[Paper Review] Young energetic PSR J1617-5055, its underluminous nebula and unidentified TeV source HESS J1616-508

Oleg Kargaltsev, George G. Pavlov+1 more|arXiv (Cornell University)|May 7, 2008

Pulsars and Gravitational Waves Research37 references14 citations

TL;DR

This study presents Chandra X-ray observations of the young, energetic pulsar PSR J1617−5055, revealing an underluminous pulsar wind nebula (PWN) with a total X-ray luminosity only 0.02% of the pulsar's spin-down power. Despite energetic properties and proximity to the TeV source HESS J1616−508, no morphological or spectral evidence supports a physical association, suggesting the TeV emission may originate from a separate source such as a star-forming region or undetected SNR.

ABSTRACT

We observed the young energetic pulsar J1617-5055 with the Chandra ACIS detector for 60 ks. In addition to the pulsar, the X-ray images show a faint pulsar-wind nebula (PWN) seen up to ~1' from the pulsar. Deconvolution and reconstruction of the image reveal a brighter compact PWN component of ~1'' size, possibly with a jet-torus morphology. The PWN spectrum fits an absorbed power-law (PL) model with the photon index Gamma=1.5. The total PWN luminosity in the 0.5-8 keV band, L_{pwn}=3.2 imes10^{33} ergs s^{-1} for d=6.5 kpc, is a fraction of 2 imes 10^{-4} of the pulsar's spin-down power and a fraction of 0.2 of the pulsar's X-ray luminosity, which is a factor of 20 lower than one would expect from an average empirical relation found for a sample of PWNe observed with Chandra. The pulsar's spectrum can be described by an absorbed PL with n_{H}=3.5 imes10^{22} cm^{-2} and Gamma=1.1, harder than any other pulsar spectrum reliably measured in the soft X-ray band. This non-thermal emission is 50% pulsed showing one peak per period. We have also investigated a possible connection between J1617 and the extended TeV source HESS J1616-508 whose center is located about 10' west of the pulsar. We find no preferential extension of the X-ray PWN toward the TeV source. Therefore, the Chandra data do not provide conclusive evidence for PSR J1617-5055 and HESS J1616-508 association. We have also analyzed archival X-ray, radio, and IR data on the HESS J1616-508 region and found traces of diffuse emission (resembling a shell in the radio) coinciding with the central part of HESS J1616-508. We speculate that the TeV source may be multiple, with most of the emission coming from an unknown SNR or a star-forming region, while some fraction of the TeV emission still may be attributed to the J1617 PWN.

Motivation & Objective

• To investigate the X-ray properties of the young, energetic pulsar PSR J1617−5055 and its surrounding pulsar wind nebula (PWN).
• To assess the physical association between PSR J1617−5055 and the extended TeV source HESS J1616−508 using high-resolution X-ray imaging and spectral analysis.
• To determine whether the faint X-ray PWN is consistent with theoretical expectations for wind-powered nebulae and to explore possible causes for its low luminosity.
• To examine archival radio, infrared, and X-ray data for diffuse or extended emission coinciding with the HESS J1616−508 region to evaluate alternative origins for the TeV emission.

Proposed method

• Chandra ACIS observations were conducted for 60 ks to obtain high-resolution X-ray imaging and spectroscopy of PSR J1617−5055.
• Image deconvolution and source reconstruction techniques were applied to resolve the compact PWN component and assess its morphology.
• Spectral fitting of the pulsar and PWN emission was performed using an absorbed power-law model to derive photon indices and hydrogen column densities.
• The spatial distribution of the PWN was compared with the position of the TeV source HESS J1616−508 to test for directional alignment or extension toward the TeV source.
• Archival X-ray (XMM-Newton, Suzaku), radio, and infrared data were analyzed to search for diffuse or extended emission structures in the HESS J1616−508 field.
• Statistical and morphological comparisons were used to evaluate the likelihood of a physical connection between PSR J1617−5055 and HESS J1616−508.

Experimental results

Research questions

• RQ1 Is the pulsar wind nebula (PWN) associated with PSR J1617−5055 consistent with typical luminosities observed in other young, energetic pulsars?
• RQ2 Does the X-ray morphology of the PWN show a preferred extension toward the TeV source HESS J1616−508, indicating a physical connection?
• RQ3 What is the intrinsic X-ray spectral shape of PSR J1617−5055, and how does it compare to theoretical models of pulsar magnetospheric emission?
• RQ4 Could the TeV emission from HESS J1616−508 originate from a different source, such as a star-forming region or an undetected supernova remnant, rather than from the PWN of PSR J1617−5055?
• RQ5 Are there diffuse or extended X-ray, radio, or infrared structures in the HESS J1616−508 field that could host the TeV emission?

Key findings

• The pulsar wind nebula (PWN) around PSR J1617−5055 has a total X-ray luminosity of 3.2×10³³ erg s⁻¹ in the 0.5–8 keV band, corresponding to only 2×10⁻⁴ of the pulsar’s spin-down power, making it significantly underluminous compared to typical PWNe.
• The PWN exhibits a compact component of ~1″ size with a possible jet-torus morphology, and its spectrum fits an absorbed power-law with a photon index of Γ ≈ 1.5.
• The pulsar’s X-ray spectrum is best fit by an absorbed power-law with a photon index of Γ ≈ 1.1 and a hydrogen column density of nH ≈ 3.5×10²² cm⁻², indicating a harder spectrum than typically observed in soft X-ray band pulsars.
• The pulsar’s X-ray emission is ~50% pulsed with a single asymmetric peak, confirming its non-thermal, magnetospheric origin.
• No significant extension of the X-ray PWN is observed toward the TeV source HESS J1616−508, and no convincing morphological or spectral evidence supports a physical association between the two sources.
• Archival data reveal diffuse radio and infrared emission resembling a shell, and a faint X-ray source (X) in the HESS J1616−508 field, suggesting the TeV emission may originate from a separate source such as a star-forming region or undetected SNR.