Only these 3 DOFs Degree of Freedom have the potential to introduce errors large enough that they must be measured. Figure 5 illustrates the DOFs that need to be measured. Legend to Figure 5 : The sketch is utilizing a coordinate system that is fixed on the optical bench where the star tracker is mounted.
The laser metrology system is implemented as two laser pointers mounted on a bench with the optics. A block diagram of the electronics is shown in Figure 7. The lasers are driven by a processor, through analog laser drivers.
The electronics components are space qualified. The electronics power cycle the lasers and make a background measurement 4 times a second to subtract out the background signal produced by dark current, the moon or the Earth in the FOV, sun stray light. Thermal stability is the key to achieving this requirement. The laser is mounted behind the optics in an invar barrel. This barrel is placed inside another invar barrel to mechanically hold it, to serve as a thermal shield, and to spread the thermal variation from the sun.
It is expected that if one laser diode fails but the other laser diode survives the mission, it will be possible to recover scientific data. Therefore, since, 1 the laser are interchangeable, 2 since no laser diode illustrates any signs of superiority over the other and 3 it is more likely that one laser will survive if 2 different equally reliable lasers are chosen, a project decision was made to fly one laser diode from each vendor on the NuSTAR metrology system Ref.
The June launch came almost three months after a planned early March launch date. The results, from a remnant named Cassiopeia A Cas A , reveal how shock waves likely rip apart massive dying stars. Figure 12 : This is the first map false color image of radioactivity in a supernova remnant, the blown-out bits and pieces of a massive star that exploded.
The new view shows a more complete picture of Cassiopeia A, the remains of a star that blew up in a supernova event whose light reached Earth about years ago, when it could have appeared to observers as a star that suddenly brightened.
The remnant is located 11, light-years away from Earth. NuSTAR is the first telescope capable of taking detailed pictures of the radioactive material in the Cassiopeia A supernova remnant.
While other telescopes have detected radioactivity in these objects before, NuSTAR is the first capable of pinpointing the location of the radioactivity, creating maps. When massive star explode, they create many elements: non-radioactive ones like iron and calcium found in your blood and bones; and radioactive elements like titanium, the decay of which sends out high-energy X-ray light that NuSTAR can see.
By mapping titanium in Cassiopeia A, astronomers get a direct look at what happened in the core of the star when it was blasted to smithereens. These NuSTAR data complement previous observations made by Chandra, which show elements, such as iron, that were heated by shock waves farther out from the remnant's center.
In this image, the red, yellow and green data were collected by Chandra at energies ranging from 1 to 7 keV. The red color shows heated iron, and green represents heated silicon and magnesium. The yellow is what astronomers call continuum emission, and represents a range of X-ray energies. Figure 13 of NuSTAR shows the energized remains of a dead star, a structure nicknamed the "Hand of God" after its resemblance to a hand.
The dead star, called a pulsar, is the leftover core of a star that exploded in a supernova. The pulsar is only about 19 km in diameter but packs a big punch: it is spinning around nearly seven times every second, spewing particles into material that was upheaved during the star's violent death. These particles are interacting with magnetic fields around the ejected material, causing it to glow with X-rays. The result is a cloud that, in previous images, looked like an open hand.
Over the first year of the mission, NuSTAR has undertaken a range of studies, from observations of energetic events towards the center of the Milky Way galaxy to detailed studies of distant supermassive black holes.
NuSTAR's view is providing new clues to the puzzle. The hand actually shrinks in the NuSTAR image, looking more like a fist, as indicated by the blue color. The northern region, where the fingers are located, shrinks more than the southern part, where a jet lies, implying the two areas are physically different.
The red cloud at the end of the finger region is a different structure, called RCW Astronomers think the pulsar's wind is heating the cloud, causing it to glow with lower-energy X-ray light.
In this image, X-ray light seen by Chandra with energy ranges of 0. The first batch of data from the black-hole hunting telescope is publicly available today, Aug. The more distant black holes are some of the most luminous objects in the universe, radiating X-rays as they ferociously consume surrounding gas. One type of black hole in the new batch of data is a blazar, which is an active, supermassive black hole pointing a jet toward Earth.
Systems known as X-ray binaries, in which a compact object such as a neutron star or black hole feeds off a stellar companion, are also in the mix, along with the remnants of stellar blasts called supernovas. The supermassive black hole lies at the dust- and gas-filled heart of a galaxy called NGC , and it is spinning almost as fast as Einstein's theory of gravity will allow.
The observations also are a powerful test of Einstein's theory of general relativity, which says gravity can bend space-time, the fabric that shapes our universe, and the light that travels through it. Scientists use these and other telescopes to estimate the rates at which black holes spin Figure Figure The artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Until now, these measurements were not certain because clouds of gas could have been obscuring the black holes and confusing the results.
The new data demonstrate that X-rays are not being warped by the clouds, but by the tremendous gravity of the black hole. This proves that spin rates of supermassive black holes can be determined conclusively. Measuring the spin of a supermassive black hole is fundamental to understanding its past history and that of its host galaxy. Supermassive black holes are surrounded by pancake-like accretion disks, formed as their gravity pulls matter inward.
Einstein's theory predicts the faster a black hole spins, the closer the accretion disk lies to the black hole. The closer the accretion disk is, the more gravity from the black hole will warp X-ray light streaming off the disk Ref.
Legend to Figure 15 : Scientists measure the spin rates of supermassive black holes by spreading the X-ray light into different colors. The light comes from accretion disks that swirl around black holes, as shown in both of the artist's concepts. They use X-ray space telescopes to study these colors, and, in particular, look for a "fingerprint" of iron — the peak shown in both graphs, or spectra — to see how sharp it is.
The "rotation" model shown at top of Figure 15 held that the iron feature was being spread out by distorting effects caused by the immense gravity of the black hole. If this model were correct, then the amount of distortion seen in the iron feature should reveal the spin rate of the black hole. The alternate model held bottom of Figure 15 that obscuring clouds lying near the black hole were making the iron line appear artificially distorted.
If this model were correct, the data could not be used to measure black hole spin. NuSTAR helped to solve the case, ruling out the alternate "obscuring cloud" model.
Its high-energy X-ray data — shown at top as green bump to the right of the peak — revealed that features in the X-ray spectrum are in fact coming from the accretion disk and not from the obscuring clouds. Together with XMM-Newton, the space observatories were able to make the first conclusive measurement of a black hole's spin rate, and more generally, confirm that the "gravitational distortion" model is accurate Ref.
The red line explains the emission using a model where clouds of dust and gas partially block the X-ray light, and the green line represents a model in which the emission is reflected off the inner edge of the accretion disk, very close to the black hole. The results show that the iron feature, the sharp peak at left, is being affected black hole's immense gravity and not intervening clouds.
The degree to which the iron feature is spread out reveals the spin rate of the black hole. Mission and science operations have settled down into a mostly predictable daily routine, and the science team is making good progress toward achieving the primary, or "Level 1," science goals. Examples of some of the key NuSTAR observations performed to date include mapping of the central regions of our Milky Way galaxy, studying the remnants of exploded stars in our galaxy, and surveys of several well-studied extragalactic fields.
The mission has looked at a range of extreme, high-energy objects already, including black holes near and far, and the incredibly dense cores of dead stars. High-energy X-ray data from NuSTAR have been translated to the color magenta, and superimposed on a visible-light view highlighting the galaxy and its star-studded arms.
NuSTAR is the first orbiting telescope to take focused pictures of the cosmos in high-energy X-ray light; previous observations of this same galaxy taken at similar wavelengths blurred the entire object into one pixel. With NuSTAR's complementary data, astronomers can start to home in on the black holes' mysterious properties. Instead, they may be intermediate in mass, or there may be something else going on to explain their extremely energetic state.
NuSTAR will help solve this puzzle. The visible-light image is from the Digitized Sky Survey. Since the science operations began on August 1, , the NuSTAR team has wrestled with learning to point the telescope's flexible system of optics, mast, spacecraft bus and solar array. Characterization of the behavior of NuSTAR in space took an additional six weeks, but has now been completed. Several adjustments to attitude control parameters — factors in pointing the telescope — were necessary to bring the spacecraft into the required specifications, and the satellite's slew rate, or the speed at which it points to new targets, has recently been enhanced by a factor of two.
Calibrating the telescope is now a primary focus for the science team. The first two are neutron stars in our Milky Way galaxy, and the latter two are accreting black holes in the centers of nearby galaxies. The first images from the observatory show Cygnus X-1, a black hole in our galaxy that is siphoning gas off a giant-star companion. This particular black hole was chosen as a first target because it is extremely bright in X-rays, allowing the NuSTAR team to easily see where the telescope's focused X-rays are falling on the detectors.
The NuSTAR team will now begin to verify the pointing and motion capabilities of the satellite, and fine-tune the alignment of the mast. In about five days, the team will instruct NuSTAR to take its "first light" pictures, which are used to calibrate the telescope.
All systems are nominal. The instrument has the same name as the spacecraft. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass.
Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: During its baseline two-year mission, NuSTAR will also undertake a broad program of targeted observations. Instrument: The NuSTAR instrument is the first astronomical telescope in orbit to utilize the new generation of hard X-ray optics and solid-state detector technologies to carry out high-sensitivity observations at X-ray energies significantly greater than 10 keV.
It consists of two co-aligned depth-graded multilayer coated grazing incidence optics focused onto solid state CdZnTe pixel detectors with a focal length of Figure 19 shows the total effective area for both telescopes as a function of energy, with a comparison to Chandra and XMM. The energy band extends from about 5 - 79 keV, being limited at the low-energy end by the optics thermal cover and shield entrance window, and at the high energy end by the K-edge at This is the angular diameter of the image of a point source, which contains half the flux at a given energy focused by the telescope.
From the standpoint of detecting and measuring sources with an X-ray telescope, the HPD proves more useful than other imaging metrics—e. Table 3: Key instrument performance parameters Ref. The instrument FOV is energy-dependent due to changes in multilayer reflectance as a function of energy and optics shell radius, which results in overall loss of reflectance and more vignetting at high energy Figure The target of opportunity ToO response time is required to be less than 24 hours; however, on average the turnaround will be faster, with targets typically acquired within 6 hours.
Understand explosion dynamics and nucleosynthesis in core collapse and Type Ia SNe. Constrain particle acceleration in relativistic jets in supermassive black holes.
Figure 20 : Effective area as a function of off-axis angle, as a fraction of on-axis area, for several energies image credit: NuSTAR collaboration. The NuSTAR instrument is launched in a compact, stowed configuration, and after launch a 10 m mast is deployed to achieve a focal length of Since the absolute deployment location of the mast is difficult to measure on the ground, due to complications associated with complete gravity off-loading, an adjustment mechanism is built into the last section of the mast to enable a one-time alignment to optimize the location of the optical axes on the focal plane.
This mechanism provides two angular adjustments as well as rotation. They occur when magnetic field lines become tangled and broken, and then reconnect.
But it can help measure the energy of smaller microflares, which produce only one-millionth the energy of the larger flares. Nanoflares — which may help explain why the sun's atmosphere, or corona, is much hotter than expected — would be hard to spot due to their small size. Astronomers suspect that these tiny flares, like their larger brethren, can send electrons flying at tremendous velocities.
As the electrons zip around, they give off high-energy X-rays. While it is known that the energy is generally liberated in the upper solar atmosphere, the locations and detailed mechanisms are not precisely known. There is a slim chance the telescope could detect a hypothesized dark matter particle called the axion.
Dark matter is a mysterious substance in our universe that is about five times more abundant than the regular matter that makes up everyday objects and anything that gives off light. NuSTAR might be able to address this and other mysteries of the sun. Figure Flaring, active regions of our sun are highlighted in this new image combining observations from several telescopes.
The project scientists see a completely new component of the center of our galaxy with NuSTAR's images. The center of our Milky Way galaxy is bustling with young and old stars, smaller black holes and other varieties of stellar corpses — all swarming around a supermassive black hole called Sagittarius A.
When stars die, they don't always go quietly into the night. Unlike stars like our sun, collapsed dead stars that belong to stellar pairs, or binaries, can siphon matter from their companions. This zombie-like "feeding" process differs depending on the nature of the normal star, but the result may be an eruption of X-rays. Pulsars are the collapsed remains of stars that exploded in supernova blasts.
They can spin extremely fast and send out intense beams of radiation. As the pulsars spin, the beams sweep across the sky, sometimes intercepting the Earth, like lighthouse beacons.
Our sun is such a star, and is destined to become a white dwarf in about five billion years. Because these white dwarfs are much denser than they were in their youth, they have stronger gravity and can produce higher-energy X-rays than normal. Another theory points to small black holes that slowly feed off their companion stars, radiating X-rays as material plummets down into their bottomless pits.
The cosmic rays might originate from the supermassive black hole at the center of the galaxy as it devours material. When the cosmic rays interact with surrounding, dense gas, they emit X-rays. The smaller circle shows the area where the NuSTAR image was taken -- the very center of our galaxy, where a giant black hole resides.
The X-ray light, normally invisible to our eyes, has been assigned the color magenta. The brightest point of light near the center of the X-ray picture is coming from a spinning dead star, known as a pulsar, which is near the giant black hole.
While the pulsar's X-ray emissions were known before, scientists were surprised to find more high-energy X-rays than predicted in the surrounding regions, seen here as the elliptical haze. Astronomers aren't sure what the sources of the extra X-rays are, but one possibility is a population of dead stars. Supermassive black holes blast matter into their host galaxies, with X-ray emitting winds traveling at up to one-third the speed of light.
In the new study, astronomers determined PDS , an extremely bright black hole known as a quasar more than 2 billion light-years away, sustains winds that carry more energy every second than is emitted by more than a trillion suns.
Previous XMM-Newton observations had identified black hole winds blowing toward us, but could not determine whether the winds also blew in all directions. XMM-Newton had detected iron atoms, which are carried by the winds along with other matter, only directly in front of the black hole, where they block X-rays. Combining higher-energy X-ray data from NuSTAR with observations from XMM-Newton, scientists were able to find signatures of iron scattered from the sides, proving the winds emanate from the black hole not in a beam, but in a nearly spherical fashion.
The winds blow in every direction, in a nearly spherical fashion, coming from both sides of a galaxy only one side is shown in the artist's impression here. The plot shows the brightness of X-ray light from an extremely luminous quasar called PDS , with the highest-energy rays on the right.
At that time, it had measured the X-rays up to an energy level of 11 keV. From those data, researchers detected a dip in the X-ray light, called an absorption feature see dip in plot. The dip is caused by iron atoms — which are carried by the winds along with other matter — absorbing the X-ray light of a particular energy. What's more, the absorption feature is 'blue-shifted," meaning that the winds are speeding toward us. These data told researchers that at least some of the winds were blowing toward us — but they didn't reveal whether those winds were confined to a narrow beam along our line of sight, or were blowing in all directions.
That's because XMM-Newton had only detected absorption features, which by definition occur in front of a light source, in this case, the quasar. To probe what was happening at the other sides of the quasar, the astronomers needed to find an emission feature, which would indicate that the iron was scattering X-ray light at a particular energy in all directions, not only toward the observer.
The NuSTAR data reveal the baseline of the "continuum" quasar light see gray line — or what the quasar would look like without any winds. What stands out is the bump to the left of the dips. That is an iron emission signature, the telltale sign that the black-hole winds blow to the sides and in all directions. This first solar image from NuSTAR demonstrates that the telescope can in fact gather data about sun.
And it gives insight into questions about the remarkably high temperatures that are found above sunspots — cool, dark patches on the sun. Future images will provide even better data as the sun winds down in its solar cycle. Nanoflares, should they exist, may explain why the sun's outer atmosphere, called the corona, is sizzling hot, a mystery called the "coronal heating problem. It is like a flame coming out of an ice cube.
Nanoflares, in combination with flares, may be sources of the intense heat. The field of view covers the west limb of the sun. The NuSTAR data, seen in green and blue, reveal solar high-energy emission green shows energies between 2 and 3 keV volts, and blue shows energies between 3 and 5 keV.
The high-energy X-rays come from gas heated to above 3 million degrees. This is the brightest pulsar — a dense stellar remnant left over from a supernova explosion — ever recorded.
Until now, all ULXs were thought to be black holes. ULXs are generally thought to be black holes feeding off companion stars — a process called accretion. They also are suspected to be the long-sought after "medium-size" black holes — missing links between smaller, stellar-size black holes and the gargantuan ones that dominate the hearts of most galaxies. But research into the true nature of ULXs continues toward more definitive answers. Astronomers had been observing a recent supernova in the galaxy when they serendipitously noticed pulses of bright X-rays coming from the ULX known as M82 X Black holes do not pulse, but pulsars do.
They also measured its energy output at the equivalent of 10 million suns, or 10 times more than that observed from other X-ray pulsars.
This is a big punch for something about the mass of our sun and the size of Pasadena. At this point, it is not clear whether M82 X-2 is an oddball or whether more ULXs beat with the pulse of dead stars. NuSTAR, a relatively small telescope, has thrown a big loop into the mystery of black holes. Figure A rare and mighty pulsar pink can be seen at the center of the galaxy Messier 82 in this new multi-wavelength portrait.
A compact source of X-rays that sits near the black hole, called the corona, has moved closer to the black hole over a period of just days. The corona recently collapsed in toward the black hole, with the result that the black hole's intense gravity pulled all the light down onto its surrounding disk, where material is spiraling inward.
The result was an extreme blurring and stretching of the X-ray light. Such events had been observed previously, but never to this degree and in such detail. Supermassive black holes are thought to reside in the centers of all galaxies. Some are more massive and rotate faster than others.
The black hole in this new study, referred to as Markarian , or Mrk , is about million light-years from Earth in the direction of the Pegasus constellation. It is one of the most extreme of the systems for which the mass and spin rate have ever been measured.
The black hole squeezes about 10 million times the mass of our sun into a region only 30 times the diameter of the sun, and it spins so rapidly that space and time are dragged around with it. The light is coming from two areas: a superheated disk of material feeding the black hole, called the accretion disk; and a cloud of particles traveling near the speed of light, called the corona.
The exact shape and nature of coronas are not clear, but researchers know that X-ray light from the corona is reflected off the accretion disk. That reflected light, and the corona's direct light, are mapped in this plot over a range of X-ray energies.
The yellow line is a model that shows what the data are predicted to look like if X-ray light has been stretched, or blurred. The blue line shows what the plot would look like without the blurring effects. What's blurring the light? It's a combination of factors. First, there is a Doppler shift happening due to the spinning disk. As one side of the disk moves toward us and the other side away, the light is squeezed or stretched.
A second effect has to do with the enormous speeds of the spinning black hole, which approach the speed of light. A final effect is from the enormous gravity of the black hole, which pulls on the light, making it harder to escape its grasp. The light loses energy in this process. All of these factors contribute to the smeared look of the data as seen in the plot. These data were taken after a dramatic dip in brightness had first been observed by NASA's Swift satellite. NuSTAR's high-energy X-ray data pointed to the cause for the observed change: Markarian 's corona had shifted closer to the black hole itself — and this closer proximity meant that the black hole's gravity could yank harder on the corona's light, stretching it to lower energies than observed before.
The astronomers say that the corona moved over a period of days, and is still in the close configuration. They don't know if and when it would move back to where it was previously, or why the corona moved. The results, from a remnant named Cassiopeia A Cas A , reveal how shock waves likely rip apart massive dying stars. Figure This is the first map false color image of radioactivity in a supernova remnant, the blown-out bits and pieces of a massive star that exploded.
The new view shows a more complete picture of Cassiopeia A, the remains of a star that blew up in a supernova event whose light reached Earth about years ago, when it could have appeared to observers as a star that suddenly brightened.
The remnant is located 11, light-years away from Earth. NuSTAR is the first telescope capable of taking detailed pictures of the radioactive material in the Cassiopeia A supernova remnant. While other telescopes have detected radioactivity in these objects before, NuSTAR is the first capable of pinpointing the location of the radioactivity, creating maps. When massive star explode, they create many elements: non-radioactive ones like iron and calcium found in your blood and bones; and radioactive elements like titanium, the decay of which sends out high-energy X-ray light that NuSTAR can see.
By mapping titanium in Cassiopeia A, astronomers get a direct look at what happened in the core of the star when it was blasted to smithereens. These NuSTAR data complement previous observations made by Chandra, which show elements, such as iron, that were heated by shock waves farther out from the remnant's center.
In this image, the red, yellow and green data were collected by Chandra at energies ranging from 1 to 7 keV. The red color shows heated iron, and green represents heated silicon and magnesium.
The yellow is what astronomers call continuum emission, and represents a range of X-ray energies. Figure 37 of NuSTAR shows the energized remains of a dead star, a structure nicknamed the "Hand of God" after its resemblance to a hand. The dead star, called a pulsar, is the leftover core of a star that exploded in a supernova.
The pulsar is only about 19 km in diameter but packs a big punch: it is spinning around nearly seven times every second, spewing particles into material that was upheaved during the star's violent death.
These particles are interacting with magnetic fields around the ejected material, causing it to glow with X-rays. The result is a cloud that, in previous images, looked like an open hand. Over the first year of the mission, NuSTAR has undertaken a range of studies, from observations of energetic events towards the center of the Milky Way galaxy to detailed studies of distant supermassive black holes.
NuSTAR's view is providing new clues to the puzzle. The hand actually shrinks in the NuSTAR image, looking more like a fist, as indicated by the blue color. The northern region, where the fingers are located, shrinks more than the southern part, where a jet lies, implying the two areas are physically different.
The red cloud at the end of the finger region is a different structure, called RCW Astronomers think the pulsar's wind is heating the cloud, causing it to glow with lower-energy X-ray light. In this image, X-ray light seen by Chandra with energy ranges of 0. The first batch of data from the black-hole hunting telescope is publicly available today, Aug. The more distant black holes are some of the most luminous objects in the universe, radiating X-rays as they ferociously consume surrounding gas.
One type of black hole in the new batch of data is a blazar, which is an active, supermassive black hole pointing a jet toward Earth. Systems known as X-ray binaries, in which a compact object such as a neutron star or black hole feeds off a stellar companion, are also in the mix, along with the remnants of stellar blasts called supernovas. The supermassive black hole lies at the dust- and gas-filled heart of a galaxy called NGC , and it is spinning almost as fast as Einstein's theory of gravity will allow.
The observations also are a powerful test of Einstein's theory of general relativity, which says gravity can bend space-time, the fabric that shapes our universe, and the light that travels through it. Scientists use these and other telescopes to estimate the rates at which black holes spin Figure Figure The artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Until now, these measurements were not certain because clouds of gas could have been obscuring the black holes and confusing the results.
The new data demonstrate that X-rays are not being warped by the clouds, but by the tremendous gravity of the black hole. This proves that spin rates of supermassive black holes can be determined conclusively. Measuring the spin of a supermassive black hole is fundamental to understanding its past history and that of its host galaxy.
Supermassive black holes are surrounded by pancake-like accretion disks, formed as their gravity pulls matter inward. Einstein's theory predicts the faster a black hole spins, the closer the accretion disk lies to the black hole. The closer the accretion disk is, the more gravity from the black hole will warp X-ray light streaming off the disk Ref. Legend to Figure 39 : Scientists measure the spin rates of supermassive black holes by spreading the X-ray light into different colors.
The light comes from accretion disks that swirl around black holes, as shown in both of the artist's concepts. They use X-ray space telescopes to study these colors, and, in particular, look for a "fingerprint" of iron — the peak shown in both graphs, or spectra — to see how sharp it is. The "rotation" model shown at top of Figure 39 held that the iron feature was being spread out by distorting effects caused by the immense gravity of the black hole.
If this model were correct, then the amount of distortion seen in the iron feature should reveal the spin rate of the black hole. The alternate model held bottom of Figure 39 that obscuring clouds lying near the black hole were making the iron line appear artificially distorted. If this model were correct, the data could not be used to measure black hole spin.
NuSTAR helped to solve the case, ruling out the alternate "obscuring cloud" model. Its high-energy X-ray data — shown at top as green bump to the right of the peak — revealed that features in the X-ray spectrum are in fact coming from the accretion disk and not from the obscuring clouds. Together with XMM-Newton, the space observatories were able to make the first conclusive measurement of a black hole's spin rate, and more generally, confirm that the "gravitational distortion" model is accurate Ref.
The red line explains the emission using a model where clouds of dust and gas partially block the X-ray light, and the green line represents a model in which the emission is reflected off the inner edge of the accretion disk, very close to the black hole. The results show that the iron feature, the sharp peak at left, is being affected black hole's immense gravity and not intervening clouds.
The degree to which the iron feature is spread out reveals the spin rate of the black hole. Mission and science operations have settled down into a mostly predictable daily routine, and the science team is making good progress toward achieving the primary, or "Level 1," science goals.
Examples of some of the key NuSTAR observations performed to date include mapping of the central regions of our Milky Way galaxy, studying the remnants of exploded stars in our galaxy, and surveys of several well-studied extragalactic fields. The mission has looked at a range of extreme, high-energy objects already, including black holes near and far, and the incredibly dense cores of dead stars.
High-energy X-ray data from NuSTAR have been translated to the color magenta, and superimposed on a visible-light view highlighting the galaxy and its star-studded arms. NuSTAR is the first orbiting telescope to take focused pictures of the cosmos in high-energy X-ray light; previous observations of this same galaxy taken at similar wavelengths blurred the entire object into one pixel.
With NuSTAR's complementary data, astronomers can start to home in on the black holes' mysterious properties. Instead, they may be intermediate in mass, or there may be something else going on to explain their extremely energetic state. NuSTAR will help solve this puzzle. The visible-light image is from the Digitized Sky Survey. Since the science operations began on August 1, , the NuSTAR team has wrestled with learning to point the telescope's flexible system of optics, mast, spacecraft bus and solar array.
Characterization of the behavior of NuSTAR in space took an additional six weeks, but has now been completed. Several adjustments to attitude control parameters — factors in pointing the telescope — were necessary to bring the spacecraft into the required specifications, and the satellite's slew rate, or the speed at which it points to new targets, has recently been enhanced by a factor of two. Calibrating the telescope is now a primary focus for the science team. The first two are neutron stars in our Milky Way galaxy, and the latter two are accreting black holes in the centers of nearby galaxies.
The first images from the observatory show Cygnus X-1, a black hole in our galaxy that is siphoning gas off a giant-star companion. This particular black hole was chosen as a first target because it is extremely bright in X-rays, allowing the NuSTAR team to easily see where the telescope's focused X-rays are falling on the detectors. The NuSTAR team will now begin to verify the pointing and motion capabilities of the satellite, and fine-tune the alignment of the mast.
In about five days, the team will instruct NuSTAR to take its "first light" pictures, which are used to calibrate the telescope. All systems are nominal. The instrument has the same name as the spacecraft.
The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass.
Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: During its baseline two-year mission, NuSTAR will also undertake a broad program of targeted observations. Instrument: The NuSTAR instrument is the first astronomical telescope in orbit to utilize the new generation of hard X-ray optics and solid-state detector technologies to carry out high-sensitivity observations at X-ray energies significantly greater than 10 keV.
It consists of two co-aligned depth-graded multilayer coated grazing incidence optics focused onto solid state CdZnTe pixel detectors with a focal length of Figure 43 shows the total effective area for both telescopes as a function of energy, with a comparison to Chandra and XMM.
The energy band extends from about 5 - 79 keV, being limited at the low-energy end by the optics thermal cover and shield entrance window, and at the high energy end by the K-edge at This is the angular diameter of the image of a point source, which contains half the flux at a given energy focused by the telescope.
From the standpoint of detecting and measuring sources with an X-ray telescope, the HPD proves more useful than other imaging metrics—e. Table 3: Key instrument performance parameters Ref. The instrument FOV is energy-dependent due to changes in multilayer reflectance as a function of energy and optics shell radius, which results in overall loss of reflectance and more vignetting at high energy Figure The target of opportunity ToO response time is required to be less than 24 hours; however, on average the turnaround will be faster, with targets typically acquired within 6 hours.
Understand explosion dynamics and nucleosynthesis in core collapse and Type Ia SNe. Constrain particle acceleration in relativistic jets in supermassive black holes.
Table 4: Baseline mission science plan. Figure Effective area as a function of off-axis angle, as a fraction of on-axis area, for several energies image credit: NuSTAR collaboration. The NuSTAR instrument is launched in a compact, stowed configuration, and after launch a 10 m mast is deployed to achieve a focal length of Since the absolute deployment location of the mast is difficult to measure on the ground, due to complications associated with complete gravity off-loading, an adjustment mechanism is built into the last section of the mast to enable a one-time alignment to optimize the location of the optical axes on the focal plane.
This mechanism provides two angular adjustments as well as rotation. The mast is not perfectly rigid, it is being subjected to thermal distortions particularly when going in and out of Earth's shadow which translate into changes in telescope alignment of 1 -2 arcmin. These mast alignment changes are measured by the combination of an optics bench-mounted star tracker and a laser metrology system. The same combination of sensors also provides the absolute instrument aspect.
In order to limit the FOV open to the detectors, and therefore the diffuse cosmic background, an aperture stop consisting of three rings deploys with the mast. The aperture stop is shown in the deployed configuration in Figure In the stowed configuration, the top will be 0.
A blowup of an individual optics module is also shown in Figure Each layer of the optic has an upper and lower conic shell equivalent to the parabola-hyperbola sections of a Wolter-I optic. Each shell is composed of multiple glass segments formed by thermal slumping.
Each piece of glass is coated with a depth-graded multilayer to enhance reflectivity. The enhanced reflectivity provided by the multilayers, along with the shallow graze angles afforded by the long focal length of the optics There are concentric layers which together form each optic. The glass layers a Titanium-glass-epoxy-graphite composite structure are built up on a Titanium mandrel.
Titanium support spiders located on the top and bottom of each optic connect it to the optical bench. The compliant, radially-symmetric spiders accommodate thermal expansion effects.
The first two modules are the flight units, and the third module is to provide for more extensive X-ray characterization than is permitted for either of the flight modules, given the compressed delivery schedule of the optics.. The layers of glass are physically separated from and attached to each other by means of precisely-machined graphite spacers which run lengthwise down the glass segments, and which constrain the glass to the proper conical shape of the Wolter 1 geometry.
The spacers are 1. The spacers are bonded to the Titanium mandrel and to the glass layers by means of a low outgassing epoxy Henkel F The number of graphite spacers is fixed at 5 per glass segment for fabrication simplicity.
The transition from sextants to dodecants provides for a reduction in the spacer span between glass segments as the radius of the layers grows, thus maintaining good control of the glass figure. The mandrel, sextant and dodecant glass layers and spacers are visible. Double width spacers azimuthally tie the dodecants to the sextant glass at the intermediate mandrel, increasing torsional stiffness and providing a path for distribution of launch loads.
The glass segments are coated with depth-graded multilayers. The entire assembly is built on, and aligned to, the central Titanium mandrel. After construction, support spiders are attached to the optic for instrument integration. During fabrication, glass and graphite layers are built outward from the central mandrel and all ground handling and alignment activities use the inner mandrel as a support and reference axis.
Once the optics are mounted to the optics bench, each is supported and aligned from attachment points on the spider supports. Table 6 summarizes the primary characteristics of the focal plane.
Table 6: Summary of the focal plane configuration. To achieve a low energy threshold and good spectral performance, the detector readout is designed for very low noise. The electronic noise contribution including detector leakage current to the energy resolution is eV, and the low-energy threshold is 2.
Over most of the energy range the detector spectral resolution is limited by charge collection uniformity in the CdZnTe crystal. At in-flight operating temperatures, the detector leakage current is a negligible contributor to the resolution. The readout of each focal plane module is controlled by an FPGA-embedded microprocessor.
Because each pixel triggers independently, and the electronics shaping time is short, there are no pile-up issues equivalent to the CCD focal planes on XMM and Chandra.
The readout system is designed so that source fluxes can be measured up to count rates of cps. The focal plane is surrounded by an active 2 cm thick CsI Na shield and incorporates a deployable aperture stop.
Figure 52 shows the expected background counts per unit detector area. At low energies the background is dominated by diffuse leakage through the portion of the aperture stop FOV not blocked by the optics bench. The spectral features between 25 and 35 keV are fluorescence from the CsI shield. The background level shown in Figure 52 assumes the use of the depth-of-interaction measurement to reject interactions in the back of the detector, which results in about a factor two background reduction at 60 keV Ref.
Figure Predicted detector background count rate per unit area as a function of energy image credit: NuSTAR collaboration.
Most science targets will be viewed for a week or more, so that after a day in-orbit checkout and commissioning period, commanding will be rare. The turnaround time for ToO Target of Opportunity observations depends largely on timing relative to the ground station passes. The SOC is in charge to process and validate the data, and distribute products to the science team. The NuSTAR science data has no proprietary period, and after a six-month interval during which the instrument calibration will be understood and the performance verified, data will enter the public science archive, located at the HEASARC.
Harrison, Y. Gudipati, Bryana L. Corcoran, Julian M. Russell, Brian W. Grefenstette, Daniel R. Wik, Theodore R. Gull, Noel D. Richardson, Thomas I. Gandhi, M. Bachetti, V. Dhillon, R. Satellites at altitudes of a few hundred kilometers and in orbits inclined relative to the equator experience intense particle radiation during passages through the SAA. This is particularly problematic for high energy X-ray telescopes due to the high level of radioactive background thus produced in the detectors.
The Nuclear Spectroscopic Telescope Array science operations center is located on the campus of the California Institute of Technology.
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