LONG-DURATION X-RAY FLASH AND X-RAY-RICH GAMMA-RAY BURSTS FROM LOW-MASS POPULATION III STARS

Recent numerical simulations suggest that Population III (Pop III) stars were born with masses not larger than similar to 100 M-circle dot and typically similar to 40 M-circle dot. By self-consistently considering the jet generation and propagation in the envelope of these low-mass Pop III stars, we find that a Pop III blue supergiant star has the possibility of giving rise to a gamma-ray burst (GRB) even though it keeps a massive hydrogen envelope. We evaluate observational characteristics of Pop III GRBs and predict that Pop III GRBs have a duration of similar to 10(5) s in the observer frame and a peak luminosity of similar to 5 x 10(50) erg s(-1). Assuming that the E-p-L-p (or E-p-E-gamma,E-iso) correlation holds for Pop III GRBs, we find that the spectrum peak energy falls at approximately a few keV (or similar to 100 keV) in the observer frame. We discuss the detectability of Pop III GRBs by future satellite missions such as EXIST and Lobster. If the E-p-E-gamma,E-iso correlation holds, we have the possibility to detect Pop III GRBs at z similar to 9 as long-duration X-ray-rich GRBs by EXIST. Conversely, if the E-p-L-p correlation holds, we have the possibility to detect Pop III GRBs up to z similar to 19 as long-duration X-ray flashes by Lobster.