MISSIONI PASSATE di ASTRONONOMIA X Università di Tor Vergata - Master Scienza e Tecnologia Spaziale...

MISSIONI PASSATE di ASTRONONOMIA X

Università di Tor Vergata - Master Scienza e Tecnologia Spaziale - Strumentazione- Enrico Costa

Enrico CostaIstituto di Astrofisica e Plantologia Spaziale di Roma

INAF

The dawn of X-ray Astronomy


The space physics and astrophysics was boosted at the ene of the World War 2 by the possibility to carry instrumentation in the upper atmosphere aboard rocketts.In october 1946 a team from Naval Research Laboratory, lead by Edward O. Hulburt detected UV radiation from the sun. On september 1949 a team lead by Herbert Friedman, performed a rockett (V2 !) borne experiment searching for extreme UV and X-rays from outside the atmosphere. The experiment was based on geiger counters with different wndows acting as filters to discriminate radiation of different energies . This was the first detection of astronomic X-rays.

The measurement showed that the Sun is an intense source of X and UV radiation that plays a major role in the ionization of the upper atmosphere.The result was improved by following experiments aboard Aerobee rocketts with improved instrumentation. In 1956 a rockett launched from a balloon detected X-rays in coincidence with a solar eruption. In 1958 a launch during an eclipse allowed to localize the emission at the corona.

From the sun to other stars


The discovery that the sun was a source of X-rays suggested that also other stars could have a similar phenomenology. But scaling the flux of the sun to near stars with the square of the distance the fluxes expected were so low that a detection with the same technique would be hopeless.

Although fluxes could be in some cases higher than that from the sun R.Giacconi, arrived to the conclusion that to detect extrasolar X-rays we should wait for the development of X-ray telescopes.

Yet in 1962, pushed by B.Rossi, Giacconi and his team at the private company American Science & Engineering proposed a rockett to search for X-rays produced on the moon surface from cosmic rays of solar wind.

The rockett was launched on june 18 1962.

The first rockett


The rockett was an Aerobee. It arrived 225 km and was above 80 km for 5m50s.Instrumentation was based on proportional counters, that could measure the energy of X-ray photons, and discriminate the signal from particles, so reducing the background. The detectors had no real collimator but a wide field of view. The rockett was spinning at 2 Hz so that at each phase photons arrived from a certain region of the sky.

It was clear that the flux of X-rays was was much higher than expected.A huge flux was consistent with a poin-like source from a well distinguished direction of the sky. It was Scorpius X-1: the first non solar X-ray source identified.

The paper of the discoveryof extrasolar X-Ray Astronomy


A time of big discoveries


The discovery of the first X-ray source falls in an epoch of extraordinary discoveries: a revolution for Astrophysics.• In 1959 Konstantin Gringauz detected and measured Solar Wind with Luna 1. •In 1962 Maarten Schmidt found the association of a radio source and an optical source a took the optical spectrum finding the red-shift. This is the first identification of Quasars, until then known as serndipitous point like sources in optical and radio surveys. • In 1964 Arno Penzias and Robert Wilson discovered the Cosmic Microwave Background.•In 1967 Jocelyn Bell and Anthony Hewish observed the first pulsar.

The NOBEL Prize in 2002


Riccardo Giacconi was awarded the Nobel Prize in 2002 for opening the new window of X-ray Astronomy.

A short history of the discovery ad of further steps in X-ray Astronomy can be found in the Nobel Prize dissertation: “THE DAWN OF X-RAY ASTRONOMYNobel Lecture”, December 8, 2002, by RICCARDO GIACCONI:

http://nobelprize.org/nobel_prizes/physics/laureates/2002/giacconi-lecture.html

A vivid history of the X-ray Astronomy can be found in:R.Giacconi and W.Tucker, “The X-Ray Universe” Harvard University Press (1985). Italian Translaion “L’Universo in Raggi X”, Mondadori 1987.

What about γ-ray Astronomy?


The discovery of very strong X-ray diffuse background and sources was somehow unexpected.On the contrary wealth of predictions were there for γ-rays. The most convincing was from Morrison on 1958.

The stars are nuclear reactors. In explosive processes radioactive materials can be ejected to space.Moreover cosmic rays are there. They must collide with nucleons of ordinary matter and produce γ-ray photons via π mesons.High energy electrons must produce γ-rays by bremmstrahlung or by synchrotron in intense magnetic fields.

Numerous experiments aboard balloons, rocketts and satellites to search for γ-rays of different energies and sources. In most cases without any unambiguous detection. The existence of an intense diffuse γ-ray background was detected by Greisen on 1966. Clark with OSO-3 detected on 1968 extraterrestrial γ-rays from the galactic disk. The first detection of an extraterrestrial 511 keV line was by Johnson on 1972. The first γ-ray lines from the Sun are by Chupp on 1973.

The pioneering era: from rocketts to UHURU


Numerous experiments aboard rocketts were launched to improve the localization of Sco X-1 and find more stellar-like sources. The second was the Crab, since then the most famous and observed X-ray source. Several X-ray stars were discovered. The idea that the source of so high energy could be the accretion of matter from an ordinary star into a super compact objec (neutron star or white dwarf) became the favourite interpretation. On 1965 the first images of the Sun in X-rays were achieved while the first high resoluton image of the sun should wait for the development of X-ray

On 1963 Riccardo Giacconi and Herbert Gursky submitted to NASA a proposal for a satellite dedicated to survey the X-ray sky. If X-ray sources could be detected with few minutes observations with rocketts, a satellite adequately designed could cover the whole sky and produce the first map in X-ray band. Some data on X-ray and γ-ray sources could be derived as a byproduct of satellites designed to completely different purpouses but it was clear that X-rays and γ-ray astronomy would deserve dedicated missions.

NASA approved a program of 3 Small Astronomical satellites to be launched from San Marco platform in Kenya.

26 Missions of X-Ray Astronomy: not all the same impact; we select


A complete list in the site of NASA’s High Energy Astrophysics Science Archive Research Center (HEASARC): http://heasarc.nasa.gov/docs/heasarc/missions/past.html

SAS-1/UHURU


Uhuru was launched on 12 December 1970 into an orbit of 560 km apogee, 520 km perigee, 3°inclination, a period of 96 minutes. Spin period of ~12 minutes . Detectors were A filled proportional counters sensitive in the 2-20 keV. Range.Slat collimators limited the field of view on one side to 0°.5 × 5° and, on the other side to 5°× 5°. The limiting sensitivity was 1.5 X 10-11 ergs/cm2/s = 0.5 mCrab.

UHURU and all the satellites without telescopes were spinning continuously. The collimators allows the photons from a sky direction arrive to the detector with an efficiency phase-dependent. A change in the counts following the collimator profile is assumed to be a source.

UHURU Sky Map


Sources of the IV UHURU Catalogue in galactic coordinates. Brighter sources are clustered on the Galactic Plane. The Galactic Bulge is particularly crowded. Sources off the plane are near galactic stars or belong to Magellatic Clouds. Other are extragalactic.

hsaaGOhsaaPS2600_000_PRINTERPRINThsaaPS2200_000_PRINTERPRINThsaaPS1200_000_PRINTERPRINThsaaPCL600_000_300PRINTERPRINThsaaPCL200_000_150PRINTERPRINThsaaPS2006600PRINTER000PRINThsaaPS2006200PRINTER000PRINT

Major results from UHURU


A Catalogue of 339 X-ray sources

In the domain of Galactic Astronomy •Binaries with Neutron Stars: Pulsators: similar to pulsars but spin-up and therefore accretion driven. Binaries with a NS and a low mass companion star, with irregular variability. • Binaries with White Dwarfs•Binaries with Black-Holes. First evidence of existence of BHs.• X-ray emission from Super Nova Remnants both powered by the pulsar (nowadays named Pulsar Wind Nebulae) and shell like where the mass ejected in the explosion shocks and heaths the Inter Stellar Medium.

In the domain of Extra Galactic Astronomy• X-ray emission showing the existence of very hot gas between galaxies in Clusters, more than doubling the mass of the Universe and providing a new tool to cosmology.• X-ray emission from a selected sample of the brighter Active Galactic Nuclei: Radio-Galaxies, Seyfert Galaxies, Quasars. The first step to the discvery of Super Massive Black Hoses an another tool to X-ray based cosmology.

What UHURU could not do


• Resolve images of extended sources: poor angular resolution.• Perform continuous observation of aperiodically variable sources: scanning collimator philosophy covering observations with continuously varying area.• Probe a rich sample of extragalactic source to perform statistical sudies a arrive to far objects: poor sensitivity.

The possibility to achieve these results was made possible by the development of X-ray telescopes that completely changed the measurement approach:

UHURU EINSTEIN

HEAO-2/EINSTEIN


Einstein was launched into low Earth orbit by an Atlas-Centaur rocket on November 13, 1978 and operated without significant interruption until April 1981.

The X-ray telescope (Wolter-1) has 3.4m focal length with effective area of 400 cm2 at 0.25 keV and 30 cm2 at 4 keV. Angular resolution was 4” Half Power Radius.

4 major instruments could be alternated in the focal plane. Each instrument was optimized for a particular measurement. A conventional collimated Monitor Proportional Counters was pointing the same field of view.

Notice the poor quality of the image. Prehistory of the outreach era.

Focal Plane Instruments


(Giacconi et al. ApJ 230,540,1979

A shocking improvement in imaging


CAS A with IPC and with HRI (Murray 1979)

This also implies a high capability to associate X-ray sources to objects in other wavelengths.A noticeable case: X-ray emission from stars of all spectral types

The improvement of sensitivity is a facto 103 with respect to UHURU.

And the first spectra of high quality


The first use of Si detector in the focus of a telescope allowed, for the first time, to perform spectroscopy with 160 eV resolution.The interstellar Medium shocked by the matter ejected in the explosion emits a bremmstrahlung continuum and lines of different elements

X-rays from almost all astrophysical objects


The Gamma-Ray Observatory


NASA satellite active from 1991 to 2000.Low Earth Orbit (450 km, inclined 28.5 °)15.6 tons3 instruments.:•EGRET (Energetic Gamma Ray Experiment Telescope)•COMTEL (Imaging Compton Telescope)•OSSE (Oriented Scintillation Spectrometer Experiment )•BATSE (Burst and Transient Source Experiment )

EGRET


Based on pair production Γ-ray photons produce pairs e+ e- on thin converters of W. These converters are stacked alternated with gaps of a spark chamber. The pair is tracked sfter the vertex. Eventually the two electrons are absorbed by a NaI caloimeter that measures the total energy.

The external plastc scintillator anti-coincidence and the time of flight coincidence removes electrons and protons arriving from outside, reducing background of spurious events. Notice that sources have fluxes of 10-6 ph/cm2s while the environment charged particles are of the order of 1 particle/cm2s

• Discovered at the end the 60’s with the American Vela spy satellites, devoted to monitor compliance with the 1963 “Partial Test Ban Treaty” by the Soviet Union, and other nuclear-capable states.

• Published by R. Klebesadel, I. Strong & R. Olson (1973)

One backstep: GRB discovery by VELA satellites

Vela satellites

Università di Tor Vergata - Master Scienza e Tecnologia Spaziale - Strumentazione-

Enrico Costa

• Sudden bright flashes of hard X--/soft gamma-ray radiation

• Variable duration of tens of milliseconds to tens of seconds

• 4-5 events/day

• Unpredictable sky directions

• Unpredictable arrival times

The mistery of Gamma Ray Burst phenomenon

Università di Tor Vergata - Master Scienza e Tecnologia Spaziale - Strumentazione- Enrico Costa - 2


Enrico Costa

BATSE


• Isotropic distribution of GRBs directions (localization uncertainty ranging from 2° to 30°)

• Paucity of weak events with respect to what expected in an euclidean space

• Hints for a cosmological origin of GRBs, but also consistent with a local origin or Galactic halo.

More X-Ray Missions


Many more missions contribute to the development of X-ray Astronomy In terms of imaging ROSAT was the most performant.

4 japaneese satellite contributed to the field and in particular ASCA was the first to use extensively CCD’s as spectroscopic imagers.

Rossi/XTE observed bright sources with large area and studied fast timing properties of binaries.

Something that was really missing was the capability to perform broad band study of sources with a single measurement. Another point was to have aboard the same satellite Wide Field Imaging and Narrow Field sensitivity.

The backbone idea of BeppoSAX was to fill these two vacancies together.

BeppoSAX an ASI (NIVR) mission led by L. Scarsi

Payload• Narrow Field Instruments:

– 4 focusing telescopes LECS+MECS (0.2-10 keV), PI G. Boella

– HPGSPC (4-60 keV), PI G. Manzo

– PDS (15-200 keV), PI Frontera

• WFCs (2-28 keV, PI R. Jager):– 2 units in opposite

directions, – proportional counters +

coded mask, ang. res. 3’-4’

– FOV 20°x20° (fwhm)Università di Tor Vergata - Master Scienza e Tecnologia Spaziale - Strumentazione- Enrico Costa

The BeppoSAX Payload

• Telescopes have a band extended up to 10 keV. One was sensitive down to 0.1 keV. The other 3 down to 1.5 keV

• From 15 to 300 keV sources were studied with phoswich detectors with rocking collimators.

• The two ranges were bridged by a High Pressure gas scintillation counter, less sensitive than PDS but with better spectral performance.

• Two Wide Field Cameras monitored the sky at directions orthogonal to the telescopes axis and to the sun aspect.

• The active shields of PDS were sensitive to Gamma-Ray Bursts from any direction.


Enrico Costa

BeppoSAX launch and phases


• Launch, on 30 April 1996 from Cape Canaveral with an Atlas-Centaure rocket ;

• Commissioning phase: 2 months;

• Science Verification Phase (SVP): July - September 1996;

• Operational phase: from October 1996.

• Switched off on 2002

Main Results from Beppo


Broad-band observation of sources

Cyg X-1, Frontera et al. 2001NGC4151 De Rosa 2007

From GRB discovery to BeppoSAX launch

• Many satellite missions (most French-Russian), but small progress:– Very rough localizations. The most

accurate with IPN after a long time from events.

– No evidence of counterparts.– No idea of the power output.The largest effort with BATSE

experiment : Isotropy, non homogeinity

IPN principle

BeppoSAX could do imaging of X-rays with the coded mask Wide Field Cameras. But GRBs are not eminent at all in X-ray band.


Enrico Costa

GRBs from GRBM


Detect GRB with Gamma –Ray Burst MonitorCheck whether an excess of counts is present in one of the WFCsAccumulate data at the excess and deconvolve the image If a source is present verify that it was not present before or afterDetermine source coordinates and repoint the more sensitive telescopes

GRB afterglow discovery by BeppoSAX

• Unsuccessful search with the first localized GRB: 970111.

• Second GRB promptly identified and well localized occurred on 28 Feb 1997: 970228

• Follow up after 8 hrs: afterglow emission discovered.

Costa, Frontera et al. 1997


Van Paradjis, Groot, Galama et al. 1997

First discovery of the optical afterglow from

GRB970228The error box given by

BeppoSAX was at last compatible with a search in optical images within a reasonable small field.

Various teams observed the field at the BeppoSAX coordinates distributed by a telegram to the International Astronomical Union (Costa et.al 1997)

Paul Groot of the team of Ian Van Paradijs was the first to observe twice the field with William Herschel Telescope and to detect the optical afterglow decaying with the same power-law index of X-ray afterglow.


GRB970228 afterglow observation with HST

• The AG was observed with HST. A decaying point source was included within a faint nebulosity, possibly a far galaxy.


Metzger et al 1997

First measurement of GRB redshift: GRB970508 (z = 0.835)


Enrico Costa

Consequences of the redshift measurement

From the distance we derived the energetics of GRB970508. Assuming isotropy:

Eiso = (0.61±0.13)x1052 ergs

On December 14, 1997 the redshift of another BeppoSAX GRB (971214) was determined: z = 3.42.

The corresponding energetics was Eiso = (2.45±.28)x1053 ergs → 0.14 mʘ×c2


The ladderSAX – GRBM ~ 45° 100 m

SAX – WFC 5-3 arcmin 3h

SAX – NFI 1 arcmin 8h

Optical Telescopes 1 arcsec 2-10d

Hubble 0.2 arcsec 1 month

• Every improved error box is included in the previous and has a transient object.• All detected transients decay with the same power-law.It is the same object


MISSIONI PASSATE di ASTRONONOMIA X Università di Tor Vergata - Master Scienza e Tecnologia Spaziale...

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