Supersoft X-ray source: Difference between revisions

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==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 |url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V3S-4MBT29S-2&_user=10&_origUdi=B6V3S-3YN948T-5&_fmt=high&_coverDate=12%2F31%2F2006&_rdoc=1&_orig=article&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3a3d0440365be046b322ab561aae9230 |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=Ap 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}}</ref><ref name=Kahabka/>

Apparently, luminous SSSs 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=Ann Rev Astron Astrophys. |yeardate=1997 |volume=35 |issue=1 |pages=69–100 |bibcode=1997ARA&A..35...69K |doi=10.1146/annurev.astro.35.1.69 }}</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/>

==Milky Way SSXSs==

SSXSs have now been discovered in our galaxy and in globular cluster M3.<ref name=White/> MR Velorum (RX J0925.7-4758) is one of the rare MW super soft X-ray binaries.<ref name=Greiner>{{ cite journal |doi=10.1016/S1384-1076(00)00018-X |author=Greiner J |title=Catalog of supersoft X-ray sources |journal=New Astron. |yeardate=2000 |volume=5 |issue=3 |pages=137–41 |url=http://www.mpe.mpg.de/~jcg/sss/ssscat.html |arxiv = astro-ph/0005238 |bibcode = 2000NewA....5..137G }}</ref> "The source is heavily reddened by interstellar material, making it difficult to observe in the blue and ultraviolet."<ref name=Schmidtke>{{ cite journal |doi=10.1086/322155 |author=Schmidtke PC, |author2=Cowley AP |title=SYNOPTIC OBSERVATIONS OF THE SUPERSOFT BINARY MR VELORUM (RX J0925.7-4758): DETERMINATION OF THE ORBITAL PERIOD |journal=Astron J. |date=Sep 2001 |volume=122 |issue= 3|pages=1569–71 |url=http://www.iop.org/EJ/article/1538-3881/122/3/1569/201190.text.html |bibcode=2001AJ....122.1569S}}</ref> The period determined for MR Velorum at ~4.03 d is considerably longer than that of other supersoft systems, which is usually less than a day.<ref name=Schmidtke/>

==Close-binary supersoft source (CBSS)==

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==Noninteracting white dwarfs==

The youngest, hottest WD is very close to 100,000 K, of type DO and is the first single WD recorded as an X-ray source with ROSAT.<ref name=Fleming>{{ cite journal |author=Fleming TA "|author2=et al." |journal=Ap J. |yeardate=1994 |volume=411 |pages=L79 }}</ref><ref name=Werner1994>{{ cite journal |title=Spectral analysis of the hottest known helium-rich white dwarf: KPD 0005+5106 |author=Werner |journal=Astron Astrophys. |yeardate=1994 |volume=284 |pages=907 |bibcode = 1994A&A...284..907W }}</ref>

==Cataclysmic variables==

{{main|Cataclysmic variable star}}

"Cataclysmic variables (CVs) are close binary systems consisting of a white dwarf and a red-dwarf secondary transferring matter via the Roche lobe overflow."<ref name=Kato>{{ cite journal |author=Kato T, |author2=Ishioka R, |author3=Uemura M |title=Photometric Study of KR Aurigae during the High State in 2001 |journal=Publ Astron Soc Japan |volume=54 |issue=6 |date=Dec 2002 |pages=1033–9 |url=http://pasj.asj.or.jp/v54/n6/540624/540624-frame.html |arxiv = astro-ph/0209351 |bibcode = 2002PASJ...54.1033K |doi=10.1093/pasj/54.6.1033}}</ref> Both fusion- and accretion-powered cataclysmic variables have been observed to be [[X-ray]] sources.<ref name=nasa2>{{ cite web |title=Introduction to Cataclysmic Variables (CVs) |url=http://heasarc.gsfc.nasa.gov/docs/objects/cvs/cvstext.html }}</ref> The accretion disk may be prone to [[instability]] leading to [[dwarf nova]] outbursts: a portion of the disk material falls onto the white dwarf, the cataclysmic outbursts occur when the [[density]] and [[temperature]] at the bottom of the accumulated hydrogen layer rise high enough to ignite [[nuclear fusion]] reactions, which rapidly burn the hydrogen layer to helium.

Apparently the only SSXS nonmagnetic cataclysmic variable is V Sge: bolometric luminosity of (1 - 10) x 10³⁷, a binary including a blackbody (BB) accretor at T < 80 eV, and an orbital period of 0.514195 d.<ref name=Greiner/>

The accretion disk can become thermally stable in systems with high mass-transfer rates (Ṁ).<ref name=Kato/> Such systems are called nova-like (NL) stars, because they lack outbursts characteristic of dwarf novae.<ref name=Osaki>{{ cite journal |doi=10.1086/133689 |last1=Osaki |first1=Yoji |title=Dwarf-Nova Outbursts |journal=PASP |yeardate=1996 |volume=108 |pages=39 |bibcode=1996PASP..108...39O }}</ref>

==VY Scl cataclysmic variables==

Among the NL stars is a small group which shows a temporary reduction or cessation of Ṁ from the secondary. These are the VY Scl-type stars or anti-dwarf novae.<ref name=Warner>{{ cite book |author=Warner B |yeardate=1995 |title=Cataclysmic Variable Stars |publisher=Cambridge University Press |___location=Cambridge |url=http://adsabs.harvard.edu/cgi-bin/bib_query?1995cvs..book.....W }}</ref>

===V751 Cyg===

V751 Cyg (BB, MW) is a VY Scl CV, has a bolometric luminosity of 6.5 x 10³⁶ erg/s,<ref name=Greiner/> and emits soft X-rays at quiescence.<ref name=Patterson>{{ cite journal |doi=10.1086/317973 |display-authors=4 |author=Patterson J, |author2=Thorstensen JR, |author3=Fried R, |author4=Skillman DR, |author5=Cook LM, |author6=Jensen L |title=Superhumps in Cataclysmic Binaries. XX. V751 Cygni |journal=Publ Astron Soc Pacific (PASP) |date=Jan 2001 |volume=113 |issue=779 |pages=72–81 |bibcode=2001PASP..113...72P }}</ref> The discovery of a weak soft X-ray source of V751 Cyg at minimum presents a challenge as this is unusual for CVs which commonly display weak hard X-ray emission at quiescence.<ref name=Patterson/>

The high luminosity (6.5 x 10³⁶ erg/s) is particularly hard to understand in the context of VY Scl stars generally, because observations suggest that the binaries become simple red dwarf + white dwarf pairs at quiescence (the disk mostly disappears).<ref name=Patterson/> "A high luminosity in soft X-rays poses an additional problem of understanding why the spectrum is of only modest excitation."<ref name=Patterson/> The ratio He II λ4686/Hβ did not exceed ~0.5 in any of the spectra recorded up to 2001, which is typical for accretion-powered CVs and does not approach the ratio of 2 commonly seen in supersoft binaries (CBSS).<ref name=Patterson/>

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==Magnetic cataclysmic variables==

{{main|Polar (cataclysmic variable)}}

X-rays from magnetic cataclysmic variables are common because accretion provides a continuous supply of coronal gas.<ref name=Trimble/> A plot of number of systems vs. orbit period shows a statistically significant minimum for periods between 2 and 3 hr which can probably be understood in terms of the effects of magnetic braking when the companion star becomes completely convective and the usual dynamo (which operates at the base of the convective envelope) can no longer give the companion a magnetic wind to carry off angular momentum.<ref name=Trimble/> The rotation has been blamed on asymmetric ejection of planetary nebulae and winds<ref name=Spruit>{{ cite journal |title=Origin of the rotation rates of single white dwarfs |author=Spruit HC |yeardate=1998 |journal=Astron Astrophys. |volume=333 |pages=603 |arxiv = astro-ph/9802141 |bibcode = 1998A&A...333..603S }}</ref> and the fields on in situ dynamos.<ref name=Schmidt>{{ cite journal |doi=10.1086/304746 |author=Schmidt GD, |author2=Grauer AD |yeardate=1997 |title=Upper Limits for Magnetic Fields on Pulsating White Dwarfs |journal=Ap J. |volume=488 |issue=2 |pages=827 |bibcode=1997ApJ...488..827S}}</ref> Orbit and rotation periods are synchronized in strongly magnetized WDs.<ref name=Trimble/> Those with no detectable field never are synchronized.

With temperatures in the range 11,000 to 15,000 K, all the WDs with the most extreme fields are far too cool to be detectable EUV/X-ray sources, e.g., Grw +70°8247, LB 11146, SBS 1349+5434, PG 1031+234 and GD 229.<ref name=Schmidt>{{ cite journal |doi=10.1086/175962 |author=Schmidt GD, |author2=Smith PS |title=A Search for Magnetic Fields among DA White Dwarfs |journal=Ap J. |yeardate=1995 |volume=448 |pages=305 |bibcode=1995ApJ...448..305S}}</ref>

Most highly magnetic WDs appear to be isolated objects, although G 23-46 (7.4 MG) and LB 1116 (670 MG) are in unresolved binary systems.<ref name=Barstow/>

RE J0317-853 is the hottest magnetic WD at 49,250 K, with an exceptionally intense magnetic field of ~340 MG, and implied rotation period of 725.4 s.<ref name=Barstow>{{ cite journal |display-authors=4|author=Barstow MA, |author2=Jordan S, |author3=O'Donoghue D, |author4=Burleigh MR, |author5=Napiwotzki R, |author6=Harrop-Allin MK |title=RE J0317-853: the hottest known highly magnetic DA white dwarf |yeardate=1995 |journal=MNRAS |volume=277 |issue=3 |pages=931–85 |bibcode=1995MNRAS.277..971B }}</ref> Between 0.1 and 0.4 keV, RE J0317-853 was detectable by ROSAT, but not in the higher energy band from 0.4 to 2.4 keV.<ref name=Fleming1995>{{ cite journal |journal=Astron Astrophys |title= |author=Fleming TA |yeardate=1995 }}</ref> RE J0317-853 is associated with a blue star 16 arcsec from LB 9802 (also a blue WD) but not physically associated.<ref name=Barstow/> A centered dipole field is not able to reproduce the observations, but an off-center dipole 664 MG at the south pole and 197 MG at the north pole does.<ref name=Barstow/>

Until recently (1995) only PG 1658+441 possessed an effective temperature > 30,000 K.<ref name=Barstow/> Its polar field strength is only 3 MG.<ref name=Barstow/>

The [[ROSAT]] Wide Field Camera (WFC) source RE J0616-649 has an ~20 MG field.<ref name=Jordan>{{cite journal

| display-authors = 4| last = Barstow

| first = M. A.

| last2 = Jordan

| first2 = S.

| author3 = O'Donoghue, D.,
| author4 = Burleigh, M. R.,
| author5 = Napiwotzki, R.,
| &author6 = Harrop-Allin, M. K.,

| last-author-amp = yes

| date = December 1995

| title = RE J0317-853: the hottest known highly magnetic DA white dwarf

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| volume = 277

| issue = 3

| pages = 971-985971–985

| bibcode = 1995MNRAS.277..971B

| doi =

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}}</ref>

PG 1031+234 has a surface field that spans the range from ~200 MG to nearly 1000 MG and rotates with a period of 3^h24^m.<ref name=Latter>{{ cite journal |doi=10.1086/165543 |author=Latter WB, |author2=Schmidt GD, |author3=Green RF |title=The rotationally modulated Zeeman spectrum at nearly 10 to the 9th Gauss of the white dwarf PG 1031 + 234 |journal=Ap J. |yeardate=1987 |volume=320 |pages=308 |bibcode=1987ApJ...320..308L}}</ref>

The magnetic fields in CVs are confined to a narrow range of strengths, with a maximum of 7080 MG for RX J1938.4-4623.<ref name=Schwope>{{ cite journal |title=Two-pole accretion in the high-field polar RXJ 1938.6-4612 |author=Schwope AD, "|author2=et al." |journal=Astron Astrophys. |yeardate=1995 |volume=293 |pages=764 |bibcode = 1995A&A...293..764S }}</ref>

None of the single magnetic stars has been seen as of 1999 as an X-ray source, although fields are of direct relevance to the maintenance of coronae in main sequence stars.<ref name=Trimble/>

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==PG 1159 stars==

PG 1159 stars are a group of very hot, often pulsating WDs for which the prototype is [[PG 1159-035|PG 1159]] dominated by carbon and oxygen in their atmospheres.<ref name=Trimble>{{ cite journal |author=Trimble V |title=White dwarfs in the 1990's |journal=Bull Astron Soc India. |yeardate=1999 |volume=27 |pages=549–66 |bibcode=1999BASI...27..549T }}</ref>

PG 1159 stars reach luminosities of ~10³⁸ erg/s but form a rather distinct class.<ref name=Dreizler>{{ cite journal |author=Dreizler S, |author2=Werner K, |author3=Heber U |journal=Lect Notes Phys. |yeardate=1995 |volume=443 |pages=160 |editor=Kӧster D, |editor2=Werner K |title=White Dwarfs |publisher=Springer |___location=Berlin |doi=10.1007/3-540-59157-5_199}}</ref> RX J0122.9-7521 has been identified as a galactic PG 1159 star.<ref name=Cowley>{{ cite journal |doi=10.1086/133640 |author=Cowley AP, |author2=Schmidtke PC, |author3=Hutchings JB, |author4=Crampton D |title=X-Ray Discovery of a Hot PG1159 Star, RX J0122.9-7521 |journal=PASP |volume=107 |pages=927 |yeardate=1995 |bibcode=1995PASP..107..927C}}</ref><ref name=Werner>{{ cite journal |display-authors=4|author=Werner K, |author2=Wolff B, |author3=Cowley AP, |author4=Schmidtke PC, |author5=Hutchings JB, |author6=Crampton D, |yeardate=1996 |title=Supersoft X-ray Sources |editor=Greiner |journal=Lect Notes Phys. |volume=472 |publisher=Springer |___location=Berlin |pages=131 }}</ref>

==Nova==

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==Large amplitude outbursts==

Large amplitude outbursts of super soft X-ray emission have been interpreted as [[tidal disruption event]]s.<ref name=Komossa>{{ cite journal |title=Discovery of a giant and luminous X-ray outburst from the optically inactive galaxy pair RX J1242.6-1119 |author=Komossa S, |author2=Greiner J |journal=Astron Astrophys. |volume=349 |yeardate=1999 |pages=L45 |arxiv = astro-ph/9908216 |bibcode = 1999A&A...349L..45K }}</ref>

== See also ==