flux is provided by the CXB (~33%) and the local hot bubble (~18%). Moreover, the eROSITA data require the presence of an additional component associated with the elusive Galactic corona plus a possible contribution from unresolved M dwarf stars. This component has a temperature of kT ~ 0.4– 0.7 keV, a considerable (~ kiloparsec) scale height, and might be out of thermal equilibrium. It contributes ~9% to the total emission in the 0.6—2 keV band, and is therefore a likely candidate to produce part of the unresolved CXB flux observed in X-ray ultra-deep fields. We also observe a significant contribution to the soft X-ray flux due to SWCX, during periods characterized by stronger solar wind activity, and causing the largest uncertainty on the determination of the CGM temperature. Conclusions. We constrain temperature, emission measure, abundances, thermal state, and spectral shape of the outer hot CGM of the Milky Way.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202243992
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 3
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    eROSITA calibration and performance verification phase: High-mass X-ray binaries in the Magellanic Clouds
    EDP Sciences ; 2022
    In:  Astronomy & Astrophysics Vol. 661 ( 2022-5), p. A25-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 661 ( 2022-5), p. A25-
    Abstract: Context. During its performance verification phase, the soft X-ray instrument eROSITA on board the Spektrum-Roentgen-Gamma (SRG) spacecraft observed large regions in the Magellanic Clouds in which almost 40 known high-mass X-ray binaries (HMXBs, including candidates) are located. Aims. We looked for new HMXBs in the eROSITA data, searched for pulsations in HMXB candidates, and investigated the long-term behaviour of the full sample using archival X-ray and optical data. Methods. For sufficiently bright sources, we performed a detailed spectral and temporal analysis of their eROSITA data. A source detection analysis of the eROSITA images in different energy bands provided count rates and upper limits for the remaining sources. Results. We report the discovery of a new Be/X-ray binary in the Large Magellanic Cloud. The transient SRGEt J052829.5–690345 was detected with a 0.2–8.0 keV luminosity of~10 35 erg s −1 . It exhibits a hard X-ray spectrum, typical for this class of HMXBs. The OGLE I -band light curve of the V~ 15.7mag counterpart shows large variations up to 0.75 mag, which occur with a quasi-period of~511 days. The eROSITA observations of the Small Magellanic Cloud covered 16 Be/X-ray binary pulsars, 5 of which were bright enough for an accurate determination of their current pulse period. The pulse periods for SXP 726 and SXP 1323 measured from eROSITA data are~800 s and~1006 s, respectively, which is very different from their discovery periods. Including archival XMM - Newton observations, we update the spin-period history of the two long-period pulsars, which have shown nearly linear trends in their period evolution for more than 15 yr. The corresponding average spin-down rate for SXP 726 is 4.3 s yr −1 , while SXP 1323 has a spin-up rate of –23.2 s yr −1 . We discuss the spin evolution of the two pulsars in the framework of quasi-spherical accretion.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202141878
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2022
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 4
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    Detection of large-scale X-ray bubbles in the Milky Way halo
    Springer Science and Business Media LLC ; 2020
    In:  Nature Vol. 588, No. 7837 ( 2020-12-10), p. 227-231
    Details
    In: Nature, Springer Science and Business Media LLC, Vol. 588, No. 7837 ( 2020-12-10), p. 227-231
    Type of Medium: Online Resource
    ISSN: 0028-0836 , 1476-4687
    URL: Article
    DOI: 10.1038/s41586-020-2979-0
    RVK:
    TA 1000
    RVK:
    UA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2020
    detail.hit.zdb_id: 120714-3
    detail.hit.zdb_id: 1413423-8
    SSG: 11
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  • 5
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    SN 1987A: Tracing the flux decline and spectral evolution through a comparison of SRG/eROSITA and XMM-Newton observations
    EDP Sciences ; 2022
    In:  Astronomy & Astrophysics Vol. 661 ( 2022-5), p. A30-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 661 ( 2022-5), p. A30-
    Abstract: Context. SN 1987A is the supernova closest to us observed in the past four centuries. It provides the unique opportunity of witnessing the birth and evolution of a supernova remnant. Monitoring the source in X-rays provides insights into the physics of the shock, the X-ray emitting plasma, and the interaction of the shock with the structures in the circumstellar medium. The source has been monitored by XMM-Newton EPIC-pn from 2007 to 2020. SRG/eROSITA also observed the source during its commissioning phase and first light in September and October 2019. Aims. We investigated the spectral and flux evolution of SN 1987A in X-rays in the last 14 yr up to November 2020 using XMM-Newton and eROSITA observations. Methods. We performed a detailed spectral analysis using a three-component plane-parallel shock model and analysed and modelled the EPIC-pn monitoring and eROSITA observations in a consistent manner. Results. This paper reports a complete and the most recent flux evolution of SN 1987A in the soft (0.5−2 keV) and hard (3−10 keV) X-ray band. The flux in the soft band flattened around 9424 days and then displayed a turnover between 10 142 and 10 493 days, after which it showed a continued decline. At about the same time, a break in the hard-band flux time evolution slope was detected. This implies that the blast wave has now passed beyond the dense structures of the equatorial ring and is expanding farther into more tenuous circumstellar medium. The temporal evolution of the normalisations of the three shock components match the results of hydrodynamical simulations well, which predict a blue supergiant progenitor scenario. The trend in recent epochs indicates that the emission caused by the forward shock after leaving the equatorial ring and by the reverse shock in the ejecta is now becoming more dominant. The elemental abundances in the hot plasma component are significantly higher than those in the cooler component, indicating an origin in the reverse shock that propagates into the ejecta.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202141104
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2022
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 6
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    Characterizing the patchy appearance of the circumgalactic medium and the influence of foreground absorption
    EDP Sciences ; 2023
    In:  Astronomy & Astrophysics Vol. 670 ( 2023-02), p. A99-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 670 ( 2023-02), p. A99-
    Abstract: Context. Recent studies have demonstrated that the emission from the circumgalactic medium displays a relatively high degree of patchiness on angular scales of ∼10°. Aims. Taking advantage of the Spectrum Roentgen Gamma eROSITA Final Equatorial Depth Survey, we aim to constrain any variation in the X-ray surface brightness on scales ranging from sub-degrees to a hundred square degrees. Result. The surface brightness in the soft X-ray band (0.3–0.45 keV) shows modulations of about 60% on scales of several degrees. The amplitude of such variations decreases at higher energies. The observed patchiness is stable over a period of two years, therefore excluding the possiblity that it could have been induced by solar wind charge exchange. We also observe no correlation between such an excess and the density of galaxies in the Local Universe, suggesting no strong contribution from the hot baryons in the filaments of the cosmic web. Instead, the soft X-ray emission is anti-correlated with the column density of absorbing material. Indeed, we can reproduce the spectrum of the bright and dark regions by simply varying the column density of the matter absorbing the emission components located beyond the Local Hot Bubble, while no modulation of the intrinsic emission is required. At high Galactic latitudes, the eROSITA all-sky map shows patchiness of the soft X-ray diffuse emission similar to the one observed in the eFEDS field; it is therefore likely that the same “absorption-modulation”is present over the entire sky. Conclusions. The observed patchiness of soft X-ray diffuse emission within the eFEDS field is primarily a consequence of absorption. Our spectral decomposition of the soft X-ray background appears accurate, predicting that (apart from the Local Hot Bubble) all other spectral components are modulated by clouds beyond ∼200 pc from the Sun. These results highlight the importance of an accurate treatment of the absorption effects in determining the patchiness of the circumgalactic medium.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202244430
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2023
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 7
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    The eROSITA X-ray telescope on SRG
    EDP Sciences ; 2021
    In:  Astronomy & Astrophysics Vol. 647 ( 2021-3), p. A1-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 647 ( 2021-3), p. A1-
    Abstract: eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the primary instrument on the Spectrum-Roentgen-Gamma (SRG) mission, which was successfully launched on July 13, 2019, from the Baikonour cosmodrome. After the commissioning of the instrument and a subsequent calibration and performance verification phase, eROSITA started a survey of the entire sky on December 13, 2019. By the end of 2023, eight complete scans of the celestial sphere will have been performed, each lasting six months. At the end of this program, the eROSITA all-sky survey in the soft X-ray band (0.2–2.3 keV) will be about 25 times more sensitive than the ROSAT All-Sky Survey, while in the hard band (2.3–8 keV) it will provide the first ever true imaging survey of the sky. The eROSITA design driving science is the detection of large samples of galaxy clusters up to redshifts z 〉 1 in order to study the large-scale structure of the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGNs, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars, and diffuse emission within the Galaxy. Results from early observations, some of which are presented here, confirm that the performance of the instrument is able to fulfil its scientific promise. With this paper, we aim to give a concise description of the instrument, its performance as measured on ground, its operation in space, and also the first results from in-orbit measurements.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202039313
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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