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Fermi

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Fermi and solar eclipses

 Posted on Jan 03, 2011 10:46:08 PM | Julie McEnery  0 Comments | Permalink |

A solar eclipse occurs when the moon comes between the Sun and the Earth and thus casts a shadow on Earth. The shadow can be quite large - as you can see from the excellent image in the January 2, APOD. There will be a partial solar eclipse tomorrow (January 4). Fermi orbits the Earth every 96 minutes: for two of those orbits tomorrow Fermi will pass through the shadow of the eclipse. This won't cause any problems - each orbit, we pass through the nighttime and thus dark side of the Earth. Passing through the eclipse means that we will spend a little more time recharging the spacecrafts battery from the solar panels than we would ordinarily need. The Fermi flight operations team closely monitors the performance of the observatory,  they need to know if we will pass through an eclipse so that we won't interpret the change in battery charging performance as a potential problem on the spacecraft. It's neat to think that a observatory designed to detect gamma-rays from the Universe can notice more classical local phenomena on Earth.

Fermi's Spectacular Second Year

 Posted on Jun 11, 2010 11:25:39 PM | Elizabeth Hays  0 Comments | Permalink |

Happy Launch Anniversary to Fermi!! Only two short years ago we watched Fermi take a perfect ride into orbit. It turns out that the only thing better than Fermi's fantastic first year is its spectacular second year. The data from both instruments are now being analyzed by scientists around the world. The Large Area Telescope team released a first catalog, which was based on 11 months of observations and contains 1451 gamma-ray sources (this is 5x larger than previous catalogs at similar energies).  One of the great things about Fermi is that even though we have been observing for almost 2 years that is not the end of the story. The gamma-ray sky changes every day. Because Fermi sees so much much of the sky for so much of the time, we not only see things we expect to be interesting, but also get to watch the unscripted reality show that is the gamma-ray universe. Here are some of the highlights from the past year.

• the active galaxy 3C 454.3 briefly became the brightest persistent object ever seen in the gamma-ray sky in December -- link
• the microquasar Cygnus X-3 (a compact object and massive star binary system) flared and was definitively detected in gamma rays for the first time -- link
• the gamma-ray bursts burst (and gave us some insight into properties of space-time) -- link

As Fermi continues to watch the sky, we will continue to catch gamma-rays sources doing amazing things. It has been a wonderful two years, and I am looking forward to the next one.

Fermi in Cambodia

 Posted on Apr 13, 2010 12:36:59 PM | Julie McEnery 5 Comments | Permalink |

      Last March, I spent an afternoon talking about Fermi to the children at Aziza's place in Phnom Penh, Cambodia.  Aziza's place is a home and learning center for impoverished children. I was in Cambodia to visit my sister. She lived in an apartment next door to Aziza's place and and had come to know the people at Aziza's place. She suggested that I might like to visit and talk with the children about Astronomy, NASA and Fermi. It was a remarkable experience. The children had several astronomy lessons and activities in anticipation of my visit and were extremely enthusiastic and friendly. The discussion started with Fermi and astronomy and rapidly expanded to include rockets, spaceflight and the nature of the moon.

Our first Target of Opportunity observation

 Posted on Apr 05, 2010 05:44:54 PM | Julie McEnery 1 Comments | Permalink |

Today has been an exciting day. This morning we noticed that one of the many active galaxies in the Fermi sky had become extremely bright in gamma-rays. We decided to interrupt our usual mode of continuously scanning the entire sky, and instead repointed the spacecraft to stare right at this galaxy for the next few days. This will allow us to track very carefully how it behaves during these bright outbursts. This is the first time that we have ever chosen to repoint the spacecraft to look at an interesting flaring object. We call these kinds of unplanned observations "Targets of Opportunity". This object, known as 3C 454.3, has been exciting to watch throughout the mission. Shortly after launch in 2008, when we first turned on the telescope, we noticed an unexpected bright object in the newly observed gamma-ray sky. This bright source was the topic of our very first Fermi scientific communication - an "Astronomers Telegram" to communicate to other astronomers that this was an object to watch. It then dimmed somewhat and behaved more quietly for the next year. In December 2009 it flared up again, becoming the brightest persistent source ever seen in high energy gamma-rays (gamma-ray bursts are momentarily brighter, but they are over in a few minutes). We think that 3C 454.3 may now be getting as bright as it was in December 2009, or even brighter! The location of this flaring active galaxy is very fortunate. It is about 38 deg away from a star known as V407 Cyg. Last month, we discovered a bright gamma-ray flare from the direction of this star while it was undergoing a huge optical outburst. Seeing gamma-rays from this kind of stellar outburst was unexpected - this is the kind of surprise that we love to find. We have been monitoring the star very closely with Fermi and many other telescopes to try to figure out what is going on (this could be the topic of a whole blog entry all by itself).  While 38 degrees seems like a big distance (it is around 80 times larger than the size of the moon), the Large Area Telescope on Fermi sees a huge fraction of the sky at once. We can easily point at V407 Cyg and 3C 454.3 at the same time. I can't wait to see what we find from these observations!

A Milestone!

 Posted on Feb 25, 2010 03:44:37 PM | Julie McEnery  0 Comments | Permalink |

More than 100 billion events have been detected by the Large Area Telescope on Fermi after 616 days in orbit. That is a lot of events. What is an event? The Large Area Telescope detects gamma-rays, one at a time, at a rate of a few per second. We measure where each one comes from and use this information to build up a deeper and deeper picture of the gamma-ray sky.  However for each gamma-ray,  we detect over one thousand cosmic-rays - charged particles moving at close to the speed of light. We call each cosmic-ray or gamma-ray detected by the LAT an event. We don't send the data from all events down to the ground. We are primarily interested in the gamma-rays so we run software onboard the Large Area Telescope to identify and delete events that are clearly cosmic-rays. This reduces the rate of events from 4000 per second to around 400 per second. This allows us to make better use of the precious data transfer connection between the observatory and the ground. Once we get the data down to the ground, we use a large computer farm (>1000 machines) to process the data carefully and pick out the real gamma rays, which arrive a few per second. Lots and lots of gamma rays! Compared with previous gamma-ray telescopes the LAT detects gamma-rays at a far greater rate. The plot shows the number of gamma-rays detected by four previous gamma-ray telescopes over their operating lifetime compared to the number of gamma-rays detected by LAT in a single year. There are so many gamma-rays detected by LAT that you can barely see that any are detected by the previous missions (OSO-3, SAS-2, COS-B and EGRET). The enhanced ability of LAT to detect gamma-rays so efficiently is one of the reasons that Fermi is such a ground-breaking mission.

A full year of sky survey observations!

 Posted on Aug 04, 2009 04:40:59 PM | Julie McEnery 12 Comments | Permalink |

One year ago today, Fermi started sky survey observations after completing observatory and instrument commissioning ahead of schedule.

What a year! 

The previous entry described our first light results. Since then, we have discovered new populations of pulsars in  our Galaxy. We have observed a extraordinary gamma-ray burst, which was the most powerful explosion in the Universe ever seen. We have explored the properties of the diffuse gamma-ray radiation, which permeates the Milky Way. We see the the Sun, the Moon and the Earth shining in high energy gamma-rays. Our continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts powered by supermassive black holes at the center of distant galaxies.

Comings and goings...

We were sad to see Steve Ritz leave NASA in July. As project scientist he has overseen the development of all aspects of the GLAST/Fermi mission from before launch and guided the transition into the smoothly operating mission that we have now. I am daunted to be filling such big shoes. Happily, Liz Hays has has joined Dave Thompson, and Neil Gehrels as Fermi Deputy project scientists so we remain at full strength. We are looking forward to continuing this blog to share mission highlights, science results and interesting operations tidbits.

GLAST First Light and a New Name!

 Posted on Aug 27, 2008 10:31:49 AM | Steve Ritz  0 Comments | Permalink |

First Light!

We had our first-light press teleconference this afternoon.  You can find the information and the slides here.  The gorgeous full-sky image, based only on about 95 hours of the first engineering data is shown below, and here is a link to higher-resolution versions (with annotation and without annotation).   Because we look in all directions, it's a bit challenging to map all those directions onto a flat screen or piece of paper.  The image you see is an unrolling and flattening of the whole sky.  If you prefer to see the whole "globe", there is a movie here.  That bright band is our own milkyway galaxy glowing brightly in gamma rays.  The brightly flaring object billions of light years away, 3C454.3, mentioned in the previous post, is the bright source in the lower left side of the image. This is what we saw just opening our eyes and taking a first glimpse of the universe with this wonderful new facility, and it is comparable with the image that took years to make with the previous instrument, EGRET, on the Compton Gamma-ray Observatory.  Here is one way to think about this: the advent of air travel enabled the crossing of a continent in just a few hours, instead of many months by wagon, and that fundamentally changed our culture.  By analogy, I hope you can get a sense of what this new facility means to us! It took many people from around the world working together to produce this image.  I will include remarks from some of them in future posts, along with more perspectives about what the images mean to us and what we are learning.

A new name: the Fermi Gamma-ray Space Telescope

The teleconference concluded with an announcement of the new name for the observatory, dedicated to Enrico Fermi.  Quoting from the teleconference site:
Biography of Enrico Fermi

Enrico Fermi (1901-1954) was an Italian physicist who immigrated to the United States. He was the first to suggest a viable mechanism for astrophysical particle acceleration. This work is the foundation for our understanding of many types of sources to be studied by NASA’s Fermi Gamma-ray Space Telescope, formerly known as GLAST.

Fermi is most noted for his work on the development of the first nuclear reactor and for his major contributions to the development of quantum theory, nuclear and particle physics, and statistical mechanics. He was awarded the Nobel Prize in Physics in 1938 for his work on induced radioactivity and is today regarded as one of the top scientists of the 20th century.

In addition to his direct connection to the science, Fermi holds special significance to the U.S. Department of Energy, the Italian Space Agency, and the Italian Particle Physics Agency. We also have a spiffy new logo: The "f" is an abstraction of a black hole system with an accretion disk (swirling matter falling into the black hole) and emerging jets of very high-energy particles, which emit gamma rays.  This is one of the key topics for us to study with the new data.