Nano-satellite MeV telescope is becoming attractive nowadays. The dominant interaction mechanism of the electromagnetic spectrum around 1MeV is Compton scattering. However, the gamma-rays generated ...by primary particles hitting the atmosphere and the pair production events are the two significant background events when the satellite is operating in Low Earth Orbit. In this paper, we applied Machine Learning models to identify and reject the two troublesome background event types. Ensemble technique and imbalance solution are explored in order to obtain a better performance. Experiments demonstrated that the proposed methods can discriminate the pair events with a high accuracy, and the satellite’s sensitivity has also been improved dramatically.
Fermi LAT Flare Advocate Activity Ciprini, Stefano; Gasparrini, Dario; Bastieri, Denis
Proceedings of the International Astronomical Union,
09/2011, Letnik:
7, Številka:
S285
Journal Article
Recenzirano
Odprti dostop
The Fermi Flare Advocate (also known as Gamma-ray Sky Watcher, FA-GSW) service provides a daily quick-look analysis and review of the high-energy gamma-ray sky seen by the Fermi Gamma-ray Space ...Telescope. The duty offers alerts for potentially new gamma-ray sources, interesting transients and flares. A weekly digest containing the highlights about the GeV gamma-ray sky is published in the web-based Fermi Sky Blog. During the first 3 years of all-sky survey, more than 150 Astronomical Telegrams, several alerts to the TeV Cherenkov telescopes, and targets of opportunity to Swift and other observatories, were realized. That increased the rate of simultaneous multi-frequency observing campaigns and the level of international cooperation. Many gamma-ray flares from blazars (such as extraordinary outbursts of 3C 454.3, intense flares of PKS 1510-089, 4C 21.35, PKS 1830-211, AO 0235+164, PKS 1502+106, 3C 279, 3C 273, PKS 1622-253), short/long flux duty cycles, unidentified transients near the Galactic plane (like J0910-5041, J0109+6134, the Galactic center region), flares associated with Galactic sources (like the Crab nebula, the nova V407 Cyg, the microquasar Cyg X-3), emission of the quiet and active sun, were observed by Fermi and communicated by FA-GSWs.
We report the discovery of {gamma}-ray pulsations ({ge}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{sub -0.7}{sup +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{sup -8} cm{sup -2} s{sup -1}, which implies for a distance of 3.2 kpc and assuming a broad fan-like beam a luminosity of 8.3 x 10{sup 34} erg s{sup -1} and an efficiency {eta} of 0.3%. Finally, we report a 95% upper limit on the flux of 1.7 x 10{sup -8} cm{sup -2} s{sup -1} for off-pulse emission from the object.
Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m{sup 2}sr at 300 GeV. Building on the gamma-ray ...analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply-falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E{sup -3.0} and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.
We report the detection of pulsed gamma-rays from the young, spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope ...(formerly GLAST). The light curve consists of two narrow peaks of similar amplitude separated by 0.468 {+-} 0.002 in phase. The first peak lags the maximum of the 2 GHz radio pulse by 0.162 {+-} 0.004 {+-} 0.01 in phase. The integral gamma-ray photon flux above 100 MeV is (56 {+-} 3 {+-} 11) x 10{sup -8} cm{sup -2} s{sup -1}. The photon spectrum is well-described by an exponentially cut-off power law of the form dF/dE = kE{sup -{Gamma}}e{sup (-E/E{sub c})} where the energy E is expressed in GeV. The photon index is {Gamma} = 1.5 {+-} 0.1 {+-} 0.1 and the exponential cut-off is E{sub c} = 2.4 {+-} 0.3 {+-} 0.5 GeV. The first uncertainty is statistical and the second is systematic. The integral photon flux of the bridge is approximately 10% of the pulsed emission, and the upper limit on off-pulse gamma-ray emission from a putative pulsar wind nebula is < 10% of the pulsed emission at the 95% confidence level. Radio polarization measurements yield a rotation measure of RM = 524 {+-} 4 rad m{sup -2} but a poorly constrained magnetic geometry. Re-analysis of Chandra data enhanced the significance of the weak X-ray pulsations, and the first peak is roughly phase-aligned with the first gamma-ray peak. We discuss the emission region and beaming geometry based on the shape and spectrum of the gamma-ray light curve combined with radio and X-ray measurements, and the implications for the pulsar distance. Gamma-ray emission from the polar cap region seems unlikely for this pulsar.
We report the discovery of gamma-ray pulsations from the nearby isolated millisecond pulsar PSR J0030+0451 with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). ...This discovery makes PSR J0030+0451 the second millisecond pulsar to be detected in gamma-rays after PSR J0218+4232, observed by the EGRET instrument on the Compton Gamma Ray Observatory. The spin-down power {dot E} = 3.5 x 10{sup 33} ergs s{sup -1} is an order of magnitude lower than the empirical lower bound of previously known gamma-ray pulsars. The emission profile is characterized by two narrow peaks, respectively 0.07 {+-} 0.01 and 0.08 {+-} 0.02 wide, separated by 0.44 {+-} 0.02 in phase. The first gamma-ray peak falls 0.15 {+-} 0.01 after the main radio peak. The pulse shape is similar to that of the 'normal' gamma-ray pulsars. An exponentially cut-off power-law fit of the emission spectrum leads to an integral photon flux above 100 MeV of (6.76 {+-} 1.05 {+-} 1.35) x 10{sup -8} cm{sup -2} s{sup -1} with cut-off energy (1.7 {+-} 0.4 {+-} 0.5) GeV. Based on its parallax distance of (300 {+-} 90) pc, we obtain a gamma-ray efficiency L{sub {gamma}}/{dot E} {approx_equal} 15% for the conversion of spin-down energy rate into gamma-ray radiation, assuming isotropic emission.
A two-component model of radio emission has been used to explain some radio
observational properties of Active Galactic Nuclei (AGNs) and, in particular,
of blazars. In this work, we extend the ...two-component idea to the $\gamma$-ray
emission and assume that the total $\gamma$-ray output of blazars consists of
relativistically beamed and unbeamed components. The basic idea leverages the
correlation between the radio core-dominance parameter and the $\gamma$-ray
beaming factor. To do so, we evaluate this correlation for a large sample of
584 blazars taken from the fourth source catalog of the Fermi Large Area
Telescope (Fermi-LAT) and correlated their $\gamma$-ray core-dominance
parameters with radio core-dominance parameters. The $\gamma$-ray beaming
factor is then used to estimate the beamed and unbeamed components. Our
analysis confirms that the $\gamma$-ray emission in blazars is mainly from the
beamed component.
Blazars are a subclass of active galactic nuclei (AGNs) with extreme
observation properties, which is caused by the beaming effect, expressed by a
Doppler factor, in a relativistic jet. Doppler ...factor is an important parameter
in the blazars paradigm to indicate all of the observation properties, and many
methods were proposed to estimate its value. In this paper, we present a method
following Mattox et al. to calculate the lower limit on gamma-ray Doppler
factor for 809 selected Fermi/LAT-detected gamma-ray blazars by adopting the
available gamma-ray and X-ray data. Our sample included 342 flat-spectrum radio
quasars (FSRQs) and 467 BL Lac objects (BL Lacs), out of which 507 sources are
compiled with available radio core-dominance parameter (R) from our previous
study. Our calculation shows that the average values of the lower limit on
gamma-ray Doppler factor for FSRQs and BL Lacs are 6.87 and 4.31, respectively.
We compare and discuss our results with those from the literature. We found
that the derived lower limit on gamma-ray Doppler factor for some sources are
higher than that from the radio estimation, which could be possibly explained
by the jet bending within those blazars. Our results also suggest that the
gamma-ray and radio regions perhaps share the same relativistic effects. The
gamma-ray Doppler factor has been found to be correlated with both the
gamma-ray luminosity and core-dominance parameter, implying that the jet is
possibly continuous in the gamma-ray bands, and R is perhaps an indicator for a
beaming effect.
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