Young massive stars warm up the large amount of gas and dust which condenses in their vicinity, exciting a forest of lines from different molecular species. Their line brightness is a diagnostic tool of the gas physical conditions locally, which we u
se to set constraints on the environment where massive stars form. We made use of the Atacama Large Millimeter/submillimeter Array at frequencies near 349 GHz, with an angular resolution of $0.1$, to observe the methyl cyanide (CH$_3$CN) emission which arises from the accretion disk of a young massive star. We sample the disk midplane with twelve distinct beams, where we get an independent measure of the gas (and dust) physical conditions. The accretion disk extends above the midplane showing a double-armed spiral morphology projected onto the plane of the sky, which we sample with ten additional beams: along these apparent spiral features, gas undergoes velocity gradients of about $rm 1 km s^{-1}$ per 2000 au. The gas temperature (T) rises symmetrically along each side of the disk, from about 98 K at 3000 au to 289 K at 250 au, following a power law with radius, R$^{-0.43}$. The CH$_3$CN column density (N) increases from $rm 9.2times10^{15} cm^{-2}$ to $rm 8.7times10^{17} cm^{-2}$ at the same radii, following a power law with radius, R$^{-1.8}$. In the framework of a circular gaseous disk observed approximately edge-on, we infer an H$_2$ volume density in excess of $rm 4.8times10^9 cm^{-3}$ at a distance of 250 au from the star. We study the disk stability against fragmentation following the methodology by Kratter et al. (2010), appropriate under rapid accretion, and we show that the disk is marginally prone to fragmentation along its whole extent.
The HERMES-TP/SP (High Energy Rapid Modular Ensemble of Satellites -- Technologic and Scientific Pathfinder) is an in-orbit demonstration of the so-called distributed astronomy concept. Conceived as a mini-constellation of six 3U nano-satellites host
ing a new miniaturized detector, HERMES-TP/SP aims at the detection and accurate localisation of bright high-energy transients such as Gamma-Ray Bursts. The large energy band, the excellent temporal resolution and the wide field of view that characterize the detectors of the constellation represent the key features for the next generation high-energy all-sky monitor with good localisation capabilities that will play a pivotal role in the future of Multi-messenger Astronomy. In this work, we will describe in detail the temporal techniques that allow the localisation of bright transient events taking advantage of their almost simultaneous observation by spatially spaced detectors. Moreover, we will quantitatively discuss the all-sky monitor capabilities of the HERMES Pathfinder as well as its achievable accuracies on the localisation of the detected Gamma-Ray Bursts.
The dipping source XB 1916-053 is a compact binary system with an orbital period of 50 min harboring a neutron star. Using ten new {it Chandra} observations and one {it Swift/XRT} observation, we are able to extend the baseline of the orbital ephemer
is; this allows us to exclude some models that explain the dip arrival times. The Chandra observations provide a good plasma diagnostic of the ionized absorber and allow us to determine whether it is placed at the outer rim of the accretion disk or closer to the compact object. From the available observations we are able to obtain three new dip arrival times extending the baseline of the orbital ephemeris from 37 to 40 years. From the analysis of the dip arrival times we confirm an orbital period derivative of $dot{P}=1.46(3) times 10^{-11}$ s s$^{-1}$. We show that the $dot{P}$ value and the luminosity values are compatible with a mass accretion rate lower than 10% of the mass transfer rate. We show that the mass ratio $q=m_2/m_1$ of 0.048 explains the apsidal precession period and the nodal precession period. The observed absorption lines are associated with the presence of ion{Ne}{x}, ion{Mg}{xii}, ion{Si}{xiv}, ion{S}{xvi,} and ion{Fe}{xxvi} ions. We observe a redshift in the absorption lines between $1.1 times 10^{-3}$ and $1.3 times 10^{-3}$. By interpreting it as gravitational redshift, as recently discussed in the literature, we find that the ionized absorber is placed at a distance of $10^8$ cm from the neutron star with a mass of 1.4 M$_{odot}$ and has a hydrogen atom density greater than $10^{15}$ cm$^{-3}$. (Abstract abridged)
We extend the two leading methods for the emph{ab initio} computational descrip tion of phonon-mediated superconductors, namely Eliashberg theory and density fu nctional theory for superconductors (SCDFT), to include plasmonic effects. Furth ermore,
we introduce a hybrid formalism in which the Eliashberg approximation fo r the electron-phonon coupling is combined with the SCDFT treatment of the dynam ically screened Coulomb interaction. The methods have been tested on a set of we ll-known conventional superconductors by studying how the plasmon contribution a ffects the phononic mechanism in determining the critical temperature (tc). Our simulations show that plasmonic SCDFT leads to a good agreement between predict ed and measured tcs, whereas Eliashberg theory considerably overestimates the plasmon-mediated pairing and, therefore, tc. The hybrid approach, on the other hand, gives results close to SCDFT and overall in excellent agreement with exper iments.
We report on the phase-coherent timing analysis of the accreting millisecond X-ray pulsar IGR J17591-2342, using Neutron Star Interior Composition Explorer (NICER) data taken during the outburst of the source between 2018 August 15 and 2018 October 1
7. We obtain an updated orbital solution of the binary system. We investigate the evolution of the neutron star spin frequency during the outburst, reporting a refined estimate of the spin frequency and the first estimate of the spin frequency derivative ($dot{ u} sim -7times 10^{-14}$ Hz s$^{-1}$), confirmed independently from the modelling of the fundamental frequency and its first harmonic. We further investigate the evolution of the X-ray pulse phases adopting a physical model that accounts for the accretion material torque as well as the magnetic threading of the accretion disc in regions where the Keplerian velocity is slower than the magnetosphere velocity. From this analysis we estimate the neutron star magnetic field $B_{eq} = 2.8(3)times10^{8}$ G. Finally, we investigate the pulse profile dependence on energy finding that the observed behaviour of the pulse fractional amplitude and lags as a function of energy are compatible with a thermal Comptonisation of the soft photons emitted from the neutron star caps.
GrailQuest (Gamma Ray Astronomy International Laboratory for QUantum Exploration of Space-Time) is a mission concept based on a constellation (hundreds/thousands) of nano/micro/small-satellites in low (or near) Earth orbits. Each satellite hosts a no
n-collimated array of scintillator crystals coupled with Silicon Drift Detectors with broad energy band coverage (keV-MeV range) and excellent temporal resolution ( below or equal 100 nanoseconds) each with effective area around 100 cm2. This simple and robust design allows for mass-production of the satellites of the fleet. This revolutionary approach implies a huge reduction of costs, flexibility in the segmented launching strategy, and an incremental long-term plan to increase the number of detectors and their performance: a living observatory for next-generation, space-based astronomical facilities. GrailQuest is conceived as an all-sky monitor for fast localisation of high signal-to-noise ratio transients in the X/gamma-ray band, e.g. the elusive electromagnetic counterparts of gravitational wave events. Robust temporal triangulation techniques will allow unprecedented localisation capabilities, in the keV-MeV band, of a few arcseconds or below, depending on the temporal structure of the transient event. The ambitious ultimate goal of this mission is to perform the first experiment, in quantum gravity, to directly probe space-time structure down to the minuscule Planck scale, by constraining or measuring a first order dispersion relation for light in vacuo. This is obtained by detecting delays between photons of different energies in the prompt emission of Gamma-ray Bursts.
IGR J17503-2636 is a hard X-ray transient discovered by INTEGRAL on 2018 August 11. This was the first ever reported X-ray emission from this source. Following the discovery, follow-up observations were carried out with Swift, Chandra, NICER, and NuS
TAR. We report in this paper the analysis and results obtained from all these X-ray data. Based on the fast variability in the X-ray domain, the spectral energy distribution in the 0.5-80 keV energy range, and the reported association with a highly reddened OB supergiant at ~10 kpc, we conclude that IGR J17503-2636 is most likely a relatively faint new member of the supergiant fast X-ray transients. Spectral analysis of the NuSTAR data revealed a broad feature in addition to the typical power-law with exponential roll-over at high energy. This can be modeled either in emission or as a cyclotron scattering feature in absorption. If confirmed by future observations, this feature would indicate that IGR J17503-2636 hosts a strongly magnetized neutron star with B~2e12 G.
Centimeter continuum observations of protostellar jets have revealed the presence of knots of shocked gas where the flux density decreases with frequency. This spectrum is characteristic of nonthermal synchrotron radiation and implies the presence of
both magnetic fields and relativistic electrons in protostellar jets. Here, we report on one of the few detections of nonthermal jet driven by a young massive star in the star-forming region G035.02$+$0.35. We made use of the NSFs Karl G. Jansky Very Large Array (VLA) to observe this region at C, Ku, and K bands with the A- and B-array configurations, and obtained sensitive radio continuum maps down to a rms of 10 $mu$Jy beam$^{-1}$. These observations allow for a detailed spectral index analysis of the radio continuum emission in the region, which we interpret as a protostellar jet with a number of knots aligned with extended 4.5 $mu$m emission. Two knots clearly emit nonthermal radiation and are found at similar distances, of approximately 10,000 au, each side of the central young star, from which they expand at velocities of hundreds km s$^{-1}$. We estimate both the mechanical force and the magnetic field associated with the radio jet, and infer a lower limit of $0.4times10^{-4} $M$_{odot}$ yr$^{-1}$ km s$^{-1}$ and values in the range $0.7-1.3 $mG, respectively.
We report on the discovery by the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) of the accreting millisecond X-ray pulsar IGR J17591-2342, detecting coherent X-ray pulsations around 527.4 Hz
(1.9 ms) with a clear Doppler modulation. This implies an orbital period of ~8.8 hours and a projected semi-major axis of ~1.23 lt-s. From the binary mass function, we estimate a minimum companion mass of 0.42 solar masses, obtained assuming a neutron star mass of 1.4 solar masses and an inclination angle lower than 60 degrees, as suggested by the absence of eclipses or dips in the light-curve of the source. The broad-band energy spectrum is dominated by Comptonisation of soft thermal seed photons with a temperature of ~0.7 keV by electrons heated to 21 keV. We also detect black-body-like thermal direct emission compatible with an emission region of a few kilometers and temperature compatible with the seed source of Comptonisation. A weak Gaussian line centered on the iron K-alpha; complex can be interpreted as a signature of disc reflection. A similar spectrum characterises the NICER spectra, measured during the outburst fading.
We discuss the spectral and timing properties of the accreting millisecond X-ray pulsar SWIFT J1756.9-2508 observed by XMM-Newton, NICER and NuSTAR during the X-ray outburst occurred in April 2018. The spectral properties of the source are consistent
with a hard state dominated at high energies by a non-thermal power-law component with a cut-off at ~70 keV. No evidence of iron emission lines or reflection humps has been found. From the coherent timing analysis of the pulse profiles, we derived an updated set of orbital ephemerides. Combining the parameters measured from the three outbursts shown by the source in the last ~11 years, we investigated the secular evolution of the spin frequency and the orbital period. We estimated a neutron magnetic field of 3.1E+8 G < B_pc< 4.5E+8 G and measured an orbital period derivative of -4.1E-12 s/s < P_dot_orb < 7.1E-12 s/s. We also studied the energy dependence of the pulse profile by characterising the behaviour of the pulse fractional amplitude in the energy range 0.3-80 keV. These results are compared with those obtained from the previous outbursts of SWIFT J1756.9-2508 and other previously known accreting millisecond X-ray pulsars.
