Search for gamma-ray emission from magnetars with the Fermi Large Area Telescope

We report on the search for 0.1-10 GeV emission from magnetars in 17 months of Fermi Large Area Telescope (LAT) observations. No significant evidence for gamma-ray emission from any of the currently-known magnetars is found. The most stringent upper limits to date on their persistent emission in the Fermi-LAT energy range are estimated between ~10^{-12}-10^{-10} erg/s/cm2, depending on the source. We also searched for gamma-ray pulsations and possible outbursts, also with no significant detection. The upper limits derived support the presence of a cut-off at an energy below a few MeV in the persistent emission of magnetars. They also show the likely need for a revision of current models of outer gap emission from strongly magnetized pulsars, which, in some realizations, predict detectable GeV emission from magnetars at flux levels exceeding the upper limits identified here using the Fermi-LAT observations.Comment: ApJ Letters in press; Corresponding authors: Caliandro G. A., Hadasch D., Rea N., Burnett

Detection of Gamma-Ray Emission from the Starburst Galaxies M82 and NGC 253 with the Large Area Telescope on Fermi

We report the detection of high-energy gamma-ray emission from two starburst galaxies using data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Steady point-like emission above 200 MeV has been detected at significance levels of 6.8 sigma and 4.8 sigma respectively, from sources positionally coincident with locations of the starburst galaxies M82 and NGC 253. The total fluxes of the sources are consistent with gamma-ray emission originating from the interaction of cosmic rays with local interstellar gas and radiation fields and constitute evidence for a link between massive star formation and gamma-ray emission in star-forming galaxies.Comment: Submitted to ApJ Letter

Fermi Gamma-ray Imaging of a Radio Galaxy

The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (>1/2) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton scattered relic radiation from the cosmic microwave background (CMB), with additional contribution at higher energies from the infrared-to-optical extragalactic background light (EBL). These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, and a promising method to probe the cosmic relic photon fields.Comment: 27 pages, includes Supplementary Online Material; corresponding authors: C.C. Cheung, Y. Fukazawa, J. Knodlseder, L. Stawar

Fermi Large Area Telescope observations of PSR J1836+5925

The discovery of the gamma-ray pulsar PSR J1836+5925, powering the formerly unidentified EGRET source 3EG J1835+5918, was one of the early accomplishments of the Fermi Large Area Telescope (LAT). Sitting 25 degrees off the Galactic plane, PSR J1836+5925 is a 173 ms pulsar with a characteristic age of 1.8 million years, a spindown luminosity of 1.1$\times10^{34}$ erg s$^{-1}$, and a large off-peak emission component, making it quite unusual among the known gamma-ray pulsar population. We present an analysis of one year of LAT data, including an updated timing solution, detailed spectral results and a long-term light curve showing no indication of variability. No evidence for a surrounding pulsar wind nebula is seen and the spectral characteristics of the off-peak emission indicate it is likely magnetospheric. Analysis of recent XMM observations of the X-ray counterpart yields a detailed characterization of its spectrum, which, like Geminga, is consistent with that of a neutron star showing evidence for both magnetospheric and thermal emission.Comment: Accepted to Astrophysical Journa

A change in the optical polarization associated with a gamma-ray flare in the blazar 3C 279

It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and gamma-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10^5 gravitational radii.Comment: Published in Nature issued on 18 February 2010. Corresponding authors: Masaaki Hayashida and Greg Madejsk

EFFECTS OF DIFFERENT BENDING PARAMETERS ON MOMENT VALUES IN BEECH WOOD

FARKLI BÜKME PARAMETRELERİNİN KAYIN ODUNUNUN MOMENT DEĞERLERİ ÜZERİNE ETKİLERİ Özet Bükme için uygun ağaç türü seçiminde bükülme özellikleri, malzemenin mevcudiyeti ve bükme sonrası ahşabın direnç özellikleri dikkate alınmaktadır Kayın ahşabı, farklı alanlarda düz yada bükülmüş olarak kullanılmaktadır. Bükülmüş halde değerlendirildiği önemli yerlerden birisi de mobilyadır. Masif halde bükme elemanlar farklı yüklemelerin etkisi altında kalmakta, mobilyanın mukavemeti büyük ölçüde bu yüklemelere karşı koyma derecesine bağlı bulunmaktadır. Bu çalışmada bükme yarıçapı (200 ve 300 mm), buhar basıncı (0,2 ve 1,3 atm) ile farklı set etme (kurutma odası ve yüksek frekans) parametrelerinin bükülmüş masif kayında diyagonal basma ve diyagonal eğme momentleri üzerine etkileri araştırılmıştır. Buhar basıncının ve set etme farklılığının etkisi sadece 200 mm bükme yarıçapına sahip örneklerde araştırılmıştır. Bükme yarıçapının etkisi ise hem yüksek frekans hem de sabit sıcaklıkta set edilmiş örneklerde incelenmiştir. İstatistik analizlerde F ve t testleri kullanılmıştır. Sonuç olarak diyagonal eğilme momenti üzerine tüm parametrelerin, diyagonal basma moment değerleri üzerine sadece kurutma odasında set edilmiş grupta bükme yarıçapının etkisinin % 5 güven düzeyinde istatistiki olarak anlamlı olduğu bulunmuştur. Anahtar Kelimeler: Kayın, Bükme, Diyagonal eğme, Diyagonal basma, Momen