Gravitational Waves from a Newly Born Accreting Magnetar

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Gravitational waves from a newly born accreting magnetar

AnkanAnkan SurSur

with Brynmor Haskell Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences

Virtual Conference of the Polish Society on Relativity 2020

Introduction

● Fallback accretion onto the magnetar with millisecond spin period (1)(frequency < Keplerian breakup limit).

● Magnetic moment axis inclined at an angle alpha with respect to the rotation axis.

● Closed fieldlines Two important radii, z

z’ y’

Two accretion column forms when x

y ● Gravitational potential radiative luminosity balances neutrino cooling via x’ electron-positron pair annihilation gives the height of accretion column GWs Zhong et al PRD (2019):

Accretion Open fieldlines

1Ott et al ApJS 2006

Accreting magnetar

● Mass accretion rate , being the supernova explosion parameter. We consider = 10. (1)

● Mass of accretion column (zhong et.al PRD 2019)

● Equation of state 3.0

2.5 )

2.0

M 1.5 Mass M ( 1.0 EOS1(rot) EOS2(rot) ● (2) Fully relativistic models using RNS code . 0.5 EOS1(non-rot) EOS2(non-rot) ● Rapid rotation allows for a higher maximum mass. 8 10 12 14 16 18 20 Radius R(km)

● Radius of the NS change as the NS becomes massive.

● The accretion column reduces magnetic dipole moment (Payne & Melatos MNRAS 2004)

1 Piro&Ott ApJ, 2011 2Stergioulas & Friedman 1999 Accreting magnetar

● Mass accretion rate , being the supernova explosion parameter. We consider = 10. (1)

● Mass of accretion column (zhong et.al PRD 2019)

● Equation of state 3.0

2.5 )

2.0

● Radius of the NS change as the NS becomes massive.

● The accretion column reduces magnetic dipole moment (Payne & Melatos MNRAS 2004)

1 Piro&Ott ApJ, 2011 2Stergioulas & Friedman 1999 Accreting magnetar

● Mass accretion rate , being the supernova explosion parameter. We consider = 10. (1)

● Mass of accretion column (zhong et.al PRD 2019)

● Equation of state 3.0

2.5 )

2.0

● Radius of the NS change as the NS becomes massive.

● The accretion column reduces magnetic dipole moment (Payne & Melatos MNRAS 2004)

1 Piro&Ott ApJ, 2011 2Stergioulas & Friedman 1999 Accreting magnetar

● Mass accretion rate , being the supernova explosion parameter. We consider = 10. (1)

● Mass of accretion column (zhong et.al PRD 2019)

● Equation of state 3.0

2.5 )

2.0

● Radius of the NS change as the NS becomes massive.

● The accretion column reduces magnetic dipole moment (Payne & Melatos MNRAS 2004)

1 Piro&Ott ApJ, 2011 2Stergioulas & Friedman 1999 Gravitational waves

● The moment of inertia along the x’, y’, z’ axes respectively.

● The quadrupole moment is given by

● The gravitational wave luminosity is1 100

● The gravitational wave amplitude1 is given by 60 [deg]

α α0 = 2.8◦ 40 α0 = 5.7◦ α0 = 7◦ ● The evolution of the inclination 20 α0 = 8.6◦ α = 90 ● The GW amplitude is maximum ◦ 0 1.0000 1.0025 1.0050 1.0075 1.0100 1.0125 1.0150 1.0175 1.0200 time [s]

1 Shapiro&Teuloksky Spin evolution

The spin evolution is affected by the following torques:

Magnetic dipole radiation GW radiation

Spitkovsky ApJL 2006 Credit: AEI Potsdam / LIGO Credit: NRAO

Neutrino torque (1) Credit: Stan Woosely Accretion torque (1)

Fastness parameter (2)

AAS Nova

1Piro&Ott ApJ 2011 Different Radii

30.0 rm 27.5 rc 25.0 R 22.5

20.0

17.5 radii (km) 15.0

12.5

10.0

0 10 20 30 40 50 time [s]

Sur&Haskell (in prep) Results: Spin

Core-collapsed supernovae (CCS) Binary neutron star merger(BNS) 4.0 8 Ndip Nacc Ndip 3.5 Ngw Ndip + Ngw + Nν + Nacc 7 Ngw Nν Nν 3.0 6 Nacc Ndip + Ngw + Nν + Nacc

2.5 5

2.0 4 P [1 ms] P [1 ms] Spin-down 1.5 3

1.0 2 Spin-up 0.5 1

0 10 20 30 40 50 0 10 20 30 40 50 time [s] time [s] Fallback accretion, the star becomes massive with When mass available for accretion ~ 0.2 (1,2) before becoming a black hole.

1Radice et al. ApJ 2018 2Bernuzzi et al. MNRAS 2020 Sur&Haskell (in prep)

Results: GW strain Core-collapsed supernovae (CCS) Binary neutron star merger(BNS) 4 P0 = 1.1 ms 7

1 P0 = 2.0 ms

− 3 P0 = 1.1 ms s 6

) ergs 2

42 5 10 (

1 ) gw 24 L 4 −

0 (10 3 c

14 h P0 = 1.1 ms 12 P0 = 2.0 ms 2 10

) 1 24

− 8 (10 c 6 h 0 4 5 10 15 20 25 30 35 40 time [s] 2 Collapse 0 0 10 20 30 40 50 time [s]

Sur&Haskell (in prep) Results: GW strain

14 M0 = 1.25 M 22.5 EOS1

M0 = 1.4 M EOS2 20.0 M0 = 1.6 M 12 M0 = 1.8 M 17.5

) )

10 24 24 15.0 − −

(10 12.5 (10

8 c c h h 10.0 6 7.5

4 5.0

0 10 20 30 40 50 0 10 20 30 40 50 time [s] time [s]

Changing the initial mass or the EOS does not change the GW strain significantly.

Sur&Haskell (in prep) Detectability

Advanced LIGO Advanced Virgo 18 10− advanced LIGO Einstein Telescope D

19 advanced Virgo GW signal 10− Cosmic Explorer

20 10−

21 LIGO 10−

10 22 Einstein Telescope −

23 10− Characteristic Strain

24 10−

25 10− Pulsars Core-collapse supernovae

26 10− 100 101 102 103 104 https://cosmicexplorer.org/ Frequency (Hz) (Credit: Marco Kraan, Nikhef)

Summary

● We studied how a newly born magnetar could form accretion mountains.

● The magnetic moment axis becomes orthogonal to the rotation axis in few ms.

● Spin evolution is dominated by the neutrino and the accretion torques.

● Gravitational wave strain does not depend on the initial spin, initial mass or the EOS but it does depend on the mass available for accretion.

● Potential targets for future observatories.

Summary

● We studied how a newly born magnetar could form accretion mountains.

● The magnetic moment axis becomes orthogonal to the rotation axis in few ms.

● Spin evolution is dominated by the neutrino and the accretion torques.

● Gravitational wave strain does not depend on the initial spin, initial mass or the EOS but it does depend on the mass available for accretion.

● Potential targets for future observatories. THANK YOU