Supersoft X-ray source: Difference between revisions

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A '''luminous supersoft X-ray source''' (SSXS, or SSS) is an [[Astronomy|astronomical]] source that emits only low energy (i.e., soft) [[X-rays]]. Soft X-rays have energies in the 0.09 to 2.5 [[keV]] range, whereas hard X-rays are in the 1–20 keV range.<ref name=Supersoft>{{ cite web |title=Supersoft X-Ray Sources |url=http://library.thinkquest.org/27930/supersoft.htm |deadurlurl-status=yesdead |archiveurl=https://web.archive.org/web/20080607122110/http://library.thinkquest.org/27930/supersoft.htm |archivedate=2008-06-07 |df= }}</ref> SSSs emit few or no photons with energies above 1 keV, and most have effective temperatures below 100 eV. This means that the radiation they emit is highly ionizing and is readily absorbed by the interstellar medium. Most SSSs within our own galaxy are hidden by interstellar absorption in the galactic disk.<ref name=White/> They are readily evident in external galaxies, with ~10 found in the Magellanic Clouds and at least 15 seen in M31.<ref name=White/>

As of early 2005, more than 100 SSSs have been reported in ~20 external galaxies, the [[Large Magellanic Cloud]] (LMC), [[Small Magellanic Cloud]] (SMC), and the [[Milky Way]] (MW).<ref name=Kahabka/> Those with luminosities below ~3 x 10³⁸ erg/s are consistent with steady [[Stellar surface fusion|nuclear burning]] in accreting [[white dwarf]]s (WD)s or post-novae.<ref name=Kahabka/> There are a few SSS with luminosities ≥10³⁹ erg/s.<ref name=Kahabka/>

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Super soft X-rays are believed to be produced by steady [[nuclear fusion]] on a [[white dwarf]]'s surface of material pulled from a [[binary star|binary companion]],<ref name=SSXSmpe>{{ cite web |title=Super Soft X-ray Sources - Discovered with ROSAT |url=http://www.mpe.mpg.de/~jcg/sss/sss_high.html |author=Max Planck Institute for Extraterrestrial Physics }}</ref> the so-called close-binary supersoft source (CBSS).<ref name=Greiner/> This requires a flow of material sufficiently high to sustain the fusion. Contrast this with the [[nova]], where less flow causes the material to only fuse sporadically. Super soft X-ray sources can evolve into [[type Ia supernova]], where a sudden fusion of material destroys the white dwarf, and neutron stars, through collapse.<ref name=SSXSws>{{ cite web |title=Proceedings of the Workshop on Supersoft X-ray Sources |url=http://www.mpe.mpg.de/~jcg/sss/sssw.html |author=Max Planck Institute for Extraterrestrial Physics }}</ref>

Super soft X-ray sources were first discovered by the [[Einstein Observatory]]. Further discoveries were made by [[ROSAT]].<ref name=SSXScat>{{ cite web |title=Catalog of Supersoft X-ray Sources |url=http://www.aip.de/~jcg/sss/ssscat.html |deadurlurl-status=yesdead |archiveurl=https://web.archive.org/web/20071128104800/http://www.aip.de/~jcg/sss/ssscat.html |archivedate=2007-11-28 |df= }}</ref> Many different classes of objects emit supersoft X-radiation (emission dominantly below 0.5 keV).<ref name=Greiner/>

==Luminous supersoft X-ray sources==

Luminous super soft X-ray sources have a characteristic blackbody temperature of a few tens of eV (~20–100 eV)<ref name=Kahabka>{{ cite journal |author=Kahabka P |title=Supersoft X-ray sources |journal=Adv. Space Res. |date=Dec 2006 |volume=38 |issue=12 |pages=2836–9 |doi=10.1016/j.asr.2005.10.058 |bibcode=2006AdSpR..38.2836K}}</ref> and a bolometric luminosity of ~10³⁸ erg/s (below ~ 3 x 10³⁸ erg/s).<ref name=White>{{ cite journal|display-authors=4|author=White NE|author2=Giommi P|author3=Heise J|author4=Angelini L|author5=Fantasia S|title=RX J0045.4+4154: A Recurrent Supersoft X-ray Transient in M31|journal=Astrophys. J. Lett.|volume=445|pages=L125|url=http://lheawww.gsfc.nasa.gov/users/white/wgacat/apjl.html|doi=10.1086/187905|bibcode=1995ApJ...445L.125W|date=1995|deadurlurl-status=yesdead|archiveurl=https://web.archive.org/web/20090703002924/http://lheawww.gsfc.nasa.gov/users/white/wgacat/apjl.html|archivedate=2009-07-03|df=}}</ref><ref name=Kahabka/>

Apparently, luminous SSXSs can have equivalent blackbody temperatures as low as ~15 eV and luminosities ranging from 10³⁶ to 10³⁸ erg/s.<ref name=KahabkaHeuvel>{{ cite journal |author=Kahabka P|author2=van den Heuvel EPJ |title=Luminous Supersoft X-Ray Sources |journal=Annu. Rev. Astron. Astrophys. |date=1997 |volume=35 |issue=1 |pages=69–100 |bibcode=1997ARA&A..35...69K |doi=10.1146/annurev.astro.35.1.69 |url=https://pure.uva.nl/ws/files/4067674/37187_162193y.pdf }}</ref> The numbers of luminous SSSs in the disks of ordinary spiral galaxies such as the MW and M31 are estimated to be on the order of 10³.<ref name=KahabkaHeuvel/>