X-ray emission from novae - CSIC · RNe occur on massive white dwarfs, close to Chandrasekhar mass...

X-ray emission from novaeX-ray emission from novae

Glòria Sala

Univ. Politècnica de Catalunya (UPC)

Institut d'Estudis Espacials de Catalunya (IEEC)

OUTLINE

● Novae: What? Where? How? When? How many?

● As seen in the soft X-rays

● Recent and current observational programs

● As seen in the hard X-rays

X-ray emission from novaeX-ray emission from novae

NOVA OUTBURSTSWHAT?

Explosive Thermonuclear events in a white dwarf accreted envelope;

Ejection of fraction of envelope, enriched with nucleosynthetic products

NOVA OUTBURSTSWHAT?



SEE MORE AT JORDI JOSÉ'S

TALK ON WEDNESDAY

NOVA OUTBURSTSWHAT?



WHERE?

CATACLYSMIC VARIABLE(short orbital period, hours) White dwarf + dwarf star

accretion via Roche-Lobe overflow and accretion disk

SYMBIOTIC BINARY(long orbital periods, months-years)

White dwarf+ red giant or Mira accretion of red giant wind

Credit:Romano Corradi ant the IAC

Strong magnetic CV: polar

CATACLYSMIC VARIABLE (CV)

magnetic CV:

Intermediate polar

non-magnetic CV

NOVA OUTBURSTS


In Symbiotics,ejecta expands whithin

dense and complex giant wind

HOW?

In CVs: free balistic expansion,With internal or external (CSM) shocks

HOW MANY?

Total novae ~ 200Galactic rate ~30 novae/yr

(but just ~10 visible )

HOW OFTEN?

Classical novae (CNe): outburst every 105 years => obsserved once

Recurrent novae (RNe): outburst every few years/decades, more than one burst historically recorded

Nova outbursts in symbiotics are exotic.

9 Symbiotic novae(very long nova outburst,

evolving through years-decades)

4-5? Symbiotic recurrent novae known to date:

RS Oph, V745 Sco,

V3890 Sgr,T CrBand V407 Cyg ?


HOW MANY?

Total novae ~160 (up to year 2000)Galactic rate ~30 novae/yr (~10 seen)

HOW OFTEN?Classical novae (CNe):

every 105 years.

Recurrent novae (RNe):every a few years/decades, more than

one burst historically detected

RS Oph, V745 Sco,

V3890 Sgr,T CrBand V407 Cyg

Symbiotic recurrent novae

RNe occur on massive white dwarfs, close to Chandrasekhar mass

=> SNIa progenitor candidates!!

X-ray emission from classical novae

Super SOFT (photon energy <1 keV), “SSS”

- SOURCE: non-explosive H-burning in envelope left on the WD surface

- SPECTRUM: white dwarf atmosphere, kTeff ~30-50 eV (Teff ~2-10×105 K)

- LUMINOSITY: L~105 LSun

~ 1038 erg/s.

TRACES H-MASS LEFT ON WD SURFACE

Ejected materialEjected material

WD

ROSAT X-ray observations of V1974 Cyg (Krautter et al. 1996).

Rise due to decrease ofAbsorption => timescale related to ejected mass

Time (days)

X-r

ay f

lux

Soft X-ray emission due to residual H-burning

(black-body-like spectrum).



(Krautter et al. 1996).

Rise due to decrease ofabsorption

Energy (10 eV)

X-r

ay f

lux

Plateau, evolution path and duration related to white dwarf mass and envelope composition

Time (days)

X-r

ay f

lux



Final decay due to fuel exhaustion, related to envelope mass left on WD after outburst


(black-body-like spectrum). Nova Cyg 1992

(V1974 Cyg)

Comparison

of spectral evolution during

plateau and decay

with models

(Sala & Hernanz 2005a, A&A, 439, 1061)

provided limits on

white dwarf mass

(0.9-1.0 Msun)

(Sala & Hernanz 2005b A&A, 439, 1057)

XMM-Newton: observational follow-up of post-outburst Galactic novaeXMM-Newton: observational follow-up of post-outburst Galactic novaeXMM-Newton obsetvations between 2000-2007, PI: M. Hernanz

OBSERVATIONAL PROGRAMS AIMED TO CATCH THE SSS EMISSION OF NOVAE :

Target Discovery date

Date of observation – Time after outburst

Detection

N Sco 1997V1141 Sco

June 5 Oct. 11, 2000 – 1224d, 3.4yrMar. 24, 2001 – 1388d, 3.8yrSep. 7, 2001 – 1555d, 4.3yr

NO

N Sgr 1998V4633 Sgr

March 22 Oct. 11, 2000 – 934d, 2.6yrMar. 9, 2001 – 1083d, 3.0yrSep. 7, 2001 – 1265d, 3.5yr

YESbut no but no SSSSSS

N Oph 1998 V2487 Oph

June 15 Feb. 25, 2001 – 986d, 2.7 yrSep. 5, 2001 – 1178d, 3.2 yrFeb. 2002 – 1352d, 3.7yrSept. 24, 2002 – 1559d, 4.3yr


N Sco 1998V1142 Sco

October 21 Oct. 11, 2000 – 721 d, 2.0 yrMar. 24, 2001 – 885 d, 2.4 yrSep. 7, 2001 – 1052 d, 2.9 yr

2.62.6±±0.3 0.3 2.22.2±±0.4 0.4 1.21.2±±0.2 0.2

(10(10-2-2 cts/s) cts/s)

N Mus 1998LZ Mus

December 29

Dec. 28, 2000 – 730 d, 2.0 yrJun. 26, 2001 – 910 d, 2.5 yrDec. 26, 2001 – 1093 d 3.0 yr

NO?

• No supersoftNo supersoft X-ray emission related to residual H-burning detected X-ray emission related to residual H-burning detected all novae had already turned-offall novae had already turned-off • 3 out of 5 were emitting [thermal plasma (+ BB)] spectrum 3 out of 5 were emitting [thermal plasma (+ BB)] spectrum ejecta/accretion ejecta/accretion

XMM-Newton: observational follow-up of post-outburst Galactic novaeXMM-Newton: observational follow-up of post-outburst Galactic novae




Detection


June 15 Mar. 24, 2007 – 8.8yrAO6 long exposure

YESbut no SSSbut no SSS

N Cyg 2005V2361 Cyg

February 10

May 13, 2006 - 15mo – bkg Oct. 20, 2006 - 20monthsAO5

--YES

marginal: (4.0marginal: (4.0±±0.8)x100.8)x10-3-3 cts/scts/s

N Sgr 2005aV5115 Sgr

March 28 Sep. 27, 2006 – 18monthsApr. 4, 2009 – 49 months

YES supersoft sourceYES but no SSS

N Sgr 2005bV5116 Sgr

July 4 Mar. 20, 2007 – 20 monthsMar. 13, 2009 – 44 months

YES supersoft sourceYES but no SSS

N Cyg 2006V2362 Cyg

April 2 May 5, 2007 – 13 monthsaffected by bkg AO6Dec. 22, 2008 – 32 months

YES but no SSS

YES but no SSS

N Oph 2006aV2575 Oph

February 9 Sep. 4, 2007 – 19 monthsAO6

NO

N Oph 2006bV2576 Oph

April 6 Oct. 3, 2007 – 18monthsAO6

NO

SupersoftSupersoft X-ray emission related to residual H-burning found in 2 novae from X-ray emission related to residual H-burning found in 2 novae from 2005 (V5115 Sgr & V5116 Sgr)2005 (V5115 Sgr & V5116 Sgr) novae had not turned-off yetnovae had not turned-off yet

MONITORING PROGRAMS AIMED TO CATCH THE SSS EMISSION OF NOVAE :

Swift: TOO triggered observations on Galactic

and Magellanic Cloud novae.

International collaboration, see www.swift.ac.uk/nova-cv/

Wolfgang Pietsch

Valerio Ribeiro

Mark Rushton

Gloria Sala (UPC-IEEC)

Brad Schaefer

Eric Schlegel

Greg Schwarz

Allen Shafter

Steve Shore

Gerry Skinner

Sumner Starrfield

Dai Takei

Gagik Tovmassian

Jim Truran

Neil Vaytet

R. Mark Wagner

Fred Walter

Pete Wheatley

Bob Williams

Graham Wynn

Andrew Helton

Arne Henden

Martin Henze (ESAC)

Margarida Hernanz (CSIC-IEEC)

Rebekah Hounsell

Aitor Ibarra (ESAC)

Jordi Jose (UPC-IEEC)

Amanpreet Kaur

Joachim Krautter

Erik Kuulkers (ESAC)

David Lynch

Elena Mason

Michael Philip Maxwell

Koji Mukai

Ulisse Munari

Jan-Uwe Ness (ESAC)

Tim O'Brien

Marina Orio

Kim Page

Ashley Pagnotta

Julian Osborne

Solen Balman

Andy Beardmore

Tomaso Belloni

Mike Bode

Laura Chomiuk

Matt Darnley

Ivan De Gennaro Aquino

Massimo Della Valle

Andrej Dobrotka

Jeremy Drake

Phil Evans

Stewart Eyres

Bob Gehrz

Ami Glasner

Rosario Gonzalez (ESAC)

Jochen Greiner

Daniel Harman


Swift: TOO triggered observations on Galactic

and Magellanic Cloud novae.

RS Oph, outburst in 2006

(Osborne et al 2011, ApJ 727, 124)

RS Oph, outburst in 2006

(Osborne et al 2011, ApJ 727, 124)

V2491 Cyg

(Page et al 2010 A&A 507, 923)

International collaboration, see www.swift.ac.uk/nova-cv/

Good monitoring and follow-up of the SSS phase, both in X-ray and UV


Martin Henze

Novae in M31: monitoring program with XMM-Newton, Chandra and Swift.

LARGER STATISTICS THAN IN THE GALAXY, 1-2 OPTICAL NOVAE PER MONTH

EASY MONITORING OF SSS IN CENTRAL AREA,COVERED WITH EPIC FOV AND LOW ABSOPRTION => 79 SSS NOVAE UP TO NOW!



FIRST RELATIONS BETWEEN X-RAY AND OPTICAL PARAMETERS AVAILABLE,

Henze et al. 2011, A&A, 533, A52



(lead by Wolfgang Pietsch, MPE; Martin Henze, ESAC)

see www.mpe.mpg.de/~m31novae/)

Papers from this work:

“Supersoft X-rays reveal a classical nova in the M 31 globular cluster Bol 126”Henze, M.; Pietsch, W.; Haberl, F.; Della Valle, M.; Riffeser, A.; Sala, G.; Hatzidimitriou, D. et al. 2013, A&A, 549, A120

“M31N 2008-05d: a M 31 disk nova with a dipping supersoft X-ray light curve”Henze, M.; Pietsch, W.; Haberl, F.; Hernanz, M.; Sala, G.; Della Valle, M.; Stiele, H. 2012, A&A, 544, A44

“X-ray monitoring of classical novae in the central region of M 31, II. Autumn and winter 2007/2008 and 2008/2009”Henze, M., Pietsch, W., Haberl, F., Hernanz, M., Sala, G., Hatzidimitriou, D., Della Valle, M., Rau, A., Hartmann, D.H., Burvitz, V.2011, A&A, 533, A52

Nova M31N 2007-12b: supersoft X-rays reveal an intermediate polar?Pietsch, W., Henze, M., Haberl, F., Hernanz, M., Sala, G., Hartmann, D.H., Della Valle, M.2011, A&A, 531, A22

X-ray monitoring of classical novae in the central region of M 31, I. June 2006 - March 2007Henze, M., Pietsch, W., Haberl, F., Hernanz, M., Sala, G., Della Valle, M., Hatzidimitriou, D., Rau, A., Hartmann, D.H., Greiner, J., Burvitz, V., Fliri, J.2010, A&A, 523, A89

The very short supersoft X-ray state of the classical nova M31N 2007-11aHenze, M., Pietsch, W., Sala, G., Della Valle, M., Hernanz, M., Greiner, J., Burwitz, V., Freyberg, M.J., Haberl F., Hartmann, D.H., Milne, P., Williams, G.G.2009, A&A, 498, L13

The first two transient supersoft X-ray sources in M 31 globular clusters and the connection to classical novaeHenze, M., Pietsch, W., Haberl F., Sala, G., Quimby, R., Hernanz, M., Della Valle, M., Milne, P., Williams, G.G., Burwitz, V., Greiner, J., Stiele, H., Hartmann, D.H., Kong, A.K.H., Hornoch, K.2009, A&A, 500, 769

X-ray monitoring of optical novae in M31 from July 2004 to February 2005Pietsch, W., Haberl, F., Sala, G., Stiele, H., Hornoch, K., Riffeser, A., Fliri, J., Bender, R., Buehler, S., Burwitz, V., Greiner, J., Seitz, S. 2007, A&A, 465, 375

Optical novae: the major class of supersoft X-ray sources in M 31Pietsch, W., Fliri, J., Freyberg, M. J., Greiner, J., Haberl, F., Riffeser, A., Sala, G.2005, A&A, 442, 879





MONITORING PAPERS“Supersoft X-rays reveal a classical nova in the M 31 globular cluster Bol 126”Henze, M.; Pietsch, W.; Haberl, F.; Della Valle, M.; Riffeser, A.; Sala, G.; Hatzidimitriou, D. et al. 2013, A&A, 549, A120

“M31N 2008-05d: a M 31 disk nova with a dipping supersoft X-ray light curve”Henze, M.; Pietsch, W.; Haberl, F.; Hernanz, M.; Sala, G.; Della Valle, M.; Stiele, H. 2012, A&A, 544, A44

“X-ray monitoring of classical novae in the central region of M 31, II. Autumn and winter 2007/2008 and 2008/2009”Henze, M., Pietsch, W., Haberl, F., Hernanz, M., Sala, G., Hatzidimitriou, D., Della Valle, M., Rau, A., Hartmann, D.H., Burvitz, V.2011, A&A, 533, A52











EXTRAORDINARY SSS NOVAE: SSS and NOVAE in GLOBULAR CLUSTERS


“M31N 2008-05d: a M 31 disk nova with a dipping supersoft X-ray light curve”Henze, M.; Pietsch, W.; Haberl, F.; Hernanz, M.; Sala, G.; Della Valle, M.; Stiele, H. 2012, A&A, 544, A44“X-ray monitoring of classical novae in the central region of M 31, II. Autumn and winter 2007/2008 and 2008/2009”Henze, M., Pietsch, W., Haberl, F., Hernanz, M., Sala, G., Hatzidimitriou, D., Della Valle, M., Rau, A., Hartmann, D.H., Burvitz, V.2011, A&A, 533, A52











EXTRAORDINARY SSS NOVAE: SSS and NOVAE in GLOBULAR CLUSTERS









All three novae in M31 GCs are hot and fast => massive WD!





EXTRAORDINARY SSS NOVAE: VARIABLE SSS LIGHT-CURVES“Supersoft X-rays reveal a classical nova in the M 31 globular cluster Bol 126”Henze, M.; Pietsch, W.; Haberl, F.; Della Valle, M.; Riffeser, A.; Sala, G.; Hatzidimitriou, D. et al. 2013, A&A, 549, A120








(Pietsch et al. 2011, A&A 531, 22)

Soft X-ray => Nova M31N 2007-12b: an intermediate polar?

20-60 days after outburstVARIABILITY in the SSS!!

Stable 1100 s period (WD spin)Dips suggest 4.9 or 9.8 hr orbit

Sala, Hernanz, Ferri, Greiner, ApJ 675, L93 (2008)

VARIABILITY in the SSS!!Orbital period: occultation of

the central WD during 2/3 of orbitAsymmetric disk?

OPEN PROBLEMS 1:

variability in the SSS emission: dips, flares and periodicities

V5116 Sgr

Soft X-ray => H-burning

The symbiotic recurrent nova

RS Oph (2006 outburst)

SSS emission as seen by Swift

VARIABILITY in the SSS!!Transient 35 s modulation;fusion driven instability?(Osborne et al 2006, 2011)

RS Oph

variability in the SSS emission


V1494 Aql: 2500s peaks

(non-radial g+ modes of WD)

(Drake et al 2003)

RS Oph: transient 35 s modulation

fusion instability?

(Osborne 2006, Ness 2007)

V4743 Sgr: 1330 s periodicity (WD spin?)

And long dip

(Dobrotka & Ness 2010)

V5116 Sgr: orbital period, 3.2 hrs,

(Sala et al 2008)

M31N 2007-12b: IP-like,

WD spin and orbital period?

(Pietsch et al. 2011)

V2491 Cyg:

37min period and a dip

WD spin??

(Ness et al 2011)

V2491Cyg: RGS spectra. Good NLTE models of expanding atmospheres still missing

(Ness et al. ApJ, 733, 70)

OPEN PROBLEMS 2:

white dwarf atmosphere spectral models

V2491Cyg: RGS spectra. Good NLTE models of expanding atmospheres still missing

(Ness et al. ApJ, 733, 70)

OPEN PROBLEMS 2:

white dwarf atmosphere spectral models

SEE MORE AT JAN-UWE NESS'S

TALK ON WEDNESDAY


1. Super SOFT (photon energy <1 keV), “SSS”

TRACES H-MASS LEFT ON WD SURFACE


WD

2. Ejecta's HARD (photon energy 1-50 keV)

- SOURCE: shocks in ejecta or from ejecta with CSM

- SPECTRUM: thermal plasma, highly ionized species

- LUMINOSITY: L~1033-34 erg/s.

TRACES EJECTA AND CSM

- In Symbiotic systems => shocks with red

giant wind => strong hard X-rays and particle acceleration

3. Accretion's HARD (photon energy 1-50 keV), “CV like”

- SOURCE: hot accretion disk reestablished

- SPECTRUM: Thermal bremsstrahlung, Fe I

- LUMINOSITY: L~1033-34 erg/s.TRACES ACCRETION FLOW

XMM-Newton: observational follow-up of post-outburst Galactic novaeXMM-Newton: observational follow-up of post-outburst Galactic novaeXMM-Newton obsetvations between 2000-2007, PI: M. Hernanz




Detection

N Sco 1997V1141 Sco

June 5 Oct. 11, 2000 – 1224d, 3.4yrMar. 24, 2001 – 1388d, 3.8yrSep. 7, 2001 – 1555d, 4.3yr

NO

N Sgr 1998V4633 Sgr

March 22 Oct. 11, 2000 – 934d, 2.6yrMar. 9, 2001 – 1083d, 3.0yrSep. 7, 2001 – 1265d, 3.5yr



June 15 Feb. 25, 2001 – 986d, 2.7 yrSep. 5, 2001 – 1178d, 3.2 yrFeb. 2002 – 1352d, 3.7yrSept. 24, 2002 – 1559d, 4.3yr


N Sco 1998V1142 Sco

October 21 Oct. 11, 2000 – 721 d, 2.0 yrMar. 24, 2001 – 885 d, 2.4 yrSep. 7, 2001 – 1052 d, 2.9 yr

2.62.6±±0.3 0.3 2.22.2±±0.4 0.4 1.21.2±±0.2 0.2

(10(10-2-2 cts/s) cts/s)

N Mus 1998LZ Mus

December 29

Dec. 28, 2000 – 730 d, 2.0 yrJun. 26, 2001 – 910 d, 2.5 yrDec. 26, 2001 – 1093 d 3.0 yr

NO?

• No supersoftNo supersoft X-ray emission related to residual H-burning detected X-ray emission related to residual H-burning detected all novae had already turned-offall novae had already turned-off • 3 out of 5 were emitting [thermal plasma (+ BB)] spectrum 3 out of 5 were emitting [thermal plasma (+ BB)] spectrum ejecta/accretion ejecta/accretion

Glòria Sala (GAA, FEN UPC)19 de Novembre de 2008, EUETIB

Nova Sgr 1998(V4633 Sgr)

Hard X-ray emission associated to the ejected material

(Hernanz & Sala 2007, The Astrophysical Journal, 664, 467)

2. Hard X-ray emission due to schocked shell

(thermal bremsstrahlung spectrum)

WD

kT1

kT2 kT

3

XMM-Newton, EPIC unfolded spectra



Nova Oph 1998(V2487 Oph)Hard X-ray emission,

2T Thermal plasma (kT1~ 0.22 keV, kT2 >

48 keV) + Gaussian line E = 6.4 keV

Fluorescence FeKα line,signature of accretion

disc, reestablished less than 1000 days after the nova explosion

Also detected by ROSAT during RASS in 1990!!

(Hernanz & Sala 2002, Science 664, 467)

Low THigh T

Fe Kα

3. Hard X-rays due to accretion disk (thermal bremsstrahlung spectrum)

XMM-Newton, EPIC spectra and best-fit model

Prompt (day 9) superhard (up to 70 keV) and later (days 29-150) hard X-rays

V2491 Cyg as seen by XMM, Suzaku and Swift

Takei et al 2009, ApJL: prompt superhard X-rays

Takei et al. 2011 PASJ: X-ray study of rekindled accretion...


1. Super SOFT (photon energy <1 keV), “SSS”

2. Ejecta's HARD (photon energy 1-50 keV)

- SOURCE: shocks in ejecta or from ejecta with CSM

- SPECTRUM: thermal plasma, highly ionized species

- LUMINOSITY: L~1033-36 erg/s.

TRACES EARLY EJECTA

PROPERTIES AND CSM

3. Accretion's HARD (photon energy 1-50 keV), “CV like”

- SOURCE: hot accretion disk reestablished

- SPECTRUM: Thermal bremsstrahlung, Fe I

- LUMINOSITY: L~1033-34 erg/s.TRACES ACCRETION FLOW

BUT TIMING IN THE HARD BAND NOT TESTED AS IN THE sss

BECAUSE OF LOW/BAD STATISTICS

LOFT CAN DO IT!!!


WD

Day LAD (10 ks) cts/s WFM (1ks) cts/s

3 3.8x104 (+/-2) 46 (+/-1)

6 2.6x104 (+/-2) 30 (+/-1)

10 1.1x104 (+/-2) 13 (+/-1)

1 ks

Symbiotic Recurrent Novae:Trigger WFM early in outburst

WFM

LAD

For all novae:Probing nova ejection and accretion:Timing of Fe lines probe origin site, ejecta, accretion flow, reflection...

RS Oph simulations

RS Oph inWFM

RS Oph in LAD,10 ks

RS Oph In RXTE/PCA

Fe lines ofV2491 Cyg in LAD,10 ks

LOFT: Large Observatory For Timing in X-rays

Day LAD (10 ks) cts/s WFM (1ks) cts/s

3 3.8x10 4 (+/-2) 46 (+/-1)

6 2.6x10 4 (+/-2) 30 (+/-1)

10 1.1x10 4 (+/-2) 13 (+/-1)

1 ks

Symbiotic Recurrent Novae:Trigger WFM early in outburst

WFM

LAD

For all novae:Probing nova ejection and accretion:Timing of Fe lines probe origin site, ejecta, accretion flow, reflection...

RS Oph simulations

RS Oph inWFM

RS Oph in LAD,10 ks

RS Oph In RXTE/PCA

Fe lines ofV2491 Cyg in LAD,10 ks

LOFT: Large Observatory For Timing in X-rays

SEE MORE ON LOFT AT MARGARITA HERNANZ'S

TALK AFTER THE COFFEE BREAK

Higher energy emission from novae in symbioticsAbdo et al. 2010, Science

π0 decay produces gamma rays,

π0 originated in shock front of ejecta with red giant wind =>RSOph-like!

NOW TWO MORE RECENT FERMIDETECTIONS OF NOVAE:

Nova Mon 2012(Cheung et al. ATel #4284)Nova Sco 2012 (Cheung et al. ATel #4310)

Tatischeff & Hernanz (2007ApJ) predicted gammas for RS Oph, but no Fermi to see them in 2006!

Summary and conclusions

● Soft X-rays from novae trace envelope left on WD

● Good monitoring programs plus pointed observations arise new questions: Variability? Expanding atmospheres?

● Hard X-rays from novae probe ejection and accretion

● LOFT opens a new window in the timing studies of nova ejecta => time resolved Fe lines spectroscopy would probe emission site (ejecta, disk, reflection)

● Shocks of ejecta with red giant wind in Symbiotic-like Recurrent Novae (like RS Oph) produce very bright prompt hard X-ray emission => trigger in WFM in LOFT

Summary and conclusions

● Soft X-rays from novae trace envelope left on WD

● Good monitoring programs plus pointed observations arise new questions: Variability? Expanding atmospheres?

● Hard X-rays from novae probe ejection and accretion

● LOFT opens a new window in the timing studies of nova ejecta => time resolved Fe lines spectroscopy would probe emission site (ejecta, disk, reflection)

● Shocks of ejecta with red giant wind in Symbiotic-like Recurrent Novae (like RS Oph) produce very bright prompt hard X-ray emission => trigger in WFM in LOFT

SEE MORE ON NOVAE ON WEDNESDAY

X-ray emission from novae - CSIC · RNe occur on massive white dwarfs, close to Chandrasekhar mass...

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Transcript of X-ray emission from novae - CSIC · RNe occur on massive white dwarfs, close to Chandrasekhar mass...