NGC 4395 is a dwarf galaxy at a distance of about 4.3 Mpc (scale: ∼0.021 pc mas−1). It hosts an intermediate-mass black hole (IMBH) with a mass between ∼104 and ∼105 solar masses. The early radio observations of NGC 4395 with the very long baseline interferometry (VLBI) network, High Sensitivity Array (HSA), at 1.4 GHz in 2005 showed that its nucleus has a sub-mJy outflow-like feature (E) extending over 15 mas. To probe the possibility of the feature E as a continuous jet with a base physically coupled with the accretion disc, we performed deep VLBI observations with the European VLBI Network (EVN) at 5 GHz, and analysed the archival data obtained with the HSA at 1.4 GHz in 2008, NSF’s Karl G. Jansky Very Large Array (VLA) at 12–18 GHz and the Atacama Large Millimetre/submillimetre Array (ALMA) at 237 GHz. The feature E displays more diffuse structure in the HSA image of 2008 and has no compact substructure detected in the EVN image. Together with the optically thin steep spectrum and the extremely large angular offset (about 220 mas) from the accurate optical Gaia position, we explain the feature E as nuclear shocks likely formed by the IMBH’s episodic ejection or wide-angle outflow. The VLA and ALMA observations find amore »
We present general relativistic radiation magnetohydrodynamics (GRRMHD) simulations of super-Eddington accretion flows around supermassive black holes (SMBHs), which may apply to tidal disruption events (TDEs). We perform long duration ($t\ge 81,200\, GM/c^3$) simulations that achieve mass accretion rates ≳11 times the Eddington rate and produce thermal synchrotron spectra and images of their jets. Gas flowing beyond the funnel wall expands conically and drives a strong shock at the jet head while variable mass ejection and recollimation, along the jet axis, results in internal shocks and dissipation. Assuming the ion temperature (Ti) and electron temperature (Te) in the plasma are identical, the radio/submillimetre spectra peak at >100 GHz and the luminosity increases with BH spin, exceeding $\sim 10^{41} \, \rm {erg\, s^{-1}}$ in the brightest models. The emission is extremely sensitive to Ti/Te as some models show an order-of-magnitude decrease in the peak frequency and up to four orders-of-magnitude decline in their radio/submillimetre luminosity as Ti/Te approaches 20. Assuming a maximum VLBI baseline distance of 10 Gλ, 230 GHz images of Ti/Te = 1 models shows that the jet head may be bright enough for its motion to be captured with the EHT (ngEHT) at D ≲ 110 (180) Mpc at the 5σ significance level. more »
- Award ID(s):
- 1816420
- Publication Date:
- NSF-PAR ID:
- 10390214
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 519
- Issue:
- 2
- Page Range or eLocation-ID:
- p. 2812-2837
- ISSN:
- 0035-8711
- Publisher:
- Oxford University Press
- Sponsoring Org:
- National Science Foundation
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