VLT Suzaku observations of the Fermi pulsar PSR J1028-5819

TL;DR

This study combines optical VLT imaging and Suzaku X-ray observations to search for and analyze the counterparts of pulsar PSR J1028-5819, providing constraints on its optical brightness and evidence for potential diffuse emission.

Contribution

It presents the deepest optical flux limits for PSR J1028-5819 and confirms the X-ray counterpart with spectral analysis, also suggesting possible pulsar wind nebula detection.

Findings

Optical counterpart not detected down to B~25.4 and V~25.3.

X-ray spectrum best-fit by a power-law with index 1.7.

Possible diffuse emission consistent with a pulsar wind nebula.

Abstract

We used optical images taken with the Very Large Telescope (VLT) in the B and V bands to search for the optical counterpart of PSR J1028-5819 or constrain its optical brightness. At the same time, we used an archival Suzaku observation to confirm the preliminary identification of the pulsar's X-ray counterpart obtained by Swift. Due to the large uncertainty on the pulsar's radio position and the presence of a bright (V = 13.2) early F-type star at < 4", we could not detect its counterpart down to flux limits of B~25.4 and V ~25.3, the deepest obtained so far for PSR J1028-5819. From the Suzaku observations, we found that the X-ray spectrum of the pulsar's candidate counterpart is best-fit by a power-law with spectral index 1.7 +/- 0.2 and an absorption column density NH < 10^21 cm-2, which would support the proposed X-ray identification. Moreover, we found possible evidence for the presence of diffuse emission around the pulsar. If real, and associated with a pulsar wind nebula (PWN), its surface brightness and angular extent would be compatible with the expectations for a ~100 kyr old pulsar at the PSR J1028-5819 distance.