More from the Galactic Center


This sequence of images from the X-ray Telescope aboard the Swift satellite shows changes in the central region of the Milky Way galaxy from 2006 through 2013. Watch for flares from binary systems containing either a neutron star or q black hole and the changing brightness of the galaxy’s central black hole Sgr A*.

Video Credit: NASA

Gamma Ray Burst


When a massive star collapses to form a black hole, a burst of gamma rays results as particles are blasted outward at nearly the speed of light. This animation shows the most common type of gamma-ray burst. An end-on view of a jet greatly boosts its apparent brightness. One especially bright burst (GRB 130427A) was detected last April by the Fermi and Swift satellites. A Fermi image of that burst ends the animation sequence.

Video Credit: NASA

An Near-Earth Asteriod


On 9 November, 2012, Asteroid 2005 YU55 passed by the Earth. In this video the asteroid moves through the field of view of Swift‘s Ultraviolet/Optical Telescope (UVOT) shortly after the space rock made its closest approach. The video plays on a background image from the Digital Sky Survey that shows the same region, which lies within the Great Square asterism of the constellation Pegasus (times are UTC).

Video Credit: NASA

Things I’ve Done


240px-Swift_spacecraftI began working the power system for the Burst Alert Telescope of the Swift satellite in 2000. I designed several bits and pieces that wound up in various assemblies in the BAT, but I was primarily responsible for the low-noise voltage regulators that powered the amplifiers in the sensor array. That regulator assembly was called the XA1VR. There were 16 of them in the BAT.

Because house calls are impossible on most of NASA’s hardware once it gets on orbit, reliability is a major design concern. That means that so-called space-class parts are used almost exclusively. This was a significant problem in the design of the XA1VR because there were several key components which were not yet available as space- or even military-grade parts. The pass transistors were a particular problem. Not only were they not available in the sort of hermetic packages normally used, the manufacturer had no plan to make space-class parts available until well after the scheduled launch date for the mission. Because commercial plastic parts had to be used, there were additional handling precautions that had be taken with the assemblies.

All 16 flight units of the XA1VR and all the spare units were delivered on time. They were the only assemblies delivered for integration into the BAT on schedule. They were the only assemblies that required no rework. The service life requirement for the mission was two years. All 16 XA1VRs are still working on orbit after almost a decade.xa1vr

Image Credits: NASA

The picture shows an XA1VR (mounted in the frame that holds it and 8 sensor blocks) being inspected after handling during system integration. The bundle of white wires carries the high-voltage bias power for the x-ray sensors. The bias potential is supplied by an adjustable regulator in an assembly called the Block Voltage Regulator. The BVR takes power from a low-voltage bus and generates a slightly-greater-than 300 V low-current internal bus. (That part of the BVR and the overall design of the BVR assembly was done by my colleague Lowell Fry.) That bus fed individual 0 to 300 V adjustable regulators, one for each sensor block. I designed the adjustable regulators. Because the currents being controlled were so tiny, bipolar transistors had to be used in those regulators. Here we had the opposite availability problem. Such transistors were common parts back in the days of discrete transistor television sets, but, by 2001, they were no longer readily available as current production and completely unavailable as new space- or military-grade parts. Fortunately, we found some old-stock military parts, and I was able to design a workable solution using them.

From time to time, I’m able to post some new science from the Swift mission. I feels good to have been a small part of getting it off the ground.

UPDATE—Broken link fixed.

The Big Chill


During my time at NASA, I worked on subsystems for a couple of instruments used for x-ray astronomy. The first was the Burst Alert Telescope which is a key part of the Swift satellite. The BAT detects gamma ray bursts and provides information to steer the satellite so the other instruments aboard can observe the new x-ray event. My main contribution was the low-noise power regulators that run the detector array. I also design the pulse-width modulation regulator that were a part of the thermal control system for the sensors. They operate at 295 K (±0.5 K), which is roughly room temperature.

The most recent instrument I worked on was the Soft X-ray Spectrometer that is scheduled to fly on the ASTRO-H mission. ASTRO-H is a Japanese mission with NASA providing the SXS instrument. I worked on the temperature control system for the sensors in the SXS.

The SXS not only detects x-ray photons but also measures the energy of individual photons. When a photon hits a surface and is absorbed, the energy transferred to the target warms it. Of course, an individual photon doesn’t have much energy, so for the warming to cause a significant percentage change in the temperature, the target has to be really cold. In the case of the SXS, really cold means 50 mK, that’s 50 millikelvin or 0.05 degrees above absolute zero. To put that level of cold into perspective, its about the same percentage change from room temperature is as room temperature is below the surface temperature of the Sun. And for the changes caused by photons to be noticeable, the variation in sensor temperature allowed by the control system must be less than 1 µK. That’s one microkelvin or 0.000001 K.

OK, liquid helium at low pressures has a temperature of around 1.3 K. That’s the coldest naturally occurring matter in the Universe. How do you get colder than that? The answer involves salt, but not in the same way we use salt in ice cream freezers. My next post on this subject will explain how.

The Magellanic Clouds in UV


During my early days working at Goddard Space Flight Center, I designed one of the subsystems in the instrument that normally serves as the viewfinder on the Swift satellite, the Burst Alert Telescope. There are two other instrument aboard, an X-ray Telescope and a UV Optical Telescope. The Swift mission team has used the UVOT to create detailed images of the two galaxies nearest the Milky Way, the Large and Smaller Magellanic Clouds.

A “Young” Supernova Remnant


g306_wideAstronomers estimate that a supernova explosion occurs perhaps a couple of times a century in the Milky Way. The expanding blast wave and hot stellar debris slowly dissipate over hundreds of thousands of years, eventually mixing with and becoming indistinguishable from interstellar gas. The Swift satellite uncovered the previously unknown remains of a shattered star during an X-ray survey of the galaxy’s central regions. The new object, named G306.3-0.9 after it’s coordinates in the sky,is among the youngest of the 300+ known supernova remnants in the Milky Way. Analysis indicates that G306.3–0.9 is probably less than 2,500 years old. That would make it one of the 20 youngest supernova remnants identified.

This composite image of G306.3–0.9 (the blob in the lower left) was stitched together using data from Chandra X-ray observations (blue), infrared data acquired by the Spitzer Space Telescope (red and cyan) and radio observations (purple) from the Australia Telescope Compact Array.

G306_Swift_XRTjpgThe image on the left was taken in February, 2011, using Swift’s X-ray Telescope as part of the Galactic Plane Survey. The dots in the image indicate where X-rays struck the detector. Despite this short 8.5-minute exposure, the extended circular patch of G306.3–0.9 stands out quite nicely.

Image Credits: NASA

Gamma Rays!


Fermi_LAT_GRB_673Just after 07:47 UTC last Saturday, the Gamma-ray Burst Monitor (GBM) aboard the Fermi satellite triggered on an eruption of high-energy light in the constellation Leo. Click on the image to see an animation showing a more detailed Fermi Large Area Telescope view. GRB 130427A produced the highest-energy light ever detected from gamma ray burst. The sequence shows high-energy (100 MeV to 100 GeV) gamma rays from a 20-degree-wide region of the sky starting three minutes before the burst to 14 hours after. After a one-second spike, the burst’s output remained relatively quiet for the next 15 seconds while Fermi‘s GBM showed bright, variable lower-energy emission. Then the burst re-brightened in the LAT over the next few minutes and remained bright for almost half a day. The record-setting blast of gamma rays came from a dying star in a distant galaxy roughly 3.6 billion light-years away.

Fermi’s Large Area Telescope (LAT) recorded one gamma ray with an energy of at least 94 billion electron volts (GeV), or some 35 billion times the energy of visible light, and about three times greater than any previous GRB. The GeV emission from the burst lasted for several hours, and it remained detectable by the LAT for the most of the day, making it the longest gamma-ray emission from a GRB detected to date.

The burst occurred as NASA’s Swift satellite was slewing between targets, which delayed its Burst Alert Telescope’s (BAT) detection by less than a minute. (The BAT is a wide-angle detector that can quickly determine the bearing to a gamma ray source. I designed the low-noise power regulators that feed the detector array in the BAT.) The burst was detected in optical, infrared and radio wavelengths by ground-based observatories using the rapid, accurate position from Swift.

Swift_XRTSwift‘s X-Ray Telescope took this image of GRB 130427A at 07:50 UTC on 27 April, moments after Swift and Fermi triggered on the GRB.

Gamma-ray bursts are the universe’s most luminous explosions. We believe that most occur when massive stars run out of nuclear fuel and collapse under their own weight. As the core collapses into a black hole, jets of material explode outward at almost the speed of light.

Image Credits: NASA

Gamma Rays for Christmas


GRB_111209AThe gamma ray burst (GRB) from GRB 111209A (aka the Christmas Burst) was detected in early December, 2011. The blast produced high-energy emission for an astonishing seven hours, the longest-duration GRB ever observed. This false-color image shows the event as captured by the X-ray Telescope aboard NASA’s Swift satellite. Because the distance to the burst was not measured initially, astronomers came up with a couple of radically different interpretations. In one scenario, a solitary neutron star in our own galaxy shredded and accreted an approaching comet-like body. In the other, a neutron star spiraled into and was eaten by a giant star in a distant galaxy. Now, a third explanation has been advanced. After a measurement of the Christmas Burst’s host galaxy, it appears that the GRB resulted from the collapse and explosion of a supergiant star hundreds of times larger than the sun.

Image Credit: NASA

Comet ISON


Astronomers from the University of Maryland at College Park and Lowell Observatory have used NASA’s Swift satellite to check out comet C/2012 S1 (ISON), which may become one of the most dazzling in decades when it rounds the sun later this year. Using images acquired over the last two months from Swift‘s Ultraviolet/Optical Telescope (UVOT), the team has made initial estimates of the comet’s water and dust production and used them to infer the size of its icy nucleus.Swift_ISONThe UVOT imaged comet ISON (center) at the end of January, when it was located about 3.3 degrees from the bright star Castor in the constellation Gemini. When this 5.5 min time exposure was taken, the comet was about 5,000 times fainter than the limit of human vision.

Based on ISON’s orbit, astronomers think the comet is making its first-ever trip through the inner solar system. Before beginning its long fall toward the Sun, the comet resided in the Oort comet cloud, a vast shell of icy bodies that extends from the outer reaches of the planetary system to about a third of the distance to the star nearest the Sun.

On 1 October, the inbound comet passes about 10.8 million km from Mars. During this close encounter, NASA and ESA spacecraft now orbiting Mars may be able to observe the comet. It may also have its picture taken by the Curiosity rover from the surface of Mars.

On 28 November, ISON will swing around around the sun. The comet will approach within about 1.2 million km of the Sun’s visible surface, which classifies it as a sungrazing comet. In late November, icy material will furiously sublimate and torrents of dust will be released as the ISON’s surface erodes because of the Sun’s fierce heat—as sun-monitoring satellites look on. Around this time, the comet may become bright enough to be seen from Earth just by holding up a hand to block the Sun’s glare.

Following ISON’s solar encounter, the comet will move toward Earth, appearing in evening twilight through December. It will swing past Earth on the day after Christmas, coming within 64.2 million km or about 167 times farther than the moon.

Image and Video Credit: NASA

The Crab Nebula in UV


Crab_nebula_uv_SwiftAbout 7,500 years ago, a star went supernova. The Crab Nebula is the wreckage of that supernova whose explosion was seen on Earth in the year AD 1054. The expanding cloud of gas is located 6,500 light-years away in the constellation Taurus. This false color composite of three ultraviolet images taken by the UV Optical Telescope carried on the Swift satellite highlights the hot gas in the supernova remnant. The image is constructed from exposures using these filters centered at 260 nm (red), at 225 nM (green), and centered at 193 nm (blue). (Click the image to embiggen it.)

Image Credit: NASA

Supernova in M101


These images from the Ultraviolet/Optical Telescope (UVOT) on board NASA’s SWIFT satellite show the nearby spiral galaxy M101 before and after the appearance of SN 2011fe (circled, right). The supernova was discovered on 24 August, 2011. Only about 21 million light-years away, it was the nearest Type Ia supernova since 1986. Left: This view was constructed from images taken in March and April, 2007. Right: The supernova was so bright that most UVOT exposures were short, so this view includes imagery from August through November, 2011 to better show the galaxy.

Image Credit: NASA

Andromeda in UV


This mosaic of M31 merges 330 individual images taken by the Ultraviolet/Optical Telescope aboard NASA’s Swift spacecraft. It is the highest-resolution image of the galaxy ever recorded in the ultraviolet. Also known as the Andromeda Galaxy, M31 is more than 220,000 light-years across and lies 2.5 million light-years away. On a clear, dark night, the galaxy is faintly visible as a misty patch to the naked eye.

The irregular shape of the image results when the more than 300 images were assembled to make the final image.

Image Credit: NASA/Swift/Stefan Immler (GSFC) and Erin Grand (UMCP)

There are three instruments on the Swift satellite—a UV telescope, an X-ray telescope, and the Burst Alert Telescope which serves as the gamma ray burst detector for the spacecraft. I contributed to the design of the ultra-quiet regulators powering the detector blocks in the BAT.

NASA’s Swift Catches Asteroid Flyby


As asteroid 2005 YU55 swept past Earth in the early morning hours of Wednesday, 9 Nov., UV and X-ray telescopes aboard NASA’s Swift satellite joined professional and amateur astronomers around the globe in monitoring the fast-moving space rock. The unique ultraviolet data will aid scientists in understanding the asteroid’s surface composition. Image Credit: NASA

Learn more and watch a video of the flyby here.

A Galaxy with Two Black Holes


A study using NASA’s Swift satellite and the Chandra X-ray Observatory has found a second supersized black hole at the heart of an unusual nearby galaxy already known to be sporting one. Viewed in visible light, Markarian 739 resembles a smiling face, with a pair of bright cores underscored by an arcing spiral arm. The object is really a pair of merging galaxies. Data from Swift and Chandra reveal the western core (right) to be a previously unknown active galactic nucleus (AGN); past studies already had identified an AGN in the eastern core. The two supermassive black holes are separated by about 11,000 light-years. The galaxy is 425 million light-years away. Image Credit: SDSS

A Star Eaten By A Black Hole


Images from Swift’s Ultraviolet/Optical (white, purple) and X-ray telescopes (yellow and red) were combined in this view of GRB 110328A, which is now known as Sw 1644+57. The blast was detected only in X-rays, which were collected over a 3.4-hour period on March 28. Credit: NASA/Swift/Stefan Immler

On March 28, NASA’s Swift’s Burst Alert Telescope discovered a series of powerful X-ray blasts coming from a source in the constellation Draco. Astronomers around the world studied the unusual explosion, which is now known as Sw 1644+57. More than two months later, and with high-energy X-rays still coming from the spot, astronomers are convinced they’re witnessing the destruction of a star as it plunges into the central black hole of a galaxy nearly 4 billion light-years away. The star was ripped apart by the black hole’s intense tidal forces, and its gas continues to stream inward. “With this event, we’re seeing a new class of object in the sky, one we think is directly tied to the feeding behavior of a galaxy’s supermassive black hole,” said Neil Gehrels, Swift’s lead scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “Such events likely will give us unprecedented insight into what happens deep in the heart of active galaxies, such as quasars and blazars.”

I worked on the Burst Alert Telescope. I designed the low-noise power regulators that power the sensors and thermal controls for heaters used in the BAT and in the star trackers in the satellite guidance system. It’s pleasing to see work from almost a decade ago still helping to do some real science.

More about the SWIFT mission here.