| Abstract from DBPedia | X-ray bursters are one class of X-ray binary stars exhibiting X-ray bursts, periodic and rapid increases in luminosity (typically a factor of 10 or greater) that peak in the X-ray region of the electromagnetic spectrum. These astrophysical systems are composed of an accreting neutron star and a main sequence companion 'donor' star. There are two types of X-ray bursts, designated I and II. Type I bursts are caused by thermonuclear runaway, while type II arise from the release of gravitational (potential) energy liberated through accretion. For type I (thermonuclear) bursts, the mass transferred from the donor star accumulates on the surface of the neutron star until it ignites and fuses in a burst, producing X-rays.The behavior of X-ray bursters is similar to the behavior of recurrent novae. In that case the compact object is a white dwarf that accretes hydrogen that finally undergoes explosive burning. The compact object of the broader class of X-ray binaries is either a neutron star or a black hole; however, with the emission of an X-ray burst, the compact object can immediately be classified as a neutron star, since black holes do not have a surface and all of the accreting material disappears past the event horizon.X-ray binaries hosting a neutron star can be further subdivided based on the mass of the donor star; either a high mass (above 10 solar masses (M☉)) or low mass (less than 1 M☉) X-ray binary, abbreviated as HMXB and LMXB, respectively. X-ray bursts typically exhibit a sharp rise time (1 – 10 seconds) followed by spectral softening (a property of cooling black bodies). Individual burst energetics are characterized by an integrated flux of 1032–33 joules, compared to the steady luminosity which is of the order 1030 W for steady accretion onto a neutron star. As such the ratio α, of the burst flux to the persistent flux, ranges from 10 to 103 but is typically on the order of 100. The X-ray bursts emitted from most of these systems recur on timescales ranging from hours to days, although more extended recurrence times are exhibited in some systems, and weak bursts with recurrence times between 5–20 minutes have yet to be explained but are observed in some less usual cases. The abbreviation XRB can refer either the object (X-ray burster) or the associated emission (X-ray burst).X線バースター（Xせんバースター、X-ray burster）は、X線連星の種類の1つで、X線域にピークを持つ光度が周期的で高速に増大（通常は10倍以上）するものである。これらの連星は、融合しつつあるコンパクト星、通常は中性子星かブラックホールとドナーとなる恒星から構成される。ドナーとなる恒星の質量は、系を分類する基準として用いられる。質量が10太陽質量以上、または1太陽質量以下の場合は、それぞれHMXB、LMXBと呼ばれる。X線バースターは、X線パルサーやsoft X-ray transient等の他の一時的なとは見かけが異なり、1秒から10秒のシャープな立ち上がり時間の後に、冷えたブラックホールに特徴的なスペクトルの軟化が続く。それぞれのバーストのエネルギー流束は1039-40erg程度で、中性子星上の降着円盤の1037ergに匹敵する。バーストの流束と通常の流束の比自体はαの文字で表され、10から1000の範囲であるが、通常は100の桁である。X線バーストでは、数時間から数日の間隔で系の質量のほとんどを放出するが、5-20分という短い間隔のものも観測される。XRBという略称は、X線バースターという天体とX線バーストという天文現象の両方を意味する。 (Source: http://dbpedia.org/resource/X-ray_burster) |
