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MINDS. Hydrocarbons detected by JWST/MIRI in the inner disk of Sz28 consistent with a high C/O gas-phase chemistry
Get PDFWith the advent of JWST, we acquire unprecedented insights into the physical
and chemical structure of the inner regions of planet-forming disks where
terrestrial planet formation occurs. The very low-mass stars (VLMS) are known
to have a high occurrence rate of the terrestrial planets around them.
Exploring the chemical composition of the gas in these inner regions of the
disks can aid a better understanding of the connection between planet-forming
disks and planets. The MIRI mid-Infrared Disk Survey (MINDS) project is a large
JWST Guaranteed Time program to characterize the chemistry and physical state
of planet-forming and debris disks. We use the JWST-MIRI/MRS spectrum to
investigate the gas and dust composition of the planet-forming disk around the
very low-mass star Sz28 (M5.5, 0.12\,M). We use the dust-fitting tool
(DuCK) to determine the dust continuum and to get constraints on the dust
composition and grain sizes. We use 0D slab models to identify and fit the
molecular spectral features, yielding estimates on the temperature, column
density and the emitting area. To test our understanding of the chemistry in
the disks around VLMS, we employ the thermo-chemical disk model {P{\tiny
RO}D{\tiny I}M{\tiny O}} and investigate the reservoirs of the detected
hydrocarbons. We explore how the C/O ratio affects the inner disk chemistry.
JWST reveals a plethora of hydrocarbons, including \ce{CH3}, \ce{CH4},
\ce{C2H2}, \ce{^{13}CCH2}, \ce{C2H6}, \ce{C3H4}, \ce{C4H2} and \ce{C6H6}
suggesting a disk with a gaseous C/O\,>\,1. Additionally, we detect \ce{CO2},
\ce{^{13}CO2}, \ce{HCN}, and \ce{HC3N}. \ce{H2O} and OH are absent in the
spectrum. We do not detect PAHs. Photospheric stellar absorption lines of
\ce{H2O} and \ce{CO} are identified. Notably, our radiation thermo-chemical
disk models are able to produce these detected hydrocarbons in the surface
layers of the disk when the ..
X-ray polarization measurement of the gold standard of radio-quiet active galactic nuclei: NGC 1068
Get PDFContext. NGC 1068 is the most observed radio-quiet active galactic nucleus (AGN) in polarimetry, yet its high-energy polarization has never been probed before due to a lack of dedicated polarimeters. Aims. Using the first X-ray polarimeter sensitive enough to measure the polarization of AGNs, we want to probe the orientation and geometric arrangement of (sub)parsec-scale matter around the X-ray source. Methods. We used the Imaging X-ray Polarimetry Explorer (IXPE) satellite to measure, for the first time, the 2–8 keV polarization of NGC 1068. We pointed IXPE at the target for a net exposure time of 1.15 Ms, in addition to using two Chandra snapshots of ∼10 ks each in order to account for the potential impact of several ultraluminous X-ray sources (ULXs) within IXPE's field of view. Results. We measured a 2–8 keV polarization degree of 12.4% ± 3.6% and an electric vector polarization angle of 101° ± 8° at a 68% confidence level. If we exclude the spectral region containing bright Fe K lines and other soft X-ray lines where depolarization occurs, the polarization fraction rises to 21.3% ± 6.7% in the 3.5–6.0 keV band, with a similar polarization angle. The observed polarization angle is found to be perpendicular to the parsec-scale radio jet. Using a combined Chandra and IXPE analysis plus multiwavelength constraints, we estimated that the circumnuclear "torus" may sustain a half-opening angle of 50–55° (from the vertical axis of the system). Conclusions. Thanks to IXPE, we have measured the X-ray polarization of NGC 1068 and found comparable results, both in terms of the polarization angle orientation with respect to the radio jet and the torus half-opening angle, to the X-ray polarimetric measurement achieved for the other archetypal Compton-thick AGN: the Circinus galaxy. Probing the geometric arrangement of parsec-scale matter in extragalactic objects is now feasible thanks to X-ray polarimetry
The Nature of X-Rays from Young Stellar Objects in the Orion Nebula Cluster—A Chandra HETGS Legacy Project
Get PDFThe Orion Nebula Cluster (ONC) is the closest site of very young (∼1 Myr) massive star formation The ONC hosts more than 1600 young and X-ray bright stars with masses ranging from ∼0.1-35 M⊙. The Chandra HETGS Orion Legacy Project observed the ONC with the Chandra High Energy Transmission Grating Spectrometer (HETGS) for 2.1 Ms. We describe the spectral extraction and cleaning processes necessary to separate overlapping spectra. We obtained 36 high-resolution spectra, which include a high-brilliance X-ray spectrum of θ 1 Ori C with over 100 highly significant X-ray lines. The lines show Doppler broadening between 300 and 400 km s−1. Higher spectral diffraction orders allow us to resolve line components of high Z He-like triplets in θ 1 Ori C with unprecedented spectral resolution. Long-term light curves spanning ∼20 yr show all stars to be highly variable, including the massive stars. Spectral fitting with thermal coronal emission line models reveals that most sources show column densities of up to a few times 1022 cm−2 and high coronal temperatures of 10-90 MK. We observe a bifurcation of the high-temperature component where some stars show a high component of 40 MK, while others show above 60 MK, indicating heavy flaring activity. Some lines are resolved with Doppler broadening above our threshold of ∼200 km s−1, up to 500 km s−1. This data set represents the largest collection of HETGS high-resolution X-ray spectra from young pre-main-sequence stars in a single star-forming region to date
The Smallest Scale of Hierarchy Survey (SSH) III. Dwarf-dwarf satellite merging phenomena in the low-mass regime
Get PDFWe present new deep, wide-field Large Binocular Telescope (LBT) and
imaging data from the Smallest Scale of Hierarchy Survey (SSH) revealing
previously undetected tidal features and stellar streams in the outskirts of
six dwarf irregular galaxies (NGC 5238, UGC 6456, UGC 6541, UGC 7605, UGC 8638,
and UGC 8760) with stellar masses in the range M to
M. The six dwarfs are located 1-2 Mpc away from
large galaxies, implying that the observed distortions are unlikely to be due
to tidal effects from a nearby, massive companion. At the dwarfs' distances of
3-4 Mpc, the identified tidal features are all resolved into individual
stars in the LBT images and appear to be made of a population older than 1-2
Gyr, excluding the possibility that they result from irregular and asymmetric
star formation episodes that are common in gas-rich dwarf galaxies. The most
plausible explanation is that we are witnessing the hierarchical merging
assembling of these dwarfs with their satellite populations, a scenario also
supported by the peculiar morphology and disturbed velocity field of their HI
component. From the SSH sample we estimate a fraction of late type dwarfs
showing signs of merging with satellites of 13\%, in agreement with other
recent independent studies and theoretical predictions within the CDM
cosmological framework
Probing the face-on disc-corona system of the bare AGN Mrk 110 from UV to hard X-rays: A moderate changing-state AGN?
Get PDFContext. The X-ray broadband spectra of the bare active galactic nucleus (AGN) Mrk 110, obtained by simultaneous XMM-Newton and NuSTAR observations performed in November 2019 and April 2020, are characterised by the presence of a prominent and absorption-free smooth soft X-ray excess, moderately broad O VII and Fe Kα emission lines, and a lack of a strong Compton hump. The disc-corona system is almost viewed face-on as inferred from the O VII accretion disc lines. While relativistic reflection as the sole emission is ruled out, a simplified combination of soft and hard Comptonisation (using COMPTT) from a warm and a hot corona, plus mild relativistic disc reflection (occuring at a few 10 s Rg) reproduces the data very well. Aims: We aim to confirm the physical origin of the soft X-ray excess of Mrk 110 and to determine its disc-corona system properties from its energetics using two new sophisticated models: REXCOR and RELAGN, respectively. Methods: We applied these models to the 0.3-79 keV X-ray broadband spectra and to the spectral energy distribution (SED) from UV to hard X-rays, respectively. Results: At both epochs, the inferred high values of the warm-corona heating from the X-ray broadband spectral analysis using REXCOR confirm that the soft X-ray excess of Mrk 110 mainly originates from a warm corona rather than relativistic reflection. The intrinsic best-fit SED determined at both epochs using RELAGN show a high X-ray contribution relative to the UV and are very well reproduced by a warm and hot corona plus mild relativistic reflection. The outer radii of the hot and warm corona are located at a few 10 s and ∼100 Rg, respectively. Moreover, combining the inferred low Eddington ratio (approximatively a few percent) from this work, and previous multi-wavelength spectral and timing studies suggest that Mrk 110 could be classified as a moderate changing-state AGN. Conclusions: Our analysis confirms the existence of a warm corona as a significant contribution to the soft X-ray excess and UV emission in Mrk 110, adding to growing evidence that AGN accretion deviates from standard disc theory. This strengthens the importance of long-term multi-wavelength monitoring on both single targets and large AGN surveys to reveal the real nature of the disc-corona system in AGNs
Prospects for a survey of the galactic plane with the Cherenkov Telescope Array
Get PDFApproximately one hundred sources of very-high-energy (VHE) gamma rays are known in the Milky Way, detected with a combination of targeted observations and surveys. A survey of the entire Galactic Plane in the energy range from a few tens of GeV to a few hundred TeV has been proposed as a Key Science Project for the upcoming Cherenkov Telescope Array Observatory (CTAO). This article presents the status of the studies towards the Galactic Plane Survey (GPS). We build and make publicly available a sky model that combines data from recent observations of known gamma-ray emitters with state-of-the-art physically-driven models of synthetic populations of the three main classes of established Galactic VHE sources (pulsar wind nebulae, young and interacting supernova remnants, and compact binary systems), as well as of interstellar emission from cosmic-ray interactions in the Milky Way. We also perform an optimisation of the observation strategy (pointing pattern and scheduling) based on recent estimations of the instrument performance. We use the improved sky model and observation strategy to simulate GPS data corresponding to a total observation time of 1620 hours spread over ten years. Data are then analysed using the methods and software tools under development for real data. Under our model assumptions and for the realisation considered, we show that the GPS has the potential to increase the number of known Galactic VHE emitters by almost a factor of five. This corresponds to the detection of more than two hundred pulsar wind nebulae and a few tens of supernova remnants at average integral fluxes one order of magnitude lower than in the existing sample above 1 TeV, therefore opening the possibility to perform unprecedented population studies. The GPS also has the potential to provide new VHE detections of binary systems and pulsars, to confirm the existence of a hypothetical population of gamma-ray pulsars with an additional TeV emission component, and to detect bright sources capable of accelerating particles to PeV energies (PeVatrons). Furthermore, the GPS will constitute a pathfinder for deeper follow-up observations of these source classes. Finally, we show that we can extract from GPS data an estimate of the contribution to diffuse emission from unresolved sources, and that there are good prospects of detecting interstellar emission and statistically distinguishing different scenarios. Thus, a survey of the entire Galactic plane carried out from both hemispheres with CTAO will ensure a transformational advance in our knowledge of Galactic VHE source populations and interstellar emission...
A magnetar giant flare in the nearby starburst galaxy M82
Get PDFMagnetar giant flares are rare explosive events releasing up to 1047 erg in gamma rays in less than 1 second from young neutron stars with magnetic fields up to 1015−16 G (refs. 1,2). Only three such flares have been seen from magnetars in our Galaxy3,4 and in the Large Magellanic Cloud5 in roughly 50 years. This small sample can be enlarged by the discovery of extragalactic events, as for a fraction of a second giant flares reach luminosities above 1046 erg s−1, which makes them visible up to a few tens of megaparsecs. However, at these distances they are difficult to distinguish from short gamma-ray bursts (GRBs); much more distant and energetic (1050−53 erg) events, originating in compact binary mergers6. A few short GRBs have been proposed7-11, with different amounts of confidence, as candidate giant magnetar flares in nearby galaxies. Here we report observations of GRB 231115A, positionally coincident with the starburst galaxy M82 (ref. 12). Its spectral properties, along with the length of the burst, the limits on its X-ray and optical counterparts obtained within a few hours, and the lack of a gravitational wave signal, unambiguously qualify this burst as a giant flare from a magnetar in M82
Applying augmented reality to historical telescopes images: the IMAGO project
Get PDFThe IMAGO (IMAGer with mOdified eyepiece) project is finalized to the realization of a prototype for the application of Augmented Reality to what can be normally seen when putting the eye at an historical telescope. The main motivation for such a system is to offer an innovative experience to the public, who can be quite unimpressed after a first glimpse through a telescope, especially under bad seeing conditions, thus increasing their interest in astronomy and possibly revitalizing those telescopes, no longer suitable for scientific purposes but still impressive and evocative. The idea behind IMAGO, the IMAGO prototype design and possible future developments are here described
Examining the local Universe isotropy with galaxy cluster velocity dispersion scaling relations
Get PDFIn standard cosmology, the late Universe is assumed to be statistically
homogeneous and isotropic. However, a recent study based on galaxy clusters by
Migkas et al. (2021, arXiv:2103.13904) found an apparent spatial variation of
approximately in the Hubble constant, , across the sky. The authors
utilised galaxy cluster scaling relations between various cosmology-dependent
cluster properties and a cosmology-independent property, i.e., the temperature
of the intracluster gas . A position-dependent systematic bias of
measurements can, in principle, result in an overestimation of apparent
variations. In this study, we search for directional measurement biases by
examining the scaling relation between the member galaxy velocity dispersion
and the gas temperature . Additionally, we search for
apparent angular variations independently of by analysing the
relations between the X-ray luminosity and Sunyaev-Zeldovich signal with the
velocity dispersion, and
. We utilise Monte Carlo simulations of
isotropic cluster samples to quantify the statistical significance of any
observed anisotropies. We find no significant directional measurement
biases, and the probability that a directional bias causes the previously
observed anisotropy is only . On the other hand, from the joint
analysis of the and
relations, the maximum variation of is
found in the direction of with a
statistical significance of , fully consistent with
arXiv:2103.13904. Our findings strongly corroborate the previously detected
spatial anisotropy of galaxy cluster scaling relations using a new independent
cluster property,