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Status of the small-sized telescopes programme for the Cherenkov Telescope Array Observatory
Get PDFThe Cherenkov Telescope Array Observatory (CTAO) will include telescopes of three different sizes, the smallest of which are the Small-Sized Telescopes (SSTs). In particular, the SSTs will be installed at the southern site of CTAO, on the Chilean Andes, and will cover the highest energy range of CTAO (up to ~300 TeV). The SSTs are developed by an international consortium of institutes that will provide them as an in-kind contribution to CTAO. The optical design of the SSTs is based on a Schwarzschild-Couder-like dual-mirror polynomial configuration, with a primary aperture of 4.3m diameter. They are equipped with a focal plane camera based on SiPM detectors covering a field of view of ~9°. The preliminary design of the SST telescopes was evaluated and approved during the Product Review (PR) organised with CTAO in February 2023. The SST project is now going through a consolidation phase leading to the finalisation and submission of the final design to the Critical Design Review (CDR), expected to occur late 2024, after which the production and construction of the telescopes will begin leading to a delivery of the telescopes to CTAO southern site starting at the end of 2025-early 2026 onward. In this contribution we will present the progress of the SST programme, including the results of the PDR, the consolidation phase of the project and the plan up to the on-site integration of the telescopes...
Fluorine fluid experimental determination of the refractive index, spectral and thermal variation, and transparency quantification of the MezzoCielo telescope
Get PDFThe MezzoCielo (or "half of the sky") is a telescope that aims to revolutionize the way astronomical observations are carried out: once operational, it will be able to continuously patrol the whole sky due to its extremely large field of view estimated to be around 104 square degrees, showing, at the same time, the spatial resolution required for scientific purposes. It is a monocentric optical device designed on the concept of an optical sphere; the latter requires the filling of its inner volume with special fluid in order to be actually convergent with a reasonable focal ratio (for spherical aberration reduction). This fluid must exhibit two main properties, namely, a low refractive index and an extremely high transparency in the visible range. In addition, many other characteristics are also required: thermal and chemical stability over time, no toxicity or flammability, and compatibility with glass and metals are some examples. On the basis of these considerations, two fluorine liquids have been selected: the fluids commercially known as FC-72, perfluorohexane with nd = 1.251 at T = 25°C, and Novec7200, ethoxy-nonafluorobutane with nd = 1.282 at T = 25°C. In this work, the experimental evaluation of their optical properties (refractive index and transparency) in the visible range and in the thermal interval [-10,+25]°C has been carried out in order to verify the data supplied by the manufacturer and to fully characterize their optical behaviour both spectrally and thermally. All the employed techniques have been firstly applied to commercial pure water, for which extensive literature could be used as reference for the procedures validation
The Northern Cross Fast Radio Burst project: IV. Multi-wavelength study of the actively repeating FRB 20220912A
Get PDFContext. Fast radio bursts (FRBs) are energetic, millisecond-duration radio pulses observed at extragalactic distances and whose origins are still a subject of heated debate. A fraction of the FRB population have shown repeating bursts, however it's still unclear whether these represent a distinct class of sources. Aims. We investigated the bursting behaviour of FRB 20220912A, one of the most active repeating FRBs known thus far. In particular, we focused on its burst energy distribution, linked to the source energetics, and its emission spectrum, with the latter directly related to the underlying emission mechanism. Methods. We monitored FRB 20220912A at 408 MHz with the Northern Cross radio telescope and at 1.4 GHz using the 32-m Medicina Grueff radio telescope. Additionally, we conducted 1.2 GHz observations taken with the upgraded Giant Meter Wave Radio Telescope (uGMRT) searching for a persistent radio source coincident with FRB 20220912A, and included high energy observations in the 0.3–10 keV, 0.4–100 MeV and 0.03–30 GeV energy range. Results. We report 16 new bursts from FRB 20220912A at 408 MHz during the period between October 16th 2022 and December 31st 2023. Their cumulative spectral energy distribution follows a power law with slope αE = ‑1.3 ± 0.2 and we measured a repetition rate of 0.19 ± 0.03 hr‑1 for bursts having a fluence of ℱ ≥ 17 Jy ms. Furthermore, we report no detections at 1.4 GHz for ℱ ≥ 20 Jy ms. These non-detections imply an upper limit of β ν ≥ 1031 erg Hz‑1, a feature seen thus far in only two hyperactive repeaters. In particular, we highlight a strong similarity between FRB 20220912A and FRB 20201124A, with respect to both the energy and repetition rate ranges. We also find a radio continuum source with 240 ± 36 μJy flux density at 1.2 GHz, centered on the FRB 20220912A coordinates. Finally, we place an upper limit on the γ to radio burst efficiency η to be η 9 at 99.7% confidence level, in the 0.4–30 MeV energy range. Conclusions. The strong similarity between the cumulative energy distributions of FRB 20220912A and FRB 20201124A indicate that bursts from these sources are generated via similar emission mechanisms. Our upper limit on β suggests that the spectrum of FRB 20220912A is intrinsically narrow-band. The radio continuum source detected at 1.2 GHz is likely due to a star formation environment surrounding the FRB, given the absence of a source compact on millisecond scales brighter than 48 μJy beam‑1. Finally, the upper limit on the ratio between the γ and radio burst fluence disfavours a giant flare origin for the radio bursts unlike observed for the Galactic magnetar SGR 1806-20
Lessons learned and challenges in maintaining the ViaLactea knowledge base
Get PDFThe ViaLactea Knowledge Base (VLKB) was designed and initially developed within the EU FP7 VIALACTEA project that included a Work Package dedicated to create infrastructure and tools to perform research in Milky-Way astrophysics. The infrastructure's goal was to set up an archive and services to enable that research. About 50 dataset collections ( 35k datasets of various sizes, in FITS format), ten catalogues of compact sources (from thousands to a few million rows), a catalogue of morphological complex sources (few thousand sources), and a few other catalogues and simulated datasets were included in the archive, worth about 1TB of data. On top of those data, and their metadata descriptions, a set of services was deployed: a search and access (cutout and merge) service for the datasets, a general Table Access Protocol (TAP) service for all metadata and catalogues and some other dedicated attempts for serving specific user requirements. All the interfaces were developed in combination with the dedicated client, the ViaLactea Visual Analytics (VLVA) but were designed keeping in mind the discovery and access scenario that is continuously developed in the Virtual Observatory (VO) ecosystem. Indeed, interoperability was brought inside the VLKB afterwards, slowly (depending on the limited resources available after the end of the Vialactea project), mostly when the VLKB resources kept being used in galactic astrophysics projects or as a comprehensive resource of data and services in technical demonstrator projects. Those projects provided the continuity in funding basic maintenance of the VLKB and some updates (even if occasionally rather than continuously). With the first release of the VLKB in 2016, the subsequent maintenance gap spanning from then until 2020, and the restart of development since then, the current adoption of standards in the VLKB includes: an ObsCore table to keep the metadata for the observational datasets' catalogue, the TAP service to expose the general metadata content for all its data resources (catalogues, images, radial velocity cubes and morphological complex objects, . . . ), a custom implementation of the SODA (Server-side Operation for Data Access) standard set up to replace the dataset cutouts (with UWS - Universal Worker Service - used to manage asynchronous cutout and merge requests). Furthermore, authentication and authorization infrastructure (AAI) solutions using OAuth/OIDC have been tested on top of the cutout service, and a multi-cutout solution has been presented at VO level as a feedback for the SODA and DataLink evolution. Other features (management of complex morphology, of simulated data, and registration of the VLKB resources into the VO Registry) are still undergoing or missing. In particular, enabling more standard interface for the VLKB and making VLVA aware and able to consume them, will let both the client be more general and easier to maintain and the server resources be consumed by non-dedicated client applications. This contribution reports the challenges in maintaining and improving the VLKB, the actual status of the technologies and standards in use for its resources, and the present and future perspectives for the VLKB itself...
Three-dimensional modelling of the shock-turbulence interaction
Get PDFThe complex interaction between shocks and plasma turbulence is extremely
important to address crucial features of energy conversion in a broad range of
astrophysical systems. We study the interaction between a supercritical,
perpendicular shock and pre-existing, fully-developed plasma turbulence,
employing a novel combination of magnetohydrodynamic (MHD) and small-scale,
hybrid-kinetic simulations where a shock is propagating through a turbulent
medium. The variability of the shock front in the unperturbed case and for two
levels of upstream fluctuations is addressed.We find that the behaviour of
shock ripples, i.e., shock surface fluctuations with short (a few ion skin
depths, ) wavelengths, is modified by the presence of pre-existing
turbulence, which also induces strong corrugations of the shock front at larger
scales. We link this complex behaviour of the shock front and the shock
downstream structuring with the proton temperature anisotropies produced in the
shock-turbulence system. Finally, we put our modelling effort in the context of
spacecraft observations, elucidating the role of novel cross-scale,
multi-spacecraft measurements in resolving shock front irregularities at
different scales. These results are relevant for a broad range of astrophysical
systems characterised by the presence of shock waves interacting with plasma
turbulence
A 100 kpc ram pressure tail trailing the group galaxy NGC 2276
No full textWe present the discovery of a 100 kpc low-frequency radio tail behind the nearby group galaxy, NGC 2276. The extent of this tail is a factor of ten larger than previously reported from higher-frequency radio and X-ray imaging. The radio morphology of the galaxy disc and tail suggest that the tail was produced via ram-pressure stripping, cementing NGC 2276 as the clearest known example of ram-pressure stripping in a low-mass group. With multi-frequency imaging, we extract radio continuum spectra between ∼50 MHz and 1.2 GHz as a function of projected distance along the tail. All of the spectra are well fit by a simple model of spectral ageing due to synchrotron and inverse-Compton losses. From these fits we estimate a velocity of 870 km s‑1 for the stripped plasma across the plane of the sky, and a three-dimensional orbital velocity of 970 km s‑1 for NGC 2276. The orbital speed that we derive is in excellent agreement with the previous estimates from an X-ray shock analysis, despite the completely independent methodology
MINDS. JWST/MIRI Reveals a Dynamic Gas-rich Inner Disk inside the Cavity of SY Cha
No full textSY Cha is a T Tauri star surrounded by a protoplanetary disk with a large cavity seen in the millimeter continuum but has the spectral energy distribution of a full disk. Here we report the first results from JWST/Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) observations taken as part of the MIRI mid-INfrared Disk Survey (MINDS) GTO Program. The much improved resolution and sensitivity of MIRI-MRS compared to Spitzer enables a robust analysis of the previously detected H2O, CO, HCN, and CO2 emission as well as a marginal detection of C2H2. We also report the first robust detection of mid-infrared OH and rovibrational CO emission in this source. The derived molecular column densities reveal the inner disk of SY Cha to be rich in both oxygen- and carbon-bearing molecules. This is in contrast to PDS 70, another protoplanetary disk with a large cavity observed with JWST, which displays much weaker line emission. In the SY Cha disk, the continuum, and potentially the line, flux varies substantially between the new JWST observations and archival Spitzer observations, indicative of a highly dynamic inner disk
Mid-infrared evidence for iron-rich dust in the multi-ringed inner disk of HD 144432 (erratum: https://doi.org/10.1051/0004-6361/202554515e)
No full textContext. Rocky planets form by the concentration of solid particles in the inner few au regions of planet-forming disks. Their chemical composition reflects the materials in the disk available in the solid phase at the time the planets were forming. Studying the dust before it gets incorporated in planets provides a valuable diagnostic for the material composition. Aims: We aim to constrain the structure and dust composition of the inner disk of the young Herbig Ae star HD 144432, using an extensive set of infrared interferometric data taken by the Very Large Telescope Interferometer (VLTI), combining PIONIER, GRAVITY, and MATISSE observations. Methods: We introduced a new physical disk model, TGMdust, to image the interferometric data, and to fit the disk structure and dust composition. We also performed equilibrium condensation calculations with GGchem to assess the hidden diversity of minerals occurring in a planet-forming disk such as HD 144432. Results: Our best-fit model has three disk zones with ring-like structures at 0.15, 1.3, and 4.1 au. Assuming that the dark regions in the disk at ~0.9 au and at ~3 au are gaps opened by planets, we estimate the masses of the putative gap-opening planets to be around a Jupiter mass. We find evidence for an optically thin emission (τ 3 µm. Our silicate compositional fits confirm radial mineralogy gradients, as for the mass fraction of crystalline silicates we get around 61% in the innermost zone (r 300 K). Conclusions: We propose that in the warm inner regions (r Based on observations collected at the European Southern Observatory under ESO programmes 190.C-0963(D), 190.C-0963(E), 190.C-0963(F), 0100.C-0278(E), 0103.D-0153(C), 0103.C-0347(C), 0103.D-0153(G), 108.225V.003, 108.225V.011, and 108.225V.006
The most variable VVV sources: eruptive protostars, dipping giants in the nuclear disc and others
No full textWe have performed a comprehensive search of a VISTA Variables in the Via Lactea (VVV) data base of 9.5 yr light curves for variable sources with ΔKs ≥ 4 mag, aiming to provide a large sample of high amplitude eruptive young stellar objects (YSOs) and detect unusual or new types of infrared variable source. We find 222 variable or transient sources in the Galactic bulge and disc, most of which are new discoveries. The sample mainly comprises novae, YSOs, microlensing events, Long Period Variable stars (LPVs), and a few rare or unclassified sources. Additionally, we report the discovery of a significant population of aperiodic late-type giant stars suffering deep extinction events, strongly clustered in the Nuclear Disc of the Milky Way. We suggest that these are metal-rich stars in which radiatively driven mass loss has been enhanced by super-solar metallicity. Among the YSOs, 32/40 appear to be undergoing episodic accretion. Long-lasting YSO eruptions have a typical rise time of ~2 yr, somewhat slower than the 6-12 month time-scale seen in the few historical events observed on the rise. The outburst durations are usually at least 5 yr, somewhat longer than many lower amplitude VVV events detected previously. The light curves are diverse in nature, suggesting that multiple types of disc instability may occur. Eight long-duration extinction events are seen wherein the YSO dims for a year or more, attributable to inner disc structure. One binary YSO in NGC 6530 displays periodic extinction events (P=59 d) similar to KH 15D
The enigma of Gaia18cjb: A possible rare hybrid of FUor and EXor properties
Get PDFContext. Gaia18cjb is one of the Gaia-alerted eruptive young star candidates that has been experiencing a slow and strong brightening during the last 13 years, similarly to some FU Orionis-type objects. Aims. The aim of this work is to derive the young stellar nature of Gaia18cjb and determine its physical and accretion properties to classify its variability. Methods. We conducted monitoring observations using multi-filter optical and near-infrared (NIR) photometry, as well as NIR spectroscopy. We present an analysis of pre-outburst and outburst optical and IR light curves, color-magnitude diagrams in different bands, the detection of NIR spectral lines, and estimates of both stellar and accretion parameters during the burst. Results. The optical light curve shows an unusually long (over 8 years) brightening event of 5 mag in the last 13 years, before reaching a plateau indicating that the burst is still ongoing, suggesting a FU Orionis-like (FUor-like) nature. The same outburst is less strong in the IR light curves. The NIR spectra, obtained during the outburst, exhibit emission lines typical of highly accreting low-intermediate mass young stars with typical EX Lupi-type (EXor) features. The spectral index of Gaia18cjb SED classifies it as a Class I in the pre-burst stage and a flat-spectrum young stellar object (YSO) during the burst. Conclusions. Gaia18cjb is an eruptive YSO that exhibits FUor-like photometric features (in terms of brightening amplitude and length of the burst) as well as EXor-like spectroscopic features and accretion rate. Its nature appears similar to that of V350 Cep and V1647 Ori, which have been classified as objects in between FUors and EXors