On the origin of the system PSR B 1757 − 24 / SNR G 5 . 4 − 1 . 2

A scenario for the origin of the system PSR B 1757−24/supernova remnant (SNR) G 5.4−1.2 is proposed. It is suggested that both objects are the remnants of a supernova (SN) that exploded within a pre-existing bubble blown-up by a runaway massive star (the SN progenitor) during the final (Wolf-Rayet) phase of its evolution. This suggestion implies that (a) the SN blast centre was significantly offset from the geometric centre of the wind-blown bubble (i.e. from the centre of the future SNR), (b) the bubble was surrounded by a massive wind-driven shell, and (c) the SN blast wave was drastically decelerated by the interaction with the shell. Therefore, one can understand how the relatively young and low-velocity pulsar PSR B 1757−24 was able to escape from the associated SNR G 5.4−1.2 and why the inferred vector of pulsar transverse velocity does not point away from the geometric centre of the SNR. A possible origin of the radio source G 5.27−0.9 (located between PSR B 1757−24 and the SNR G 5.4−1.2) is proposed. It is suggested that G 5.27−0.9 is a lobe of a low Mach number (≃ 1.7) jet of gas outflowing from the interior of G 5.4−1.2 through the hole bored in the SNR's shell by the escaping pulsar. It is also suggested that the non-thermal emission of the comet-shaped pulsar wind nebula originates in the vicinity of the termination shock and in the cylindric region of subsonically moving shocked pulsar wind. The role of magnetized wind-driven shells (swept-up during the Wolf-Rayet phase from the ambient interstellar medium with the regular magnetic field) in formation of elongated axisymmetric SNRs is discussed.