OA@INAF - Istituto Nazionale di Astrofisica
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HYPERION. Shedding light on the first luminous quasars: A correlation between UV disc winds and X-ray continuum
Get PDFOne of the main open questions in the field of luminous (Lbol>1047 erg s1) quasars (QSOs) at z & 6 is the rapid formation ( 6 QSOs, which includes 16 sources from the rapidly grown QSOs from the HYPERION sample and five other luminous QSOs with available high-quality archival X-ray data. We discovered a strong and statistically significant (>3) relation between the X-ray continuum photon index () and the C iv disc wind velocity (vCiv) in z > 6 luminous QSOs, whereby the higher the vC iv, the steeper the . This relation suggests a link between the disc corona configuration and the kinematics of disc winds. Furthermore, we find evidence at >2 3. level that and vC iv are correlated to the growth rate history of the SMBH. Although additional data are needed to confirm it, this result may suggest that, in luminous z > 6 QSOs, the SMBH predominantly grows via fast accretion rather than via initial high seed BH mass
Serendipitous Discovery of a 431 ms Pulsar in the Background of Westerlund 1
Get PDFWe report the discovery of PSR J1646−4545, a 431 ms isolated pulsar, in the direction of the young massive cluster Westerlund 1. The pulsar was found in data taken between the years 2005 and 2010 with the “Murriyang” Parkes radio telescope in Australia. Thanks to the numerous detections of the pulsar, we were able to derive a phase-connected timing solution spanning the whole data set. This allowed us to precisely locate the pulsar at the border of the cluster and to measure its spin-down rate. The latter implies a characteristic age of ∼25 Myr, about twice as large as the estimated age of Westerlund 1. The age of PSR J1646−4545, together with its dispersion measure of ∼1029 pc cm−3, more than twice the value predicted by the two main galactic electron density models for Westerlund 1, makes the association of the pulsar with the cluster highly unlikely. We also report on ramifications from the presence of a magnetar in Westerlund 1 and the apparent lack of ordinary radio pulsars
Study of solar brightness profiles in the 18–26 GHz frequency range with INAF radio telescopes I: Solar radius
Get PDFContext. The Sun is an extraordinary workbench, on which several fundamental astronomical parameters can be measured with high precision. Among these parameters, the solar radius R⊙ plays an important role in several aspects, for instance, in evolutionary models. Moreover, it conveys information about the structure of the different layers that compose the solar interior and its atmosphere. Despite the efforts to obtain accurate measurements of R⊙, the subject is still debated, and measurements are puzzling and/or lacking in many frequency ranges.
Aims: We determine the mean, equatorial, and polar radii of the Sun (R_c, R_eq, and R_pol) in the frequency range 18.1 − 26.1 GHz. We employed single-dish observations from the newly appointed Medicina Gavril Grueff Radio Telescope and the Sardinia Radio Telescope (SRT) in five years, from 2018 to mid-2023, in the framework of the SunDish project for solar monitoring.
Methods: Two methods for calculating the radius at radio frequencies were employed and compared: the half-power, and the inflection point. To assess the quality of our radius determinations, we also analysed the possible degrading effects of the antenna beam pattern on our solar maps using two 2D models (ECB and 2GECB). We carried out a correlation analysis with the evolution of the solar cycle by calculating Pearson's correlation coefficient ρ in the 13-month running means.
Results: We obtained several values for the solar radius, ranging between 959 and 994 arcsec, and ρ, with typical errors of a few arcseconds. These values constrain the correlation between the solar radius and solar activity, and they allow us to estimate the level of solar prolatness in the centimeter frequency range.
Conclusions: Our R⊙ measurements are consistent with the values reported in the literature, and they provide refined estimates in the centimeter range. The results suggest a weak prolateness of the solar limb (R_eq > R_pol), although R_eq and R_pol are statistically compatible within 3σ errors. The correlation analysis using the solar images from the Grueff Radio Telescope shows (1) a positive correlation between solar activity and the temporal variation in R_c (and R_eq) at all observing frequencies, and (2) a weak anti-correlation between the temporal variation of R_pol and solar activity at 25.8 GHz
Snapshot of a magnetohydrodynamic disk wind traced with water masers
Get PDFDisk-jet systems are common in astrophysical sources of different nature, from black holes to gaseous giant planets. The disk drives the mass accretion onto a central compact object and the jet ejects material along the disk rotation axis. Magnetohydrodynamic disk winds can provide the link between mass accretion and ejection, which is essential to ensure that the excess angular momentum is removed and accretion can proceed. However, up to now, we have been lacking direct observational proof of disk winds. This work presents a direct view of the velocity field of a disk wind around a forming massive star. Achieving a very high spatial resolution of 0.05 au, our water maser observations trace the velocities of individual streamlines emerging from the disk orbiting the forming star. We find that, at low elevation above the disk midplane, the flow co-rotates with its launch point in the disk, in agreement with magneto-centrifugal acceleration. Beyond the co-rotation point, the flow rises spiraling around the disk rotation axis along a helical magnetic field. We have performed (resistive-radiative-gravito-) magnetohydrodynamic simulations of the formation of a massive star and record the development of a magneto-centrifugally launched jet presenting many properties in agreement with our observations
Probing the polarized emission from SMC X-1: The brightest X-ray pulsar observed by IXPE
Get PDFRecent observations of X-ray pulsars (XRPs) performed by the Imaging X-ray Polarimetry Explorer (IXPE) have made it possible to investigate the intricate details of these objects in a new way, thanks to the added value of X-ray polarimetry. Here we present the results of the IXPE observations of SMC X-1, a member of the small group of XRPs displaying super-orbital variability. SMC X-1 was observed by IXPE three separate times during the high state of its super-orbital period. The observed luminosity in the 2–8 keV energy band of L ∼ 2 × 1038 erg s‑1 makes SMC X-1 the brightest XRP ever observed by IXPE. We detect significant polarization in all three observations, with values of the phase-averaged polarization degree (PD) and polarization angle (PA) of 3.2 ± 0.8% and 97° ±8° for Observation 1, 3.0 ± 0.9% and 90° ±8° for Observation 2, and 5.5 ± 1.1% and 80° ±6° for Observation 3, for the spectro-polarimetric analysis. The observed PD shows an increase over time with decreasing luminosity, while the PA decreases in decrements of ∼10°. The phase-resolved spectro-polarimetric analysis reveals significant detection of polarization in three out of seven phase bins, with the PD ranging between ∼2% and ∼10%, and a corresponding range in the PA from ∼70° to ∼100°. The pulse-phase resolved PD displays an apparent anti-correlation with the flux. Using the rotating vector model, we obtain constraints on the pulsar's geometrical properties for the individual observations. The position angle of the pulsar displays an evolution over time supporting the idea that we observe changes related to different super-orbital phases. Scattering in the wind of the precessing accretion disk may be responsible for the behavior of the polarimetric properties observed during the high-state of SMC X-1's super-orbital period
The PEPSI Exoplanet Transit Survey (PETS) - IV. Assessing the atmospheric chemistry of KELT-20b
Get PDFMost ultra-hot Jupiters (UHJs) show evidence of temperature inversions, in which temperature increases with altitude over a range of pressures. Temperature inversions can occur when there is a species that absorbs the stellar irradiation at a relatively high level of the atmospheres. However, the species responsible for this absorption remains unidentified. In particular, the UHJ KELT-20b is known to have a temperature inversion. Using high resolution emission spectroscopy from LBT/PEPSI we investigate the atomic and molecular opacity sources that may cause the inversion in KELT-20b, as well as explore its atmospheric chemistry. We confirm the presence of Fe I with a significance of 17σ. We also report a tentative 4.3σ detection of Ni I. A nominally 4.5σ detection of Mg I emission in the PEPSI blue arm is likely in fact due to aliasing between the Mg I cross-correlation template and the Fe I lines present in the spectrum. We cannot reproduce a recent detection of Cr I, while we do not have the wavelength coverage to robustly test past detections of Fe II and Si I. Together with non-detections of molecular species like TiO, this suggests that Fe I is likely to be the dominant optical opacity source in the dayside atmosphere of KELT-20b and may be responsible for the temperature inversion. We explore ways to reconcile the differences between our results and those in literature and point to future paths to understand atmospheric variability...
Circuiti di automazione e controllo remoto per la cupola del telescopio APT2
Get PDFIl team ringrazia Giovanni Occhipinti, Stefano Sardone, Massimo Miraglia.Circuiti di automazione e controllo remoto per la cupola del telescopio APT2
Criteri di progetto, schemi elettrici e manuale di manutenzione e verific
First characterization of the emission behavior of Mrk 421 from radio to very high-energy gamma rays with simultaneous X-ray polarization measurements
Get PDFAims: We have performed the first broadband study of Mrk 421 from radio to TeV gamma rays with simultaneous measurements of the X-ray polarization from IXPE. Methods: The data were collected as part of an extensive multiwavelength campaign carried out between May and June 2022 using MAGIC, Fermi-LAT, NuSTAR, XMM-Newton, Swift, and several optical and radio telescopes to complement IXPE data. Results: During the IXPE exposures, the measured 0.2-1 TeV flux was close to the quiescent state and ranged from 25% to 50% of the Crab Nebula without intra-night variability. Throughout the campaign, the very high-energy (VHE) and X-ray emission are positively correlated at a 4σ significance level. The IXPE measurements reveal an X-ray polarization degree that is a factor of 2-5 higher than in the optical/radio bands; that implies an energy-stratified jet in which the VHE photons are emitted co-spatially with the X-rays, in the vicinity of a shock front. The June 2022 observations exhibit a rotation of the X-ray polarization angle. Despite no simultaneous VHE coverage being available during a large fraction of the swing, the Swift-XRT monitoring reveals an X-ray flux increase with a clear spectral hardening. This suggests that flares in high synchrotron peaked blazars can be accompanied by a polarization angle rotation, as observed in some flat spectrum radio quasars. Finally, during the polarization angle rotation, NuSTAR data reveal two contiguous spectral hysteresis loops in opposite directions (clockwise and counterclockwise), implying important changes in the particle acceleration efficiency on approximately hour timescales. All data shown in Figs. 1, 2, 5, 7, and 8 are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/684/A127</A
Insights into the broadband emission of the TeV blazar Mrk 501 during the first X-ray polarization measurements
Get PDFAims: We present the first multiwavelength study of Mrk 501 that contains simultaneous very-high-energy (VHE) γ-ray observations and X-ray polarization measurements from the Imaging X-ray Polarimetry Explorer (IXPE). Methods: We used radio-to-VHE data from a multiwavelength campaign carried out between March 1, 2022, and July 19, 2022 (MJD 59639 to MJD 59779). The observations were performed by MAGIC, Fermi-LAT, NuSTAR, Swift (XRT and UVOT), and several other instruments that cover the optical and radio bands to complement the IXPE pointings. We characterized the dynamics of the broadband emission around the X-ray polarization measurements through its multiband fractional variability and correlations, and compared changes observed in the polarization degree to changes seen in the broadband emission using a multi-zone leptonic scenario. Results: During the IXPE pointings, the VHE state is close to the average behavior, with a 0.2-1 TeV flux of 20%-50% of the emission of the Crab Nebula. Additionally, it shows low variability and a hint of correlation between VHE γ-rays and X-rays. Despite the average VHE activity, an extreme X-ray behavior is measured for the first two IXPE pointings, taken in March 2022 (MJD 59646 to 59648 and MJD 59665 to 59667), with a synchrotron peak frequency > 1 keV. For the third IXPE pointing, in July 2022 (MJD 59769 to 59772), the synchrotron peak shifts toward lower energies and the optical/X-ray polarization degrees drop. All three IXPE epochs show an atypically low Compton dominance in the γ-rays. The X-ray polarization is systematically higher than at lower energies, suggesting an energy stratification of the jet. While during the IXPE epochs the polarization angles in the X-ray, optical, and radio bands align well, we find a clear discrepancy in the optical and radio polarization angles in the middle of the campaign. Such results further support the hypothesis of an energy-stratified jet. We modeled broadband spectra taken simultaneous to the IXPE pointings, assuming a compact zone that dominates in the X-rays and the VHE band, and an extended zone stretching farther downstream in the jet that dominates the emission at lower energies. NuSTAR data allow us to precisely constrain the synchrotron peak and therefore the underlying electron distribution. The change between the different states observed in the three IXPE pointings can be explained by a change in the magnetization and/or the emission region size, which directly connects the shift in the synchrotron peak to lower energies with the drop in the polarization degree. The MWL data are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/685/A117</A
Environmental dependence of AGN activity and star formation in galaxy clusters from Magneticum simulations
Get PDF(Abridged) Cluster environment has a strong impact on the star formation rate
and AGN activity in cluster galaxies. In this work, we investigate the
behaviour of different galaxy populations in galaxy clusters and their vicinity
by means of cosmological hydrodynamical simulations. We studied galaxies with
stellar mass in galaxy clusters with mass
extracted from box2b (640 comoving Mpc/) of the
Magneticum Pathfinder suite of cosmological hydrodynamical simulations at
redshifts 0.25 and 0.90. We examined the influence of stellar mass, distance to
the nearest neighbouring galaxy, clustercentric radius, substructure membership
and large-scale surroundings on the fraction of galaxies hosting an AGN, star
formation rate and the ratio between star-forming and quiescent galaxies. We
found that in low-mass galaxies, AGN activity and star formation are similarly
affected by the environment and decline towards the cluster centre. In massive
galaxies, the impact is different; star-formation level increases in the inner
regions and peaks between 0.5 and 1 with a rapid decline in the
centre, whereas AGN activity declines in the inner regions and rapidly rises
below towards the centre - likely due to stellar mass stripping and
the consequent selection of galaxies with more massive black holes. After
disentangling the contributions of neighbouring cluster regions, we found an
excess of AGN activity in massive galaxies on the cluster outskirts (). We also found that the local density, substructure membership and
stellar mass strongly influence star formation and AGN activity but verified
that they cannot fully account for the observed radial trends