The Compton Observatory's Quest: Bursts and Maps

Among the observatories established by NASA, the Compton Gamma Ray Observatory holds a special place because of the unique discoveries it made during its golden age. Compton followed the Hubble into orbit as a great observatory to examine the events corresponding to the high energy light or the Gamma rays. The observations it made significantly helped humans to open a new dimension to the cosmos. Supernovae, the explosive deaths of massive stars; pulsars, the spinning corpses of supernova explosions; black holes, the collapse of stars; and quasars, bright central regions of faraway galaxies, are such discoveries.

The CGRO comprised of four instruments that served four different functions. They were the,

Burst And Transient Source Experiment (BATSE),
The Oriented Scintillation Spectrometer Experiment (OSSE)
The Imaging Compton Telescope (COMPTEL)
The Energetic Gamma Ray Experiment Telescope (EGRET).

Discovery of Gamma-Ray Bursts

Because satellites could not provide accurate information about Gamma-ray bursts, scientists were confused whether they occurred in the Milky Way or beyond our galaxy. The four instruments onboard the Compton examined these theories in detail. These instruments could cover an area of 20 keV to 30 GeV of radiation found in the galactic plane at once. The BATSE instrument was able to identify at least a single gamma-ray burst per day, identifying nearly over 2800 detections.

The images showed that a large number of gamma-ray bursts originate in faraway galaxies, not nearby in our Milky Way and that they must be energetic. These led to the implementation of the Fermi Gamma-ray Space Telescope and the Swift Gamma-Ray Burst Explorer in the later years that observed Gamma-Ray bursts in great detail. They identified that Gamma Ray bursts were occurring due to the exploding and merging of neutron stars creating black holes.

Discovery of a Young Supernova Remnant (SNR)

The COMPTEL was able to identify a young supernova remnant called Vela that is believed to have been seen to earth in the 14th century. It observed that some of the Gamma-ray bursts create an afterglow. Further observations revealed that when a large star uses fuel and explodes its substance, it emits more photons. The supernova remnant is the residue that can be seen as a flame after being ignited for thousands of years.

The All-Sky Map

The all-sky map produce by one of the instruments in the CGRO revealed the emission from interactions between cosmic rays and the interstellar gas along the plane of the Milky Way. This was done in the light of a radioactive isotope of Aluminum. With help of this map, astronomers were able to carry out several other findings.

Pulsing Radiation in Compton’s Map

Pulsars are born due to supernova explosions. They are rotating neutron stars, which we refer to as magnetars. The charged particles confined in the magnetic field of the neutron star produce a radiation beam. This, coupled with the rotation of the neutron star, emits a “pulsating” radiation signal.

Here the pulses produced across the electromagnetic spectrum by a variety of pulsars are depicted. The rotation periods are noted down at the bottom of each panel in milliseconds. It’s of note as to how clear the Gamma-ray observations of these signals are, as compared to the other ranges of the spectrum.

The Galactic Center: Blazars and Anti-matter Clouds

The EGRET all-sky map shows an image of the sky at gamma-ray energies above 100 MeV in Galactic coordinates. The diffuse emission, which appears brightest along the Galactic plane, is primarily due to cosmic-ray interactions with the interstellar medium. The Vela, Geminga, and Crab pulsars are clearly visible as bright knots of emission in the Galactic plane in the right portion of the image. The blazar 3C279 is seen as the brightest knot of emission above the plane.

These are a type of quasars that emit the majority of their electromagnetic energy in the 30 MeV to 30 GeV portion of the spectrum. The CGRO surveyed the galactic center and discovered a possible antimatter cloud above the center. It also discovered that when a particle collides with its anti-particle partner, it produces intense photons or gamma rays that cause them to destroy each other.

Several observations made by the COMPTEL experiment aboard the Compton Gamma Ray Observatory during the first phase of constructing the all-sky survey led to the composition of this image. Here we can see several sources of Gamma-ray radiation. The Crab pulsar and nebula are shown as the region with high intensity in the center. Slightly below and to the left is the quasar PKS 0528+134. Toward the top of the field is the cosmic gamma-ray burst recorded on the 3rd of May, 1991 (GRB 910503); and toward the edge is the hard X-ray/gamma-ray transient GRO J0422+32 (Nova Persei).

The significance of this observatory lies in the discoveries it did rather than the images it captured. Although Compton no longer roams the space in search of mystery, the part it did for humanity is undeniably worth it.

References

01. https://heasarc.gsfc.nasa.gov/docs/cgro/batse/
02. https://www.scientificamerican.com/article/the-great-observatories-c/
03. https://asd.gsfc.nasa.gov/blueshift/index.php/2016/04/13/lookingbackcgro/
04. https://svs.gsfc.nasa.gov/12194
05. https://www.jstor.org/stable/40680588
06. https://www.encyclopedia.com/science/science-magazines/astronomy-and-space-science-pulsars-quasars-and-distant-questions

Image Courtesies

01. Featured Image: https://go.nasa.gov/2VowLhf
02. Image 01: https://go.nasa.gov/3CEt9bA
03. Image 02: https://go.nasa.gov/3yBOjER
04. Image 03: https://go.nasa.gov/3lWSh7r
05. Image 04: https://go.nasa.gov/3Ayy4ZR
06. Image 05: https://go.nasa.gov/3CGqwGc
07. Image 06: https://go.nasa.gov/2VPds0o
08. Image 07: https://go.nasa.gov/3fUnjJy

The Compton Observatory’s Quest: Bursts and Maps