The presence of large ionised gaseous nebulae found around some ultraluminous X-ray sources (ULXs) provides the means to assess the mechanical and radiative feedback of the central source, and hence constrain the efficiency and impact on the surroundings of the super-Eddington regime powering most of these sources. NGC 1313 X--1 is an archetypal ULX which has been reported to be surrounded by abnormally high [O I]$λ$6300/H$α>$ 0.1 ratios and for which high-resolution spectroscopy in X-rays has hinted the presence of powerful outflows. We report observations taken with the Multi-Unit Spectroscopic Explorer of NGC 1313 X--1 in order to confirm the presence of a nebula inflated by the winds, investigate its main sources of ionisation and estimate the mechanical output of the source. We detect a bubble of 452 $\times$ 266\,pc in size, roughly centred around the ULX, which shows clear evidence for shock ionisation in the outer edges. We estimate shock velocities to be in the $\approx160-180$\,km/s range based on the line ratios. This suggests that an average and continuous outflow power of $\sim(2-4.5) \times 10^{40}$ erg/s over a timescale of $(4.5-7.8) \times10^5$\,yr is required to inflate the bubble. In the interior of the bubble and closer to the ULX we detect an extended ($\sim$140\,pc) X-ray ionised region. Additionally, we detect two supernova remnants coincidentally close to the bubble of which we also report age and explosion energy estimates. The elongated morphology and the kinematics of the bubble strongly suggest that the bubble is being inflated by winds and/or jets emanating from the central source, supporting the presence of winds found through X-ray spectroscopy. The estimated mechanical power is comparable or higher than the X-ray luminosity of the source, providing additional evidence in support of NGC 1313 X--1 harbouring a super-Eddington accretor.
Most Ultraluminous X-ray sources (ULXs) are thought to be powered by super-Eddington accretion onto stellar-mass compact objects. Accretors in this extreme regime are naturally expected to ionise copious amounts of plasma in their vicinity and launch powerful radiation-driven outflows from their discs. High spectral resolution X-ray observations (with RGS gratings onboard XMM-Newton) of a few ULXs with the best datasets indeed found complex line spectra and confirmed such extreme (0.1-0.3c) winds. However, a search for plasma signatures in a large ULX sample with a rigorous technique has never…
We analysed data from five XMM-Newton observations of GX 13+1 to investigate the variability of the photo-ionised absorber present in this source. We fitted EPIC and RGS spectra obtained from the "least-variable" intervals with a model consisting of disc-blackbody and blackbody components together with a Gaussian emission feature at ~6.55-6.7 keV modified by absorption due to cold and photo-ionised material. We found a significant correlation between the hard, ~6-10 keV, flux, the ionisation and column density of the absorber and the equivalent width of the broad iron line. We interpret the co…
Atomic data and plasma models play a crucial role in the diagnosis and interpretation of astrophysical spectra, thus influencing our understanding of the universe. In this investigation we present a systematic comparison of the leading photoionisation codes to determine how much their intrinsic differences impact X-ray spectroscopic studies of hot plasmas in photoionisation equilibrium. We carry out our computations using the Cloudy, SPEX, and XSTAR photoionisation codes, and compare their derived thermal and ionisation states for various ionising spectral energy distributions. We examine the …
We present results from a Chandra study of ultraluminous X-ray sources (ULXs) in a sample of 17 nearby (D_L<60 Mpc) luminous infrared galaxies (LIRGs), selected to have star formation rates (SFRs) in excess of 7 M_sun yr^-1 and low foreground Galactic column densities (N_H < 5*10^20 cm^-2). A total of 53 ULXs were detected and we confirm that this is a complete catalogue of ULXs for the LIRG sample. We examine the evolution of ULX spectra with luminosity by stacking the spectra of individual objects in three luminosity bins, finding a distinct change in spectral index at luminosity ~2 *10^39 e…
The luminosities of ultraluminous X-ray sources (ULXs) require an exotic solution with either super-critical accretion modes onto stellar mass black holes or sub-critical accretion onto intermediate mass black holes (IMBHs) being invoked. Discriminating between the two is non-trivial due to the present lack of a direct mass measurement. A key expectation of the super-critical mode of accretion is the presence of powerful radiatively-driven winds. Here we analyse XMM-Newton data from NGC 5408 X-1 and NGC 6946 X-1 and find that strong soft residuals present in the X-ray spectra can be reconciled…
Most ULXs are believed to be powered by super-Eddington accreting neutron stars and, perhaps, black holes. Above the Eddington rate the disc is expected to thicken and to launch powerful winds through radiation pressure. Winds have been recently discovered in several ULXs. However, it is yet unclear whether the thickening of the disc or the wind variability causes the switch between the classical soft and supersoft states observed in some ULXs. In order to understand such phenomenology and the overall super-Eddington mechanism, we undertook a large (800 ks) observing campaign with XMM-Newton t…
NGC 1365 is a Seyfert 2 galaxy with a starburst ring in its nuclear region. In this work we look at the XMM Reflection Grating Spectrometer (RGS) data from four 2012-13, three 2007 and two 2004 observations of NGC 1365. We characterise the narrow-line emitting gas visible by XMM RGS and make comparisons between the 2012-13 spectra and those from 2004-07, already published. This source is usually absorbed within the soft X-ray band, with a typical neutral column density of >1.5 x 10$^{23}$ cm$^{-2}$, and only 1 observation of the 9 we investigate shows low enough absorption for the continuum to…
Aims. We aim to investigate and characterise the photoionised X-ray emission line regions within NGC 7469. Methods. We apply the photoionisation model, PION, within the spectral fitting code SPEX to analyse the 640 ks RGS spectrum of NGC 7469 gathered during an XMM-Newton observing campaign in 2015. Results. We find the emission line region in NGC 7469 to be multiphased, consisting of two narrow components with ionisation parameters of $\log ξ= 0.4$ and 1.6. A third, broad emission component, with a broadening velocity of $v_b \sim 1400$ km s\textsuperscript{-1} and an outflow velocity of $v_{…
Optical and radio observations of shock-ionised bubble nebulae surrounding ultraluminous X-ray sources (ULXs) suggest that they are powered by jets or super-critical outflows presumably launched from the ULX accretion disc. Recent simulations of these systems have shown that the shocked wind can emit thermal X-rays with estimated luminosities $\sim 10^{36}$ erg s$^{-1}$. In this work, we investigated whether it is possible to detect and spatially resolve the X-ray emission from these systems using archival Chandra observations of the ULX Holmberg IX X-1. This source is an ideal target to study…
If ultraluminous X-ray sources (ULXs) are powered by accretion onto stellar remnant black holes, then many must be accreting at super-Eddington rates. It is predicted that such high accretion rates should give rise to massive, radiatively-driven winds. However, observational evidence of a wind, in the form of absorption or emission features, has remained elusive. As such, the reported detection of X-ray spectral residuals in XMM-Newton spectra of NGC 5408 X-1, which could be related to absorption in a wind is potentially very exciting. However, it has previously been assumed by several authors…
Ultraluminous X-ray sources are non-nuclear point sources exceeding the Eddington luminosity of a 10 Solar mass black hole. Modern consensus for a majority of the ULX population is that they are powered by stellar-mass black holes or neutron stars accreting well above the Eddington limit. Theoretical models of super-Eddington accretion predict existence of powerful outflows of moderately ionised gas at mildly relativistic velocities. So far, these winds have been found in 3 systems: NGC 1313 X-1, NGC 5408 X-1, NGC 55 ULX. In this work, we create a sample of all ULXs with usable archival high r…
In the local Universe, integrated X-ray emission from high-mass X-ray binaries (HMXBs) is dominated by the brightest ultraluminous X-ray sources (ULXs) with luminosity >10^40 erg/s. Such rare objects probably also dominated the production of X-rays in the early Universe. We demonstrate that a ULX with Lx~10^40-10^41 erg/s (isotropic-equivalent luminosity in the 0.1-10 keV energy band) shining for ~10^5 years (the expected duration of a supercritically accreting phase in HMXBs) can significantly ionise the ISM in its host dwarf galaxy of total mass M~10^7-10^8 Msun and thereby reduce its opacit…
Owing to their quiet evolutionary histories, nearby dwarf galaxies (stellar masses $M_\star \lesssim 3 \times 10^9 M_\odot$) have the potential to teach us about the mechanism(s) that 'seeded' the growth of supermassive black holes, and also how the first stellar mass black holes formed and interacted with their environments. Here, we present high spatial-resolution observations of three dwarf galaxies in the X-ray (Chandra), the optical/near-infrared (Hubble Space Telescope), and the radio (Karl G. Jansky Very Large Array). These three galaxies were previously identified as hosting candidate …
The eclipsing low-mass X-ray binary X1822-371 is the prototype of the accretion disc corona (ADC) sources. We analyse two Chandra observations and one XMM-Newton observation to study the discrete features and their variation as a function of the orbital phase, deriving constraints on the temperature, density, and location of the plasma responsible for emission lines. The HETGS and XMM/Epic-pn observed X1822-371 for 140 and 50 ks, respectively. We extracted an averaged spectrum and five spectra from five selected orbital-phase intervals that are 0.04-0.25, 0.25-0.50, 0.50-0.75, 0.75-0.95, and, …
High ionisation lines in the soft X-ray band are generally associated to either interstellar hot gas along the line of sight or to photoionised gas intrinsic to the source. In the low-mass X-ray binary 4U 1820-30, the nature of these lines is not well understood. We characterised the ionised gas present along the line of sight towards the source producing the X-ray absorption lines of Mg XI, Ne IX, Fe XVII, O VII, and O VIII. We analysed all the observations available for this source in the XMM-Newton and Chandra archives, taken with the RGS, HETG, and LETG spectrometers. The high-resolution g…
4U 1624-490 as a possible intermediate-mass X-ray binary: constraints from XRISM and NuSTAR spectroscopy
Università degli Studi di Palermo（巴勒莫大学）；Osservatorio Astronomico di Cagliari, Istituto nazionale di astrofisica（卡利亚里天文台，意大利国家天体物理研究所）；INAF – IASF Palermo（意大利国家天体物理研究所帕勒莫天文空间物理研究所）；INAF – Osservatorio Astronomica di Brera（意大利国家天体物理研究所布雷拉天文台）
Multi-epoch X-ray spectroscopy (0.3-25 keV) of the Seyfert 1.2 galaxy Mrk 79 (UGC 3973) spanning nearly eight years and a factor of three in broadband flux are analysed. The data are obtained at seven epochs with either XMM-Newton or Suzaku. Comparison with contemporaneous RXTE monitoring indicate that all flux states of Mrk 79 are represented by the data. The spectra are fitted in a self-consistent manner adopting a power law and ionised reflection to describe the broadband continuum. Modification of the spectra by a distant photoionised medium, seen predominantly in emission, are also includ…
Unveiling the biconical geometry of the outflow in the ultraluminous X-ray source NGC 5204 X-1
Università degli Studi di Palermo（巴勒莫大学）；INAF – IASF Palermo（意大利国家天体物理研究所 - 巴勒莫天文台）；Center for Astrophysics | Harvard & Smithsonian（哈佛与史密森尼天体物理中心）；Centre for Astrophysics Research, University of Hertfordshire（赫特福德大学天体物理学研究中心）；School of Physics & Astronomy, University of Southampton（南安普顿大学物理与天文学院）；Institute of Astronomy, University of Cambridge（剑桥大学天体物理研究所）；INAF – Osservatorio Astronomico di Brera（意大利国家天体物理研究所 - 布雷拉天文台）
We investigate the photoionised X-ray emission line regions (ELRs) within the Seyfert 2 galaxy NGC 1068, to determine if there are any characteristic changes between observations taken fourteen years apart. We compare XMM-Newton observations collected in 2000 and 2014, simultaneously fitting the reflection grating spectrometer (RGS) and EPIC-pn spectra of each epoch, for the first time, with the photoionisation model, PION, in SPEX. We find that four PION components are required to fit the majority of the emission lines in the spectra of NGC 1068, with $\log ξ=1-4$, $\log N_H>26 m^{-2}$, and $…
