11 intZand densestmatter

X-ray bursts as probes of thenature of the densest matter in the observable universe: 

X-ray bursts as probes of the nature of the densest matter in the observable universe Jean in ‘t Zand, Didier Barret, with help from others

Slide2: 

Conclusion EDGE, by quickly slewing to particular kinds of X-ray bursts, can constrain the composition of neutron stars through measurements of gravitationally redshifted absorption lines and edges

Outline: 

Outline Goal: constrain nature of the densest matter in the observable universe Present status: measuring up NSs (in particular through X-ray bursts) New prospects: going after super-Eddington X-ray bursts EDGE observation plan

Neutron stars ..: 

Neutron stars .. Are the most compact objects without event horizons due to densities larger than that of nucleonic matter (>3 1014 g cm-3), present unique laboratories for dense matter physics  probe of strong interaction at high ρ and low T may harbor exotic matter (e.g., strange quark matter which is ‘self bound’ [NS is one giant hadron]) provide a bridge between astrophysics, nuclear physics, particle physics, and relativistic/gravitational physics form a centerpiece of one Cosmic Vision Theme: (Lattimer & Prakash 2007)

NS structure: 

NS structure 5 distinct regions Inner core content uncertain 3 possible phases with increasing compressibility: normal matter Bose condensate Deconfined quarks Each phase has its own EOS EOS dictates mass M and radius R  constrain M and R and find out what NSs are made of and how matter behaves at supranuclear densities Figure from Dany Page

EOSs: 

EOSs Lattimer & Prakash 2007 maximum mass (>1.44 Msun certain; 2.1+/-0.2 Msun tentative) NS spin (716 Hz certain; 1122 Hz tentative) Radii model dependent Simultaneous accurate M and R measurements seem mutually exclusive Most opportune route is through M(R) constraints, like spin

Constraining EOS: masses are ‘easy’: 

Constraining EOS: masses are ‘easy’ Lattimer & Prakash 2007

Constraining EOS: radii are difficult: 

Constraining EOS: radii are difficult Timing Crustal properties from glitches, QPOs in SGR giant flares kHz QPOs in LMXBs Thermal Radiation thermal in nature  basics are simple L=4 π R2 σT4 Types of NSs: Cooling NSs with low B (<108 G), no accretion and independent distance estimates  isolated non-pulsing nearby NSs and quiescent LMXBs in GCs X-ray bursts with distances from Eddington limit Model complicating factors: radiation transfer in H atmosphere, residual magnetic effects

Even more difficult: M and R simultaneously : 

Even more difficult: M and R simultaneously  try multiple M/R instead, presuming the same EOS applies to all measured NSs use gravitational redshift best targets: super-Eddington X-ray bursts because they may have much larger metal abundances and are difficult to detect with Chandra and XMM-Newton due to long recurrence times

What are X-ray bursts?: 

What are X-ray bursts? Local accretion rate in low-B NSs 10 to 105 gr s-1 cm-2 After hours to days, accumulate columns of y=105-8 gr cm-2 Pressure (y*g) builds up to ignition condition for thermonuclear flashes through CNO cycle (burning H), triple-alpha reactions (burning He) and C burning Layer heats up to ~109 K within a few tenths of seconds and then cools radiatively over tens of seconds to minutes  photospheric radiation gives X-ray burst Fig. courtesy A. Cumming

Burst profiles: 

Burst profiles Den Hartog et al. 2003; Strohmayer & Brown 2002; Strohmayer & Markwardt 2002; in ‘t Zand et al. 2007

Slide12: 

Photospheric radius expansion Molkov et al. 2001; Galloway et al. 2006 Flux can become super-Eddington if there is a lot of helium involved Photosphere expands, often up to several tens of km, sometimes up to 1000s of km 1% of accreted matter may be lost (energy argument), rest returns to NS surface

New prospects – large absorption edges in PRE bursts (Weinberg, Bildsten & Schatz 2005): 

New prospects – large absorption edges in PRE bursts (Weinberg, Bildsten & Schatz 2005)

New prospects – bursts from UCXB: 

New prospects – bursts from UCXB Bursts from many ultracompact X-ray binaries (UCXBs) always show PRE and are often long (in ‘t Zand et al. 2007)

Simulation 1, conservative case: 

Simulation 1, conservative case Burst with peak flux of 1 Crab E-folding decay time 100 s (intermediate burst) NH=2 x 1022 cm-2 Redshifted Si edge at 2.03 keV (EW 150 eV) Redshifted S edge at 2.65 keV (EW 400 eV) Slew response time 60 s, kT ~ 1.5 keV Fluence caught: 50%

Simulations with XRT, PN, WFT and LET: 

Simulations with XRT, PN, WFT and LET

Simulation 2, nice case: 

Simulation 2, nice case Burst from SLX 1737-282 Burst with peak flux of 2 Crab E-folding decay time 682 s NH=2 x 1022 cm-2 Redshifted Si edge at 2.03 keV (EW 150 eV) Redshifted S edge at 2.65 keV (EW 400 eV) Slew response time 60 s, kT ~ 2.5 keV Fluence caught: 90%

Simulation 2, before and after fit of S edge: 

Simulation 2, before and after fit of S edge

A classification of X-ray bursts: 

A classification of X-ray bursts

Observational plan: 

Observational plan Get triggers from WFM monitor sensitivity should be able to detect 2 keV black body spectrum with bolometric flux of 10-8 erg s-1 cm-2 within 1 s Detect rise within a few seconds from a known burster Create smart triggering algorithm, to lower probability for false triggers (ie bursts that are not PRE or super): filter sources, trigger after 10 min for SBs, detect PRE (2 peaks) and decide for slew if it can be fast enough Fast slew to target  between ~60 s and 1 hour. With 60 s one will detect at least 50% of all fluence Make dedicated observation of 1 hour for PRE burst and 5 hours for superburst Succes may need at least ~5 z measurements. This may need ~50 burst follow ups? Load to EDGE: 20 bursts per year, 1-2 superbursts  about 0.5% of total time

Possible EDGE outcome: 

Possible EDGE outcome

Preemptive scenarios and cautionary remark: 

Preemptive scenarios and cautionary remark Succes of confirmation of EXO result Accurate measurement of truly heavy NS (>2.0 Msun) Succes of Swift rapid follow up of X-ray bursts (program about to be installed?, but XRT has lower sensitivity) Better radius measurements for quiescent LMXBs through better modeling and more accurate Chandra and XMM-Newton measurements of qLMXBs in GCs SN neutrinos GW from a merger Prospects depend heavily on one theoretical prediction