Download or read book Fermi LAT Discovery of Gamma Ray Emission From the Flat Spectrum Radio Quasar PKS 1454 354 written by and published by . This book was released on 2009 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gamma Ray Flaring Activity from the Gravitationally Lensed Blazar PKS 1830 211 Observed by Fermi LAT written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope routinely detects the MeV-peaked flat-spectrum radio quasar PKS 1830-211 (z = 2.507). Its apparent isotropic [gamma]-ray luminosity (E> 100 MeV), averaged over ~3 years of observations and peaking on 2010 October 14/15 at 2.9 × 10(50) erg s( - )(1), makes it among the brightest high-redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time-delayed variability to follow about 25 days after a primary flare, with flux about a factor of 1.5 less. Two large [gamma]-ray flares of PKS 1830-211 have been detected by the LAT in the considered period, and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the [gamma]-ray flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum with no significant correlation of X-ray flux with the [gamma]-ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and [gamma]-ray flux ratios are discussed. Microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy-dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results.

Download or read book Fermi LAT Discovery of Gamma Ray Emission From a Relativistic Jet in the Narrow Line Quasar PMN J0948 0022 written by and published by . This book was released on 2011 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fermi LAT Discovery of GeV Gamma ray Emission from the Vicinity of SNR W44 written by and published by . This book was released on 2013 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fermi LAT Discovery of Extended Gamma Ray Emission in the Direction of Supernova Remnant W51C written by and published by . This book was released on 2012 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: The discovery of bright gamma-ray emission coincident with supernova remnant (SNR) W51C is reported using the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. W51C is a middle-aged remnant (≈104 yr) with intense radio synchrotron emission in its shell and known to be interacting with a molecular cloud. The gamma-ray emission is spatially extended, broadly consistent with the radio and X-ray extent of SNR W51C. The energy spectrum in the 0.2-50 GeV band exhibits steepening toward high energies. The luminosity is greater than 1 x 1036 erg s−1 given the distance constraint of D> 5.5 kpc, which makes this object one of the most luminous gamma-ray sources in our Galaxy. The observed gamma-rays can be explained reasonably by a combination of efficient acceleration of nuclear cosmic rays at supernova shocks and shock-cloud interactions. The decay of neutral p mesons produced in hadronic collisions provides a plausible explanation for the gamma-ray emission. The product of the average gas density and the total energy content of the accelerated protons amounts to {bar n}{sub H} W{sub p} ≃ 5 x 1051 (D/6 kpc)2 erg cm−3. Electron density constraints from the radio and X-ray bands render it difficult to explain the LAT signal as due to inverse Compton scattering. The Fermi LAT source coincident with SNR W51C sheds new light on the origin of Galactic cosmic rays.

Download or read book Fermi LAT Discovery of GeV Gamma ray Emission from the Young Supernova Remnant Cassiopeia A written by and published by . This book was released on 2011 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Localising the Gamma ray Emission in Flat Spectrum Radio Quasars and an Extragalactic Population Study for the Cherenkov Telescope Array written by Atreya Acharyya and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Radio Emission from Gamma ray Flare Sources Discovered by Fermi lat written by Pfesesani Victoria Van Zyl and published by . This book was released on 2016 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Luminosity Function of Fermi detected Flat Spectrum Radio Quasars written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Fermi has provided the largest sample of?-ray selected blazars to date. In this work we use a complete sample of FSRQs detected during the first year of operation to determine the luminosity function (LF) and its evolution with cosmic time. The number density of FSRQs grows dramatically up to redshift ≈0.5-2.0 and declines thereafter. The redshift of the peak in the density is luminosity dependent, with more luminous sources peaking at earlier times; thus the LF of?-ray FSRQs follows a luminosity-dependent density evolution similarly to that of radio-quiet AGN. Also using data from the Swift Burst Alert Telescope we derive the average spectral energy distribution of FSRQs in the 10 keV-100GeV band and show that there is no correlation of the peak?-ray luminosity with?-ray peak frequency. The coupling of the SED and LF allows us to predict that the contribution of FSRQs to the Fermi isotropic?-ray background is 9.3{sub -1.0}{sup +1.6}% (±3% systematic uncertainty) in the 0.1-100GeV band. Finally we determine the LF of unbeamed FSRQs, finding that FSRQs have an average Lorentz factor of? = 11.7{sub -2.2}{sup +3.3}, that most are seen within 5{sup o} of the jet axis, and that they represent only ≈0.1% of the parent population.

Download or read book Fermi Discovery of Gamma Ray Emission from NGC 1275 written by and published by . This book was released on 2009 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: We report the discovery of high-energy (E> 100 MeV)?-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?-ray source is only ≈3′ away from the NGC 1275 nucleus, well within the 95% LAT error circle of ≈5′. The spatial distribution of?-ray 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{sub?} = (2.10 ± 0.23) x 10−7 ph (>100 MeV) cm−2 s−1 and? = 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{sub {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.

Download or read book Early Fermi Gamma ray Space Telescope Observations of the Quasar 3C454 3 written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 (LAT), covering 2008 July 7-October 6, indicate strong, highly variable [gamma]-ray emission with an average flux of H"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 time scale of about three 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 VLBI observations of superluminal expansion ([delta] H"25). The observed [gamma]-ray spectrum is not consistent with a simple power-law, but instead steepens strongly above H"2 GeV, and is well described by a broken power-law with photon indices of H"2.3 and H"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 2GeV could be due to -ray absorption via photonphoton pair production on the soft X-ray photon field of the host AGN, but such an interpretation would require the dissipation region to be located very close (H" 100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source.

Download or read book Fermi LAT Study of Gamma Ray Emission in the Direction of Supernova Remnant W49B written by and published by . This book was released on 2013 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Multiwavelength and Polarimetric Analysis of the Flat Spectrum Radio Quasars 3C 273 and 3C 279 written by Sunil Anthony Fernandes and published by . This book was released on 2016 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents results of multiwavelength analyses of 3C 273 and 3C 279. The main goals were to identify the gamma-ray emission region and dominant high-energy emission processes. Our methodology consisted of analyzing light curves from radio to gamma-rays over 6 - 8 years and polarimetric, spectral and line emission behavior. In 3C 279, we found that the emission from millimeter to ultraviolet was simultaneous and therefore co-spatial. We identified two active states where different high-energy emission processes were dominant. We found multiwavelength flaring events consistent with component ejections and shocks. We proposed that the gamma-ray emission region changed over time based on observations of both simultaneous and delayed gamma-rays emission with respect to low-energy emission during different time-frames. In 3C 273, we identified a non-thermal flare related to a component ejection and a thermal flare related to accretion. From reverberation mapping we found that the broad line region dynamical behavior over time possibly affects the derived supermassive black hole mass. In both objects we found that the gamma-ray spectral index was variable, and a trend of harder spectral index with higher gamma-ray luminosity. From the identification of different dominant high-energy emission processes, we concluded that the dominant high-energy emission mechanism changes with time. Overall, we concluded that similar results from both objects points to behavior that is potentially common to flat spectrum radio quasars. Increasing the sample size of objects analyzed with similar methodologies will provide more results to confirm or refine our conclusions.

Download or read book Broad Line Radio Galaxies Observed with Fermi LAT written by and published by . This book was released on 2012 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: We report on a detailed investigation of the?-ray emission from 18 broad line radio galaxies (BLRGs) based on two years of Fermi Large Area Telescope (LAT) data. We confirm the previously reported detections of 3C 120 and 3C 111 in the GeV photon energy range; a detailed look at the temporal characteristics of the observed?-ray emission reveals in addition possible flux variability in both sources. No statistically significant?-ray detection of the other BLRGs was however found in the considered dataset. Though the sample size studied is small, what appears to differentiate 3C 111 and 3C 120 from the BLRGs not yet detected in?-rays is the particularly strong nuclear radio flux. This finding, together with the indications of the?-ray flux variability and a number of other arguments presented, indicate that the GeV emission of BLRGs is most likely dominated by the beamed radiation of relativistic jets observed at intermediate viewing angles. In this paper we also analyzed a comparison sample of high accretion-rate Seyfert 1 galaxies, which can be considered radio-quiet counterparts of BLRGs, and found none were detected in?-rays. A simple phenomenological hybrid model applied for the broad-band emission of the discussed radio-loud and radio-quiet type 1 active galaxies suggests that the relative contribution of the nuclear jets to the accreting matter is e"1% on average for BLRGs, while d"0.1% for Seyfert 1 galaxies.

Download or read book Fermi Large Area Telescope Measurements of the Diffuse Gamma Ray Emission at Intermediate Galactic Latitudes written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The diffuse galactic?-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess?-ray emission ≥1 GeV relative to diffuse galactic?-ray emission models consistent with directly measured CR spectra (the so-called 'EGRET GeV excess'). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse?-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10{sup o} ≤.

Download or read book Fermi LAT Observations of LS I 61 303 written by and published by . This book was released on 2012 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Letter presents the first results from the observations of LS I +61{sup o}303 using Large Area Telescope data from the Fermi Gamma-Ray Space Telescope between 2008 August and 2009 March. Our results indicate variability that is consistent with the binary period, with the emission being modulated at 26.6 ± 0.5 days. This constitutes the first detection of orbital periodicity in high-energy gamma rays (20 MeV-100 GeV, HE). The light curve is characterized by a broad peak after periastron, as well as a smaller peak just before apastron. The spectrum is best represented by a power law with an exponential cutoff, yielding an overall flux above 100 MeV of 0.82 ± 0.03(stat) ± 0.07(syst) 10−6 ph cm−2 s−1, with a cutoff at 6.3 ± 1.1(stat) ± 0.4(syst) GeV and photon index? = 2.21 ± 0.04(stat) ± 0.06(syst). There is no significant spectral change with orbital phase. The phase of maximum emission, close to periastron, hints at inverse Compton scattering as the main radiation mechanism. However, previous very high-energy gamma ray (>100 GeV, VHE) observations by MAGIC and VERITAS show peak emission close to apastron. This and the energy cutoff seen with Fermi suggest that the link between HE and VHE gamma rays is nontrivial.

Download or read book Fermi Gamma Ray Observatory Science Highlights for the First 8 Months written by Alexander Moiseev and published by BiblioGov. This book was released on 2013-07 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: This viewgraph presentation reviews the science highlights for the first 8 months of the Fermi Gamma-Ray Observatory. Results from pulsars, flaring AGN, gamma ray bursts, diffuse radiation, LMC and electron spectrum are also presented.