Gamma-ray astronomy

Abstract:

Abstract The origin of cosmic rays from outside the Solar system are unknown, as they are deflected by the interstellar magnetic field. Supernova remnants are the main candidate for cosmic rays up to PeV energies but due to lack of evidence, they cannot be concluded as the sources of the most energetic Galactic CRs. We investigate discrete ejecta produced in state transitions of black hole X-ray binary systems as a potential source of cosmic rays, motivated by recent >100 TeV γ-ray detections by LHAASO. Starting from MAXI J1820+070, we examine the multi-wavelength observations and find that efficient particle acceleration may take place (i.e. into a robust power-law), up to ∼2 × 1016μ−1/2 eV, where μ is the ratio of particle energy to magnetic energy. From these calculations, we estimate the global contribution of ejecta to the entire Galactic spectrum to be $\sim 1~{{\ \rm per\ cent}}$, with the cosmic ray contribution rising to $\sim 5~{{\ \rm per\ cent}}$ at PeV energies, assuming roughly equal energy in non-thermal protons, non-thermal electrons and magnetic fields. In addition, we calculate associated γ-ray and neutrino spectra of the MAXI J1820+070 ejecta to investigate new detection methods with CTAO, which provide strong constraints on initial ejecta size of order 107 Schwarzschild radii (10−5 pc) assuming a period of adiabatic expansion.

Abstract:

Abstract We investigate the relationship between disc winds, radio jets, accretion rates and black hole masses of a sample of ∼100k quasars at z ≈ 2. Combining spectra from the 17th data release of the Sloan Digital Sky Survey (SDSS) with radio fluxes from the 2nd data release of the Low Frequency ARray (LOFAR) Two-Meter Sky Survey (LoTSS), we statistically characterise a radio loud and radio quiet population using a two-component Gaussian Mixture model, and perform population matching in black hole mass and Eddington fraction. We determine how the fraction of radio loud sources changes across this parameter space, finding that jets are most efficiently produced in quasars with either a very massive central black hole (MBH > 109M⊙) or one that is rapidly accreting (λEdd > 0.3). We also show that there are differences in the blueshift of the $\textrm {C}\, \rm \small {IV}$ λ1549Å line and the equivalent width of the $\rm {He}\, \rm \small {II}$ λ1640Å line in radio loud and radio quiet quasars that persist even after accounting for differences in the mass and accretion rate of the central black hole. Generally, we find an anti-correlation between the inferred presence of disc winds and jets, which we suggest is mediated by differences in the quasars’ spectral energy distributions. The latter result is shown through the close coupling between tracers of wind kinematics and the ionising flux– which holds for both radio loud and radio quiet sources, despite differences between their emission line properties– and is hinted at by a different Baldwin effect in the two populations.

Abstract:

Radiation pressure on spectral lines is a promising mechanism for powering disc winds from accreting white dwarfs (AWDs) and active galactic nuclei (AGNs). However, in radiation-hydrodynamic simulations, overionization reduces line opacity and quenches the line force, which suppresses outflows. Here, we show that small-scale clumping can resolve this problem. Adopting the microclumping approximation, our new simulations demonstrate that even modest volume filling factors () can dramatically increase the wind mass-loss rate by lowering its ionization state – raising and yielding for such modest filling factors. Clumpy wind models produce the UV resonance lines that are absent from smooth wind models. They can also reprocess a significant fraction of the disc luminosity and thus dramatically modify the broad-band optical/UV SED. Given that theory and observations indicate that disc winds are intrinsically inhomogeneous, clumping offers a physically motivated solution. Together, these results provide the first robust, self-consistent demonstration that clumping can reconcile line-driven wind theory with observations across AWDs and AGNs.

Abstract:

Context. Jets from accreting black-hole (BH) X-ray binary (XRB) systems are powerful outflows that release a large fraction of the accretion energy to the surrounding environment, providing a feedback mechanism that may alter the properties of the interstellar medium (ISM). Studying accretion processes alongside their feedback on the environment may enable one to estimate the matter and energy input and output around accreting BHs. Aims. We aim to study the extended jet structures around the BH XRB GRS 1758–258. First observed in VLA data, these parsec-scale jet structures originate from jet-ISM interaction, and are characterised by a peculiar Z-shape morphology. Methods. Using the MeerKAT radio telescope we observed GRS 1758–258 in the L band for a total exposure of 7 hr. Following a calorimetry-based method originally proposed for active galactic nuclei (AGN) and later applied to X-ray binaries, we estimated the properties of the jets and of the surrounding ISM. Results. We detect a jet and a counter-jet terminating in bow-shock structures induced by their interaction with the ISM. We identified both synchrotron and bremsstrahlung emitting regions within the northern lobe, while the southern lobe is dominated by thermal emission. We measured an ISM particle density of between 10 and 40 cm −3 across both the northern and southern jets, slightly lower in the northern region. The estimated ages of the two jet sides range from 6 to 51 kyr, with the northern jet seemingly younger than the southern one. The time-averaged transferred jet energy for both jets falls between 4.4 × 10 33 and 3.3 × 10 36 erg s −1 , with slight differences between the northern and southern jets ascribed to different local environmental conditions. Comparing the new MeerKAT with archival VLA observations, we measured a proper motion of a portion of the northern jet of ∼130 mas/year. Conclusions. Jet-ISM interaction structures on both sides of GRS 1758–258 reveal different local ISM properties. The comparison between the morphology of these structures and those from other XRBs indicates that the lobes in GRS 1758–258 may be younger and may result from a number of jet activity phases. The estimated time-averaged energy transferred to the environment is slightly lower than, but comparable to, that observed in other XRBs, consistent with the younger age of the lobes in GRS 1758–258 relative to those of other systems.