Observing Orbital Motion in Strongly Curved Spacetime

Institute of Physics, Silesian University in OpavaGabriel Török

CZ.1.07/2.3.00/20.0071 Synergy , GAČR 209/12/P740, 202/09/0772, SGS-11-2013, www.physics.cz

Observing Orbital Motion in Strongly Curved Spacetime

Institute of Physics, Silesian University in OpavaGabriel Török

CZ.1.07/2.3.00/20.0071 Synergy , GAČR 209/12/P740, 202/09/0772, SGS-11-2013, www.physics.cz

Pavel Bakala, Kateřina Goluchová, Martin Wildner(see Kateřina today, Martin at INAP conf.)

Institute of Physics, Silesian University in OpavaGabriel Török

CZ.1.07/2.3.00/20.0071 Synergy , GAČR 209/12/P740, 202/09/0772, SGS-11-2013, www.physics.cz

On marginally stable circular orbits around neutron stars

CO-AUTHORS:Martin Urbanec, Karel Adámek, Gabriela Urbancová

KERR

1. ISCO and NS Compactness

OBLATENESS

The influence of NS oblateness on the orbital frequencies has been extensively studied in the last decade, e.g.,Morsink, Stella, ApJ (1999); Rosinska et al. A&A (2001); Amsterdamski et al., A&A (2002), Urbanec et al., MNRAS (2013), Kluzniak & Rosinska (2013)

Kluzniak et al., ApJ (1990)

Toro

k et

al.

(201

0),A

pJ

ISCO FREQUENCY:

1. ISCO and NS Compactness

ISCO RADIUS (Hartle-Thorne Spacetime):

The ISCO radius decreases with spin, but increases with quadrupole.

j

q

1. ISCO and NS Compactness

Neutron star radii R evolve with j rather slowly. The non-monotonic behaviour of r_ISCO thus imply non-monotonic behaviour of the quantity

K= r_ISCO/ R_NS.

j

q

ISCO RADIUS (Hartle-Thorne Spacetime):

1. ISCO and NS Compactness

SPIN [Hz]

In the case of high mass, the ISCO is above the NS surface. In the case of low mass, the ISCO is above the NS surface only for very high spins (when these are allowed).

ISCO below NS surface

ISCO above NS surface

Inverse compactness K= r_ISCO / R_NS (calculated for particular SKI5 EOS).K=

rISC

O /

RN

S

1. ISCO and NS Compactness

In the case of intermediate NS mass, the ISCO is above the NS surface for low and high spins, but not for the intermediate spins. Clearly, there are implications for the ISCO-NS distribution.

SPIN [Hz]

ISCO below NS surface

ISCO above NS surface

Inverse compactness K= r_ISCO / R_NS (calculated for particular SKI5 EOS).K=

rISC

O /

RN

S

2. NS distribution

M

ASS

[MSu

n]

SPIN [Hz]

Initial Distribution of NS[K<>1] =>

Distribution of ISCO-NS

2. NS distribution

SPIN [Hz]

MAS

S [M

Sun]

Initial Distribution of NS (one concrete EoS)

SPIN [Hz]

MAS

S [M

Sun]

2. NS distribution

Initial Distribution of NS (one concrete EoS)

0 500 1000 1500 Spin [Hz]

Mass [M

sun]

0 1 1.5 2

MAS

S [M

Sun]

SPIN [Hz]

2. NS distribution

ISCO-NS Distribution

0 500 1000 1500 Spin [Hz]

Mass [M

sun]

0 1 1.5 2

MAS

S [M

Sun]

SPIN [Hz]

3. Particular application:

ISCO-NS Distribution

Several QPO models require ISCO-NS -> the influence on QPO sources distribution

HF QPOs due to Paczynski modulation -> fast and slow rotators

4. Conclusions

SPIN [Hz]

Num

ber o

f NS

[rel

ative

uni

ts]

Distribution ofall NS

The ISCO-NS distribution has the peaks at the values of the spin which can be very different from the peak in the distribution of all NS.• High M -> peak at the original value of spin• Low M -> peak at the high value of spin• Inter. M -> two peaks

4. Conclusions

SPIN [Hz]

Num

ber o

f ISC

O-N

S [r

elati

ve u

nits

]

Distribution ofall NS

The ISCO-NS distribution has the peaks at the values of the spin which can be very different from the peak in the distribution of all NS.• High M -> peak at the original value of spin• Low M -> peak at the high value of spin• Inter. M -> two peaks

4. Conclusions

SPIN [Hz]

Num

ber o

f ISC

O-N

S [r

elati

ve u

nits

]

Distribution ofall NS

The ISCO-NS distribution has the peaks at the values of the spin which can be very different from the peak in the distribution of all NS.• High M -> peak at the original value of spin• Low M -> peak at the high value of spin• Inter. M -> two peaks

4. Conclusions

SPIN [Hz]

Num

ber o

f ISC

O-N

S [r

elati

ve u

nits

]

The ISCO-NS distribution has the peaks at the values of the spin which can be very different from the peak in the distribution of all NS.• High M -> peak at the original value of spin• Low M -> peak at the high value of spin• Inter. M -> two peaks

4. Conclusions

SPIN [Hz]

Num

ber o

f ISC

O-N

S [r

elati

ve u

nits

]

The ISCO-NS distribution has the peaks at the values of the spin which can be very different from the peak in the distribution of all NS.• High M -> peak at the original value of spin• Low M -> peak at the high value of spin• Inter. M -> two peaks

applications