Approaches to study the EOS for neutron star matter from X-ray astronomy satellites (Report from Group C01)

Transcription

1 Approaches to study the EOS for neutron star matter from X-ray astronomy satellites (Report from Group C01) Tadayuki Takahashi, Tadayasu Dotani, Masahiro Tsujimoto Institute of Space and Astronautical Science (ISAS)/JAXA Toru Tamagawa RIKEN Yasunobu Uchiyama Rikkyo Univ. ( Collaborators: Hirokazu Odaka, Teruaki Enoto, Dmitry Khangulyan, Atsushi Harayama, Hirokazu Ikeda, Masachika Iwai, Chris Done, Hiroki Yoneda) Program for Specific topics (talks) Kazuo Maxima (RIKEN), Teruaki Enoto (Kyoto U.)

2 T,Takahashi, T. Dotani, M. Tsujimoto, T. Tamagawa, Y. Uchiyama, NSMAT 2016, Nov , 2016 Topics covered in the C-01 research project 1) Neutron star observations with X-ray missions such as ASTRO-H. (1) Prepare for high-resolution observations by using the micro-calorimeter (SXS) onboard ASTRO-H. (e.g. high counting rate Pulse Shape Processor (PSP)) (2) Prepare for wide-band observations from 0.3 kev to 600 kev by using SXI (X-ray CCD), HXI (CdTe DSD) and SGD (Si/CdTe Compton Camera) onboard ASTRO-H (e.g. ground calibration) (3) Find good targets to be observed by ASTRO-H based on studies by using archival data from Chandra, XMM, Suzaku. SXS Dewar HXI Test Model

3 Topics covered in the C-01 research project 2) Study new X-ray missions, to open up a new field for studying neutron star matter (1) Participate in international mission proposals 1. NICER (Enoto s talk) 2. PRAXyS 3. LOFT (2) Develop new detectors for future X-ray missions (Si and CdTe Imaging detectors wth high counting & high resolution capability) 3) MonteCarlo calculation code to simulate the emission from neutron star surface (under strong magnetic field) 4) Use GeV Gamma-ray observatory (Fermi Satellite) to find another approach to study the neutron star. X-ray Path in the MC Simulation of Accretion Column

4 T,Takahashi, Recent Development of CdTe Imagers", Arizona, 25 Aug ASTRO-H (Hitomi) Chandra (Marshall et al. 2001) 2.7 ton/14 m

5 T,Takahashi, Recent Development of CdTe Imagers", Arizona, 25 Aug ASTRO-H (Hitomi) But lost its function on March 26, 2016 All mission instruments showed good Chandra performance (Marshall et al. 2001) as expected. Part A of this presentation (Tsujimoto)

6 New Missions (PRAXyS, NICER, LOFT) PRAXyS (Polarimeter for Astrophysical X-ray Sources) Project deployable optical boom X-ray polarimeters X-ray mirror f=4.5m 7.0m 2014/12: Proposed to NASA's Small Explorer program 2015/07: Selected for Phase A study (three projects selected) 2016/07: Submitted Conceptual Study Report to NASA HQ 2017/02: Down selection (only one project will be selected.) 2020/08: Launch

7 GeV/TeV Gamma-ray Observations of Pulsars/Pulsar Wind Nebulae Some Radio-quiet pulsars show large Gammaray luminosity close to its Spin-down power: Gamma-ray observations can constrain NS s moment of inertia, I. Spin-down power: Ė = I =4 2 IPP 3 Fermi Satellite Lγ=E for I0 gamma-ray luminosity of pulsar/pulsar wind nebula pulse measurement (radio/gamma) Then, moment of inertia, I, can constrain EOS. I = kmr 2 Figure 6.9: γ-ray luminosity L γ vs. spin-down power Ė in the energy band of 100 MeV 100 GeV. The vertical error bars in color are from the statistical uncertainty on the energy flux G 100, while in black are due to the distance uncertainties. Horizontal error bars come from Doppler corrections (Section 4.1.2) applied to MSPs with known proper motions. The upper diagonal line indicates 100% conversion of Ė into γ rays, and the lower diagonal line indicates the heuristic Number of gamma-ray pulsars detected with Fermi-LAT is 205! (as of 2016 Feb), including PSRJ in LMC (Large Magellanic Cloud).

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9 X-ray micro-calorimeter array. 6x6 pixels : 10.6 μm HgTe absorber + Si thermometer at 50 mk. Measure T increase (about 1 mk) by energy deposit of individual X-ray photons (about 1 fj). Ts ( 50 m K) 8 0 m s Multi-stage cooling using (a) 3 ADRs, (b) 4 Stirling coolers, (c) 1 Joule- Thomson cooler, (d) 30 litter liquid He. Thermal relaxation time scale : about 5 ms = 200 Hz/pixel

10 Onboard Digital Electronics Waveform : ADU(t) is cross-correlated with a template to derive energy by optimum filtering. Onboard digital electronics is the bottleneck in total throughput. 150 Hz/ array (about 1/10 of Crab flux) required. Efforts for high CR performance made in development phase.

11 In-orbit Performance Energy resolution : 4.9 ev (FWHM) at 5.9 kev. Energy range : 2-20 kev.

12 High CR observation Crab nebula observed. About 200 Hz events processed. Most illuminated pixels have >25% live time. Superb spectroscopic performance verified for a high CR observation.

13 Spectroscopy of high CR Most stringent upper limit for X-ray line emission from Crab, a super-nova remnant. Constraint on the origin of this super nova SN1054.

14 Summary (Topic A) SXS worked successfully in the orbit. No major problems. The first satellite-borne X-ray micro-calorimeter to observe X-ray sources. Superb spectroscopic performance achieved. Tremendous advantages beyond all other X-ray spectrometers for various topics, including NS. Efforts to make high CR observations paid off. Verified with Crab.

15 Topic B: X-ray Observations of Neutron Stars to Study the EOS Importance of X-ray observations In order to get information on the radius, we need to observe radiation from the neutron star surface. Thermal emission from the mass-accreting neutron stars T = 1.8 M M 1/4 R 10km 1/2 L L Edd 1/4 kev X-ray observations are essential to get information on radius of the neutron stars.

16 Observational Methods to probe the neutron star radius (1)Mass-Radius Ratio Gravitational redshift of the atomic features in the X-ray spectrum from the NS surface. X-ray bursts (2) Radius (and Mass) Light bending and Doppler boosting Pulse profile of the millisecond pulsars with thermal emission NICER: Talk by T. Enoto

17 Low-mass X-ray binaries and X-ray Bursts Accretion disk Neutron star Low-mass star Duration : ~ sec Interval : hours ~ days Luminosity : Eddington limit ~10 38 erg/s Burst oscillation is used to infer the spin frequency.

18 Why X-ray bursts? (1) Enrichment of heavy elements in the atmosphere Heavy elements up to Z~50 are produced in X-ray bursts. Atomic features in the spectra. Mean composition of the envelope Metal poor Solar Parikh et al. 2013, Prog. Part. Nucl. Phys. 69, 225 (2) Temperature structure of the atmosphere Mass number A Photons created at the bottom of the atmosphere will go through the relatively cool layer, where absorption lines/edges are formed. Caveat: Rapid spin of the neutron star X-ray bursters: typical spin Hz Spectral features may be smeared out.

19 Candidate 1: A unique burst source Terzan 5 X2 Frequency (Hz) Cavecchi et al. 2011, ApJ, 740, L8 Independent of distance, radiation isotropy, details of the emission region, continuum models

20 Association with SNR is revealed. SNR age is estimated to be <4600 yr. No spin-up due to mass-accretion is expected for such a young neutron star. It should preserve the original spin frequency at birth, which may be a few tens Hz. No X-ray burst occur in the high state, which may last ~5-10 yrs. (Heinz et al. 2013, ApJ, 779, 171) SNR associated with Cir X-1 Chandra X-ray image (1-3 kev) Heinz et al. 2013, ApJ, 779, 171

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22 Summary (Topic B) 1. We have studied various methods to obtain information on the NS radius, and selected the best one: Parameters: Gravitational redshift Methods: Atomic features in the burst spectra Targets: T5X2, Cir X-1 2. We searched existing burst data for the spectral features, and found a candidate from GRS It is important to get a wide band coverage to understand various types of neutron stars, eg. magnetars, pulsar wind nebulae, and X-ray binaries. This was realized with ASTRO-H for keV, which may be utilized for the future mission.

23 Summary We succeeded to demonstrate the power of X-ray micro-calorimeter during the first one-month operation of ASTRO-H (Hitomi) before the loss of the spacecraft. SXS worked successfully in the orbit. as the first satellite-borne X-ray micro-calorimeter to observe X-ray sources. Tremendous advantages beyond all other X-ray spectrometers for various topics, including NS. We have identified candidates as the sources to study the EOS of neutron star matter. We participated in and contributed to future X-ray mission proposals, such as PRAXyS, NICER and LOFT. We successfully expanded our scope to GeV gamma-ray observations (Fermi) to constrain the M/R ratio.