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Ylinen, T.
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Publications (10 of 38) Show all publications
Abdo, A. A., Ackermann, M., Ajello, M., Asano, K., Atwood, W. B., Axelsson, M., . . . Ziegler, M. (2009). A limit on the variation of the speed of light arising from quantum gravity effects. Nature, 462(7271), 331-334
Open this publication in new window or tab >>A limit on the variation of the speed of light arising from quantum gravity effects
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2009 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 462, no 7271, p. 331-334Article in journal (Refereed) Published
Abstract [en]

A cornerstone of Einstein's special relativity is Lorentz invariance-the postulate that all observers measure exactly the same speed of light in vacuum, independent of photon-energy. While special relativity assumes that there is no fundamental length-scale associated with such invariance, there is a fundamental scale (the Planck scale, l(Planck) approximate to 1.62 x 10(-33) cm or E-Planck = M(Planck)c(2) approximate to 1.22 x 10(19) GeV), at which quantum effects are expected to strongly affect the nature of space-time. There is great interest in the (not yet validated) idea that Lorentz invariance might break near the Planck scale. A key test of such violation of Lorentz invariance is a possible variation of photon speed with energy(1-7). Even a tiny variation in photon speed, when accumulated over cosmological light-travel times, may be revealed by observing sharp features in gamma-ray burst (GRB) light-curves(2). Here we report the detection of emission up to similar to 31GeV from the distant and short GRB090510. We find no evidence for the violation of Lorentz invariance, and place a lower limit of 1.2E(Planck) on the scale of a linear energy dependence (or an inverse wavelength dependence), subject to reasonable assumptions about the emission (equivalently we have an upper limit of l(Planck)/1.2 on the length scale of the effect). Our results disfavour quantum-gravity theories(3,6,7) in which the quantum nature of space-time on a very small scale linearly alters the speed of light.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2808 (URN)10.1038/nature08574 (DOI)000271899300039 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2017-12-12Bibliographically approved
Abdo, A. A., Ackermann, M., Ajello, M., Atwood, W. B., Axelsson, M., Baldini, L., . . . Ziegler, M. (2009). A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope. Science, 325(5942), 848-852
Open this publication in new window or tab >>A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope
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2009 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 325, no 5942, p. 848-852Article in journal (Refereed) Published
Abstract [en]

Pulsars are born with subsecond spin periods and slow by electromagnetic braking for several tens of millions of years, when detectable radiation ceases. A second life can occur for neutron stars in binary systems. They can acquire mass and angular momentum from their companions, to be spun up to millisecond periods and begin radiating again. We searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars (MSPs) outside of globular clusters, using rotation parameters from radio telescopes. Strong gamma-ray pulsations were detected for eight MSPs. The gamma-ray pulse profiles and spectral properties resemble those of young gamma-ray pulsars. The basic emission mechanism seems to be the same for MSPs and young pulsars, with the emission originating in regions far from the neutron star surface.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2811 (URN)10.1126/science.1176113 (DOI)000269242400039 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2017-12-12Bibliographically approved
Abdo, A. A., Ackermann, M., Ajello, M., Atwood, W. B., Axelsson, M., Baldini, L., . . . Ziegler, M. (2009). BRIGHT ACTIVE GALACTIC NUCLEI SOURCE LIST FROM THE FIRST THREE MONTHS OF THE FERMI LARGE AREA TELESCOPE ALL-SKY SURVEY. Astrophysical Journal, 700(1), 597-622
Open this publication in new window or tab >>BRIGHT ACTIVE GALACTIC NUCLEI SOURCE LIST FROM THE FIRST THREE MONTHS OF THE FERMI LARGE AREA TELESCOPE ALL-SKY SURVEY
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2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 700, no 1, p. 597-622Article in journal (Refereed) Published
Abstract [en]

The first three months of sky-survey operation with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope reveal 132 bright sources at |b| > 10 degrees with test statistic greater than 100 ( corresponding to about 10 sigma). Two methods, based on the CGRaBS, CRATES, and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known active galactic nuclei (AGNs). This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely, Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 4 blazars with unknown classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs (HBLs), sources which were previously difficult to detect in the GeV range. Another 10 lower-confidence associations are found. Only 33 of the sources, plus two at |b| < 10 degrees, were previously detected with Energetic Gamma-Ray Experiment Telescope( EGRET), probably due to variability. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. No significant correlation between radio and peak gamma-ray fluxes is observed. Blazar log N-log S distributions and luminosity functions are constructed to investigate the evolution of the different blazar classes, with positive evolution indicated for FSRQs but none for BL Lacs. The contribution of LAT blazars to the total extragalactic gamma-ray intensity is estimated.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2821 (URN)10.1088/0004-637X/700/1/597 (DOI)000267768900049 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2017-12-12Bibliographically approved
Abdo, A. A., Ackermann, M., Ajello, M., Anderson, B., Atwood, W. B., Axelsson, M., . . . Ziegler, M. (2009). Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT. Science, 325(5942), 840-844
Open this publication in new window or tab >>Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT
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2009 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 325, no 5942, p. 840-844Article in journal (Refereed) Published
Abstract [en]

Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2806 (URN)10.1126/science.1175558 (DOI)000269242400037 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2017-12-12Bibliographically approved
Abdo, A. A., Ackermann, M., Ajello, M., Atwood, W. B., Axelsson, M., Baldini, L., . . . Ziegler, M. (2009). Detection of High-Energy Gamma-Ray Emission from the Globular Cluster 47 Tucanae with Fermi. Science, 325(5942), 845-848
Open this publication in new window or tab >>Detection of High-Energy Gamma-Ray Emission from the Globular Cluster 47 Tucanae with Fermi
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2009 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 325, no 5942, p. 845-848Article in journal (Refereed) Published
Abstract [en]

We report the detection of gamma-ray emissions above 200 megaelectron volts at a significance level of 17 sigma from the globular cluster 47 Tucanae, using data obtained with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. Globular clusters are expected to emit gamma rays because of the large populations of millisecond pulsars that they contain. The spectral shape of 47 Tucanae is consistent with gamma-ray emission from a population of millisecond pulsars. The observed gamma-ray luminosity implies an upper limit of 60 millisecond pulsars present in 47 Tucanae.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2819 (URN)10.1126/science.1177023 (DOI)000269242400038 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2017-12-12Bibliographically approved
Abdo, A. A., Ackermann, M., Ajello, M., Atwood, W. B., Axelsson, M., Baldini, L., . . . Ziegler, M. (2009). DISCOVERY OF PULSATIONS FROM THE PULSAR J0205+6449 IN SNR 3C 58 WITH THE FERMI GAMMA-RAY SPACE TELESCOPE. Astrophysical Journal Letters, 699(2), L102-L107
Open this publication in new window or tab >>DISCOVERY OF PULSATIONS FROM THE PULSAR J0205+6449 IN SNR 3C 58 WITH THE FERMI GAMMA-RAY SPACE TELESCOPE
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2009 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, Vol. 699, no 2, p. L102-L107Article in journal (Refereed) Published
Abstract [en]

We report the discovery of gamma-ray pulsations (>= 0.1 GeV) from the young radio and X-ray pulsar PSR J0205 + 6449 located in the Galactic supernova remnant 3C 58. Data in the gamma-ray band were acquired by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope (formerly GLAST), while the radio rotational ephemeris used to fold gamma-rays was obtained using both the Green Bank Telescope and the Lovell telescope at Jodrell Bank. The light curve consists of two peaks separated by 0.49 +/- 0.01 +/- 0.01 cycles which are aligned with the X-ray peaks. The first gamma-ray peak trails the radio pulse by 0.08 +/- 0.01 +/- 0.01, while its amplitude decreases with increasing energy as for the other gamma-ray pulsars. Spectral analysis of the pulsed gamma-ray emission suggests a simple power law of index -2.1 +/- 0.1 +/- 0.2 with an exponential cutoff at 3.0(-0.7)(+1.1) +/- 0.4 GeV. The first uncertainty is statistical and the second is systematic. The integral gamma-ray photon flux above 0.1 GeV is (13.7 +/- 1.4 +/- 3.0) x 10(-8) cm(-2) s(-1), which implies for a distance of 3.2 kpc and assuming a broad fan-like beam a luminosity of 8.3 x 10(34) erg s(-1) and an efficiency eta of 0.3%. Finally, we report a 95% upper limit on the flux of 1.7 x 10(-8) cm(-2) s(-1) for off-pulse emission from the object.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2817 (URN)10.1088/0004-637X/699/2/L102 (DOI)000267372800011 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2013-07-18Bibliographically approved
Abdo, A. A., Ackermann, M., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., . . . Weltevrede, P. (2009). DISCOVERY OF PULSED gamma-RAYS FROM THE YOUNG RADIO PULSAR PSR J1028-5819 WITH THE FERMI LARGE AREA TELESCOPE. Astrophysical Journal Letters, 695(1), L72-L77
Open this publication in new window or tab >>DISCOVERY OF PULSED gamma-RAYS FROM THE YOUNG RADIO PULSAR PSR J1028-5819 WITH THE FERMI LARGE AREA TELESCOPE
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2009 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, Vol. 695, no 1, p. L72-L77Article in journal (Refereed) Published
Abstract [en]

Radio pulsar PSR J1028-5819 was recently discovered in a high-frequency search (at 3.1 GHz) in the error circle of the Energetic Gamma-Ray Experiment Telescope (EGRET) source 3EG J1027-5817. The spin-down power of this young pulsar is great enough to make it very likely the counterpart for the EGRET source. We report here the discovery of gamma-ray pulsations from PSR J1028-5819 in early observations by the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope. The gamma-ray light curve shows two sharp peaks having phase separation of 0.460 +/- 0.004, trailing the very narrow radio pulse by 0.200 +/- 0.003 in phase, very similar to that of other known gamma-ray pulsars. The measured gamma-ray flux gives an efficiency for the pulsar of similar to 10-20% (for outer magnetosphere beam models). No evidence of a surrounding pulsar wind nebula is seen in the current Fermi data but limits on associated emission are weak because the source lies in a crowded region with high background emission. However, the improved angular resolution afforded by the LAT enables the disentanglement of the previous COS-B and EGRET source detections into at least two distinct sources, one of which is now identified as PSR J1028-5819.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2835 (URN)10.1088/0004-637X/695/1/L72 (DOI)000264539700016 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2013-07-18Bibliographically approved
Abdo, A. A., Ackermann, M., Ajello, M., Atwood, W. B., Axelsson, M., Baldini, L., . . . Ziegler, M. (2009). EARLY FERMI GAMMA-RAY SPACE TELESCOPE OBSERVATIONS OF THE QUASAR 3C 454.3. Astrophysical Journal, 699(1), 817-823
Open this publication in new window or tab >>EARLY FERMI GAMMA-RAY SPACE TELESCOPE OBSERVATIONS OF THE QUASAR 3C 454.3
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2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, no 1, p. 817-823Article in journal (Refereed) Published
Abstract [en]

This is the first report of Fermi Gamma-Ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope, covering 2008 July 7-October 6, indicate strong, highly variable.-ray emission with an average flux of similar to 3 x 10 (6) photons cm(-2) s(-1), for energies > 100 MeV. The gamma-ray flux is variable, with strong, distinct, symmetrically shaped flares for which the flux increases by a factor of several on a timescale of about 3 days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair production implies relativistic beaming with Doppler factor delta > 8, consistent with the values inferred from Very Long Baseline Interferometry observations of superluminal expansion (delta similar to 25). The observed gamma-ray spectrum is not consistent with a simple power law, but instead steepens strongly above similar to 2 GeV, and is well described by a broken power law with photon indices of similar to 2.3 and similar to 3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high-luminosity blazar above 100 MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2 GeV could be due to gamma-ray absorption via photon-photon pair production on the soft X-ray photon field of the host active galactic nucleus, but such an interpretation would require the dissipation region to be located very close (less than or similar to 100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2815 (URN)10.1088/0004-637X/699/1/817 (DOI)000267056300061 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2017-12-12Bibliographically approved
Abdo, A. A., Ackermann, M., Ajello, M., Asano, K., Baldini, L., Ballet, J., . . . Pushkarev, A. B. (2009). FERMI DISCOVERY OF GAMMA-RAY EMISSION FROM NGC 1275. Astrophysical Journal, 699(1), 31-39
Open this publication in new window or tab >>FERMI DISCOVERY OF GAMMA-RAY EMISSION FROM NGC 1275
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2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, no 1, p. 31-39Article in journal (Refereed) Published
Abstract [en]

We report the discovery of high-energy (E > 100 MeV) gamma-ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made with the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope. The positional center of the gamma-ray source is only approximate to 3' away from the NGC 1275 nucleus, well within the 95% LAT error circle of approximate to 5'. The spatial distribution of gamma-ay photons is consistent with a point source. The average flux and power-law photon index measured with the LAT from 2008 August 4 to 2008 December 5 are F-gamma = (2.10 +/- 0.23) x 10(-7) ph (>100 MeV) cm(-2) s(-1) and Gamma = 2.17 +/- 0.05, respectively. The measurements are statistically consistent with constant flux during the four-month LAT observing period. Previous EGRET observations gave an upper limit of F-gamma < 3.72 x 10(-8) ph (>100 MeV) cm(-2) s(-1) to the gamma-ray flux from NGC 1275. This indicates that the source is variable on timescales of years to decades, and therefore restricts the fraction of emission that can be produced in extended regions of the galaxy cluster. Contemporaneous and historical radio observations are also reported. The broadband spectrum of NGC 1275 is modeled with a simple one-zone synchrotron/synchrotron self-Compton model and a model with a decelerating jet flow.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2809 (URN)10.1088/0004-637X/699/1/31 (DOI)000267056300004 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2017-12-12Bibliographically approved
Abdo, A. A., Ackermann, M., Ajello, M., Atwood, W. B., Axelsson, M., Baldini, L., . . . Ziegler, M. (2009). FERMI LARGE AREA TELESCOPE DETECTION OF PULSED gamma-RAYS FROM THE VELA-LIKE PULSARS PSR J1048-5832 AND PSR J2229+6114. Astrophysical Journal, 706(2), 1331-1340
Open this publication in new window or tab >>FERMI LARGE AREA TELESCOPE DETECTION OF PULSED gamma-RAYS FROM THE VELA-LIKE PULSARS PSR J1048-5832 AND PSR J2229+6114
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2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 706, no 2, p. 1331-1340Article in journal (Refereed) Published
Abstract [en]

We report the detection of gamma-ray pulsations (>= 0.1GeV) from PSR J2229+ 6114 and PSR J1048-5832, the latter having been detected as a low-significance pulsar by EGRET. Data in the gamma-ray band were acquired by the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope, while the radio rotational ephemerides used to fold the gamma-ray light curves were obtained using the Green Bank Telescope, the Lovell telescope at Jodrell Bank, and the Parkes Telescope. The two young radio pulsars, located within the error circles of the previously unidentified EGRET sources 3EG J1048-5840 and 3EG J2227+6122, present spin-down characteristics similar to the Vela pulsar. PSR J1048-5832 shows two sharp peaks at phases 0.15 +/- 0.01 and 0.57 +/- 0.01 relative to the radio pulse confirming the EGRET light curve, while PSR J2229+ 6114 presents a very broad peak at phase 0.49 +/- 0.01. The gamma-ray spectra above 0.1 GeV of both pulsars are fit with power laws having exponential cutoffs near 3 GeV, leading to integral photon fluxes of (2.19 +/- 0.22 +/- 0.32) x 10(-7) cm(-2) s(-1) for PSR J1048-5832 and (3.77 +/- 0.22 +/- 0.44) x 10(-7) cm(-2) s(-1) for PSR J2229+6114. The first uncertainty is statistical and the second is systematic. PSR J1048-5832 is one of the two LAT sources whichwere entangled together as 3EG J1048-5840. These detections add to the growing number of young gamma-ray pulsars that make up the dominant population of GeV gamma-ray sources in the Galactic plane.

National Category
Physical Sciences
Research subject
Natural Science, Physics
Identifiers
urn:nbn:se:hik:diva-2812 (URN)10.1088/0004-637X/706/2/1331 (DOI)000271872900032 ()
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2017-12-12Bibliographically approved
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