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Milliarcsecond structure and variability of methanol maser emission in three high-mass protostars
Get PDFThe variability study of 6.7 GHz methanol masers has become a useful way to
improve our understanding of the physical conditions in high-mass star-forming
regions. Based on the single-dish monitoring using the Irbene telescopes, we
selected three sources with close sky positions. We imaged them using the
European Very Long Baseline Interferometer Network and searched available data
on VLBI archives to follow detailed changes in their structures and single
maser spot variability. All three targets show a few groups of maser
cloudlets of a typical size of 3.5 mas and the majority of them show linear or
arched structures with velocity gradients of order 0.22 km/(s mas). The
cloudlets and overall source morphologies are remarkably stable on time scales
of 7-15 yr supporting a scenario of variability due to changes in the maser
pumping rate
Measurement of gravitational and thermal effects in a liquid-actuated torsion pendulum
Get PDFWe describe a proof-of-principle experiment aiming to investigate the inverse-square law of gravitation at the centimeter scale. The sensor is a two-stage torsion pendulum, while actuation is accomplished by a variable liquid mass. The time-varying gravitational force is related to the level of the circulating fluid in one or two containers at a short distance from the test mass, with all moving mechanical parts positioned at a large distance. We provide a description of the apparatus and present the first results. We identified a systematic effect of thermal origin, producing offsets of few fNm in torque and of about 10 pN in force. When this effect is neutralized, the measurements agree well with the predictions of simulations. We also discuss the upcoming instrument upgradations and the expected sensitivity improvement that will allow us to perform measurements with adequate accuracy to investigate the unexplored regions of the α−λ parameter space of a Yukawa-like deviation from the Newtonian potential
Improvement of the MARSIS On-Board SW, on the Mars Express Mission. Preliminary scientific results on Phobos and Mars
Get PDFThe Mars Advanced Radar for Subsurface and Ion-osphere Sounding (MARSIS). Since the beginning of mission, it has performed many successful observations. At this point of this fruitful mission, we decided to improve the instrument science perfor-mances, mitigating some technical limitations
Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF
Get PDFThis article presents a few selected developments and future ideas related to the measurement of (n ,γ ) data of astrophysical interest at CERN n_TOF. The MC-aided analysis methodology for the use of low-efficiency radiation detectors in time-of-flight neutron-capture measurements is discussed, with particular emphasis on the systematic accuracy. Several recent instrumental advances are also presented, such as the development of total-energy detectors with γ -ray imaging capability for background suppression, and the development of an array of small-volume organic scintillators aimed at exploiting the high instantaneous neutron-flux of EAR2. Finally, astrophysics prospects related to the intermediate i neutron-capture process of nucleosynthesis are discussed in the context of the new NEAR activation area
Optical design and performance simulations for the 1.49 keV beamline of the BEaTriX X-ray facility
Get PDFThe BEaTriX (Beam Expander Testing X-ray) facility, now operational at INAF-Brera Astronomical Observatory, will represent a cornerstone in the acceptance roadmap of Silicon Pore Optics (SPO) mirror modules, and will so contribute to the final angular resolution of the ATHENA X-ray telescope. By expansion and collimation of a microfocus X-ray source via a paraboloidal mirror, a monochromation stage, and an asymmetric crystal, BEaTriX enables the full-aperture illumination of an SPO mirror module with a parallel, monochromatic, and broad (140 mm × 60 mm) X-ray beam. The beam then propagates in a 12 m vacuum range to image the point spread function of the mirror module, directly on a focal plane camera. Currently the 4.51 keV beamline, based on silicon crystals, is operational in BEaTriX. A second beamline at 1.49 keV, which requires a separate paraboloidal mirror and organic crystals (ADP) for beam expansion, is being realized. As for monochromators, the current design is based on asymmetric quartz crystals. In this paper, we show the current optical design of the 1.49 keV beamline and the optical simulations carried out to predict the achievable performances in terms of beam collimation, intensity, and uniformity. In the next future, the simulation activity will allow us to determine manufacturing and alignment tolerances for the optical components
The Hateful Eight: Connecting Massive Substructures in Galaxy Clusters like A2744 to Their Dynamical Assembly State Using the Magneticum Simulations
Get PDFSubstructures are known to be good tracers for the dynamical states and recent accretion histories of the most massive collapsed structures in the universe, galaxy clusters. Observations find extremely massive substructures in some clusters, especially Abell 2744 (A2744), which are potentially in tension with the ΛCDM paradigm because they are not found in simulations directly. However, the methods to measure substructure masses strongly differ between observations and simulations. Using the fully hydrodynamical cosmological simulation suite Magneticum Pathfinder, we develop a method to measure substructure masses in projection from simulations, similarly to the observational approach. We identify a simulated A2744 counterpart that not only has eight substructures of similar mass fractions but also exhibits similar features in the hot gas component. This cluster formed only recently through a major merger together with at least six massive minor merger events since z = 1, where previously the most massive component had a mass of less than 1 × 1014 M ⊙. We show that the mass fraction of all substructures and of the eighth substructure separately are excellent tracers for the dynamical state and assembly history for all galaxy cluster mass ranges, with high fractions indicating merger events within the last 2 Gyr. Finally, we demonstrate that the differences between subhalo masses measured directly from simulations as bound and those measured in projection are due to methodology, with the latter generally 2-3 times larger than the former. We provide a predictor function to estimate projected substructure masses from SubFind masses for future comparison studies between simulations and observations
Study of the GeV to TeV morphology of the γ Cygni SNR (G 78.2+2.1) with MAGIC and Fermi-LAT. Evidence for cosmic ray escape
Get PDFContext. Diffusive shock acceleration (DSA) is the most promising mechanism that accelerates Galactic cosmic rays (CRs) in the shocks of supernova remnants (SNRs). It is based on particles scattering caused by turbulence ahead and behind the shock. The turbulence upstream is supposedly generated by the CRs, but this process is not well understood. The dominant mechanism may depend on the evolutionary state of the shock and can be studied via the CRs escaping upstream into the interstellar medium (ISM). Aims: Previous observations of the γ Cygni SNR showed a difference in morphology between GeV and TeV energies. Since this SNR has the right age and is at the evolutionary stage for a significant fraction of CRs to escape, our aim is to understand γ-ray emission in the vicinity of the γ Cygni SNR. Methods: We observed the region of the γ Cygni SNR with the MAGIC Imaging Atmospheric Cherenkov telescopes between 2015 May and 2017 September recording 87 h of good-quality data. Additionally, we analysed Fermi-LAT data to study the energy dependence of the morphology as well as the energy spectrum in the GeV to TeV range. The energy spectra and morphology were compared against theoretical predictions, which include a detailed derivation of the CR escape process and their γ-ray generation. Results: The MAGIC and Fermi-LAT data allowed us to identify three emission regions that can be associated with the SNR and that dominate at different energies. Our hadronic emission model accounts well for the morphology and energy spectrum of all source components. It constrains the time-dependence of the maximum energy of the CRs at the shock, the time-dependence of the level of turbulence, and the diffusion coefficient immediately outside the SNR shock. While in agreement with the standard picture of DSA, the time-dependence of the maximum energy was found to be steeper than predicted, and the level of turbulence was found to change over the lifetime of the SNR
The pristine nature of SMSS 1605−1443 revealed by ESPRESSO
Get PDFContext. SMSS J160540.18−144323.1 is the carbon-enhanced metal-poor (CEMP) star with the lowest iron abundance ever measured, [Fe/H] = −6.2, which was first reported with the SkyMapper telescope. The carbon abundance is A(C)≈6.1 in the low-C band, as the majority of the stars in this metallicity range. Yet, constraining the isotopic ratio of key species, such as carbon, sheds light on the properties and origin of these elusive stars. Aims: We performed high-resolution observations of SMSS 1605−1443 with the ESPRESSO spectrograph to look for variations in the radial velocity (vrad) with time. These data have been combined with older MIKE and UVES archival observations to enlarge the temporal baseline. The 12C/13C isotopic ratio is also studied to explore the possibility of mass transfer from a binary companion. Methods: A cross-correlation function against a natural template was applied to detect vrad variability and a spectral synthesis technique was used to derive 12C/13C in the stellar atmosphere. Results: We confirm previous indications of binarity in SMSS 1605−1443 and measured a lower limit 12C/13C > 60 at more than a 3σ confidence level, proving that this system is chemically unmixed and that no mass transfer from the unseen companion has happened so far. Thus, we confirm the CEMP-no nature of SMSS 1605−1443 and show that the pristine chemical composition of the cloud from which it formed is currently imprinted in its stellar atmosphere free of contamination. Based on ESPRESSO GTO collected under ESO programmes 1104.C-0350, 108.2268.001, PI: P. Molaro. Based also on UVES data retrieved from the ESO archive under programme 105.20K7.001
Brightness and mass accretion rate evolution during the 2022 burst of EX~Lupi
Get PDFEX Lupi is the prototype by which EXor-type outbursts were defined. It has
experienced multiple accretion-related bursts and outbursts throughout the last
decades, whose study have greatly extended our knowledge about the effects of
these types of events. This star experienced a new burst in 2022. We used
multi-band photometry to create color-color and color-magnitude diagrams to
exclude the possibility that the brightening could be explained by a decrease
in extinction. We obtained VLT/X-shooter spectra to determine the Lacc and Macc
during the peak of the burst and after its return to quiescence using 2
methods: empirical relationships between line luminosity and Lacc, and a slab
model of the whole spectrum. We examined the 130 year light curve of EX Lupi to
provide statistics on the number of outbursts experienced during this period of
time. Our analysis of the data taken during the 2022 burst confirmed that a
change in extinction is not responsible for the brightening. Our two approaches
in calculating the Macc were in agreement, and resulted in values that are 2
orders of magnitude above what had previously been estimated, thus suggesting
that EX Lupi is a strong accretor even when in quiescence. We determined that
in 2022 March the Macc increased by a factor of 7 with respect to the quiescent
level. We also found hints that even though the Macc had returned to almost its
pre-outburst levels, certain physical properties of the gas had not returned to
the quiescent values. We found that the mass accreted during this three month
event was 0.8 lunar masses, which is approximately half of what is accreted
during a year of quiescence. We calculated that if EX Lupi remains as active as
it has been for the past 130 years, during which it has experienced at least 3
outbursts and 10 bursts, then it will deplete the mass of its circumstellar
material in less than 160000 yr
The radio detection and accretion properties of the peculiar nuclear transient AT 2019avd
Get PDFAT 2019avd is a nuclear transient detected from infrared to soft X-rays, though its nature is yet unclear. The source has shown two consecutive flaring episodes in the optical and the infrared bands, and its second flare was covered by X-ray monitoring programs. During this flare, the UVOT/Swift photometries revealed two plateaus: one observed after the peak and the other one appeared ~240 d later. Meanwhile, our NICER and XRT/Swift campaigns show two declines in the X-ray emission, one during the first optical plateau and one 70-90 d after the optical/UV decline. The evidence suggests that the optical/UV could not have been primarily originated from X-ray reprocessing. Furthermore, we detected a timelag of ~16-34 d between the optical and UV emission, which indicates the optical likely comes from UV reprocessing by a gas at a distance of 0.01-0.03 pc. We also report the first VLA and VLBA detection of this source at different frequencies and different stages of the second flare. The information obtained in the radio band - namely a steep and a late-time inverted radio spectrum, a high brightness temperature and a radio-loud state at late times - together with the multiwavelength properties of AT 2019avd suggests the launching and evolution of outflows such as disc winds or jets. In conclusion, we propose that after the ignition of black hole activity in the first flare, a super-Eddington flaring accretion disc formed and settled to a sub-Eddington state by the end of the second flare, associated with a compact radio outflow