Particle astrophysics and cosmology at SLACKIPAC--Activities in high energy astrophysics

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					Particle astrophysics and cosmology at SLAC/KIPAC: Activities in high energy astrophysics
Greg Madejski
Stanford Linear Accelerator Center and Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)

* KIPAC is the "new kid on the block" at SLAC, but very active in research
* KIPAC's charter is research in particle astrophysics and cosmology * This presentation is mainly about the current/past scientific accomplishments and future projects (Astro-E2, PoGO, NuSTAR, NeXT) with emphasis on the synergy with SLAC's mission

Current space-based astrophysics missions

• KIPAC members are engaged in a broad range of research activities, mainly in cosmology, highenergy, and particle astrophysics using data from archival and current missions, but also plans for future endeavors • This includes superb facilities such as Chandra, Hubble, XMM-Newton, and other missions

Clusters of galaxies as cosmological probes

* Clusters of galaxies are largest gravitationally bound and relaxed structures in the Universe; intra-cluster gas is a source of X-ray emission (Above: Abell 2029) * Their mass/number density as a function of time is an excellent probe of cosmological parameters – best inferred via X-rays - but this necessitates sensitive observations requiring observatories such as Chandra * This will be covered in more detail by S. Allen * Gravitational lensing of background galaxies provides an independent estimate of the cluster mass, which generally (but not always!) agrees with the X-ray data * Much of the cutting-edge work with Hubble is at KIPAC (Marshall, Allen, Peterson, Bradac, …) – and will continue with the JDEM data (talk by P. Marshall)

Supernovae and their remnants
* “Heavy” elements in the Universe were all “cooked” in stars and ejected into the interstellar space via supernovae * Neutron stars left behind the explosion gradually cool, radiating thermal continuum with temperatures measurable via X-ray spectroscopy * Measurements of the flux + distance (=luminosity) and neutron star surface temperature determine radius and thus with mass measuremets (from binary properties) provide hints to determine the equation of state * Much of this research is done at KIPAC (S. Kahn, W. Ho, M.-F. Gu, A. Spitkovsky, R. Romani, M. Sako)

Kepler’s supernova remnant

Connections to GLAST
• Besides GLAST, introduced in the presentation by E. Bloom and discussed extensively in subsequent talks, KIPAC is involved in several new space-based missions, mainly funded by NASA or international collaborations • Much of the data from those missions will be important to unraveling the details of the GLAST data • A coherent picture of physics operating in those sources requires data over broad band of photon energies

• In particular, for variable sources - simultaneous observations will be essential
• Among the most important (but also competitive) will be observations in the X-ray band – unfortunately, one object at a time - so it is good that we are involved in Astro-E2, PoGO, NuSTAR, NeXT, …

• In all cases, funds towards hardware development are mainly from NASA but also from other countries (Sweden, Japan, France, ...)

Connection to GLAST: g-rays in perspective
* Any single band (g-ray, X-ray, radio, optical) is only a small part of the electromagnetic spectrum * Studying astronomical sources across all spectral ranges can reveal very rich physical phenomena and is necessary for the “complete picture”

* Examples are broad-band spectra of active galaxies

Mkn 421: data from Macomb et al. 1995)

3C279 (data from Wehrle et al. 1998)

Connection to GLAST: jets in active galaxies

* The most numerous celestial g-ray emitters on the sky are jet-dominated active galaxies * This occurs when the relativistic jet points close to the line of sight and dominates the observed flux which can extend to the highest observable energy (TeV!) grays

* Jets are common in active galaxies – and radiate in radio, optical and X-ray wavelengths, but their origin and structure are poorly known

All-sky map from the EGRET experiment

* The correlation of the variability of the X-ray and g-ray flux (see below) should be key to determine the content of the jet – is it particle- or magnetic field dominated? (R. Blandford, T. Kamae, GM, …)

Radio, optical and X-ray images of the jet in M 87

Connection to GLAST: SN remnants as sources of high energy g- and cosmic-rays

Tycho’s supernova remnant (Chandra X-ray image)

SNR RXJ1713 HESS TeV data, Aharonian et al. 2004

* Some supernova remnants show regions (near the rims) with X-ray spectra that are clearly non-thermal as well as strong TeV emission -> relativistic non-thermal particles * The particle acceleration is best explained as occurring in shocks resulting from interaction of SN “blast wave” with the interstellar medium via Fermi process * This is the best explanation for the origin of the Galactic Cosmic rays * GLAST should see many such SNR and X-ray data will help in interpretation * Current work at SLAC/KIPAC is by T. Kamae, S. Digel, J. Cohen-Tanugi, N. Karlsson – see the next talk

Future “non-DOE” projects - overview
• Most imminent is the Japanese-US X-ray / soft gamma-ray astronomy mission Astro-E2, which will be launched in 3 weeks (!) • Several of us (T. Kamae, S. Kahn, GM) are involved in planning of the observation program for that mission (and Tune Kamae, the next speaker, invented one of Astro-E2 instruments!) • More in the future, several of us are co-investigators of the Small Explorer mission NuSTAR (Fiona Harrison/Caltech, PI; Bill Craig, GM are co-investigators) – launch will be 2009

• Locally, we are developing an X-ray polarimeter PoGO for astrophysical observations (T. Kamae is the spokesperson)
• We are also co-developing (with ISAS/Tokyo) a detector for the NeXT, a planned US/Japanese satellite (likely launch 2013; local leader is Hiro Tajima)

NEAR FUTURE (3 weeks!): Astro-E2

* The future is (almost) here: Next high energy astrophysics satellite, joint Japanese – US mission Astro-E2 will be launched soon * Astro-E2 will have multiple instruments: * X-ray calorimeter (0.3 – 10 keV) will feature the best energy resolution yet at the Fe K line region, also good resolution for extended sources (gratings can’t do those!) - but the cryogen will last only ~3 years * Four CCD cameras (0.3 – 10 keV, lots of effective area) to monitor X-ray sources when the cryogen expires * Hard X-ray detector, sensitive from 5 keV up to 700 keV

Future projects: Astro-E2
• Astro-E2 will feature a unique detector, a nondispersive cryogenic detector (running at 0.6o K) capable of high spectral resolution studies of extended celestial sources


One of main goals of Astro-E2 is understanding the details of clusters of galaxies
Clusters are strong X-ray emitters, and the Xray emitting gas must be held in place with gravity due to the mass of both luminous and dark matter Total content of clusters provides another, powerful avenue to determine the cosmological parameters, but the physics of clusters (are they fully formed, or still assembling from individual galaxies?) needs high resolution Xray spectroscopy



This high spectral resolution will allow measuring the level of turbulence of the X-ray emitting gas

An example of a cluster where turbulence should be strong: data from Markevitch et al. (X-ray data: 2004, 2005) and Clowe et al. (lensing data: 2004)

A bit further off in the future: NuSTAR
NuSTAR was recently selected for extended study, with the goal for launch in 2009 (Fiona Harrison/Caltech, PI)

It’s the first focusing mission above 10 keV
(up to 80 keV)
brings unparalleled  sensitivity,  angular resolution, and  spectral resolution to the hard x-ray band

and opens an entirely new region of the electromagnetic spectrum for sensitive study: it will bring to hard X-ray astrophysics what Einstein brought to soft X-ray astronomy

Hardware details of NuSTAR
NuSTAR is based on existing hardware developed in the 9 year HEFT program
Based on the Spectrum Astro SA200-S bus, the NuSTAR spacecraft has extensive heritage. NuSTAR will be launched into an equatorial orbit from Kwajalein.

The three NuSTAR telescopes have direct heritage to the completed HEFT flight optics.

The 10m NuSTAR mast is a direct adaptation of the 60m mast successfully flown on SRTM.

Orbit NuSTAR detector modules are the HEFT flight units.

525 km 0° inclination

Launch vehicle
Launch date Mission lifetime Coverage

Pegasus XL
2009 3 years Full sky

Science goals of NuSTAR
• NuSTAR’ s improvement in sensitivity of a factor of 1000 over the previous missions will be accomplished by the use of focusing hard Xray optics (using multi-coating) - this reduces background dramatically! • Focal plane detectors will be pixilated CdZnTe sensors • Precursor to this mission, HEFT, was flown last month with spectacular results • KIPAC will be involved in calibration of the X-ray optics, via funds from NASA, mainly at Stanford's main campus (Physics Dept.) but also in the interpretation of the data • The main goals of NuSTAR are: • (1) to unravel the details of the Cosmic X-ray Background, which is most intense at ~ 30 keV, in the middle of NuSTAR's bandpass • (2) to measure the nuclear lines from elements produced in supernova explosions, and • (3) to provide simultaneous observations of the variable hard g-ray sources detected by the hundreds (literally) by GLAST

NuSTAR goals: Origin of the Cosmic X-ray Background Spectrum

Revnivtsev et al., 2003 RXTE

Slide from G. Hasinger
XMM LH resolved Worsley et al. 2004

data from Gilli 2003
E<2 keV XRB resolved to be a sum of many active galaxies (Chandra, XMM); at E>5 keV still lots of work...

Heavily obscured AGN “hiding in the dust”: Important ingredient of the Cosmic X-ray Background?
•The origin of the diffuse Cosmic X-ray Background is one of the key questions of high energy astrophysics research •Spectrum of the CXB is hard, cannot be due to unobscured AGN (“Seyfert 1s”) -> but it (presumably) can be due to superposition of AGN with a broad range of absorption in addition to a range of Lx, z
RXTE PCA + HEXTE data Chandra Observatory data

Example: absorbed (“Seyfert 2”) active galaxy NGC 4945

New experiment under our leadership: PoGO
• • • Another, even more "local" effort (led by Tune Kamae) is an instrument to measure the polarization of celestial hard X-ray / soft gamma-ray sources Only one (not very sensitive) X-ray polarimeter was ever flown in space (about 30 years ago!) and detected only one polarized X-ray source (Crab Nebula) The detector for this experiment - known as PoGO or Polarized Gamma-ray Observer - relies on detection of the incident as well as the scattered gamma-ray with scintillating material It is a well-type phoswitch detector, where the background can be determined and accounted for via anti-coincidence / rise time, and a narrow field of view This experiment will be flown on a balloon in ~ 2008, and is being developed by an international collaboration, with funds coming from NASA, Sweden, as well as from KIPAC "seed funds" In a 6-hour flight PoGO will measure the change of the polarization angle from the Crab as a function of the pulse phase, constraining severely location of accelerated particles, responsible for the X-ray/g-ray emission Future, possibly long-duration flights will target a variety of sources such as active galaxies and pulsars studied by GLAST, accreting black holes, etc. – mainly to learn about the geometry of the emitting region in celestial sources

• •



Conceptual Design of the PoGO Instrument: Polarimeter sensitive in the ~ 25 – 100 keV band




Conceptual design of the instrument (number of units will be greater than shown here): a) Isometric view; (b) View from the front of the instrument; (c) Vertical cross-section of the instrument. The proposed instrument will have ~200-400 units and L1 + L2 in (c) will be ~60cm.

Design of PoGO: Trigger Strategy
Trigger and Pulse-Shape-Discrimination: L0, L1, L2

1 inch PMT


Detector Assembly

Pulse-Shape Discrimination

Crab Nebula in the radio, IR, optical, and X-rays
* Some supernova remnants are powered by the rotational energy of the neutron star, left after the supernova explosion (“pulsar”) * Good example is the Crab Nebula, one of the brightest celestial sources of X-rays and grays * The entire broad-band emission from the remnant is non-thermal * It is best explained as synchrotron radiation by particles energized by the pulsar (crucial test is via polarization! – PoGO is in the works)

Radio Optical

Infrared X-rays

Even farther in the future…
• • Future - what are we planning beyond GLAST, Astro-E2, NuSTAR, PoGO? Obvious synergy with SLAC is to use the expertise relevant to particle detectors in an astrophysical setting


One instrument we are heavily involved in is a med-range g-ray detector, which will use a silicon strip tracker to determine the energy and direction of the incident photon
This detector will provide data in the poorly explored med--range g-ray band, with the main goal on understanding the structure of black holes - how is the gravitational energy converted into radiation?



This instrument, the Soft Gamma-ray Detector is likely to fly on a Japanese - US mission NEXT, planned for ~ 2013
The Soft Gamma-ray Detector is a joint Japanese - US effort, led at SLAC / KIPAC by Hiro Tajima; on the US side, we applied to NASA for funds for development


Even farther in the future – we are involved in the detector work for EXIST, the all-sky hard X-ray monitor under development at Harvard/Smithsonian Center for Astrophysics

Conceptual design and performance of the Soft Gamma-ray Detector

Example of a 20 ks observation of the black-hole binary system Cyg X-1, in two spectral states; yellow area is the expected background

Conceptual design of the SGD (one module) Bandpass: from ~ 50 keV to ~1 MeV

Abs. mode Comp. mode

E ffe c tiv e


Polarization performance of the SGD
10 100 Incident Energy (keV) 1000


Backup slide: Connection to GLAST: g-rays in perspective

• Any single band (g-ray, X-ray, radio, optical) is only a small part of the electromagnetic spectrum

• Studying astronomical sources across all spectral ranges can reveal very rich physical phenomena and is necessary for the “complete picture”

Connection to GLAST: jets in active galaxies cont’d
• Presumably all AGN have the same basic ingredients: a black hole accreting galaxian gas via disk-like structure Some active galaxies contain a relativistically boosted jet pointing at us: this origin of this jet must be connected to the fueling of the black hole The correlation of the variability of the X-ray and g-ray flux should be key to determine the content of the jet – is it particle- or magnetic field dominated? (R. Blandford, T. Kamae, GM, …)



Diagram from Padovani and Urry

3C279 data: Wehrle et al. 1996

Backup slide: NuSTAR Key Parameter Overview
Energy range Angular resolution (HPD) FOV (20 keV) Strong/weak src positioning Spectral resolution Timing resolution Focal Length (deployed) Spacecraft Mission lifetime Orbit ToO response Solar angle constraint Observing efficiency (typ.) 6 - 80 keV 40 arcseconds 10 arcminutes 6 arcsec/10 arcsec 1 keV @ 60 keV 1 ms 10m 3-axis stablized 3 years Near Earth equatorial < 24 hours 20 deg (<10% of sky) 65%

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