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RXTE Update (7/2011). Tod Strohmayer NASA/Goddard Space Flight Center RXTE Project Scientist. RXTE. NASA’s Rossi X-ray Timing Explorer (RXTE). Launched in December, 1995. RXTE’s 16 th launch anniversary is about 5 months away! Cycle 15 Observations ongoing

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rxte update 7 2011
RXTE Update (7/2011)

Tod Strohmayer

NASA/Goddard Space Flight Center

RXTE Project Scientist


nasa s rossi x ray timing explorer rxte
NASA’s Rossi X-ray Timing Explorer (RXTE)

Launched in December, 1995. RXTE’s 16th launch anniversary is about 5 months away!

Cycle 15 Observations ongoing


  • RXTE’s Unique Strengths
  • Large collecting area
  • High time resolution
  • Broad bandpass
  • High telemetry capacity
  • Flexible observing
rxte strengths
RXTE Strengths
  • Unique Observing Capabilities: RXTE’s broad energy band, high throughput sub-millisecond timing, and observing “agility” remain unduplicated.
  • Cost Effective: RXTEcontinues to deliver high impact science at low cost. Midex-class science at about $1.0 M/year.
  • Continued High Productivity: > 2200 refereed papers (steady rate of ~160/year), ~60 rapid notices/year (ATels, IAUCs, GCNs).
  • RXTE data remain in high demand: Increase in Open Time proposals (46, 83 and 100) from Cycle 13 to 15. Increase in data accessed from HEASARC (6.8 to 11.7 TB) from 2007 to 2009. “My phone is still ringing.”
  • Supports many multi-wavelength and multi-mission science programs: e.g., blazars (with Fermi, ground-based TeV, optical, and radio); black hole transients (with ground-based optical/IR, radio, Suzaku, Fermi).
rxte discoveries partial
RXTE Discoveries (partial)
  • Opened the sub-millisecond X-ray window, dynamical timescales of stellar compact objects: NS kHz QPOs, BH QPOs. Evidence for GR effects. Still unique capability.
  • Found progenitors of “recyled” ms radio pulsars: first accreting ms X-ray pulsars, nuclear powered pulsars (burst oscillations), NS spin distribution.
  • Established existence of “magnetars”: spin- and spin-down rates of SGRs and AXPs (magnetic field constraints), glitches and bursts in magnetars.
  • Unification of BHs across the mass scale: characteristic timescales of Seyfert AGN (power spectral breaks), Mass, Luminosity, variability plane.
  • BH jet - disk interaction and connections: X-ray and radio correlations in BH microquasars (GRS 1915+105, GRO J1655-40), BH spin constraints.
  • New thermonuclear phenomena from neutron stars: “superbursts,” mHz QPO (marginally stable nuclear burning).


rxte is still popular and productive
RXTE is still Popular and Productive
  • All data immediately public beginning with Cycle 13. Core and Open Time programs.
  • More than 400 unique PIs (AO 1-14). 13 new PI’s in Cycle 14, many young (PhD candidates).
  • Competitive: 80% increase in Open Time proposals (Cycle 13 to 14). 2x oversubscribed for non-TOO time.
  • 6.8 TB (4x archive) downloaded in 2007, 11.7 TB in 2009 (6x archive).
  • High-impact: > 2200 refereed papers, mean citation rate of 23. ~100 with more than 100 cites.
  • 92 Ph.D. theses.



  • Publication rate (refereed) remains high and steady at ~160 per year.
  • Rapid notifications (ATel, IAUC, GCN) fluctuate around 60 per year.
  • Conference reports remain significant at ~85 per year.

Current Status

  • Cycle 15 observations ongoing. Approved funding to approximately end of December 2011. Enables observations of lunar occultations of the Crab Nebula, approximate completion of Cycle 15 program.
  • Currently no funding into calendar year 2012. If unchanged, would mean mission close-out in January 2012.
  • ASM performance degraded. SSC 1 latch ups; light leaks (solar blanket) in other cameras. Data in 2011 is sparser and with larger variance. No instrument team funding.
  • PCA stable, recent improvements and tweaks to the calibration.
  • Spacecraft performing well. Occasional ground system concerns (TDRSS scheduling).
  • Operations with one science planner and reduced MOC staffing appear stable. We could, in principle, continue at current funding levels, if maintained.
visibility impact of rxte results
Visibility - Impact of RXTE Results

~ 160 refereed publications/year, > 2200 total

~ 60/year rapid notifications (GCN, IAUC, ATel)

~ 85/year conference reports

11.7 TB downloaded in

2009! (6x archive)

Swift J1749: First eclipsing AMXP

XTE J1550: Seeing X-rays from the jet

current science goals partial
Current Science Goals (partial)
  • Accreting Neutron Stars:
    • NS spin distribution upper limit (by increasing the sample of AMPs)
    • Use iron lines and kHz QPOs to estimate NS masses (with XMM-Newton, Suzaku)
  • Rotation-powered pulsars (RPP):
    • Track ephemerides of known X-ray pulsars for Fermi gamma-ray studies
    • Search radio-quiet Fermi pulsars and TeV sources for X-ray pulsations
  • Magnetars:
    • Map out the connections between magnetar behaviors and magnetic field strength
    • Test models of crustal and magnetic field structure with glitch measurements
  • Black Hole binaries:
    • Measure BH spins with broad-band spectra
    • Test models for the jet contribution to the X-ray flux with new radio/optical facilities
    • Explore X-ray/gamma-ray correlations with Fermi (e.g., Cyg X-3; LS I+61 303)
  • Blazar jets:
    • Determine the location and structure of the emission region within the jets of blazars
    • Constrain the distribution of radiating particles
  • Seyfert AGN:
    • Test X-ray reprocessing models for the correlated optical emission
    • Test the unified disk/jet model with coordinated radio and optical observations
new accreting millisecond pulsar swift j1749 4 2807
New Accreting Millisecond Pulsar: Swift J1749.4-2807
  • Source discovered in 2006 when X-ray burst detected with Swift/BAT.
  • New outburst detected in April 2010 (INTEGRAL, Swift).
  • RXTE observations detect 518 Hz pulsar, with strong, sometimes dominant first overtone (1035.84 Hz, Altamirano et al. 2010).
  • 8.817 hr circular orbit, vsini = 112.8 km/sec (Belloni et al, 2010; Strohmayer & Markwardt 2010
swift j1749 4 2807 pulse shape variability
Swift J1749.4-2807: Pulse Shape Variability

Altamirano et al. (2010)

  • Short, ~week-long outburst, large changes in harmonic content.
swift j1749 first eclipsing amxp
Swift J1749: First Eclipsing AMXP!
  • Eclipse features evident in the PCA X-ray light curves.
  • Features are symmetric about orbital phase of superior conjunction of the NS, as expected for eclipses of NS by the donor.
  • Two egresses and one ingress observed.
  • Eclipse duration of 36.2 minutes, 6.85% of the orbital period.
  • Eclipse timing tightly constrains inclination and properties of the donor.

Markwardt & Strohmayer (2010)

shapiro delay in swift j1749
Shapiro Delay in Swift J1749?
  • High inclination, and relatively massive donor, Shapiro delay ~21 -sec is within RXTE’s timing uncertainty.
  • Joint eclipse and pulse timing tightly constrain the system.
first simultaneous observations of relativistic fe lines and kilohertz qpos
First Simultaneous Observations of Relativistic Fe Lines and Kilohertz QPOs

Pandel & Kaaret (2009)

  • Recent observations have now found relativistic Fe lines in 10 accreting neutron star binaries (Cackett et al. 2009).
  • Both Fe line profiles and kHz QPO frequencies provide inner disk diagnostics.
  • First simultaneous QPO and Fe line detections now achieved (4U 1636-53, Altamirano et al. 2011, in prep).
  • Unique RXTE synergy with XMM-Newton, Suzaku, Chandra.

vorb= (GMns/r)1/2

RXTE power spectrum

  • Supports relativistic origin for Fe lines (QPO strength).
  • Inferred radii would require > 1.9 Msun NS.

Fe lines

QPO frequencies

orb= (1/2 (GMns/r3)1/2

Mns = vorb3 / (2Gorb)

new bh results rxte with ir and radio
New BH Results: RXTE with IR and radio
  • Two tracks seen in the X-ray/radio correlation
  • Fender et al. (2010) find no evidence that radio luminosity is con-nected to BH spin



  • “Fast infrared variability from a relativistic jet in GX 339-4” (Casella et al. 2010)
  • Relies on X-ray/IR cross-correlation function that shows a symmetric peak with a small, 100 ms, IR lag.
  • IR from a jet rather than reprocessing.
  • Is there a connection to the radio-loud/radio-quiet dichotomy in AGN?

Role of RXTE in multi-wavelength campaigns of blazars

Blazars are still not well understood

Spectral Energy Distribution (SED) from the TeV blazar Markarian 421

1 - Time-evolving broad band spectra

Abdo et al. in press

Coordination of instruments covering different energies needed

2 - Poor sensitivity to study high-energy part (E>0.1 GeV) in old instruments

Fermi IACT


Two recent “performance jumps”:

New generation of TeV instruments (IACTs)

HESS, MAGIC, VERITAS: since ~5 years

New generation of GeV instrument

Fermi-LAT : since 1.5 years

RXTE/PCA brings important information:

BL Lacs  Synch. of high energy electrons from Jet

FSRQ  Inv. Compton of “low energy” elec. from Jet

Seyfert  Thermal comptonization from disk/corona

Enhanced observational capability is expected to improve our knowledge on blazars

BUT the high energy observations MUST be accompanied by low energy observations

synergies with other missions and observatories
Synergies with Other Missions and Observatories
  • Fermi: coordinated, multi-wavelength studies of blazars. Timing studies of rotation-powered pulsars. Timing and spectroscopy of gamma-ray binaries.
  • Ground-based TeV (HESS, VERITAS, MAGIC): multi-wavelength studies of blazars. Pulsar searches of TeV -- Pulsar wind nebulae associations.
  • Chandra: broad-band, continuum spectroscopy in support of high-resolution, grating spectra (X-ray binaries, Fe K line spectroscopy). High sensitivity, precision timing of Chandra-localized sources. Cycle 14 and 15 programs.
  • XMM-Newton and Suzaku: broad-band, continuum spectroscopy in support of high-resolution spectroscopy (X-ray binaries, Fe K line spectroscopy, constrain continuum above 8 keV). Millisecond timing (kHz QPOs) simultaneous with Fe line spectroscopy (cycle 14 & 15 programs).
  • Swift and INTEGRAL: sensitive timing and broad-band spectroscopy of Swift- and INTEGRAL- identified transients, and/or Swift- and INTEGRAL-localized sources (SGRs, hard X-ray transients).
  • Ground-based optical/IR facilities: coordinated multi-wavelength, fast timing and spectroscopic studies of Galactic BH binaries (jet studies), white-dwarfs, AGN (X-ray/optical) correlation studies (multiple observing programs).
  • New radio facilities (LOFAR, eVLA, ATA): coordinated, multi-wavelength studies of Galactic BH and NS binaries (jet studies).
  • LIGO/GW: provide pulse ephemerides for GW searches (pulsars, SGRs, accreting binaries, magnetar giant flares), constraints on LIGO triggers with localizations.
rxte compared to suzaku and swift
RXTE compared to Suzaku and Swift
  • Comparison to Suzaku:
  • Sun angle constraint
    • Suzaku 65-110 deg vs. RXTE 30-180 deg
    • Suzaku has limited ability to coordinate with ground-based obs. (TeV)
  • Suzaku does not plan a complex observing program (compared to RXTE)
    • For example Suzaku will not do monitoring of stellar BHs and blazars
  • Suzaku has no capabilities for millisecond variability studies
    • Does not do fast pulsar timing, NS and BH QPOs, NS spin measurements
  • Comparison to Swift:
  • RXTE has much better hard X-ray sensitivity
    • XRT has no coverage above 8 keV; BAT has a high background
  • Swift has no capabilities for millisecond variability studies
    • Does not do fast pulsar timing, NS and BH QPOs, NS spin measurements
  • Sun angle constraint and dedication to monitoring
    • Swift 46-180 deg vs. RXTE 30-180 deg
    • Swift monitoring programs are often broken up by GRBs, unlike RXTE
  • RXTE does “time-resolved” rather than “time-averaged” spectroscopy
future capabilities
Future Capabilities
  • India’s ASTROSAT: LAXPC large area proportional counter will have PCA-like capability, and perhaps with more effective area. Launch in 2nd half of 2012 (perhaps optimistic). Ambitious multi-wavelength facility, likely cannot completely replace RXTE’s flexible and dense coverage of new sources. Overlap with a well-calibrated PCA would be scientifically beneficial.
  • Large Observatory for X-ray Timing (LOFT): ESA medium class, recently approved for study. 2020+ time-frame. 10+ m2 silicon detector technology, collimated.
  • Advanced X-ray Timing Array (AXTAR): US-led team, medium Explorer class. Timing depends on NASA Explorer AO. Likely 3-5 m2 , collimated.
  • ATHENA (ESA-led): ~1 m2, focusing optics, high resolution spectroscopy, WFI imager would likely have some fast timing capability.
  • Neutron Star Interior Composition ExploreR (NICER): US-led (GSFC), concentrator optics, ISS attached payload. ~2.5 x XMM-pn. Submitted in last Explorer round as MO.

No immediate (2012-2013) replacement for unique RXTE capabilities. Some aspects present in other missions, but not all. Scientific recommendation: operate RXTE through ASTROSAT verification and checkout, if funding available.

pca calibration is state of the art
PCA Calibration is State of the Art
  • Updated PCA response matrix: better understanding of energy to channel relationship.
    • Extends useful energy band to ~50 keV.
    • More stable over mission history.
    • Better systematics.


cost reductions
Cost Reductions
  • Manpower (Full Time Equivalents):
  • 1997 (Peak) 2004 2008 2010 2011 2012*
  • Mission Ops 16.0 10.0 6.6 4.5 3.6 3.6
  • SOF 12.0 3.5 2.3 2.3 2.0 2.0
  • GOF 16.0 3.4 1.4 0.9 0.7 0.7
  • ITs 33.0 10.9 6.5 4.6 0.0 0.0
  • Total (FTE) 77 27.8 16.8 12.3 6.3 6.3
  • Total (real yr K$): 7718+ 5844 2355 1500 965 965
  • + 1997 is not full cost, GO not included.
  • * Partial year (through 12/2011)
  • Key Changes enabling cost reductions since peak:
  • Operations: from 24x7 to 8x5 with automation
  • Science processing: from XSDC with tape distribution to GOF with Internet
  • Spacecraft & auxiliary data processing: from GSFC institutional to MOC
  • Help desk: from fully staffed to bare bones
  • Instrument teams: from fully staffed to bare bones; no IT funding in 2011+
new radio facilities
New Radio Facilities
  • LOFAR: Huge FOV (observing now, today!)
  • ATA: Large FOV and GHz (observing now)
  • EVLA: Vast improvement in sensitivity (2011)
  • ASKAP: Huge FOV (2012-2013)
  • MeerKAT: FOV and sensitivity (2012-2013)
  • RXTE provides an unique combination of long-term monitoring and sensitivity, and radio facilities that are coming on-line are poised to match it.

“If RXTE were around for even one year of MeerKAT/ASKAP operation, we could more than double the simultaneous X-ray/radio measurements.” (R. Fender)