First Results from the Fermi Large Area Telescope
What's Hot in Physics, July/August 2010
By Dr. Simon Mitton
There’s only one newcomer to the physics Top Ten in this period, and it joins at #10 on the grid. The paper tells us what the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is seeing, and it is highly cited because this is the first new look at the gamma-ray sky in more than a decade.
Gamma-rays are only produced by extremely energetic objects, hence the appeal of a new telescope to spy on the most explosive events in the universe. The Fermi spacecraft, launched into a near-earth orbit on June 11, 2008, stalks the cosmic zoo in search of pulsars, interacting binary stars, supernova remnants, gamma-ray bursts, and active galactic nuclei. Paper #10 lists 205 gamma-ray sources detected in the first three months of observations at energies above 100 MeV.
This paper is a good example of how instrument development remains a strong driver of astronomical discovery. The LAT has a collecting area of 8,000 cm2, which is 6 times greater than its predecessor EGRET (operational until 2000); it is more sensitive, and it also has a larger field of view, which reduces to three hours the time required to make a sky survey.
The Fermi LAT international collaboration involves about 400 scientists in 90 institutions spread across 12 countries. The collaborators have made a policy decision that all papers list the authors strictly alphabetically, which has the interesting consequence that the reference list of #10 has 17 citations that begin: "Abdo, A.A., et al., 2009 …" For #10 the four corresponding authors are David J. Thompson (NASA GSFC, Greenbelt, MD), Jean Ballet and Isabelle Grenier (both of CEA/Saclay, Gif-sur-Yvette, France) and Seth Digel (Stanford University).
Cutaway of the LAT
instrument showing an inside view of one of the towers as an incoming
gamma ray interacts producing an electron-positron pair. Credit: LAT
Collaboration.
From NASA'S Goddard Space Flight Center,
Fermi Gamma-ray Space Telescope site.
Another remarkable feature of the collaboration is that all data are public, available almost in real time at the NASA Goddard Spaceflight Center. This crowd-sourcing approach enables astronomers conducting observations at lower energies to see if their target objects are emitting gamma rays.
So what’s on the menu in #10? It’s actually a taster menu, and the authors give a warning that these are quick-look data on the brightest sources for which detection is secure, so it is not possible to draw firm conclusions about the gamma-ray sky. Users are cautioned to refrain from generalizing, because the first definitive catalog will have many more sources. The first catalog was released in June 2010, and it contains 1,451 sources (A.A. Abdo, et al., Astrophys. J. Suppl. Ser., 188[2]: 405-36, 2010).
For each source the list has a tabulation of position, flux, variability, class, and identification or association. The classification includes 30 firm identifications with pulsars, and one match with a high-mass X-ray binary star. Active galactic nuclei (AGN) have long been recognized as a well-defined class of gamma-ray sources, and there are 121 in the list, two associated with radio galaxies, and the rest classified as blazars. The latter are giant elliptical galaxies powered by central supermassive black holes. They are among the most violent phenomena in the universe. They are of great significance to our understanding of the history of the universe and the evolution of its galaxies. In the list, about one-third of the objects are in our Galaxy, and the remainder are remote extragalactic objects.
Papers that have cited #10 are a foretaste of what we can expect in the projected 10 years of the Fermi mission. The first catalog of AGNs lists 671 sources, including 300 blazars and 296 radio quasars (A.A. Abdo, et al., Astrophys. J., 715[1]: 429-57, 2010). That’s a five-fold increase in the number of gamma-ray blazars, and it will pave the way to establishing a much better understanding of the blazar population. Fermi LAT has also stimulated investigations and papers on individual objects. For example, in September 2009 the LAT observed two exceptionally luminous outbursts of 3C 273, the first quasar identified, back in 1963.
It is also notable that Fermi LAT has dramatically increased the number of known gamma-ray pulsars. The fast survey rate of LAT, together with its ability to detect pulsation, has aided the discovery of 46 gamma-ray pulsars. These are young objects, and an estimate of their birthrate suggests a value of ~2 per century, about the same as the galactic supernova rate. Further Fermi studies should make a good contribution towards understanding pulsar demographics as well as their emission mechanisms.
Dr. Simon Mitton is a Fellow of St. Edmund’s College, University of Cambridge, U.K.
What's Hot in Physics | |||
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Rank | Paper |
Cites This Period Jan-Feb 10 |
Rank Last Period Nov-Dec 09 |
1 | E. Komatsu, et al., "Five-year Wilkinson Microwave Anisotropy Probe observations: Cosmological interpretation," Astrophys. J. Suppl. Ser., 180(2): 330-76, February 2009. [14 institutions worldwide] *406EI | 126 | 1 |
2 | J. Dunkley, et al., "Five-year Wilkinson Microwave Anisotropy Probe observations: Likelihoods and parameters from the WMAP data," Astrophys. J. Suppl. Ser., 180(2): 306-29, February 2009. [14 U.S. and Canadian institutions] *406EI | 45 | 2 |
3 | O. Adriani, et al., "An anomalous positron abundance in cosmic rays with energies 1.5-100 GeV," Nature, 458(7238): 607-9, 2 April 2009. [17 institutions worldwide] *427RK | 35 | 7 |
4 | S.H. Park, et al., "Bulk heterojunction solar cells with internal quantum efficiency approaching 100%," Nature Photonics, 3(5): 297-302, May 2009. [U. Calif., Santa Barbara; Gwangju Inst. Sci. & Tech., S. Korea; U. Laval, Quebec City, Canada] *447UY | 34 | 5 |
5 | O. Aharony, et al., "N = 6 superconformal Chern-Simons-matter theories, M2-branes and their gravity duals," J. High Energy Phys., 10: no. 091, October 2008. [Weizmann Inst., Rehovot, Israel; Inst. Adv. Study, Princeton, NJ; Technion, Haifa, Israel; Rutgers U., Piscataway, NJ] *370JT | 31 | † |
6 | K.I. Bolotin, et al., "Ultrahigh electron mobility in suspended graphene ," Solid State Comm., 146(9-10): 351-5, June 2008. [Columbia U., New York, NY; Natl. High Magnetic Field Lab, Tallahassee, FL; Bell Labs, Murray Hill, NJ] *312AM | 31 | † |
7 | K.N. Abazajian, et al., "The Seventh Data Release of the Sloan Digital Sky Survey," Astrophys. J. Suppl. Ser., 182(2): 543-58, June 2009. [110 institutions worldwide] *448UE | 31 | † |
8 | X.H. Chen, et al., "Superconductivity at 43K in SmFeAsO1-xFx ," Nature, 453(7196): 761-2, 5 June 2008. [U. Sci. & Tech., Hefei, China] *308UK | 28 | 4 |
9 | M. Kowalski, et al., "Improved cosmological constraints from new, old, and combined supernova data sets," Astrophys. J., 686(2): 749-78, 20 October 2008. [41 institutions worldwide] *364YB | 27 | 6 |
10 | A.A. Abdo, et al., "Fermi/Large Area Telescope bright gamma-ray source list," Astrophys. J. Suppl. Ser., 183(1): 46-66, July 2009. [54 institutions worldwide] *466IY | 24 | † |
SOURCE: Thomson Reuters Hot Papers Database. Read the Legend. |
KEYWORDS: LARGE AREA TELESCOPE, FERMI GAMMA-RAY SPACE TELESCOPE, BLAZARS, GAMMA-RAYS, PULSARS, JEAN BALLET, DAVID J. THOMPSON, ISABELLE GRENIER, SETH DIGEL.
Citing URL: http://sciencewatch.com/ana/hot/phy/10julaug-phy/