Letter to the Editor

The nature of the X-ray filaments around bow shock pulsar wind nebulae

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: barbara.olmi@inaf.it; elena.amato@inaf.it
² INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
³ Università degli Studi di Firenze, Via Sansone 1, 50019 Sesto Fiorentino (FI), Italy
⁴ GSSI – Gran Sasso Science Institute, Viale F. Crispi 7, 67100 L’Aquila, Italy
e-mail: pasquale.blasi@gssi.it
⁵ INFN-Laboratori Nazionali del Gran Sasso, Via G. Acitelli 22, Assergi (AQ), Italy

Received: 29 January 2024
Accepted: 4 March 2024

Abstract

Context. We propose that the X-ray filaments emerging from selected bow shock pulsar wind nebulae are due to a charge-separated outflow of electrons and/or positrons escaping the nebula and propagating along the local Galactic magnetic field.

Aims. The X-ray brightness, length, and thickness of filaments are all accounted for if a nonresonant streaming instability is excited.

Methods. This is possible if particles are released in the interstellar medium as a collimated beam, as would be expected in a reconnection region between the nebular and interstellar magnetic fields.

Results. We successfully test this idea on the Guitar Nebula filament and discuss other cases.

Conclusions. These filaments provide the best diagnostics available for particle escape from evolved pulsar wind nebulae, a process essential to assessing the contribution of these sources to cosmic ray positrons. The same phenomenology might govern the occurrence of TeV halos and their importance for cosmic ray transport.