X-ray Timing & Spectroscopy on Dynamical Timescales from Microseconds to Years

Steering Committee:Colleen Wilson-Hodge (MSFC)Tom Maccarone (Texas Tech)Zaven Arzoumanian, Keith Gendreau (GSFC)Deepto Chakrabarty, Ron Remillard (MIT)Peter Jenke (UAH), Marco Feroci (INAF), Silvia Zane (UCL), Soren Brandt (DTU) , Alessandra DeRosa (INAF), Margarita Hernanz (IEEC), Anna Watts (Amsterdam), Kent Wood (NRL), John Tomsick (Berkeley),Laura Brenneman (CfA), David Ballantyne (GA Tech), Mike McDonald (MIT), Adam Goldstein (MSFC), Abbie Stevens (MSU), Enrico Bozzo (Geneva),Dieter Hartmann (Clemson), Bernard Phlips (NRL), Marc Christophersen (NRL)

+ > 150 members of SWGThe STROBE-X study is funded by NASA

Paul Ray (U.S. Naval Research Laboratory)

Why a Flexible, High-Throughput Observatory?

• The high-energy sky is highly dynamic – requires catching the right source at the right time

– Necessitates both wide field monitoring and the ability to repoint quickly (as RXTE and Swift have demonstrated)

• Critical capability in the era of time domain and multi-messenger astronomy

• Large areas with low dead time access the shortest timescales

• Both soft and hard X-ray bands are needed to accurately measure the continuum spectral shape, constrain absorption, and understand the relationship between thermal and non-thermal components

Figure from Ron Remillard

HEA Time Domain Desirati 2020

Discovery & Monitoring

• All Sky Monitor

• Science drivers: GW cntrparts, GRBs, SNe shock breakout, accretion, tidal disruptions

• ~Daily Cadence

Rapid Response

•Rapid slew (< hr)

•Science drivers: GW cntrparts, GRBs, stellar flares/space weather, transients

•High Availability

High Time Resolution

• Sub-ms timing

• Science drivers: Strong gravity, neutron star physics, XRB/AGN physics, QPOs

• High Sensitivity

Courtesy Daryl Haggard

Coronal

Emission

T ~ 109 K Relativistic

Reflection

Distant

Reflection

Rin

T ~ 107 K

Black Holes on All Mass Scales

• Understand the spin distribution of black holes, using three complementary approaches: HFQPOs, continuum fitting and reflection fitting all accessible with STROBE-X

– Critical for understanding systematics of each technique

• X-ray reverberation maps the inner regions of the accretion flow and corona for both stellar mass BH and AGN– High throughput enables measurements on short timescales (jet

launching, recombination, state change, precession period). Note that a lag measurement made with XMM in 100 ks can be done in 100 s with STROBE-X

• Also, variable disk winds, QPOs, state changes, disk-jet connection and more!

NuSTAR+XMM

XMM-Newton

NICER

ATHENA

STROBE-X

Lag 1

-σ u

ncert

ain

ty (

Rg/c

)

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Energy (keV)

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How do black holes form and grow?

How do black holes accrete and form jets?

Neutron Stars• Fully determine the ultradense matter

equation of state by measuring the neutron star mass-radius relation using >20 pulsars– Measurements spanning low to high masses

are critical to nail down the precise EOS

• Burst oscillations, thermal surface emission, and accretion-powered pulsations all will be accessible– Multiple techniques and many systems

mitigate systematic errors

• Global oscillation modes would open a new window on NS interiors

Is there new physics at the core of neutron stars?

Strobe-X

and

Tidal Disruption Events

Katie AuchettlThe Ohio State University/CCAPP

Email: auchettl.1@osu.edu

Rapid and Extreme Explosions• Gamma-ray bursts and

X-ray flashes• LIGO and LISA EM

counterparts• Tidal disruption events• Supernova shock

breakouts• X-ray bursts and

superbursts• Stellar flares• Much more…

Key WFM Features:• Arcmin localization allows

optical follow up with single pointing

• Large instantaneous FOV probes rare events

• Autonomous repointing of pointed instruments and fast response to ground TOOs

• 300 eV spectral resolution sensitive to lines and absorption features

• Continuous event data allows timing studies

Long GRBs — Core-Collapse SNe

14

• X-Ray Flashes (XRFs)

• Jet Cocoons

• Choked bursts

• X-ray afterglow12

14

16

18

20

22

24

1e−03 1e−02 1e−01 1e+00 1e+01

1e−14

1e−13

1e−12

1e−11

1e−10

1e+02 1e+03 1e+04 1e+05 1e+06

AB

mag

nit

ud

e

Fn (

Jy)

Time (days)

Time (seconds)

X−ray H − 2.0 magJ − 1.5 magz’ − 1.0 magi’ − 0.5 magr’ g’ + 0.5 mag

Guelbenzu+ 2011

See Poster on science caseand the broader portfolio

STROBE-X Instrument Concept

X-ray Concentrator Array (0.2-12 keV)

Large Area Detector(2-30 keV)

Wide Field Monitor(2-50 keV)

Large effective area >5 m2 @ 6 keV

• STROBE-X combines the strengths of NICER and LOFT: High throughput X-ray timing with good spectroscopy

• All components are already high TRL• Highly modular design improves reliability at

reduced cost and allows easy scaling.

X-ray Concentrator Array• Scaled up version of NICER concentrators with NICER

SDDs– Focal length of 3 m for enhanced throughput >2.5 keV

– Inexpensive single-bounce foil optics: large areas w/ low background

– Energy resolution: 85-175 eV FWHM

– 80 XRCA units gives effective area @ 1.5 keV: >2.0 m2

(> 10X NICER)

• Low background, high throughput

• Enables high time resolution observations of the faintest sources, both extragalactic and galactic

• Sensitive timing and spectroscopy to thermal emission and iron lines

NICER concentrator

~XRCA concentrator

Large Area Detector

• SDDs and lightweight microcapillary plate collimators developed for ESA’s LOFT M3 & M4. – Energy resolution: 200–500 eV FWHM– 60 modules gives effective area @ 10 keV >5 m2 (~10X RXTE)

• High time resolution and good energy resolution over the 2-30 keV range– Best sensitivity to QPOs; most prominent in harder X-rays– Sensitive to non-thermal emission and Compton hump

Silicon Drift Detector (SDD)

Glass micropore collimator

LAD module

Wide Field Monitor• SDDs similar to LAD with finer pitch• Energy resolution: 300 eV FWHM• 1.5D wide-field coded mask imager• Two cameras rotated by 90° give 2D positions• Four camera pairs give instantaneous FoV: >1/3 of

sky; 50% of sky accessible to LAD• 1 day sensitivity of 2 mcrab, with source

localization of 1 arcmin• Continuous viewing, not scanning gives sensitivity

to transients from milliseconds to years• Identifies new transients and source states for

main instruments, while monitoring long-term source behavior for a large fraction of the sky

• Onboard processing can trigger autonomous repoint for GRBs, superbursts, etc.

Instrument Design Lab (Nov 2017)• Developed detailed instrument

design• Optical bench made out of

composite structure, reducing mass and improving stiffness and thermal distortions

• Deployment mechanism for LAD panel designed, no concerns

• Detailed cost model for instruments

Mission Design Lab (April 2018)

• Complete spacecraft design• Moved WFM to top, removing need for

sunshade• Control Moment Gyros (CMGs) give 15

deg/min slew rate• Includes autonomous repoint capability for

WFM triggers• TDRSS Ka band gives 300 Mbps telemetry

downlink• TDRSS S-band gives rapid burst alerts to

ground and TOO commanding • Full lifecycle costing ($880M) well under

Probe class cost cap with over 10% margin– International contributions would reduce this

further (none taken for granted so far)

• Huge collecting area, fast timing, and good spectral resolution, addressing fundamental questions in accretion, dense matter, black hole formation and evolution

• Based on existing technology and builds on experience with NICER and LOFT, enabling confidence in cost estimates at this early stage. Highly modular design allows easy scaling. Comfortably under Probe-class cost cap

• Will serve a large community in a decade of time-domain and multi-messenger astronomy with complementary capabilities to the large high spectral and spatial resolution missions– Active SWG with over 150 members open for all to discuss science impacts

of the mission Follow us on Twitter (@STROBEXastro), Facebook,and https://gammaray.nsstc.nasa.gov/Strobe-X/

BACKUP

Instrument Parameters

Technical Context from LOFT and NICER

• Solid state detectors like Silicon Drift Detectors can provide high time resolution with low dead time and CCD-like spectroscopy

• Thin, light micropore collimators a much lower mass and volume than traditional X-ray collimators, enabling large missions and modest cost

• Lightweight, inexpensive foil optics can provide large collecting area with low background at low cost

NICER• PI: Keith Gendreau (GSFC)• Operating on ISS since June 2017• Already discovering new millisecond

pulsar pulsations, burst phenomenology, spectral timing studies, AMXP orbit, responding to BHXB and HMXB TOOs, and much more!

• Demonstrating feasibility and robustness of inexpensive optics and commercial SSDs

• Nearly all data are public 2 weeks after observation

• Single bounce concentrators + SDDs cover 0.2–12 keV band

• 2 arcmin radius single pixel FOV• 56 identical units, 2-axis pointed

eXTP• China-Europe collaboration under study with 4

instruments

– Spectroscopic Focusing Array (SFA), with up to 0.8 m2 in 0.5–10 keV

– Polarimetry Focusing Array (PFA), 900 cm2 in 2–10 keV

– LAD, 40 modules = 3.4 m2 in 2–30 keV

– WFM, 3 cameras

• Goal is 2025 launch

• Not yet approved in China and European contributions not yet funded

• Factor of ~2 smaller than STROBE-X

• Long focal length mirrors likely mean slower slewing and TOO response times

GRB Science with STROBE-X• WFM wide FOV will detect many

bursts, at softer energies that other instruments– Arcmin localizations promptly

downlinked for >100 GRBs/year– Autonomous slewing to catch plateau

phase• LAD could catch magnetar pulsations or

Fe lines

– 300 eV resolution gives capability to see spectral features and thermal components

– Large number of soft bursts, XRFs and high-z GRBs• ~30 XRF/year• ~1 GRB/year at z>6

Simulation of the transient absorption feature in the X-ray energy band detected by BeppoSAX/WFC in the first 8 s of GRB 990705 as would be measured by the STROBE-X/WFM (Amati et al., 2000).

STROBE-X

spectra on a dynamical timescale!

10−3

0.01

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10

keV

(P

hoto

ns c

m−

2 s

−1 k

eV

−1)

Unfolded Spectrum

1 10

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(data−

mod

el)/e

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Energy (keV)

jsteiner 18−Sep−2017 01:50

3 Crab

15kCnt

0.01s(!)

Cost Estimate• Class B mission rules (dual string design, high

priority, low risk)• FY18 dollars• Phase A begins Oct 2023• Launch 2031• PRICE-H instrument and spacecraft component

costs• Standard MDL “wraps” for other WBS items

– We increased mission ops cost above this to be comparable to Fermi and HQ guidance

• Require 25% reserve on Phases A-D• Fits in Probe class $1B cost cap with over 10%

margin• Assumes only NASA funding

– International contributions are very likely to reduce NASA cost

WBS Source Point Estimate

Reserve (25% on Phases A-D)

Est + Reserve($M)

1.0 Project Management Wrap 29.2 7.3 36.5

2.0 Systems Engineering Wrap 29.2 7.3 36.5

3.0 Safety & Mission Assurance Wrap 18.2 4.6 22.8

4.0 Science/Technology Wrap 36.5 9.1 45.6

5.0 Payload IDL 192.7 48.2 240.9

6.0 Spacecraft MDL 172.0 43.0 215.0

7.0 Mission Ops Team 83.0 0.0 83.0

8.0 Launch Vehicle/Services NASA HQ 150 0.0 150

9.0 Ground Systems MDL 12.3 3.1 15.4

10.0 I&T MDL 20.8 5.2 26.0

11.0 E&PO Wrap 5.5 1.4 6.8

Phase A Estimate 2.0 0.5 2.5

TOTAL 751.3 129.7 881.0