May 28, 2020

Death by…Gamma-Ray Burst!

Sure, we’ve all seen the movies with the impending death by asteroid or comet. You might have even heard of the havoc that can be wrecked by the Sun or an errant black hole, but have you ever heard of death by… gamma ray burst? Very much outside of public consciousness, this was but one of the more exotic ways humanity could have an official bad day that was outlined in Phil Plait’s outstanding Death from the Skies! But what are these exotic beasties, and just how likely are they?

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23.01.11: A Hail of Anti-Matter?

An anti-matter barrage may be underway high overhead. Recently, NASA scientists have released evidence that antimatter in the form of positron emission may be created right here on Earth during terrestrial thunderstorms. The evidence comes from the Fermi Gamma-ray Space Telescope, designed to monitor extra-galactic gamma-ray bursts. Since its launch in 2008, Fermi’s Gamma-ray Burst Monitor instrument has detected 130 of what are known as Terrestrial Gamma-ray Flashes, (TGF’s) generated by lightning.

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The Great Orbiting Observatory Series: Part III: Gamma-Ray Telescopes.

By far, the portion of the spectrum with the coolest Science fiction-friendly name is gamma-ray. The highest end of the spectrum, this range starts at energies above 100 keV and wavelengths of 10 pico-meters (that’s tiny…) or less. Gamma ray energy from space had been suspected since the mid-40’s, but it took the advent of the space age for gamma ray astronomy to really take off.  Studies of gamma rays have revealed an entirely new universe full of exotic beasties such as supernovae, gamma ray bursts, pulsars and black holes. Some gamma ray studies are conducted from high mountain peaks such as the VERITAS array in Arizona or the RAPTOR telescope in New Mexico which looks for optical GRB transients, as well as balloon borne observatories searching for soft cosmic rays aloft. These however can suffer degradation of the signal by energy interactions with oxygen and nitrogen molecules at altitude. Hence,  if you really want to get above our gamma-ray absorbing atmosphere, you’ve got to go to space to do it.

So you want to build a gamma ray telescope? These types of exotic instruments do not use telescope mirrors or an optical configuration in a traditional sense; instead, the employment of scintillors or photomultiplier tubes and sometimes diffracting masks or grates are used. The idea is that as a highly energetic cosmic ray hits the gas or crystals embedded within, a signature flash of Cerenkov radiation is emitted. If enough high speed photomultipliers can catch a particle in the act, a path and a direction of origin can be traced. Early detectors such as Explorer 1 were no more than simple cosmic ray counters; modern observatories such as Fermi can sweep the entire sky looking to pin-point gamma ray bursts.

One of the earliest mysteries of the space age was the source of space born high energy bursts. Satellites sent aloft to monitor nuclear weapons testing were also detecting gamma rays from cosmic sources… just what phenomena in the universe could produce such high energies?

As time and the field of astrophysics marched on, we began to realize that the universe, as J.B. Haldane once said, is “stranger than we can imagine.” Bizarre beasts such as quasars and gamma ray bursters joined our lexicon of exotic objects. A chief issue with observing gamma-ray bursts is their rapid onset and disappearance in the sky. If we were to study these sources, a telescope would need to not only be able to refine a field of view at gamma ray frequencies, but also be capable of quickly swinging into action once a burst had occurred.

The first true gamma ray telescope was NASA’s SAS-2 (for the Second Small Astronomy Satellite) launched in November 1972. Its mission lasted for about six months, and was the first gamma ray astronomy dedicated satellite. Its main discovery was the pulsar Geminga.

Some past orbital robotic greats in the field of gamma ray astronomy were…

Compton: Some great science came “straight outta Compton…” Launched April 1991 aboard the Space Shuttle Atlantis on STS-37, Compton was actually named after Nobel Prize winner Dr. Arthur Holly Compton. During its all too short life span, Compton provided some amazing breakthroughs, including the first gamma ray all sky survey above 100 MeV, including a thorough study of the galactic core at those energy levels. Compton also discovered the first four soft gamma ray repeaters. When GRB 990123 popped off, Compton was there, nailing down the fading afterglow of a galaxy over four giga-parsecs distant. One of the true crimes of our times was the untimely demise of this instrument; Compton was purposely de-orbited June 4th, 2000 after partial gyro-scope failure.

Granat: The International Astrophysical Observatory may have been one of the greatest orbiting projects that you’ve never heard of. A joint European Russian venture, Granat was placed into geocentric orbit on December 1st 1989 and carried three x-ray, three gamma ray instruments as well as an all sky detector. During its ten year life span, Granat provided an all sky survey in the 40 to 200 keV spectrum, as well as the discovery of several new black holes and pulsars. When you see a designator in a catalog marked “GRS” that stands for GRanat Source. Other unique feats include the ‘discovery of galactic micro quasars as well as a nearly two month long (!) exposure of our galactic center at high frequencies!

Cos-B: No, this wasn’t a mid-eighties sitcom…Cos-B was a European observatory conceived in the 60’s and launched by NASA in August 1975. This was back when the European Space Agency was still known as the European Space Research Organization… (Remember?) During its six year plus mission, COS-b advanced the wealth of gamma ray data and increased the catalog of known gamma ray emitting objects in what came to be known as the 2CG catalog. COS-B also conducted the first studies of the Cygnus X-3 pulsar.

But those pioneering observatories represented a mere beginning in the fledgling field of gamma ray astronomy. Among the orbiting telescopes currently in use are…

Fermi: the telescope formerly known as GLAST, the Fermi Gamma ray space telescope is now NASA’s pioneering high energy observatory in orbit.  Fermi sports two primary instruments; the LAT or Large Area Telescope, and the GBM or Gamma Ray Burst Monitor.  The LAT collects high energy positron-electron pairs generated as photons pass through special metal sheets and funnel them into a calorimeter stack. With a FOV spanning 20 degrees of the sky, the LAT can pinpoint a gamma ray source down to several arc minutes…pretty darn good in terms of high energy astronomy. The GBM is an all-sky instrument which is made of 14 scintillation detectors. Launched in June 2008, Fermi’s credits thus far include the detection of a pulsar that exclusively emits gamma ray energy (a first). It has but also been on hand to witness the most powerful GRB so far; GRB 080916C, a GRB with the force of an estimated 9,000 supernovae! Thankfully, this burst was over 12 billion light years distant.

HETE-2: The High Energy Transient Explorer, this was a sort of bridge between the Compton and Fermi timeline. HETE was launched in October 2000 and carried both X-ray and UV instruments; unfortunately its earlier version was to have gamma ray detection capability but was doomed by the failure of its payload separating explosive bolts on launch.

Swift: The Swift Gamma Ray Burst mission has been another high energy physics high performer since its launch in 2004. The goal of Swift is much as its name implies; detect events with its Burst Alert Telescope, pin point the source to within 1 to 4’ arc minutes within 15 seconds, then notify any ground based telescopes with a clear view to swing into action. Really, the kind of quick reaction demanded of gamma ray burst monitoring is that fast! Swift also comes equipped with X-ray, UV, and optical instruments of its own to assist in catching the afterglow. To date, Swift has performed admirably, passing the 500 GRB mark earlier this year on April the 13th, 2010.

Curiously, a quick search does not reveal a wealth of proposed gamma ray observatories on the books; we suspect this is because of the growth of modern balloon borne technology making it easier to place instrument payloads for high energy physics on atmospheric platforms. Of course, we would love to be proven wrong…

Digging around various astronomy forums yields only one proposed future scope; the Advanced Compton Telescope, a gamma-ray platform and successor to the original Compton, still very much in the proposal stage. Orbiting observatories such as Swift and Fermi should be destined for long lives, and provide an awesome science bang for the buck. And as noted, the balloon borne platforms used for cosmic ray studies are less than “stellar” when it comes to the gamma ray portion of the spectrum. Now that we’ve gotten a real taste for gamma ray astronomy, our suspicion is that astronomers will always want an orbiting workhorse on hand.

So there you have it, a quick peek into the exciting realm of orbital gamma ray astronomy. If your favorite GRB scope didn’t make the cut (y’know, the one you pinned your PhD on) do drop us a line, or follow us via the big, garish Twitter “Follow Me” button to the right… we love to talk astrophysics!


Astro Event of the Week: Spot Atlantis on its Final Flight!

This week sees the first in a series of finales; three shuttle missions remain, and the first shuttle up for its final voyage is Atlantis and STS-132. This is a resupply mission to the International Space Station, as NASA prepares to enter life aboard the ISS without a shuttle next year. Atlantis first took to space on October 3, 1985 and has performed such notable feats as the launching of the Magellan & Galileo spacecraft as well as the Compton Gamma Ray Observatory and last year’s final repair of the Hubble Space Telescope aboard STS-125. Atlantis takes its name from the famous sailing ship that first scouted out Wood’s Hole in the early 20th century, the RV Atlantis. After STS-132, Atlantis will have logged nearly 300 days in space. Atlantis will be kept for a STS-335 Launch On Need standby for the final STS-134 flight of Endeavour later this year, which is also the last of the shuttle program.

The good news is several sighting opportunities should be possible for both Atlantis and the ISS during its 13 day planned mission. Launch is scheduled for 2:20 PM EDT on Friday, May 14th, and the shuttle will pass over Europe as it lifts into orbit that evening at dusk. Interestingly, it looks like the Sun angle may be setting up for some transit sighting opportunities over the US Southeast during this mission. Docking will occur on day three, which will be on the 17th if everything launches on schedule. Lit dusk passes on the pair will favor the US eastern seaboard, and generally, the farther north you are, the higher the STS-ISS pair will be. Around late June, the ISS will enter a summertime orbital phase where its orbit will actually be permanently illuminated at times, and even now, the nights aboard the ISS are drawing up short. Do track sites such as Heavens Above, CALsky, Spaceweather, and this space for updates… it’s worth it to see Atlantis do its thing one more time!

(Note: An orbital ballet of sorts is also in progess at the ISS; today, the Progress 36 module undocks from the nadir port of the Zvezda  module. Progress will deorbit and burn up over the Pacific in June. Then, on Wednesday, cosmonaut Kotokov will pilot the Soyuz TMA-17 and undock from the aft end of the Zarya module and move it to replace Progress, freeing it up for the installation of the MRM-1  carried aboard Atlantis. Talk about a cool valet job!)

The astro-word for this week is: Space Tweetup! A space tweetup is an alignment of two or more space enthusiasts for a space flight cause via that most venerable of 140 character platforms, Twitter. A Tweetup may be virtual, as in “let’s watch a launch via NASA TV and tweet about it” or in person, as in next week’s NASA tweetup for the STS-132 launch, of which Astroguyz is proud to be a member. NASA obviously “get’s it,” and is eager to promote new technology and engage its legion of fans, many whom feel disenfranchised with the “old school” media. People often ask me, “Why bother with Twitter?” I reply that events like the NASA tweetup have given me the opportunity to gain access normally reserved only for a select few, and an ability to connect to readers in a way not possible previous. It’s hard to imagine that scant decades ago, the monthly astronomy magazine bulletins would tell us about the comet that had long since come and gone; through Twitter communities, I can not only act on alerts for new objects, but share images straight from the eyepiece in real time. I highly encourage anyone interested to apply for a NASAtweetup; it’s open to all, and they’ve had events at the Kennedy and Johnson Space Center and in Baltimore at the Goddard Space Center thus far. And if you can’t make it, you can always participate vicariously online!

23.10.09:Fermi Pegs Gamma-Ray Pulsars.

NASA’s Large Area Telescope aboard the orbiting Fermi gamma-ray observatory continues to turn out some amazing science, picking up where Compton left off in 2002 as it surveys the gamma-ray sky. Of particular interest are gamma-rays emitted from pulsars. Pulsars are the swiftly rotating remnants of massive stars that have gone supernova, leaving a superdense core in their wake. These are sometimes called “neutron stars” because the matter comprising them is packed so tightly the individual nuclei are literally stacked end to end, making a spoonful weigh as much as a mountain! After all, most ordinary matter is made of….nothing. A neutron star can be thought of as a large, singular atomic nucleus, again weird stuff. Most of the 1,800 pulsars thus detected are because of their copious radio emissions beaming from their poles. Thus, we have to be in the line of sight before we see their blinking radio pulsations. Enter Fermi, which has thus far spotted 16 new pulsars via their gamma-ray emissions alone. This promises to aid in identifying pulsars whose poles aren’t tipped to our line of sight, which are probably in the majority. But even the gamma-ray sky is relatively dim; for example, the Vela pulsar is one of the brightest in the sky, and it emits a mere 1 gamma-ray photon every 2 minutes! Initially dubbed “Little Green Men” (LGMs!) during their discovery in the 1960′s, pulsars were soon naturally explained, but still continue to amaze. Watch this space and the Fermi mission for news from the high energy end of the spectrum!