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| G359.54+0.18 | |
|---|---|
| Name | G359.54+0.18 |
| Type | Radio filament / nonthermal source |
| Epoch | J2000 |
| Ra | 17h45m (approx.) |
| Dec | −29° (approx.) |
| Constellation | Sagittarius |
| Distance | ~8 kpc (Galactic Center) |
| Other names | Radio filament near Galactic Center, "The thread" |
G359.54+0.18 is a nonthermal radio filament located near the Galactic Center in the direction of the Sagittarius A* complex. It is one of several linear, magnetically influenced structures observed in radio and, in some cases, X-ray bands, and is studied in the context of processes near the Central Molecular Zone, Sgr A East, and high-energy phenomena associated with Sgr A* and surrounding clusters.
G359.54+0.18 was identified as a linear, filamentary radio source projected within the central few hundred parsecs of the Milky Way. It appears as an elongated, narrow structure with high aspect ratio and nonthermal spectral characteristics, distinguished from compact sources such as Sgr A*, the Quintuplet cluster, and the Arches cluster. The filament is cataloged in radio surveys of the Galactic Center region alongside objects like the Radio Arc, Snake (filament), and other nonthermal filaments (NTFs) that trace ordered magnetic fields near Sgr A East and the Central Molecular Zone.
Early radio imaging of the inner Galaxy by teams using the Very Large Array and the Effelsberg 100-m Radio Telescope revealed numerous linear features including G359.54+0.18. Subsequent high-resolution studies with the Very Long Baseline Array and interferometric campaigns combined data from the Australia Telescope Compact Array and the Westerbork Synthesis Radio Telescope to refine morphology and spectral index measurements. Follow-up X-ray searches with the Chandra X-ray Observatory and XMM-Newton targeted bright NTFs such as G359.54+0.18 to probe high-energy counterparts and potential particle acceleration sites in the vicinity of Sgr A* and the Central Molecular Zone.
Radio observations show G359.54+0.18 has a steep, nonthermal spectrum consistent with synchrotron emission produced by relativistic electrons gyrating in magnetic fields, similar to the emission from the Radio Arc and other NTFs. Polarimetric measurements indicate a high degree of linear polarization and ordered magnetic field vectors aligned along the filament, comparable to results for filaments near Sgr A East and features cataloged in surveys by the Galactic Center Survey teams. X-ray imaging with Chandra and XMM-Newton places limits on any coincident thermal plasma or pulsar wind nebula like those observed around PSR B1823−13 and in the Crab Nebula, while some filaments elsewhere show weak hard X-ray or nonthermal X-ray emission attributed to inverse-Compton scattering as seen in studies of the Fermi bubbles and high-energy Galactic Center sources.
G359.54+0.18 is embedded in the complex milieu of the Central Molecular Zone, near dense molecular clouds such as those mapped in CO surveys by teams using the Nobeyama Radio Observatory and the Atacama Large Millimeter/submillimeter Array. Its projected position places it close to the energetic centers of activity including Sgr A*, the Sgr B2 molecular complex, and the supernova remnant Sgr A East, linking it observationally to regions influenced by stellar clusters like the Arches cluster and the Quintuplet cluster. The filament’s orientation and polarization suggest a relationship with the large-scale vertical magnetic field inferred from measurements associated with the Radio Arc and Galactic Center magnetohydrodynamic models developed by groups at institutions such as the Max Planck Institute for Radio Astronomy and the Harvard–Smithsonian Center for Astrophysics.
Interpretations of G359.54+0.18 invoke synchrotron emission from relativistic electrons confined by strong, ordered magnetic fields, as in models applied to the Radio Arc and the Snake (filament). Proposed acceleration mechanisms include magnetic reconnection in current sheets as studied in the context of the Magnetorotational instability literature, shock acceleration from nearby supernova remnants like Sgr A East, and injection from compact objects such as pulsars analogous to PSR J1747−2958 powering the Mouse (nebula). Magnetohydrodynamic simulations developed at institutions like the Princeton Plasma Physics Laboratory and the Institute of Astrophysics of Paris explore how sheared flows and cloud–field interactions in the Central Molecular Zone can produce linear synchrotron-bright filaments. Alternative models consider fossil jets from historic activity of Sgr A* or outflows associated with star clusters including the Arches cluster as drivers of particle acceleration.
Key open questions include the origin of the relativistic particle population, the three-dimensional geometry relative to molecular clouds such as Sgr B2 and Sgr C, and the filament’s magnetic field strength and topology compared to the Radio Arc. Future observations with the Square Kilometre Array, deep polarimetric campaigns with the Very Large Array, high-frequency imaging with the Atacama Large Millimeter/submillimeter Array, and sensitive hard X-ray follow-up with missions like NuSTAR and next-generation observatories will constrain spectral cutoffs, polarization fractions, and any associated compact accelerators similar to known sources like the Crab Nebula and PSR B1823−13. Continued multiwavelength synergy involving teams at the European Southern Observatory, the NASA Goddard Space Flight Center, and university groups will be required to distinguish between reconnection, shock, and jet-origin scenarios and to place G359.54+0.18 in the broader context of Galactic Center magnetism and high-energy astrophysical processes.
Category:Nonthermal filaments Category:Galactic Center