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A unique insight into a rare outburst of GW Lib. K.Byckling, J. Osborne, G. Wynn, A. Beardmore, V. Braito (UoL), K. Mukai (NASA/GSFC), R. West (UoL) March 15-19, 2009 Wild stars in the Old West Tucson, Arizona. Motivation. X-ray behaviour during DNe outburst is not well-understood - PowerPoint PPT Presentation
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K.Byckling, J. Osborne, G. Wynn, A. Beardmore, V. Braito (UoL), K. Mukai (NASA/GSFC), R. West (UoL)
March 15-19, 2009Wild stars in the Old West
Tucson, Arizona
Motivation
X-ray behaviour during DNe outburst is not well-understood
The two well-studied systems, SS Cyg and U Gem, behave differently
Need to observe more systems
GW Lib in a nutshell!Discovered in 1983 through its first outburst (OB)
as a 9th magnitude star
First CV with non-radial WD pulsations in quiescence (Warner & van Zyl 1998, van Zyl et al. 2000) WDs in CVs were thought to be too hot to be in the DAV instability strip
Classified as a WZ Sge type DN: low mass accretion rates in quiescence & long recurrence times
XMM observations of GW Lib confirmed that the max temperature and the quiescent luminosity are low kT_max = 5 keV, L = 9 x 10^28 erg/s (Hilton et al. 2007)
The Great Superoutburst in 2007Second OB took place in April 2007 lasting ~26 days
the gap between the outbursts 24 yrs!
AAVSO observers and Swift observed the second outburst in the optical, UV (UVOT) and X-rays (XRT)
To date, only two other systems have simultaneous multiwavelength outburst lightcurves: SS Cyg and U Gem
These have longer orbital periods than GW Lib: SS Cyg 6.6 h, U Gem 4.2 h, GW Lib 77 min
Simultaneous multiwavelength data of the outbursts of SS Cyg and U Gem provide a basis to compare the outburst behaviour
The most striking difference in X-rays! Assumption: X-rays rise in the beginning not seen in GW Lib X-rays decline in ~10 d in GW Lib (cf. SS Cyg ~less than 3 hrs) The X-ray re-brightening seen at the end in SS Cyg is not clear
in GW Lib and U Gem
GW Lib (Byckling et al. (in prep.))
SS Cyg (Wheatley, Mauche, & Mattei 2003)
U Gem (Mattei, Mauche, & Wheatley2000)
Swift UVOT2200-4000 Å
AAVSO
Swift XRT0.3-10 keV
72-130 Å
2-15 keV
2-15 keV
72-130 Å
26 d 10 d 15 d
? ?
The X-ray spectra
S1S2
S3
S5S4
S1S2
S4 S5wabs Nh (x 10^20 cm^-2) Temperatures
S1: S4: kT_bb = keV S2: S5: Max. mekal T of S1 ~6 keV. S3: Abundance:
S3
05.004.083.23
38.599.361.8
23.117.115.8
28.738.325.13
86.636.463.14
001.0001.0013.0
01.001.002.0
X-ray hardness ratio
Soft0.3-1.0 keV
Hard1.0-10 keV
Hard/Soft
X-ray luminosity:
The black body luminosity notwell-constrained
In 0.3-10 keV peak luminosity L = 2.1 x 10^32 erg/s (Ṁ = 1.7 x 10^15 g/s)
At the end of the OB L = 4.7 x 10^30 erg/s(Ṁ = 3.9 x 10^13 g/s)
No periods seen in the X-raydata
Disc modelsWhy is the recurrence time much
longer than other DNe?
Why do we only see superoutbursts?
Look for solution from the models for WZ Sge: Low disc viscosity in quiescence (Smak
1993) Evaporation of the inner disc
combined with low viscosity (Meyer-Hofmeister et al. 1998)
Truncation of the inner disc by a magnetic WD with standard viscosity (Warner, Livio, & Tout 1996; Matthews et al. 2007)
ConclusionsThe X-ray behaviour is not consistent with that of SS
Cyg
The UV and optical outburst lightcurves are more closely related in structure and shape than UV and X-rays similar emission region? (cooler part of the disc away from the boundary layer)
A black body tail seen in the first outburst spectrum boundary layer luminosity?
Long recurrence time (decades) and the lack of normal OBs suggest the disc in GW Lib is truncated or the disc viscosity is ~100 times lower than in other CVs
Credit: A. Beardmore
KB acknowledges funding from the European
Commission under the Marie Curie Host Fellowship for Early Stage Research Training Spartan, University of Leicester, UK.
Acknowledgments