Speaker
Description
The origin of Galactic cosmic rays (CRs) above the PeV scale, particularly around the knee of the all-particle spectrum, remains a fundamental open question in high-energy astrophysics. Recent developments of air shower arrays, such as Tibet AS$\gamma$, HAWC, and LHAASO, opened up a new era by detecting ultra-high-energy (UHE; E>100 TeV) gamma rays. These UHE sources are possible candidates of PeV cosmic-ray accelerators $-$ PeVatrons. The number of the UHE sources is increasing and currently stands at approximately 50. The identified dominant source type is related to pulsars, pulsar wind nebulae (PWNe), and their halos. The most growing population is microquasars $-$ X-ray binaries hosting a black hole or neutron star with (semi-)relativistic jets. Remarkably, half of the UHE sources remain unidentified mainly because of lacking observations at different wavelengths.
These UHE detections have triggered extensive multiwavelength follow-up campaigns to investigate the origin of gamma rays and unveil the underlying mechanism of particle acceleration. Indeed, our XMM-Newton observations revealed new X-ray extended sources in, e.g., an unidentified source LHAASO J0341+5258 and a microquasar V4641 Sgr, which are plausible counterparts of a PWN and a microquasar lobe, respectively.
In this talk, I will present an overview of our X-ray observation campaigns of the UHE sources, including microquasars SS 433/W50 and V4641 Sgr and several unidentified LHAASO sources.
