16.01.2020
Joint journal club
Michaela Kraus will present the following paper: "The evolution of red supergiant mass-loss rates" Beasor et al., 2018, MNRAS 475, 55 https://ui.adsabs.harvard.edu/abs/2018MNRAS.475...55B/abstract and Rhys Taylor will talk about this paper on the size of Ultra Diffuse Galaxies possibly being hugely overestimated: "Are ultra-diffuse galaxies Milky Way-sized?" Chamba et al., 2020, A&A 633, L3 https://arxiv.org/abs/2001.02691
08.04.2020
Restarting radio activity in a hard X-ray selected sample
Radio activity is episodic in nature and radio galaxies witness such activity. However, the duration and the duty cycle of the jet activity is not known, notwithstanding its importance in the context of radio galaxy evolution and feedback to the environment. Due to their large scale and old age, Giant Radio Galaxies (GRG) are ideal targets to study the duty cycle of radio activity. However, GRG usually constitute only a small fraction of sources in radio surveys and a systematic study of the occurrence of restarting activity is still missing. Cross-correlating the INTEGRAL+Swift AGN population with radio catalogues (NVSS, FIRST, SUMSS), we found that 22% of the sources are GRG (a factor four higher than those selected from radio catalogues). Remarkably, all of the sources in the sample show signs of restarting radio activity. The X-ray properties are consistent with this scenario, the nuclei being in a high-accretion, high-luminosity state. I will discuss in details the multi-frequency evidence of restarting activity in this sample.
30.04.2020
Joint Journal Club
Meeting ID: 96137754167 Password: 7089 Meeting link: https://zoom.us/j/96137754167 Scheduled time: 30/04/2020 10:30 CEST (08:30 UTC) Duration: 150 minutes Julieta will present the paper: "Low-frequency gravity waves in blue supergiants revealed by high-precision space photometry by Bowman et al., https://arxiv.org/abs/1905.02120 Pavel will review the paper: "A Link Between Ram Pressure Stripping and Active Galactic Nuclei" by Ricarte et al., https://arxiv.org/abs/2003.05950
11.05.2020
Do stellar-mass and super-massive black holes have similar dining habits?
We compare the relationship between the luminosity of the accretion disc and corona in AGN and X-ray binaries in their radiatively efficient (and non-jetted) phases. The observed scatter in the log Ldisc - log Lcorona plane of XRBs is high (~0.43 dex) and significantly larger than in AGN (~0.30). On the other hand, we also find that XRBs and AGN show different accretion rate and power-law index distributions, with the latter in particular being broader and softer in XRBs. Remarkably, once similarly broad photon index and accretion rate distributions are selected, the AGN sample overlaps nicely with XRBs observations in the mass-normalised log Ldisc - log Lcorona plane, with a scatter of ~0.30-0.33 dex in both cases. This indicates that a mass-scaling of properties might hold after all, with our results being consistent with the disc-corona systems in AGNs and XRBs exhibiting the same physical processes, albeit under different conditions for instance in terms of temperature, optical depth and/or electron energy distribution in the corona, heating-cooling balance, coronal geometry and/or black hole spin.
27.05.2020
Radio Galaxies flavours: how accretion and environment can make the difference
In radio galaxies a correlation between accretion onto supermassive black hole and jet production is expected from both theoretical and obervational works. However, there is a population of radio galaxies that seems to break the classical accretion-ejection scheme. They are defined FRII-LERG and are characterized by strong jets (typical of FRII sources) up to hundreds of kpc, but inefficient accretion engine on pc-scales, testified by their NLR optical spectra. In order to understand their nature, in our work we analyzed all the FRII-LERG sources (19) belonging to the 3CR catalog with X-ray data available (both Chandra and XMM-Newton) with z<0.3. We then analyzed all classical FRII (32) from the same catalog classified both in radio and in optical band as a control sample. We compared X-ray results of FRII-LERG with classical FRII and also FRI, which data are taken from literature. Hence, we matched X-ray analysis with radio and optical data available in literature for all three populations. From our work two scenarios are the most plausible to explain FRII-LERG nature: they could be evolved FRII or they could be a distinct class of sources, inhabiting intermediate environments. Surprisingly, in the latter direction we found a general anti-correlation between accretion rate (measured both from optical and X-ray band) and extra-galactic environment.
15.06.2020
AGN spectra and the soft X-ray excess
I will discuss how AGN spectra evolve with L/LEdd, including changing look episodes, and superEddington flows. I will especially focus on the 'soft X-ray excess' component and its connection to the UV downturn in AGN, showing how we can use results from the multiwaveband intensive monitoring campaigns to understand the origin of the UV and soft X-ray emission.
04.09.2020
Joint Journal Club
07.09.2020
How granular is the obscurer of Active Galactic Nuclei?
Most active galactic nuclei are seen through thick circum-nuclear gas and dust. We would like to understand the origin and geometry of this obscurer. Is this the gas feeding the super-massive black hole? How is it related to the host galaxy gas? I will discuss new approaches to constrain the location, sub-structure and physics of the obscurer, including the search for occultation events with the new X-ray telescope eROSITA and contrasting X-ray reflection spectroscopy from NuSTAR with the open-source XARS modelling framework.
10.09.2020
The Lx–Luv–Lradio relation and corona–disc–jet connection in optically selected radio-loud quasars
Radio-loud quasars (RLQs) are more X-ray luminous than predicted by the Lx-Luv relation for radio-quiet quasars (RQQs). The excess X-ray emission depends on the radio-loudness parameter (R) and radio spectral slope (alpha_r). We construct a uniform sample of 729 optically selected RLQs with high fractions of X-ray detections and alpha_r measurements. We find that steep-spectrum radio quasars (SSRQs) follow a quantitatively similar Lx-Luv relation as that for RQQs, suggesting a common coronal origin for the X-ray emission of both SSRQs and RQQs. However, the corresponding intercept of SSRQs is larger than that for RQQs and increases with R, suggesting a connection between the radio jets and the configuration of the accretion flow. Flat-spectrum radio quasars (FSRQs) are generally more X-ray luminous than SSRQs at given Luv and R, likely involving more physical processes. The emergent picture is different from that commonly assumed where the excess X-ray emission of RLQs is attributed to the jets. We thus perform model selection to compare critically these different interpretations, which prefers the coronal scenario with a corona-jet connection. A distinct jet component is likely important for only a small portion of FSRQs. We suggest that RLQs and RQQs are in different accretion states, similar to those of microquasars when their ballistic jets are either active or quenched. The corona-jet, disk-corona, and disk-jet connections of RLQs are likely driven by independent physical processes. Furthermore, the corona-jet connection implies that small-scale processes in the vicinity of SMBHs, probably associated with the magnetic flux/topology instead of black-hole spin, are controlling the radio-loudness of quasars.
