Hubble Space Telescope detection of the millisecond pulsar J2124-3358 and its far-ultraviolet bow shock nebula

TL;DR

This study used the Hubble Space Telescope to detect the millisecond pulsar J2124-3358 in far-ultraviolet and optical bands, revealing its spectrum and a bow shock nebula, providing insights into pulsar emission and environment.

Contribution

First detection of pulsar J2124-3358 in FUV and optical bands, including its spectral analysis and the observation of its bow shock nebula in FUV.

Findings

Detected pulsar in FUV and optical bands with specific fluxes.

Spectral analysis suggests a combination of magnetospheric and thermal emission.

FUV images reveal a bow shock nebula spatially coincident with the pulsar.

Abstract

We observed a nearby millisecond pulsar J2124-3358 with the Hubble Space Telescope in broad far-UV (FUV) and optical filters. The pulsar is detected in both bands with fluxes F(1250-2000 A)= (2.5+/-0.3)x10^-16 erg/s/cm^2 and F(3800-6000 A)=(6.4+/-0.4)x10^-17 erg/s/cm^2, which correspond to luminosities of ~5.8x10^27 and 1.4x10^27 erg/s, for d=410 pc and E(B-V)=0.03. The optical-FUV spectrum can be described by a power-law model, f_nu~nu^alpha, with slope alpha=0.18-0.48 for a conservative range of color excess, E(B-V)=0.01-0.08. Since a spectral flux rising with frequency is unusual for pulsar magnetospheric emission in this frequency range, it is possible that the spectrum is predominantly magnetospheric (power law with alpha<0) in the optical while it is dominated by thermal emission from the neutron star surface in the FUV. For a neutron star radius of 12 km, the surface temperature would be between 0.5x10^5 and 2.1x10^5 K, for alpha ranging from -1 to 0, E(B-V)=0.01-0.08, and d=340-500 pc. In addition to the pulsar, the FUV images reveal extended emission spatially coincident with the known Halpha bow shock, making PSR J2124-3358 the second pulsar (after PSR J0437-4715) with a bow shock detected in FUV.