astronomia de raigs x d'objectes compactes: la … · binàries amb nana blanca (variables...

ASTRONOMIA DE RAIGS X D'OBJECTES COMPACTES: ASTRONOMIA DE RAIGS X D'OBJECTES COMPACTES:

LA GAL.LÀXIA EN CONDICIONS EXTREMESLA GAL.LÀXIA EN CONDICIONS EXTREMES

Glòria SalaGlòria Sala

Grup d'Astronomia i AstrofísicaGrup d'Astronomia i Astrofísica

DFEN-EUETIBDFEN-EUETIB

DFEN. 2 de Febrer de 2010.

Que veiem al cel? La nostra situació a la Galàxia

El cel en llum visible i en altres longituds d'ona

Per què ens calen observatoris espacials?

Cal combinar observatoris terrestres i satèl.lits


Observatoris terrestres: radiotelespistelescopis optics i infrarroig properraigs gamma de molt altes energies (Cherenkov)

telescopis Cherenkov

MAGIC

telescopis òptics

VLT


Observatoris terrestres: radiotelescopistelescopis optics i infrarroig properraigs gamma de molt altes energies (Cherenkov)

radiotelescopistelescopis Cherenkov

MAGIC


Observatoris astronòmics espacials

IR: Spitzer (3-180 microns)


Observatoris astronòmics espacials

IR: Spitzer (3-180 microns)

Raigs GAMMA:INTEGRAL (15 keV – 10 MeV)Raigs X:

XMM-Newton (0.5 keV – 10 keV)

OBJECTES COMPACTESOBJECTES COMPACTES

COMPACT OBJECTS: fossiles of the stellar evolutionCOMPACT OBJECTS: fossiles of the stellar evolution

COMPACT OBJECTS: fossiles of the stellar evolutionCOMPACT OBJECTS: fossiles of the stellar evolution

Main sequence stars

Evolució estel.lar: la vida dels estelsObjectes compactes: fossils de l'evolució estel.lar

SUN

COMPACT OBJECTSCOMPACT OBJECTS


NANA BLANCA: • Estructura suportada per la pressió d'electrons degenerats.

• Massa màxima, massa limit de Chandrasekhar: 1.4 masses solars

● Radi similar al de la Terra


• Massa: 1.4 – 2.1 masses solars● Radi: uns 10 kms• Equació d'estat encara desconeguda, hi ha diversos models però cap confirmat =>

La determinacio observacional de M i R delimita la possible equació d'estat

Oezel, Nature 2005


FORAT NEGRE:

• Absència de superfície fisica.

• Massa superior a 3 masses solars en un radi inferior al seu radi de Schwarzschild: 2GM/c2

(3 km per cada massa solar)

WHAT DO THEY LOOK LIKE?WHAT DO THEY LOOK LIKE?

1. Isolated compact objects:1. Isolated compact objects:

Thermal UV emission while cooling down after formation


1. Isolated white dwarfs1. Isolated white dwarfs


1. Isolated NS1. Isolated NS

Low magnetic field:thermal (blackbody) Xray emission while cooling down.

High magnetic field, MAGNETARS: nonthermal (synchrotron) emission arising from “starquakes” => Xray and soft gammmaray flares (SGRs)

.... but... only Xrays and gammarays?

• Very fast optical variability, 0.3-0.4 s => emission region < 100 000 km.

• From X-ray data => located in our Galaxy

• Non- thermal emission => too fast variations of flux for thermal

“Swift J1955: Very fast optical flaring from a possible new magnetar”

Stefanescu, Kanbach, Slowikowska, Greiner, McBreen & Sala. Nature, 455, 503 (2008)

Magnetars: isolated NS with high magnetic fieldMagnetars: isolated NS with high magnetic field

Swift J1955 is probably the first individual of a new class of neutron star: an intermediate stage between

active SGRs (magnetars, young neutron stars) and dim isolated (old) neutron stars.

No other objects know in

the sky shows a similar

behaviour in the optical.

But the optical light curve

reminds of the X-ray light

curve of magnetars

SGR0501+4516. X-ray light curve (XMM/EPIC)

Rea et al. MNRAS 2009 in press (arXiv. 0904.2413)

Swift J1955: Optical light curve (OPTIMA)

Stefanescu et al. Nature 2008

Stefanescu, Kanbach, Slowikowska, Greiner, McBreen & Sala. Nature, 455, 503 (2008)


1. Isolated compact objects:1. Isolated compact objects:

“Black”, no emission Can be detected in microlensing eventsOR If located in a BINARY SYSTEM

Low magnetic field; thermal Xray emission while cooling down High magnetic field, MAGNETARS: nonthermal Xray flares

Thermal UV emission while colling down after formation

Compact objects in binary systems

Secondària

Primària

Black hole or neutron star

X-ray binaries

Secondària

Primària

Black hole or neutron star

Binària de raigs X (Xray binary)

fonts de raigs X més brillants del cel el disc d'acreció és el principal responsable de l'emissió de raigs X

Objecte compacte: estel de neutrons o forat negre

Estel secondari que li transfereix material ric en H, formant un disc d'acreció

Evolució estel.lar en estels binaris

Secondària

Primària

Segons la massa de l'estel primari:

binàries amb forat negre (Xray binary)

binàries amb estrella de neutrons (Xray binary)

binàries amb nana blanca (Cataclysmic variable)

compact objectSupernova o PN


Secondària

Primària


binàries amb forat negre

binàries amb estrella de neutrons

binàries amb nana blanca (variables cataclísmiques)


Galactic Xray binaries are the brightest Xray sources in the sky

Contain a compact accreting object, either a neutron star or a blackhole

Blackhole binaries Blackhole binaries

~20 contain dynamically confirmed stellar black holes (BHs).

other ~20 are black hole candidates (BHCs).

Most are Xray transients, and many with only one Outburst detected!!

Any new Xray transient may be a new BHC!

Strategy:

Trigger XMMNewton Target of Opportunity Observations (TOOs) of new Xray transients

(mainly based on RXTE/ASM monitoring) to identify new Blackhole candidates.

Blackhole binaries Blackhole binaries

XTE J1817330: a bright and soft Xray transientXTE J1817330: a bright and soft Xray transient

Discovered on 26 January 2006 with RXTE (Remillard et al. ATel#714) @ 0.93 (+/0.03) Crab!!

Maximum of 1.9 Crab on 28 January 2006.




Exponential decline with efolding time of 27 days.





Radio counterpart discovered, with steep spectrum and fading a factor 2.6 in 4 days (Rupen et al. ATel#717,#721)






Infrared counterpart with K=15.0 in outburst (D'Avanzo et al. ATel#724)







Optical counterpart with g'=14.93 (Torres et al. Atel#733). g'K colour supports low reddening to the source.









INTEGRAL detection in 20150 keV band (Shaw et al. ATel#734)








SwiftUVOT detection in UV: U=14.4, UVW2=14.9 (Steeghs et al. ATel#742)










Chandra finds low absorption, ~1021 cm2

(Miller et al. ATel#749)














13 March 2006

20 ks exposure

0.310.0 keV

XMMNewton TOOXMMNewton TOO

XTE J1817330: XMMNewton observation XTE J1817330: XMMNewton observation

XMMNewton: OM, EPICpn and RGS spectra

OM, U filterOM, UVW1 filter

EPICpn, Burst mode

RGS1, order 2

RGS1, order 1

EPICpn residuals

OM and RGS residuals

Sala et al . A&

A, 4 73, 561 ( 2007)

XTE J1817330: XMMNewton observation XTE J1817330: XMMNewton observation

EPICpn residuals

Spectral Model

Hot corona(CompTT, kTe=50keV)

τ=0.15(±0.02)Total absorbed modelNH=1.55(±0.05)×1021 cm2

Thermal accretion disk, unabsorbed.

Contributes to UV and optical Thermal accretion disk(diskpn, Rin=6Rg, fixed)kTin=0.70(±0.01) keV

L (0.410keV) @1kpc= 1.2(±0.1) ×1036 (D/1kpc)2 erg s1

Column density is compatible with the average galactic column density: minimum distance is 1 kpc

Sala et al . A&

A, 4 73, 561 ( 2007)

Models: diskpn, Gierlinski et al 1999, MNRAS, 309, 496CompTT , Titarchuk 1994, ApJ, 434, 313

Assuming it was at LEdd at maximum in RXTE lightcurve, corresponding L at time of XMM observation (a factor 6 fainter, 16% Ledd ).

Assuming it was at a lower limit of 30% the LEdd at maximum, corresponding L at time of XMM observations (5% Ledd ).

Sala et al . A&

A, 4 73, 561 ( 2007)

XTE J1817330: mass constraint XTE J1817330: mass constraint

Assuming =1.7, 1.8M

⊙< M < 6M

⊙


Secondària

Primària






Accreting neutron stars vs accreting black-holes

Neutron StarDonor Star(“normal” star)

Accretion Disk

Neutron stars can have strong magnetic fields

If weak magnetic field:

Bright Xrays from accretion disk, like blackhole binaries, but can get closer to compact objects = > hotter

Has a physical surface where Hrich matter from donor accumulates => fresh fuel, when ignites => Type I Xray burst

Accreting neutron stars

Neutron star Xray binariesNeutron star Xray binaries

Xray pulsarsRegular pulses withperiods of 1 1000 s

High magnetic fields channel accretion flow on to magnetic poles

Xray pulsarsRegular pulses withperiods of 1 1000 s

High magnetic fields channel accretion flow on to magnetic poles

Xray burstersFrequent Outbursts of 10100s durationwith lower, persistent Xray flux inbetween

Xray burstersFrequent Outbursts of 10100s durationwith lower, persistent Xray flux inbetween

Type I Xray burstsTHERMONUCLEARBurst energy proportionalto duration of preceedinginactivity period

By far most of the bursters

Type I Xray burstsTHERMONUCLEARBurst energy proportionalto duration of preceedinginactivity period

By far most of the bursters

Type II Xray burstsSPASMODIC ACCRETIONBurst energy proportionalto duration of followinginactivity period

“Rapid burster” (also shows Type I)and GRO J174428 (Rapid Pulsar)

Type II Xray burstsSPASMODIC ACCRETIONBurst energy proportionalto duration of followinginactivity period

“Rapid burster” (also shows Type I)and GRO J174428 (Rapid Pulsar)

weak magnetic field

strong magnetic field

Accreting neutron stars: Type I X-ray bursts

Unstable, explosive burning in bursts (release over short time)

Burst energythermonuclear

Persistent fluxgravitational energy

Type I X-ray BurstsType I X-ray Bursts


• 1036 1038 erg/s• duration 10 s – 100s• recurrence: hoursdays• regular or irregular

Type I X-ray BurstsType I X-ray Bursts

For nuclesynthesis studies and hydrodynamical models see works by Jordi José, Anuj Parikh and Fermin Moreno

Accreting neutron stars: Type II X-ray bursts.The Rapid Burster in March 2009

Time of Swift observations

Sala, Haberl, Pietsch, José & Parikh (2009)

Accreting neutron stars: type II X-ray burstsThe Rapid Burster in March 2009

Sala, Haberl, Pietsch, José, Parikh. Atel 1969 (2009)

100 s

Type II Xray bursts

Xr

ay fl

ux

Time (seconds)

Accreting neutron stars: The Rapid Burster in March 2009

Xr

ay fl

ux

Time (seconds)

Type I Xray Burst with Photospheric Radius Expansion


Xr

ay fl

ux

Time (seconds)


Photospheric expansion => radiation pressure causes expansion => Eddington limit luminosity for this Neutron Star Mass =>

MEASURE MASS


Xr

ay fl

ux

Time (seconds)



Xr

ay fl

ux

Time (seconds)


After peak photosphere receedes => back to NS surface => at “touch down”: photosphericradius = neutron star radius =>

MEASURE RADIUSSala, Haberk, José et al, iIn preparation


Secondària

Primària






non-magnetic cataclysmic variable (CV)

magnetic CV:intermedate polar

Strong magnetic CV: polar

Classical novae

For nuclesynthesis studies and hydrodynamical models see works by Jordi José.

X-ray emission from classical novae

1. SOFT (photon energy <1 keV):

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

- SPECTRUM: black-body-like, kTeff ~30-50 eV (Teff ~2-10×105 K)

- LUMINOSITY: L~105 X Solar ~ 1038 erg/s.

Ejected materialEjected material

WD2. HARD (photon energy 1-10 keV)

- SOURCE: shocks in expanding shell of ejecta

- SPECTRUM: thermal bremsstrahlung, kTeff ~ 1-10 keV

- LUMINOSITY: L~1033 erg/s.

3. HARD (photon energy 1-10 keV)

- SOURCE: hot accretion disk reestablished

- SPECTRUM: Thermal bremsstrahlung + fluorescent emission line from cold matterial

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

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

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

Time (days)

Xr

ay fl

uxExample 1. Soft X-ray emission due to hot atmosphere

(black-body-like spectrum).

1. Soft X-ray emission due to hot atmosphere


(Krautter et al. 1996).

Rise due to decrease ofabsorption

Energy (10 eV)

Xr

ay fl

ux

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

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

Time (days)

Xr

ay fl

ux1. Soft X-ray emission due to hot atmosphere


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

1. Soft X-ray emission due to hot atmosphere


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)

Nova Sgr 1998(V4633 Sgr)

Hard X-ray emission associated to the ejected material

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

Example 2. Hard X-ray emission due to schocked shell

(thermal bremsstrahlung spectrum)

WD

kT1

kT2 kT3

Energy (keV)

Xr

ay fl

ux

Ejected Ejected materialmaterial

WD

Nova Oph 1998(V2487 Oph)

Fluorescence FeKα line,signature of accretion

disc => CV-like emission =>, accretion reestablished less than

1000 days after the nova explosion

Low THigh T

Fe Kα

Example 3. Hard X-rays due to accretion disk

(thermal bremsstrahlung spectrum)

Energy (keV)

Xr

ay fl

ux

(Hernanz & Sala 2002, Science 664, 467)

Thank you for your attention...

... and enjoy your coffee.

astronomia de raigs x d'objectes compactes: la … · binàries amb nana blanca (variables...

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