9. Fermi Gamma Ray Space Telescope

Fermi Gamma Ray Space Telescope orbits around Earth once per 95 minutes.

fermi.gsfc.nasa.gov

Fermi Telescope was launched on 11 June, 2008. And this year it completed 10 years in orbit. Previously it was called Gamma-ray Large Area Space Telescope (GLAST) but later in 2008 it was renamed to honour physicist Enrico Fermi.

It has two instruments on board-
1. Large Area Telescope (LAT)
2. Gamma-ray Burst Monitor (GBM)
Both of these instruments also contain many subsystems.

Fermi has detected the most distant Blazars that are 2.1 billion years old!

8. Suzaku Observatory

Suzaku was an X-ray observatory in a 96 minute orbit around earth.

www.nasa.gov

Suzaku was launched on July 10, 2005. Before its launch it was known as ASTRO-E2. And it was the second launch mission of ASTRO-E observatory which was lost on 10th Feb, 2000 due to rocket failure which crashed into ocean with its payload.

The instruments on board Suzaku are-
1. X-ray Telescope (XRT)
2. X-ray Spectrometer (XRS)
3. X-ray Imaging Spectrometer (XIS)
4. Hard X-ray Detector (HXD)

Suzaku detected chromium and manganese elements in the intergalactic space - the space between galaxies of Perseus Cluster. The gas in cluster was very hot thus emitting X-rays. Suzaku's instruments detected these X-rays and split them into its component wavelengths. As every element has a different spectrum, the two atoms were identified.

This video describes more details about the discovery-

The mission was deactivated on 2nd September, 2015.

7. Swift Observatory

Swift observatory is in a 95.74 minute orbit around earth. Its NASA's Multi-wavelength space telescope.

NASA E/PO, Sonoma State University/Aurore Simonnet

It was launched on 20th November, 2004. Swift is named after a small bird. One of its mission is to detect Gamma Ray Bursts and their afterglows in X-ray and visible light. For this, there are three instruments on board Swift -

1. Burst Alert Telescope (BAT)
2. X-Ray Telescope (XRT)
3. Ultraviolet/Optical Telescope (UVOT)
Swift detects ~100 GRBs per year.

This year in January, Swift was renamed as Neil Gehrels Swift Observatory to honour Cornelis A. Neil Gehrels, an astrophysicist who left us on February 6, 2017.

swift.gsfc.nasa.gov

It was the first image captured by the UVOT instrument - the pinwheel galaxy in UV and visible light.

6. RXTE

Rossi X-Ray Timing Explorer (RXTE) was a spacecraft in low-earth circular orbit of 90 minutes.

wikipedia.org

RXTE was launched on December 30, 1995. Its mission was to study time variation of astronomical X-ray sources. The spacecraft was named after an Italian physicist Burno Benedetto Rossi.
The mission was deactivated on 5th January, 2012 after working for 16 years and 6 days.

RXTE solved one of the deepest mysteries in Astronomy.

It was known through observations that the galactic plane glows in X-rays whose brightness increases towards the galactic center.

Other observatories like Chandra and XMM-Newton were not able to give details of what's causing the glow. So, it was assumed by astronomers that the X-rays were coming from hot, diffuse Interstellar gas.

RXTE had mapped the X-ray background for 10 years since February, 1996. And NASA's another satellite COBE (Cosmic microwave Background Explorer) in early 1990s had also mapped the near-Infrared glow from our galaxy. The data from two satellites were matched.

Credit: NASA/RXTE-COBE/Revnivtsev et al.

As lots of individual stars glow in near-Infrared, it was suggested that X-ray emission in the galactic plane came from cataclysmic variables (a binary system with a star and a white dwarf).

White dwarfs are cores of dead stars and if they are in a binary, they will accrete gas from their companion star. Due to this process very high energy X-rays are released.

(New Map of Milky Way Reveals Millions of Unseen Objects - March 2006. heasarc.gsfc.nasa.gov)

5. INTEGRAL

ESA's INTEGRAL (INTErnational Gamma Ray Astrophysics Laboratories) is orbiting in a highly elliptical orbit around Earth. And it takes three days to orbit once around Earth.

Credit: ESA/ D. Ducros

INTEGRAL was launched on 17th October, 2002. Its mission is to study black holes, neutron stars, pulsars, active galactic nuclei, Supernovae, Gamma Ray Bursts etc.

It's the most sensitive gamma-ray Observatory ever launched. To detect Gamma rays from the objects in the universe an instrument needs to go in space because Earth's protective layer prevents them from reaching the ground.

INTEGRAL can observe objects in gamma-rays, X-rays and visible light. There are two detectors on INTEGRAL to detect gamma rays from space - an imager (IBIS - Imager on-board INTEGRAL) and an spectrometer (SPI - Spectrometer on INTEGRAL). Other two instruments are JEM-X (Joint European X-ray Monitor) and OMC (Optical monitoring Camera). OMC can detect stars with visual magnitude up to 19.7. It's a standard optical refractor with 5-cm lens and a CCD of 2055×1056 pixels in the focal plane.

On 14th August, the merger of two neutron stars that triggered the LIGO detectors fifth time also triggered the instruments on board INTEGRAL. And It was recorded as a 2 second gamma-ray-burst prior to the gravitational wave detection.

It became the first event to be observed in gravitational waves and in electromagnetic spectrum by lots of ground based and space based Telescopes in addition to the LIGO detectors.

4. Chandra X-ray Observatory

Chandra X-ray Observatory (CXO) is orbiting around Earth in a highly elliptical orbit of 64 hours.

Artistic image of CXO: wikipedia.org

Chandra Observatory was launched on the space shuttle Columbia in July 23, 1999.

There are lots of objects which emit X rays, for example Stars, Supernovae, Supernova remnants, gases falling into neutron stars and black holes etcetera.

But the mirrors used in Chandra Observatory are not like in any optical telescope where parabolic mirrors are used. If the X rays fall directly on a mirror they'll be absorbed. So the mirrors are shaped like a hollow cylinder which narrows the X rays until they are focused on an electronic detector, as shown in the video.

Last year in December Chandra released a new image of the 11 thousand light years distant Supernova remnant named Cassiopeia A. In this image different colours show different elements. Silicon is shown in red, Sulfur in yellow, Calcium in green and Iron in purple.

chandra.harvard.edu

A similar but more colorful composite image was also released using the data from Spitzer Space Telescope, Hubble Space Telescope and Chandra X ray Observatory.

The best thing about these images is that you can see the remaining core of the star as a dot (white or blue) in the center which is a neutron star.

3. XMM-Newton

XMM-Newton is a space telescope that is orbiting around Earth in an elliptical orbit of 48 hours.

Artistic Image of XMM-Newton - ESA - D. Ducros

It was launched on December 10, 1999.  

Later on February 9, 2000 European Space Agency (ESA) presented the first image taken by XMM and also announced its new name : XMM-Newton after the originator of the field of spectroscopy - Issac Newton. It's now called X-ray Multi-Mirror mission. One of its goals was to identify black hole candidates. 

Some of its major instruments are-

1. European Photon Imaging Cameras (EPIC) : It has two MOS-CCD cameras of total resolution 2.5 MegaPixel to detect low energy X-rays and a single pn-CCD camera to detect high energy X-rays.

2. Reflection Grating Spectrometers (RGS)

3. Optical Monitor 

XMM-Newton and NASA's NuSTAR measured the spin rate of a Supermassive Black Hole for the first time which is at the center of galaxy NGC 1365.

Last year in December the mission was extended for two years and is expected to operate till the end of 2020.