Emmanuel K. Bempong-Manful

Context. The mechanism responsible for the high-energy emission observed in kiloparsec scale jets across cosmic time remains poorly understood. The relativistic jet associated with the z = 6.1 AGN PSO J030947.49+271757.31 represents the highest z large-scale jet currently resolved in the X-rays and provides a unique laboratory to study the evolution of these structures. Aims. We present a study aimed at constraining the morphology and spectral properties of the kiloparsec-scale jet associated with PSO J030947.49+271757.31. In addition, we intend to investigate the capabilities of future X-ray observatories in the study of extended jets. Methods. We obtained new dedicated observations of PSO J030947.49+271757.31 with the Chandra X-ray Observatory (for a total of 360 ks combined with archival data). Thanks to the improvement of a factor of ∼3 in exposure time compared to previous studies, we spatially resolved the extended X-ray emission into two distinct components and performed spatially resolved spectral analyses of the different regions. Results. We confirmed the presence of extended X-ray emission of PSO J030947.49+271757.31 with significantly improved statistics and identified two separate and slightly resolved components. The X-ray spectrum of the extended emission has a photon index of Γ = 2.25 ^+0.45 _−0.44 , i.e., steeper than that of the core (Γ = 1.86 ± 0.09), and an extended-to-core-luminosity ratio of L _ext / L _core = 18%. Using the Chandra image as input, we performed simulations for next-generation X-ray facilities. An AXIS-like mission would increase the detected photon statistics by a factor of ∼17 compared to the current Chandra dataset. Conclusions. We resolved the kiloparsec-scale jet associated with this z = 6.1 AGN into two main components and constrained its spectral properties. This extended component corresponds to the most distant and one of the most X-ray-luminous large-scale jets currently known. Simulations show that future X-ray missions with arcsecond-scale angular resolution will not only enable significantly more detailed studies of systems such as PSO J030947.49+271757.31, it will also reveal a population of fainter high-redshift jets currently beyond the reach of Chandra .

We report the milliarcsecond localization of a high (∼1379 pc cm ⁻³ ) dispersion measure (DM) repeating fast radio burst (FRB), FRB 20190417A. Combining European VLBI Network detections of five repeat bursts, we confirm the FRB’s host to be a low-metallicity, star-forming dwarf galaxy at z = 0.12817, similar to the hosts of FRB 20121102A, FRB 20190520B, and FRB 20240114A. We also confirm that it is associated with a previously reported persistent radio source (PRS), which is compact on milliarcsecond scales. Visibility-domain model fitting constrains the transverse physical size of the PRS to μ Jy at 1.4 GHz. Though we do not find significant evidence for DM evolution, FRB 20190417A exhibits a time-variable rotation measure (RM) ranging between +3958 ± 11 rad m ⁻² and +5061 ± 24 rad m ⁻² over a 50-day period. We find no evidence for intervening galaxy clusters in the FRB’s line of sight and place a conservative lower limit on the rest-frame host DM contribution of 1228 pc cm ⁻³ (90% confidence)—the largest known for any FRB so far. This system strengthens the emerging picture of a rare subclass of repeating FRBs with large and variable RMs, above-average host DMs, and luminous PRS counterparts in metal-poor dwarf galaxies. Our results suggest that these systems are the result of environmental selection, or a distinct engine for FRB emission.

Precise localizations of fast radio bursts (FRBs) are essential for uncovering their host galaxies and immediate environments. We present the milliarcsecond-precision European VLBI Network localization of FRB 20240114A, a hyperactive repeating FRB, achieving ≲90 × 30 mas (1σ) accuracy. This precision places the burst 0.5 kpc from the nucleus of its low-metallicity star-forming dwarf host at a spectroscopic redshift of z = 0.130287. Our Gran Telescopio CANARIAS spectroscopic follow-up reveals that the dwarf FRB host is gravitationally bound to a more massive, star-forming spiral galaxy. This establishes the first known instance of an FRB residing in a satellite galaxy within a larger galactic system. This configuration, analogous to the Small Magellanic Cloud orbiting the Milky Way (but at a lower overall mass scale), expands the known diversity of FRB host environments and offers important insights for interpreting seemingly “hostless” or highly offset FRBs. Furthermore, our detailed dispersion measure (DM) budget analysis indicates that the dominant contribution to FRB 20240114A’s DM likely originates from the foreground galaxy halos. This finding addresses the anomalously high DM observed for this FRB and underscores the significant role of intervening foreground structures in shaping observed FRB DMs, which is important for accurate FRB-based cosmological measurements. Our results highlight the importance of deep, high-resolution optical/infrared observations (e.g., with the Hubble or James Webb Space Telescopes) to fully leverage our precise radio localization and probe the immediate astrophysical birthplaces of FRB progenitors within these complex galactic systems.

We report the discovery of a relativistic jet in Mrk 110, a narrow-line Seyfert 1 galaxy historically classified as a radio-quiet active galactic nucleus (AGN). Very long baseline interferometry observations reveal intermittent jet activity during 2015–2016 and 2022–2024, with proper-motion measurements yielding superluminal velocities of ∼3.6 ± 0.6c and ∼2.1 ± 0.2c, respectively. The recent jet component decelerates to ∼1.5 ± 0.2c at a projected distance of 1.1 pc from the core, coinciding with the transition zone between broad-line and narrow-line regions. This deceleration accompanies dramatic spectral evolution from steep (spectral index α ≈ −0.63 ± 0.04) to inverted (α ≈ +0.69 ± 0.10) as the 7.6 GHz flux density more than doubled. These episodic jet ejections and their evolutionary pattern match theoretical predictions from magnetically arrested disk (MAD) models for temporary jet formation in systems with Mrk 110’s physical parameters on timescales of months to years. The observed jet deceleration distance matches expectations for relativistic outflows interacting with the circumnuclear environment. These findings demonstrate that the traditional radio-loud/quiet AGN dichotomy may reflect time-averaged states rather than intrinsic capabilities, suggesting that jets may form across the AGN population but become observable only during specific accretion phases when MAD conditions are temporarily established. Mrk 110 serves as a critical “missing link” between radio-loud and radio-quiet AGN, providing insight into jet formation mechanisms, environmental interactions, and physical processes that unify various AGN classifications.

We present multifrequency (5–345 GHz) and multiresolution radio observations of 1ES 1927+654, widely considered one of the most unusual and extreme changing-look active galactic nuclei (CL-AGNs). The source was first designated a CL-AGN after an optical outburst in late 2017 and has since displayed considerable changes in X-ray emission, including the destruction and rebuilding of the X-ray corona in 2019–2020. Radio observations prior to 2023 show a faint and compact radio source typical of a radio-quiet AGN. Starting in 2023 February, 1ES 1927+654 began exhibiting a radio flare with a steep exponential rise, reaching a peak 60 times previous flux levels, and has maintained this higher level of radio emission for over a year to date. The 5–23 GHz spectrum is broadly similar to gigahertz-peaked radio sources, which are understood to be young radio jets less than ∼1000 yr old. Recent high-resolution Very Long Baseline Array observations at 23.5 GHz now show resolved extensions on either side of the core, with a separation of ∼0.15 pc, consistent with a new and mildly relativistic bipolar outflow. A steady increase in the soft X-ray band (0.3–2 keV) concurrent with the radio may be consistent with jet-driven shocked gas, though further observations are needed to test alternate scenarios. This source joins a growing number of CL-AGNs and tidal disruption events that show late-time radio activity, years after the initial outburst.

We present new high-sensitivity e-MERLIN and Very Large Array (VLA) radio images of the prototypical Seyfert 2 galaxy NGC 1068 at 5, 10, and 21 GHz. We image the radio jet, from the compact components north-east (NE), C, S1, and S2 to the faint double-lobed jet structure of the NE and south-west (SW) jet lobes. We map the jet between 15 kλ and 3300 kλ spatial scales by combining enhanced-Multi Element Radio Linked Interferometer Network (e-MERLIN) and VLA data for the first time. Components NE, C, and S2 have steep spectra indicative of optically thin non-thermal emission domination between 5 and 21 GHz. Component S1, which is where the active galactic nucleus resides, has a flat radio spectrum. We report a new component, S2a, a part of the southern jet. We compare these new data with the MERLIN and VLA data observed in 1983, 1992, and 1995 and report a flux decrease by a factor of 2 in component C, suggesting variability of this jet component. With the high angular resolution e-MERLIN maps, we detect the bow shocks in the NE jet lobe that coincide with the molecular gas outflows observed with ALMA. The NE jet lobe has a jet power of |$P_{\rm jet-NElobe}\, =\,$| 6.7 × 10⁴² erg s⁻¹ and is considered to be responsible for driving out the dense molecular gas observed with ALMA around the same region.