OA@INAF - Istituto Nazionale di Astrofisica
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The IXPE Science of Pulsars and Their Nebulae
Get PDFPulsars (PSRs) and Pulsar Wind Nebulae (PWNe) form some of the most interesting high-energy astrophysical systems. Their prominent synchrotron emission makes them ideal candidates for polarimetry. Here, after briefly summarizing the scientific rationale underpinning the importance of their polarimetric studies, we review the current status and achievements obtained by the IXPE mission. For the first time, we have space- and phase-resolved X-ray data that allow us to set constraints on the geometry and level of turbulence of the magnetic field which, in turn, can help us to better understand which acceleration and radiation model(s) might be at work in these systems. Interestingly, PWNe show a large variety in terms of polarization degree that might indicate key physical differences, still to be further investigated
Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE
Get PDFThe accretion of matter by compact objects can be inhibited by radiation pressure if the luminosity exceeds a critical value known as the Eddington limit. The discovery of ultraluminous X-ray sources has shown that accretion can proceed even when the apparent luminosity considerably exceeds this limit. A high apparent luminosity might be produced due to the geometric beaming of radiation by an outflow. The outflow half-opening angle, which determines the amplification due to beaming, has never been robustly constrained. Using the Imaging X-ray Polarimetry Explorer, we measured the X-ray polarization in the Galactic X-ray binary Cygnus X-3 (Cyg X-3). We found high, >20%, nearly energy-independent linear polarization orthogonal to the direction of the radio ejections. These properties unambiguously indicate the presence of a collimating outflow from the X-ray binary Cyg X-3 and constrain its half-opening angle to ≲15°. Thus, the source can be used as a laboratory for studying the supercritical accretion regime. This finding underscores the importance of X-ray polarimetry in advancing our understanding of accreting sources
Analysis of Crab X-Ray Polarization Using Deeper Imaging X-Ray Polarimetry Explorer Observations
Get PDFWe present Crab X-ray polarization measurements using Imaging X-Ray Polarimetry Explorer (IXPE) data with a total exposure of 300 ks, three times more than the initial 2022 discovery paper. Polarization is detected in three times more pulsar phase bins, revealing an S-shaped +40° polarization angle sweep in the main pulse and >1σ departures from the OPTIMA optical polarization in both pulses, suggesting different radiation mechanisms or sites for the polarized emission at the two wavebands. Our polarization map of the inner nebula reveals a toroidal magnetic field, as seen in prior IXPE analyses. Along the southern jet, the magnetic field orientation relative to the jet axis changes from perpendicular to parallel and the polarization degree decreases by ∼6%. These observations may be explained by kink instabilities along the jet or a collision with a dense, jet-deflecting medium at the tip. Using spectropolarimetric analysis, we find asymmetric polarization in the four quadrants of the inner nebula, as expected for a toroidal field geometry, and a spatial correlation between polarization degree and photon index
SHARP -- A near-IR multi-mode spectrograph conceived for MORFEO@ELT
Get PDFThe Extremely Large Telescopes (ELTs), thanks to their large apertures and
cutting-edge Multi-Conjugate Adaptive Optics (MCAO) systems, promise to deliver
sharper and deeper data even than the JWST. SHARP is a concept study for a
near-IR (0.95-2.45 m) spectrograph conceived to fully exploit the
collecting area and the angular resolution of the upcoming generation of ELTs.
In particular, SHARP is designed for the 2nd port of MORFEO@ELT. Composed of a
Multi-Object Spectrograph, NEXUS, and a multi-Integral Field Unit, VESPER,
MORFEO-SHARP will deliver high angular (30 mas) and spectral
(R300, 2000, 6000, 17000) resolution, outperforming NIRSpec@JWST (100
mas). SHARP will enable studies of the nearby Universe and the early Universe
in unprecedented detail. NEXUS is fed by a configurable slit system deploying
up to 30 slits with 2.4 arcsec length and adjustable width, over a field
of about 1.2"1.2" (35 mas/pix). Each slit is fed by an inversion prism
able to rotate by an arbitrary angle the field that can be seen by the slit.
VESPER is composed of 12 probes of 1.7"1.5" each (spaxel 31 mas)
probing a field 24"70". SHARP is conceived to exploit the ELTs
apertures reaching the faintest flux and the sharpest angular resolution by
joining the sensitivity of NEXUS and the high spatial sampling of VESPER to
MORFEO capabilities. This article provides an overview of the scientific design
drivers, their solutions, and the resulting optical design of the instrument
achieving the required optical performance
Laboratory simulations of ice growth in space: An expected nonuniform ice mantle composition
Get PDFContext. In dense, cold molecular regions, gas-phase chemical species freeze out onto grain surfaces. These icy condensates become an important reservoir of volatile elements and feedstock for molecular diversity. Aims. While there is a fairly general agreement on the chemical composition of icy mantles, there are differences in how the various molecular components are perceived to be present. Should the materials composing the ice be mixed or are they segregated into distinct chemical zones? Methods. To answer such a question, we performed a few exploratory experiments that allowed the adsorbing surface (mimic dust grains) to slowly relax to very low temperatures while gas-phase mixtures of H2O, NH3, and CO embed onto it. Results. We find that mantles are far from being uniform, and they could evolve into completely mixed ices only if the ambient temperature undergoes a catastrophic collapse. Conclusions. Under the typical conditions of an interstellar dense cloud, ices present a high degree of molecular segregation, with possible consequences on the ice chemistry and the desorption mechanisms
Protostellar Outflows at the EarliesT Stages (POETS) V. The launching mechanism of protostellar winds via water masers
Get PDFUnderstanding the launching mechanism of winds and jets remains one of the
fundamental challenges in astrophysics. The Protostellar Outflows at the
EarliesT Stages (POETS) survey has recently mapped the 3D velocity field of the
protostellar winds in a sample (37) of luminous young stellar objects (YSOs) at
scales of 10-100 au via very long baseline interferometry (VLBI) observations
of the 22 GHz water masers. In most of the targets, the distribution of the 3D
maser velocities can be explained in terms of a magnetohydrodynamic (MHD) disk
wind (DW). We have performed Very Long Baseline Array observations of the 22
GHz water masers in IRAS 21078+5211, the most promising MHD DW candidate from
the POETS survey, to determine the 3D velocities of the gas flowing along
several wind streamlines previously identified at a linear resolution of ~1 au.
Near the YSO at small separations along ( au) and across ( au) the jet axis, water masers trace three individual DW streamlines. By
exploiting the 3D kinematic information of the masers, we determined the launch
radii of these streamlines with an accuracy of 1 au, and they lie in the
range of 10-50 au. At increasingly greater distances along the jet (110 au au), the outflowing gas speeds up while it collimates close to the
jet axis. Magneto-centrifugal launching in a radially extended MHD DW appears
to be the only viable process to explain the fast (up to 60 km/s) and
collimated (down to 10 degree) velocities of the wind in correspondence with
launch radii ranging between 10 and 50 au. At larger separations from the jet
axis ( au), the water masers trace a slow (20 km/s), radially
expanding arched shock-front with kinematics inconsistent with
magneto-centrifugal launching. Our resistive-magnetohydrodynamical simulations
indicate that this shock-front could be driven by magnetic pressure
Dark matter line searches with the Cherenkov Telescope Array
Get PDFMonochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from astrophysical or instrumental backgrounds. We provide an updated assessment of the sensitivity of the Cherenkov Telescope Array (CTA) to such signals, based on observations of the Galactic centre region as well as of selected dwarf spheroidal galaxies. We find that current limits and detection prospects for dark matter masses above 300 GeV will be significantly improved, by up to an order of magnitude in the multi-TeV range. This demonstrates that CTA will set a new standard for gamma-ray astronomy also in this respect, as the world's largest and most sensitive high-energy gamma-ray observatory, in particular due to its exquisite energy resolution at TeV energies and the adopted observational strategy focussing on regions with large dark matter densities. Throughout our analysis, we use up-to-date instrument response functions, and we thoroughly model the effect of instrumental systematic uncertainties in our statistical treatment. We further present results for other potential signatures with sharp spectral features, e.g. box-shaped spectra, that would likewise very clearly point to a particle dark matter origin...
On the Structure of the Sagittarius Spiral Arm in the Inner Milky Way
Get PDFWe report measurements of trigonometric parallax and proper motion for two 6.7 GHz methanol and two 22 GHz water masers located in the far portion of the Sagittarius spiral arm as part of the BeSSeL Survey. Distances for these sources are estimated from parallax measurements combined with three-dimensional kinematic distances. The distances of G033.64−00.22, G035.57−00.03, G041.15−00.20, and G043.89−00.78 are 9.9 ± 0.5, 10.2 ± 0.6, 7.6 ± 0.5, and 7.5 ± 0.3 kpc, respectively. Based on these measurements, we suggest that the Sagittarius arm segment beyond about 8 kpc from the Sun in the first Galactic quadrant should be adjusted radially outward relative to previous models. This supports the suggestion of Xu et al. that the Sagittarius and Perseus spiral arms might merge in the first quadrant before spiraling inward to the far end of the Galactic bar
La diretta EduINAF “SuperLuna 2023” e la stagione 2022/23 della serie “Il Cielo in salotto”
Get PDFCome ormai consolidato sin dal 2021, la redazione di EduINAF – magazine di didattica e divulgazione dell’INAF – ha organizzato un calendario di 5 appuntamenti la serie di dirette osservative “Il Cielo in salotto” lungo tutto l’anno scolastico 2022/2023 con la partecipazione dal vivo di telescopi da diverse sedi INAF. La programmazione include fenomeni astronomici come un’eclissi di Sole parziale, una cometa, osservazioni della Luna, pianeti, stelle e galassie. L’iniziativa si è rivelata una delle più apprezzate tra le proposte della testata. Questo report analizza la produzione e il gradimento delle dirette, mettendole a confronto con quelle dell’anno precedente. Inoltre, come già realizzato nel 2021 e nel 2022, l’appuntamento conclusivo del calendario, dedicato alla “SuperLuna 2023”, è stato seguito in diretta da un focus group di “spettatori tipo” i cui feedback sono stati raccolti con dei questionari di valutazione analoghi a quelli degli anni precedenti. Durante questa diretta è stato somministrato, per la prima volta dall’inizio della serie, un questionario anche al pubblico. Il report include un’analisi dell’evento e del gradimento da parte del pubblico, come emerso da entrambi i questionari, confrontando i risultati con i focus group condotti negli anni precedenti e tracciando linee guida per le prossime stagioni
The X-ray invisible Universe. A look into the haloes undetected by eROSITA
Get PDFThe paper presents the analysis of optically selected GAMA groups and clusters in the SRG/eROSITA X-ray map of eROSITA Final Equatorial Depth Survey, in the halo mass range 1013-5 × 1014 M⊙ and at z 13-1014 M⊙ remain undetected. We compare the X-ray surface brightness profiles of the eROSITA detected groups with the mean stacked profile of the undetected low-mass haloes at fixed halo mass. Overall, we find that the undetected groups exhibit less concentrated X-ray surface brightness, dark matter, and galaxy distributions with respect to the X-ray-detected haloes. The mean gas mass fraction profiles are consistent in the two samples within 1.5σ, indicating that the gas follows the dark matter profile. The low-mass concentration and the magnitude gap indicate that these systems are young. They reside with a higher probability in filaments while X-ray-detected groups favour the nodes of the Cosmic Web. Because of the lower central emission, the undetected systems tend to be X-ray underluminous at fixed halo mass and to lie below the LX-Mhalo relation. Interestingly, the X-ray-detected systems inhabiting the nodes scatter the less around the relation, while those in filaments tend to lie below it. We do not observe any strong relationship between the system X-ray appearance and the active galactic nucleus (AGN) activity. We cannot exclude the role of the past AGN feedback in affecting the gas distribution over the halo lifetime. However, the data suggests that the observed differences might be related to the halo assembly bias