Dynamics and plasma properties of an X-ray jet from SUMER, EIS, XRT and EUVI A & B simultaneous observations

Small-scale transient phenomena in the quiet Sun are believed to play an important role in coronal heating and solar wind generation. One of them named as "X-ray jet" is the subject of our study. We indent to investigate the dynamics, evolution and physical properties of this phenomenon. We combine spatially and temporally multi-instrument observations obtained simultaneously with the SUMER spectrometer onboard SoHO, EIS and XRT onboard Hinode, and EUVI/SECCHI onboard the Ahead and Behind STEREO spacecrafts. We derive plasma parameters such as temperatures and densities as well as dynamics by using spectral lines formed in the temperature range from 10 000 K to 12 MK. We also use image difference technique to investigate the evolution of the complex structure of the studied phenomenon. With the available unique combination of data we were able to establish that the formation of a jet-like event is triggered by not one but several energy depositions which are most probably originating from magnetic reconnection. Each energy deposition is followed by the expulsion of pre-existing or new reconnected loops and/or collimated flow along open magnetic field lines. We derived in great detail the dynamic process of X-ray jet formation and evolution. We also found for the first time spectroscopically in the quiet Sun a temperature of 12~MK and density of 4 10^10~cm^-3 in a reconnection site. We raise an issue concerning an uncertainty in using the SUMER Mg X 624.9 A line for coronal diagnostics. We clearly identified two types of up-flow: one collimated up-flow along open magnetic field lines and a plasma cloud formed from the expelled BP loops. We also report a cooler down-flow along closed magnetic field lines. A comparison is made with a model developed by Moreno-Insertis \etal\ (2008).Comment: 15 pages, 15 figure

Constraining Warm Dark Matter with high-zz supernova lensing

We propose a new method to constrain the warm dark matter (WDM) particle mass, $m_\chi$, based on the counts of multiply imaged, distant supernovae (SN) produced by strong lensing by intervening cosmological matter fluctuations. The counts are very sensitive to the WDM particle mass, assumed here to be $m_\chi=1, 1.5, 2$ keV. We use the analytic approach developed by Das & Ostriker to compute the probability density function of the cold dark matter (CDM) convergence ($\kappa$) on the lens plane; such method has been extensively tested against numerical simulations. We have extended this method generalizing it to the WDM case, after testing it against WDM $N$-body simulations. Using the observed cosmic star formation history we compute the probability for a distant SN to undergo a strong lensing event in different cosmologies. A minimum observing time of 2 yr (5 yr) is required for a future 100 square degrees survey reaching $z \approx 4$ ($z \approx 3$) to disentangle at 2$\sigma$ a WDM ($m_\chi=1$ keV) model from the standard CDM scenario. Our method is not affected by any astrophysical uncertainty (such as baryonic physics effects), and, in principle, it does not require any particular dedicated survey strategy, as it may come as a byproduct of a future SN survey.Comment: 7 pages, 7 figures, 1 table. Accepted for publication in MNRA