A Large X-ray Flare from a Single Weak-lined T Tauri Star TWA-7 Detected with MAXI GSC

We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of $3\times10^{-9}$ ergs cm$^{-2}$ s$^{-1}$ in 2--20 keV band during the scan transit starting at UT 2010-09-07 18:24:30.The estimated X-ray luminosity at the scan in the energy band is 3$\times10^{32}$ ergs s$^{-1}$,indicating that the event is among the largest X-ray flares fromT Tauri stars.Since MAXI GSC monitors a target only during a scan transit of about a minute per 92 min orbital cycle, the luminosity at the flare peak might have been higher than that detected. At the scan transit, we observed a high X-ray-to-bolometric luminosity ratio, log $L_{\rm X}/L_{\rm bol}$ = $-0.1^{+0.2}_{-0.3}$; i.e., the X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has neither an accreting disk nor a binary companion, the observed event implies that none of those are essential to generate such big flares in T Tauri stars.Comment: 4 pages, 2 figures, 1 table accepted for publication in PAS

Martian Moons eXploration MMX: Current Status Report 2020

The small Martian moons Phobos and Deimos are likely a byproduct of the formation of Mars, a potentially habitable rocky planet comparable with the Earth. Owing to the lack of definitive evidence, their origin is still under debate between two leading hypotheses: the capture of volatile-rich primordial asteroid(s) and the in-situ formation from a debris disk that generated by a giant impact onto early Mars. Whichever theory is correct, the Martian moons are expected to preserve key records of volatile material transport that would make the terrestrial planets habitable in the early solar system. Through close-up observations of both moons and sample return from Phobos, MMX will settle the controversy of their origin, reveal their evolution and constrain the early solar system evolution around the region near the snow line. Monitoring of global circulation and escape of the Martian atmosphere will be also conducted to reveal basic processes having shaped and altered the Martian surface environment. After the start of the conceptual study in 2015, MMX took a series of review processes and now proceeds to phase B as a project of JAXA. The MMX sample return has been classified as unrestricted through the last year’s COSPAR review because ejecta materials from Martian impact craters are probably mixed in Phobos regolith but estimated to be sufficiently sterilized. Survey and analysis of such Martian materials from returned samples are expected to provide us unique constraints for the long-term evolution of the Martian surface environment. MMX is planned to be launched in 2024, arrive at the Martian system in 2025, conduct close-up observations, landing and sampling targeting Phobos for ~3 years, depart the Martian system after Deimos multi-flyby in 2028 and return to Earth in 2029. To acquire observation data and samples enough to achieve scientific objectives, MMX will be equipped with 11 science instruments includes 7 sensing instruments, 2 sampler systems, a return capsule and a rover. MMX also has technological contributions to expanding future human activity toward deep space under international collaboration. The realization of a round trip to the Martian system is part of such contributions by this mission. As other technological contributions, MMX is planned to carry two additional sensing instruments: an interplanetary radiation environment monitor to obtain data useful for planning future human missions and a high vision camera for outreach objectives