How Circinus X-1 Became the Youngest Known X-Ray Binary

A Blast from the Past: How Circinus X-1 Became the youngest known X-ray Binary

Sebastian Heinz (UW-Madison)

Paul Sell (UW-Madison, Texas-Tech)! Norbert Schulz (MIT)! Rob Fender (Oxford)! Dan Calvelo-Santos (Southampton)! Peter Jonker (SRON)! Rudy Wijnands (Amsterdam)! Niel Brandt (PSU)! Michiel VanDer Klis (Amsterdam)! Tasso Tziumis (ATNF)! Paolo Soleri (formerly Amsterdam) Mike Nowak (MIT)! Young: X-ray Pulsar • High ﬁeld! • Steady burning polar cap

Magnetosphere Old: X-ray Transients • Low ﬁeld! • Regular accretion! • Unsteady burning (nuclear ﬂashes) 1993MNRAS.261..593S Circinus X-1

Stewart+’93 Tudose+’06 Circinus X-1 Vital Stats • Orbit:! • Neutron star XRB (Linares+’10)! ★ 16.5 day orbit! ★ Type 1 bursts! ★ Eccentricity e~0.45! ★ No pulsations! ★ X-ray dips! ★ Jets! ★ P/Ṗ ~ 3,000 yrs!! ⇒ Low ﬁeld LMXB ! • Extinction: ! • Companion (Jonker+’07)! ★ 9 < AV < 12! ★ A5-B0 Ia - HMXB? ! 22 -2 ★ NH ~ 2x10 cm ! ★ Or: 0.4 M? [?]XMB

Properties HMXB - young LMXB - old Donor O-B (M > 5M K-M or WD Optical spectrum Star-like Reprocessed Accretion disk small yes Orbital Period 1-100d 10min - 10d X-ray Eclipses common rare B-ﬁeld Strong (B>10 Weak (B~10 X-ray pulsations common (0.1-1000s) rare (0.001-100s) Type I X-ray Bursts absent common QPOs rare (0.001-1Hz) common (1-1000Hz) Jets No Yes When Cir X-1 is bright…

Pure dust scattering halo

Brandt+’01 When Cir X-1 is dim…

(Sell et al. 2010) Circinus X-1 X-ray Nebula -1 s -2

chip edge cm photons

Heinz+’13 Circinus X-1 X-ray Nebula -1 s -2 photons cm photons

Heinz+’13 ATCA radio

1.1−3.1GHz -1 Jy beam Jy

Heinz+’13 Radio/X-Ray Overlay

Heinz+’13 A (NE) Thermal– 18 – Spectrum

1 Mg XI Si XIII S XV ]

1 −1

− 10 keV 1 − s

10−2

10−3 Count rate [counts

10−4

0 ∆χ

−5 1 2 3 4 5 Energy [keV] Heinz+’13 Fig. 6.— Chandra Top panel: X-ray Spectrum of the outer portion of the supernova remnant, showing Magnesium XI and XII (1.4 keV), Silicon XIII (1.8 keV) and Sulfur XV (2.4 keV) emission lines. Error bars indicate one-sigma uncertainties. The dark gray histogram shows the best fit SEDOV shock model with photoelectric foreground absorption, the light-grey histogram shows the best-fit powerlaw model. The spectrum contains approximately 2900 net source counts and covers approximately 30% of the remnantareavisibleontheACIS CCDs. Bottom panel: fit residuals for the best fit SEDOV and powerlaw models in dark and light grey, respectively. A (NE) Thermal– 18 – Spectrum

1 Mg XI Si XIII S XV ]

1 −1

− 10 keV 1 − s

10−2 It’s a supernova remnant

10−3 Count rate [counts

10−4

0 ∆χ

Heinz+’13 Consequences (1)

• At ~ 2,600 D8 years, Circinus X-1 is the youngest known X-ray binary! • Only three other XRBs in Supernova remnants:

SS433 SXP 1062 (LMC) DEM L241 (SMC) Consequences (2) • P/Ṗ ~ 3,000 years consistent with age! • Post-SN orbit:! ★ Orbit & spins likely misaligned - precession! • Crazy light curve Consequences (2) ity, which, when combined with the source size, 3.0 3.0 ity,can which, provide when an estimate combined of with the the age. source TheP/Ṗ size, ex- ~ 3,0002.5 years consistent with age! 2.5 • 2.0 canisting provide observations an estimate are consistent of the age. with The thermal ex- 2.0 isting observations are consistent with+4 thermal 1.5 emission at a temperature of T ≈ 2−1 keV (1- +4 1.5 T ≈ 1.0 emissionsigma conﬁdence), at a temperature which is ofclearly not2−1 accuratekeVPost-SN (1- ASM flux [crabs] orbit:! • 1.0 sigmaenough conﬁdence), for a quantitative which is argument. clearly not accurate ASM flux [crabs] 0.5 0.00.5 enough for a quantitative argument. ★ −4000 −3000 −2000 −1000 0 With an age measurement and a total energyOrbit &0.0 spins likely misaligned - precession! days since 01 Jan 2009 With an age measurement and a total energy −4000 −3000 −2000 −1000 0 from the emission measure, we can directly cal- 0.6 days since 01 Jan 2009 fromculate the the emission jet power measure,W (as is we often can done directly with cal- ob- 0.50.6 culate the jet power W (as is often done withCrazy ob- light0.5 curve servations of cavities around AGN• jets), which 0.4 0.4 servationsis one of the of most cavities important around deliverables AGN jets), whichof the 0.3 0.3 isproposed one of the observation. most important The deliverables existing observa- of the 0.2 ASM flux [crabs] proposed observation. The existing observa- 0.2 tions only allow relatively rough limits to be ASM flux [crabs] 0.1 tionsplaced only on W allow. relatively rough limits to be 0.00.1 −1000 −800 −600 −400 −200 0 0.0 placed on W . days since 01 Jan 2009 (Sell et al. 2010) Given a shock velocity and the emission −1000 −800 −600 −400 −200 0 days since 01 Jan 2009

Given a shock velocity and the emission measure, we will also be able to etimate the

0.0 1.0 measure, we will also be able to etimate the ISM density the jet is running into, which is 1.00 peak phase 0.0 1.0 1.00 ISMcritical density information the jet for is running understanding into, which micro- is ACISpeak phasedose limit Trigger flux

ACIS dose limit Trigger flux criticalquasar/ISM information interaction for and understanding a powerful micro- probe 0.10 quasar/ISM interaction and a powerful probe 0.10 of the large scale environment of what is still a ASM peak flux [crab]

of the large scale environment of what is still a ASM peak flux [crab] very mysterious source. 0.01 very mysterious source. 0.010.0001 0.0010 0.0100 0.1000 1.0000 Similar considerations could be made in the ASM Flux (averaged over phase 0.0−0.5) [crab] 0.0001 0.0010 0.0100 0.1000 1.0000 caseSimilar of non-thermal considerations radiation, could be though made in in that the ASM Flux (averaged over phase 0.0−0.5) [crab] casecase of a directnon-thermal velocity radiation, and age though determination in that Figure 2: Long term (top) and short term (mid- Figure 2: Long term (top) and short term (mid- casewould a be direct impossible velocity (however, and age other determination age indi- dle) lightcurve of Cir X-1. Orbital dips at phase dle) lightcurve of Cir X-1. Orbital dips at phase wouldcators, be like impossible synchrotron (however, aging of other the X-ray age indi- elec- 0.95 are indicated by diamonds in the bottom 0.95 are indicated by diamonds in the bottom cators,trons, would like synchrotron still be available). aging of the X-ray elec- panel. Bottom panel: Average flux over the first trons, would still be available). 50%panel. ofBottom the binary panel: orbitAverage plotted flux against over the peak first flux50% in of that the binary binary orbit. orbit plotted against peak 4 Technical Feasibility flux in that binary orbit. 4 Technical Feasibility Exposure time: Our exposure time goal was instrument as safe as possible, which we have Exposure time: Our exposure time goal was set by the requirement of being able to clearly adoptedinstrument from as our safe cycle as possible, 10 ToO program. which we have set by the requirement of being able to clearly distinguish between different emission mecha- adoptedIn order from to our reach cycle our 10 spectroscopic ToO program. sensitiv- distinguish between different emission mechanisms and to constrain the spectral parameters ityIn goal, order the to total reach source our spectroscopic flux should be sensitiv- below nisms and to constrain the spectral parameters for either of the two models (temperature or theity goal, level the of the total previous source gratings flux should observation. be below for either of the two models (temperature or powerlaw index) to within better than 15%. Us- Thisthe level translates of the into previous a 2-10 gratings keV flux observation. limit of powerlaw index) to within better than 15%. Us- ing XSPEC and the existing zero order spec- 5This× 10 translates−10 ergs s− into1 cm− a2. 2-10 The keV source flux has limit been of ing XSPEC and the existing zero order spec- × −10 −1 −2 trum, we estimate that we need an order of at5 or10 belowergs this s limitcm for. The significant source hasstretches been trum, we estimate that we need an order of magnitude increase in the number of detected ofat time or below in the this last limit two years, for significant and we anticipate stretches magnitude increase in the number of detected photons This requires a 100ksec observation. thatof time it will in the continue last two this years, trend and during we anticipate cycle 11. photons This requires a 100ksec observation. Justification of ToO: For the observation to Tothat be it conservative, will continue wethis chose trend a during trigger cycle flux 11. of − − − Justificationbe successful scientifically of ToO: For and the to observation be safe for the to 1To.2 × be10 conservative,10 ergs s 1 cm we2 chose. a trigger flux of . × −10 −1 −2 beinstrument, successful it scientifically is vital that and the to source be safe be for at the 1 2Cir10 X-1’sergs flux s hascm been. declining for several instrument,lowest flux possible. it is vital After that careful the source consideration be at the yearsCir (see X-1’s Fig. flux 2). has It been is this declining trend that for several made lowestand extensive flux possible. discussions After careful with the consideration instrument theyears first (see detection Fig. 2). of It the is this jet possible trend that and made that andteam, extensive we have discussions devised a with strategy the thatinstrument maxi- wethe wish first to detection take advantage of the jet of with possible the proposed and that team,mizes the we observing have devised efficiency a strategy while keeping that maxi- the observation.we wish to take However, advantage the sourceof with also the variesproposed on mizes the observing efficiency while keeping the observation. However, the source also varies on 3 3 Consequences (3) • Type I X-ray bursts, jets, lack of pulsations:! ★ B 1012 G ( ~ 109 G?)! ★ Lowest field young neutron star?! ★ Are there others? Fig. 1. Three examples of Chandra-observed pulsar wind nebulae. (Left) The Crab nebula (the image is 50 across) with its clear toroidal morphology and jet structure (NASA/CXC/SAO/F. Seward et al.). (Center)ThePSRB1509—58 pulsar wind nebula, nicknamed the “hand of God” (image is 200 across; NASA/CXC/SAO/ P.Slane, et al., Ng et al. in prep.). (Right)The“mouse” ram-pressure-confined pulsar wind nebula [1.20 across; NASA/CXC/SAO/B.Gaensler et al. Radio: NSF/NRAO/VLA; (19)]. These images provide an indication of the variety of structures possible in PWNe. ing temperatures and luminosities with theoretical cooling curves, surroundings (see below), allowing superior spectral studies. accounting for the spectrally distorting impact of the neutron-star Major open questions on this subject include how the emission atmosphere and also by detailed modeling of x-ray light curves is generated and how is it related to observed nonthermal γ-rays (e.g., ref. 7). For reviews see, for example, refs. 8 or 9. Chandra and radio emission. highlights in this area include the detection of a surprisingly low Chandra’s great angular resolution means it has been a superb temperature for the pulsar in the young SNR 3C 58 (10), tool for studying RPP surroundings, namely, pulsar wind nebulae interesting constraints on the equation-of-state from modeling (PWNe), the often spectacular result of the confinement of the millisecond pulsar thermal emission light curves (7). Major open relativistic pulsar wind by its environment (see ref. 12 for a questions in this area are the nature and impact of the neutron- review). Among Chandra’s greatest PWN legacies are the dis- star atmosphere and whether thermal-emission observations can covery of rapid time variability in the Crab and Vela PWNe strongly constrain the equation-of-state of dense matter. (see ref. 13 and references therein) as well as of the surprisingly Second is nonthermal, usually power-law emission originating diverse morphologies these objects can have (see Fig. 1 for exam- from the magnetosphere, typically more highly pulsed than the ples and the aforementioned reviews for more). Detailed model- thermal component and strongly correlated with the pulsar’s ing of the geometries (14) and emission mechanisms (15) spin-down luminosity. The latter is defined as E_ ≡ 4π2IP_ ∕P3 constrain both the properties of the pulsar wind and shock accel- where I is the stellar moment of inertia. For a review of magneto- eration mechanisms. Important open questions here are the spheric emission, see ref. 11, although thinking on this front is nature and composition of the pulsar wind, specifically whether − currently evolving thanks to recent interesting results from Fermi it consists of only eþ∕e pairs or also ions (e.g., ref. 16), what are (3). Chandra’s primary strength in this field is its small back- the particle energy distributions, and what is the fraction of groundNeutron and ability to resolve theStar point source B-fields from its nebular energy in particles versus magnetic fields? These have great relevance to our basic understanding of the neutron star as a ra- pidly rotating magnetic dipole converting rotational kinetic energy into such a powerful particle/field wind. The shock accel- eration issues are interesting as well (e.g., ref. 17). A subset of PWNe are the ram-pressure confined variety, showing bow-shock morphology that corresponds with the pulsar’s direction of motion through the interstellar medium, e.g., refs. 18 and 19. An example is shown in Fig. 1. These are additionally useful as they provide independent determinations of directions of motion, which are often difficult to determine otherwise, especially for young pulsars. Notably, the first-known PWN around an MSP, a ram-pressure confined structure with morphology in clear agreement with the measured proper motion, was found by Chandra, demonstrating unambiguously that MSPs have winds that are similar to those of their slower cousins (20). From a grand-unification perspective, the properties of RPPs can be seen as the template against which all other classes are compared. Thermal emission, for example, is seen from all the other classes discussed below, demonstrating that it is generic Fig. 2. P-P_ diagram for 1,704 objects, including 1674 RPPs (small black dots), to neutron stars, except the very cool ones for which it is unob- 9 AXPs (blue crosses), 5 SGRs (green crosses), 3 CCOs (cyan circles), 6 INSs servable. By contrast, RPP-type magnetospheric emission is only (magenta squares), and 7 RRATs (red triangles) for which these parameters observable in high spin-down luminosity sources, as are PWNe. have been measured. Open circles indicate binary systems. Data from the When considering any new neutron-star class, in the absence of Australian Telescope National Facility Pulsar Catalog (www.atnf.csiro.au/ telltale pulsations, the spectrum is therefore crucial to consider research/pulsar/psrcat), the McGill SGR/AXP Online Catalog (www .physics.mcgill.ca/pulsar/magnetar/main.html), as well as from refs. 75 and (thermal or nonthermal?) as is the presence or absence of 59. MSPs are RPPs having periods below ∼20 ms. Lines of constant B (dashed) associated nebulosity. This will be a recurring theme in the rest and τ (dot-dashed) are provided. The solid line is a model death line (see text). of this paper.

7148 ∣ www.pnas.org/cgi/doi/10.1073/pnas.1000812107 Kaspi Fig. 1. Three examples of Chandra-observed pulsar wind nebulae. (Left) The Crab nebula (the image is 50 across) with its clear toroidal morphology and jet structure (NASA/CXC/SAO/F. Seward et al.). (Center)ThePSRB1509—58 pulsar wind nebula, nicknamed the “hand of God” (image is 200 across; NASA/CXC/SAO/ P.Slane, et al., Ng et al. in prep.). (Right)The“mouse” ram-pressure-confined pulsar wind nebula [1.20 across; NASA/CXC/SAO/B.Gaensler et al. Radio: NSF/NRAO/VLA; (19)]. These images provide an indication of the variety of structures possible in PWNe. ing temperatures and luminosities with theoretical cooling curves, surroundings (see below), allowing superior spectral studies. accounting for the spectrally distorting impact of the neutron-star Major open questions on this subject include how the emission atmosphere and also by detailed modeling of x-ray light curves is generated and how is it related to observed nonthermal γ-rays (e.g., ref. 7). For reviews see, for example, refs. 8 or 9. Chandra and radio emission. highlights in this area include the detection of a surprisingly low Chandra’s great angular resolution means it has been a superb temperature for the pulsar in the young SNR 3C 58 (10), tool for studying RPP surroundings, namely, pulsar wind nebulae interesting constraints on the equation-of-state from modeling (PWNe), the often spectacular result of the confinement of the millisecond pulsar thermal emission light curves (7). Major open relativistic pulsar wind by its environment (see ref. 12 for a questions in this area are the nature and impact of the neutron- review). Among Chandra’s greatest PWN legacies are the dis- star atmosphere and whether thermal-emission observations can covery of rapid time variability in the Crab and Vela PWNe strongly constrain the equation-of-state of dense matter. (see ref. 13 and references therein) as well as of the surprisingly Second is nonthermal, usually power-law emission originating diverse morphologies these objects can have (see Fig. 1 for exam- from the magnetosphere, typically more highly pulsed than the ples and the aforementioned reviews for more). Detailed model- thermal component and strongly correlated with the pulsar’s ing of the geometries (14) and emission mechanisms (15) spin-down luminosity. The latter is defined as E_ ≡ 4π2IP_ ∕P3 constrain both the properties of the pulsar wind and shock accel- where I is the stellar moment of inertia. For a review of magneto- eration mechanisms. Important open questions here are the spheric emission, see ref. 11, although thinking on this front is nature and composition of the pulsar wind, specifically whether − currently evolving thanks to recent interesting results from Fermi it consists of only eþ∕e pairs or also ions (e.g., ref. 16), what are (3). Chandra’s primary strength in this field is its small back- the particle energy distributions, and what is the fraction of groundNeutron and ability to resolve theStar point source B-ﬁelds from its nebular energy in particles versus magnetic fields? These have great relevance to our basic understanding of the neutron star as a ra- pidly rotating magnetic dipole converting rotational kinetic energy into such a powerful particle/field wind. The shock accel- eration issues are interesting as well (e.g., ref. 17). A subset of PWNe are the ram-pressure confined variety, showing bow-shock morphology that corresponds with the pulsar’s direction of motion through the interstellar medium, e.g., refs. 18 and 19. An example is shown in Fig. 1. These are additionally useful as they provide independent determinations of directions of motion, which are often difficult to determine otherwise, especially for young pulsars. Notably, the first-known PWN around an MSP, a ram-pressure confined structure with morphology in clear agreement with the measured proper motion, was found by Chandra, demonstrating unambiguously that MSPs have winds that are similar to those of their slower cousins (20). From a grand-unification perspective, the properties of RPPs can be seen as the template against which all other classes are compared. Thermal emission, for example, is seen from all the other classes discussed below, demonstrating that it is generic Fig. 2. P-P_ diagram for 1,704 objects, including 1674 RPPs (small black dots), to neutron stars, except the very cool ones for which it is unob- 9 AXPs (blue crosses), 5 SGRs (green crosses), 3 CCOs (cyan circles), 6 INSs servable. By contrast, RPP-type magnetospheric emission is only (magenta squares), and 7 RRATs (red triangles) for which these parameters observable in high spin-down luminosity sources, as are PWNe. have been measured. Open circles indicate binary systems. Data from the When considering any new neutron-star class, in the absence of Australian Telescope National Facility Pulsar Catalog (www.atnf.csiro.au/ telltale pulsations, the spectrum is therefore crucial to consider research/pulsar/psrcat), the McGill SGR/AXP Online Catalog (www .physics.mcgill.ca/pulsar/magnetar/main.html), as well as from refs. 75 and (thermal or nonthermal?) as is the presence or absence of 59. MSPs are RPPs having periods below ∼20 ms. Lines of constant B (dashed) associated nebulosity. This will be a recurring theme in the rest and τ (dot-dashed) are provided. The solid line is a model death line (see text). of this paper.

7148 ∣ www.pnas.org/cgi/doi/10.1073/pnas.1000812107 Kaspi Summary

• Circinus X-1 sits inside a supernova remnant! • Youngest known X-ray binary < 4,600 yrs! • Extremely low ﬁeld for a young neutron star! • Orbital evolution, X-ray variability, precession: probe post-supernova binary evolution Summary

• CircinusHappy X-1 Anniversary, sits inside a supernova Chandra remnant!! • Youngest known X-rayand binary! < 4,600 yrs! • Extremely low ﬁeld for a young neutron star! Thank you, Chandra team! • Orbital evolution, X-ray variability, precession: probe post-supernova binary evolution