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  • 1
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    The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra
    American Astronomical Society ; 2020
    In:  The Astrophysical Journal Supplement Series Vol. 249, No. 1 ( 2020-07-01), p. 3-
    Details
    In: The Astrophysical Journal Supplement Series, American Astronomical Society, Vol. 249, No. 1 ( 2020-07-01), p. 3-
    Abstract: This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library “MaStar”). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17).
    Type of Medium: Online Resource
    ISSN: 0067-0049 , 1538-4365
    URL: Article
    DOI: 10.3847/1538-4365/ab929e
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2020
    detail.hit.zdb_id: 2006860-8
    detail.hit.zdb_id: 2207650-5
    SSG: 16,12
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  • 2
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    The eROSITA Final Equatorial-Depth Survey (eFEDS) : Identification and characterization of the counterparts to point-like sources
    EDP Sciences ; 2022
    In:  Astronomy & Astrophysics Vol. 661 ( 2022-5), p. A3-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 661 ( 2022-5), p. A3-
    Abstract: Context. In November 2019, eROSITA on board of the Spektrum-Roentgen-Gamma (SRG) observatory started to map the entire sky in X-rays. After the four-year survey program, it will reach a flux limit that is about 25 times deeper than ROSAT. During the SRG performance verification phase, eROSITA observed a contiguous 140 deg 2 area of the sky down to the final depth of the eROSITA all-sky survey (eROSITA Final Equatorial-Depth Survey; eFEDS), with the goal of obtaining a census of the X-ray emitting populations (stars, compact objects, galaxies, clusters of galaxies, and active galactic nuclei) that will be discovered over the entire sky. Aims. This paper presents the identification of the counterparts to the point sources detected in eFEDS in the main and hard samples and their multi-wavelength properties, including redshift. Methods. To identifyy the counterparts, we combined the results from two independent methods ( NWAY and ASTROMATCH ), trained on the multi-wavelength properties of a sample of 23k XMM-Newton sources detected in the DESI Legacy Imaging Survey DR8. Then spectroscopic redshifts and photometry from ancillary surveys were collated to compute photometric redshifts. Results. Of the eFEDS sources, 24 774 of 27 369 have reliable counterparts (90.5%) in the main sample and 231 of 246 sourcess (93.9%) have counterparts in the hard sample, including 2514 (3) sources for which a second counterpart is equally likely. By means of reliable spectra, Gaia parallaxes, and/or multi-wavelength properties, we have classified the reliable counterparts in both samples into Galactic (2695) and extragalactic sources (22 079). For about 340 of the extragalactic sources, we cannot rule out the possibility that they are unresolved clusters or belong to clusters. Inspection of the distributions of the X-ray sources in various optical/IR colour-magnitude spaces reveal a rich variety of diverse classes of objects. The photometric redshifts are most reliable within the KiDS/VIKING area, where deep near-infrared data are also available. Conclusions. This paper accompanies the eROSITA early data release of all the observations performed during the performance and verification phase. Together with the catalogues of primary and secondary counterparts to the main and hard samples of the eFEDS survey, this paper releases their multi-wavelength properties and redshifts.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202141631
    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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  • 3
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    Live to Die Another Day: The Rebrightening of AT 2018fyk as a Repeating Partial Tidal Disruption Event
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Letters Vol. 942, No. 2 ( 2023-01-01), p. L33-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 942, No. 2 ( 2023-01-01), p. L33-
    Abstract: Stars that interact with supermassive black holes (SMBHs) can be either completely or partially destroyed by tides. In a partial tidal disruption event (TDE), the high-density core of the star remains intact, and the low-density outer envelope of the star is stripped and feeds a luminous accretion episode. The TDE AT 2018fyk, with an inferred black hole mass of 10 7.7±0.4 M ⊙ , experienced an extreme dimming event at X-ray (factor of 〉 6000) and UV (factor of ∼15) wavelengths ∼500–600 days after discovery. Here we report on the reemergence of these emission components roughly 1200 days after discovery. We find that the source properties are similar to those of the predimming accretion state, suggesting that the accretion flow was rejuvenated to a similar state. We propose that a repeated partial TDE, where the partially disrupted star is on an ∼1200 day orbit about the SMBH and periodically stripped of mass during each pericenter passage, powers its unique light curve. This scenario provides a plausible explanation for AT 2018fyk’s overall properties, including the rapid dimming event and the rebrightening at late times. We also provide testable predictions for the behavior of the accretion flow in the future; if the second encounter was also a partial disruption, then we predict another strong dimming event around day 1800 (2023 August) and a subsequent rebrightening around day 2400 (2025 March). This source provides strong evidence of the partial disruption of a star by an SMBH.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ac9f36
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 2006858-X
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  • 4
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    X-ray emission from a rapidly accreting narrow-line Seyfert 1 galaxy at z = 6.56
    EDP Sciences ; 2023
    In:  Astronomy & Astrophysics Vol. 669 ( 2023-01), p. A127-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 669 ( 2023-01), p. A127-
    Abstract: Context. The space density of X-ray-luminous, blindly selected active galactic nuclei (AGN) traces the population of rapidly accreting super-massive black holes through cosmic time. It is encoded in the X-ray luminosity function, whose bright end remains poorly constrained in the first billion years after the Big Bang as X-ray surveys have thus far lacked the required cosmological volume. With the eROSITA Final Equatorial-Depth Survey (eFEDS), the largest contiguous and homogeneous X-ray survey to date, X-ray AGN population studies can now be extended to new regions of the luminosity–redshift space ( L 2 − 10 keV   〉  10 45  erg s −1 and z   〉  6). Aims. The current study aims at identifying luminous quasars at z   〉  5.7 among X-ray-selected sources in the eFEDS field in order to place a lower limit on black hole accretion well into the epoch of re-ionisation. A secondary goal is the characterisation of the physical properties of these extreme coronal emitters at high redshifts. Methods. Cross-matching eFEDS catalogue sources to optical counterparts from the DESI Legacy Imaging Surveys, we confirm the low significance detection with eROSITA of a previously known, optically faint z  = 6.56 quasar from the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs) survey. We obtained a pointed follow-up observation of the source with the Chandra X-ray telescope in order to confirm the low-significance eROSITA detection. Using new near-infrared spectroscopy, we derived the physical properties of the super-massive black hole. Finally, we used this detection to infer a lower limit on the black hole accretion density rate at z   〉  6. Results. The Chandra observation confirms the eFEDS source as the most distant blind X-ray detection to date. The derived X-ray luminosity is high with respect to the rest-frame optical emission of the quasar. With a narrow Mg II line, low derived black hole mass, and high Eddington ratio, as well as its steep photon index, the source shows properties that are similar to local narrow-line Seyfert 1 galaxies, which are thought to be powered by young super-massive black holes. In combination with a previous high-redshift quasar detection in the field, we show that quasars with L 2 − 10 keV   〉  10 45  erg s −1 dominate accretion onto super-massive black holes at z  ∼ 6.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202244688
    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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  • 5
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    The dependence of gamma-ray burst X-ray column densities on the model for Galactic hydrogen
    EDP Sciences ; 2016
    In:  Astronomy & Astrophysics Vol. 590 ( 2016-6), p. A82-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 590 ( 2016-6), p. A82-
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201628326
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2016
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 6
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    Repeating tidal disruptions in GSN 069: Long-term evolution and constraints on quasi-periodic eruptions’ models
    EDP Sciences ; 2023
    In:  Astronomy & Astrophysics Vol. 670 ( 2023-02), p. A93-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 670 ( 2023-02), p. A93-
    Abstract: Context. GSN 069 is the first galactic nucleus where quasi-periodic eruptions (QPEs) have been identified in December 2018. These are high-amplitude, soft X-ray bursts recurring every ∼9 h, lasting ∼1 h, and during which the X-ray count rate increases by up to two orders of magnitude with respect to an otherwise stable quiescent level. The X-ray spectral properties and the long-term evolution of GSN 069 in the first few years since its first X-ray detection in 2010 are consistent with a long-lived tidal disruption event (TDE). Aims. We aim to derive the properties of QPEs and of the long-term X-ray evolution in GSN 069 over the past 12 yr. Methods. We analyse timing and spectral X-ray data from 11 XMM-Newton , one Chandra , and 34 Swift observations of GSN 069 on timescales ranging from minutes to years. Results. QPEs in GSN 069 are a transient phenomenon with a lifetime of ≳1.05 yr. The QPE intensity and recurrence time oscillate and allow for alternating strong-weak QPEs and long-short recurrence times to be defined. In observations with QPEs, the quiescent level exhibits a quasi-periodic oscillation with a period equal to the average separation between consecutive QPEs. The QPE spectral evolution is consistent with thermal emission from a very compact region that heats up quickly and subsequently cools down via X-ray emission while expanding by a factor of ∼3 in radius. The long-term evolution of the quiescent level is characterised by two repeating TDEs ∼9 yr apart. We detect a precursor X-ray flare prior to the second TDE that may be associated with the circularisation phase during disc formation. A similar precursor flare is tentatively detected just before the first TDE. Conclusions. We provide a comprehensive summary of observational results that can be used to inform further theoretical and numerical studies on the origin of QPEs in GSN 069 and we discuss our results in terms of currently proposed QPE models. Future X-ray observations of GSN 069 promise that the QPE origin and the relation between QPEs and repeating TDEs in this galactic nucleus will be constrained, with consequences for the other sources where QPEs have been identified.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202244512
    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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    Tormund’s return: Hints of quasi-periodic eruption features from a recent optical tidal disruption event
    EDP Sciences ; 2023
    In:  Astronomy & Astrophysics Vol. 675 ( 2023-07), p. A152-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 675 ( 2023-07), p. A152-
    Abstract: Context. Quasi-periodic eruptions (QPEs) are repeating thermal X-ray bursts associated with accreting massive black holes, the precise underlying physical mechanisms of which are still unclear. Aims. We present a new candidate QPE source, AT 2019vcb (nicknamed Tormund by the Zwicky Transient Facility Collaboration), which was found during an archival search for QPEs in the XMM-Newton archive. It was first discovered in 2019 as an optical tidal disruption event (TDE) at z  = 0.088, and its X-ray follow-up exhibited QPE-like properties. Our goals are to verify its robustness as QPE candidate and to investigate its properties to improve our understanding of QPEs. Methods. We performed a detailed study of the X-ray spectral behaviour of this source over the course of the XMM-Newton archival observation. We also report on recent Swift and NICER follow-up observations to constrain the source’s current activity and overall lifetime, as well as an optical spectral follow-up. Results. The first two Swift detections and the first half of the 30 ks XMM-Newton exposure of Tormund displayed a decaying thermal emission typical of an X-ray TDE. However, the second half of the exposure showed a dramatic rise in temperature (from 53.5 −7.7 +9.2 eV to 113.8 −2.7 +2.9 eV) and 0.2–2 keV luminosity (from 3.2 −1.0 +1.6  × 10 42 erg s −1 to 1.19 −0.05 +0.05 × 10 44 erg s −1 ) over ∼15 ks. The late-time NICER follow-up indicates that the source is still X-ray bright more than three years after the initial optical TDE. Conclusions. Although only a rise phase was observed, Tormund’s strong similarities with a known QPE source (eRO-QPE1) and the impossibility to simultaneously account for all observational features with alternative interpretations allow us to classify Tormund as a candidate QPE. If confirmed as a QPE, it would further strengthen the observational link between TDEs and QPEs. It is also the first QPE candidate for which an associated optical TDE was directly observed, constraining the formation time of QPEs.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202346440
    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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  • 8
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    X-ray absorption towards high-redshift sources: probing the intergalactic medium with blazars
    EDP Sciences ; 2018
    In:  Astronomy & Astrophysics Vol. 616 ( 2018-8), p. A170-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 616 ( 2018-8), p. A170-
    Abstract: The role played by the intergalactic medium (IGM) in the X-ray absorption towards high-redshift sources has recently drawn more attention in spectral analysis studies. Here, we study the X-ray absorption towards 15 flat-spectrum radio quasars at z 〉 2, relying on high counting statistic (≳10 000 photons) provided by XMM-Newton , with additional NuSTAR (and simultaneous Swift -XRT) observations when available. Blazars can be confidently considered to have negligible X-ray absorption along the line of sight within the host galaxy, likely swept by the kpc-scale relativistic jet. This makes our sources ideal for testing the absorption component along the IGM. Our new approach is to revisit the origin of the soft X-ray spectral hardening observed in high- z blazars in terms of X-ray absorption occurring along the IGM, with the help of a low- z sample used as comparison. We have verified that the presence of absorption in excess of the Galactic value is the preferred explanation to explain the observed hardening, while intrinsic energy breaks, predicted by blazars’ emission models, can easily occur out of the observing energy band in most sources. First, we performed an indirect analysis comparing the inferred amount of absorption in excess of the Galactic value with a simulated IGM absorption contribution, that increases with redshift and includes both a minimum component from diffuse IGM metals, and the additional contribution of discrete denser intervening regions. Then, we directly investigated the warm-hot IGM with a spectral model on the best candidates of our sample, obtaining an average IGM density of n 0 = 1.01 −0.72 +0.53 × 10 −7 cm −3 and temperature of log( T /K) = 6.45 −2.12 +0.51 . A more dedicated study is currently beyond our reach, but our results can be used as a stepping stone for future more accurate analysis, involving Athena .
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201732322
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2018
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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  • 9
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    Alive and kicking: A new QPE phase in GSN 069 revealing a quiescent luminosity threshold for QPEs
    EDP Sciences ; 2023
    In:  Astronomy & Astrophysics Vol. 674 ( 2023-06), p. L1-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 674 ( 2023-06), p. L1-
    Abstract: X-ray quasi-periodic eruptions (QPEs) are intense repeating soft X-ray bursts from the nuclei of nearby galaxies. Their physical origin is still largely unconstrained, and several theoretical models have been proposed ranging from disc instabilities to impacts between an orbiting companion and the existing accretion disc around the primary, or episodic mass transfer at pericentre in an extreme mass-ratio binary. We present here results from a recent XMM-Newton observation of GSN 069, the galactic nucleus where QPEs were first discovered. After about two years of absence, QPEs have reappeared in GSN 069, and we detect two consecutive QPEs separated by a much shorter recurrence time than ever before. Moreover, their intensites and peak temperatures are remarkably different, a novel addition to the QPE phenomenology. We study the QPE spectral properties from all XMM-Newton observations assuming QPEs to either represent an additional emission component superimposed on that from the disc, or the transient evolution of the disc emission itself. In the former scenario, QPEs are consistent with black-body emission from a region that expands by a factor of 2–3 during the individual QPE evolution with radius ≃5 − 10 × 10 10 cm at QPE peak. In the alternative non-additive scenario, QPEs originate from a region with an area ∼6 − 30 times smaller than the quiescent state X-ray emission, with the smallest regions corresponding to the hottest and most luminous eruptions. The QPE reappearance reveals that eruptions are only present below a quiescent luminosity threshold corresponding to an Eddington ratio λ thresh  ≃ 0.4 ± 0.2 for a 10 6 M ⊙ black hole. The disappearance of QPEs above λ thresh is most likely driven by the ratio of QPE to quiescence temperatures, kT QPE / kT quiesc , approaching unity at high quiescent luminosity, making QPE detection challenging, if not impossible, above threshold. We briefly discuss some of the consequences of our results on the proposed models for the QPE physical origin.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202346653
    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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  • 10
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    The final SDSS-IV/SPIDERS X-ray point source spectroscopic catalogue
    EDP Sciences ; 2020
    In:  Astronomy & Astrophysics Vol. 636 ( 2020-04), p. A97-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 636 ( 2020-04), p. A97-
    Abstract: Aims. We look to provide a detailed description of the SPectroscopic IDentification of ERosita Sources (SPIDERS) survey, an SDSS-IV programme aimed at obtaining spectroscopic classification and redshift measurements for complete samples of sufficiently bright X-ray sources. Methods. We describe the SPIDERS X-ray Point Source Spectroscopic Catalogue, considering its store of 11 092 observed spectra drawn from a parent sample of 14 759 ROSAT and XMM sources over an area of 5129 deg 2 covered in SDSS-IV by the eBOSS survey. Results. This programme represents the largest systematic spectroscopic observation of an X-ray selected sample. A total of 10 970 (98.9%) of the observed objects are classified and 10 849 (97.8%) have secure redshifts. The majority of the spectra (10 070 objects) are active galactic nuclei (AGN), 522 are cluster galaxies, and 294 are stars. Conclusions. The observed AGN redshift distribution is in good agreement with simulations based on empirical models for AGN activation and duty cycle. Forming composite spectra of type 1 AGN as a function of the mass and accretion rate of their black holes reveals systematic differences in the H-beta emission line profiles. This study paves the way for systematic spectroscopic observations of sources that are potentially to be discovered in the upcoming eROSITA survey over a large section of the sky.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201937272
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2020
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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