1,725,612 research outputs found
Hunting the gamma-ray emission from Fast Radio Burst with Fermi-LAT
Get PDFFast radio bursts (FRBs) are one of the most exciting new mysteries of astrophysics. Their origin is still unknown, but recent observations seems to link them to Soft Gamma Repeaters and, in particular, to magnetar giant flares (MGFs). The recent detection of a MGF at GeV energies by the \textit{Fermi} Large Area Telescope (LAT) motivated the search for GeV counterparts to the >100 currently known FRBs. Taking advantage of more than 12 years of \textit{Fermi}-LAT data, we perform a search for gamma-ray emission from all the reported repeating and non-repeating FRBs. We analyse on different-time scales the \textit{Fermi}-LAT data of each individual source separately, including a cumulative analysis on the repeating ones. In addition, we perform the first stacking analysis at GeV energies of this class of sources in order to constrain the gamma-ray properties of the FRBs that are undetected at high energies. The stacking analysis is a powerful method that allow a possible detection from below-threshold FRBs providing important information on these objects. In this talk we present the preliminary results of our study and we discuss their implications for the predictions of gamma-ray emission from this class of source
Fermi-LAT and the Gamma-Ray Line Search
No full textA distinct signature for dark matter in the form of weakly interacting massive particles (WIMPs) would be the detection of a monochromatic spectral line in the gamma-ray sky. The Fermi-LAT collaboration has searched for such a line in the energy range from 5 to 300 GeV in five sky regions around the Galactic centre. No globally significant line is detected, and 95% CL upper limits on monochromatic-line strengths are presented. The smallest search region reveals a line-like structure at 133 GeV with a local significance of 2.9 σ after 4.4 years of data, which translates to less than 1σ global significance from a trial factor of around 200
Dark matter implications of Fermi-LAT measurement of anisotropies in the diffuse gamma-ray background
No full textThe detailed origin of the diffuse gamma-ray background is still unknown. However, the contribution of unresolved sources is expected to induce small-scale anisotropies in this emission, which may provide a way to identify and constrain the properties of its contributors. Recent studies have predicted the contributions to the angular power spectrum (APS) from extragalactic and galactic dark matter (DM) annihilation or decay. The Fermi-LAT collaboration reported detection of angular power with a significance larger than 3 sigma in the energy range from 1 GeV to 10 GeV on 22 months of data (Ackermann et al., 2012 [2]). For these preliminary results the already published Fermi-LAT APS measurements (Ackermann et al., 2012 [2]) are compared to the accurate predictions for DM anisotropies from state-of-the-art cosmological simulations as presented in Fornasa et at (2013) [1] to derive constraints on different DM candidates.</p
Fermi-LAT observations of the gamma-ray emission from the quiescent sun - first 6 years in orbit
No full textThe quiescent sun is a steady source of high energy gamma-ray emission due to the interactions of cosmic ray (CR) protons and electrons with matter and photons in the solar environment. Such interactions lead to two components of the emission with distinctly different spatial distributions and spectra: a point-like emission from the solar disk due to the CR cascades in the solar atmosphere, and the extended emission from the inverse Compton (IC) scattering of CR electrons off solar photons that is coming from the whole heliosphere. The Fermi-LAT Collaboration has reported the detection of the gamma-ray emission from the quiescent sun in a previous publication, based on the first 18 months of observations. In this paper we present the results of the first 6 years of observations. The new Pass 8 event-level analysis was applied to the data set. Significantly larger photon statistics and better instrument performance allow us to explore both components of the emission in greater details and let us better comparisons of data with current models of the IC component. Moreover, the longer period of observations allows us to study the variations of the emission over the solar cycle
Fermi LAT observation of quiet gamma-ray emission from the Sun and first solar flares detection
No full textWe show the latest results of Fermi-LAT observations of the quiescent Sun during the first 18 months of the mission. During this period the solar activity was at its minimum, hence the solar emission induced by cosmic rays was at its maximum. Two emission components are clearly distinguished: the point-like emission from the solar disk due to the cosmic-ray cascades in the solar atmosphere, and the extended emission due to inverse Compton scattering of cosmic ray electrons on solar photons in the heliosphere. We present the entire analysis, showing spectra and angular profiles of both components and discuss the comparison with models and future plans. Finally we report on Fermi Large Area Telescope (LAT) detection of the first solar flares and discussing the possible emission mechanisms
The first scientific experiment using Global e-VLBI observations: a multiwavelength campaign on the gamma-ray Narrow-Line Seyfert 1 PMN J0948+0022
Get PDFThe detection of gamma-ray emission by Fermi-LAT from the radio loud Narrow Line Seyfert 1 PMN J0948+0022 (Abdo et al. 2009, ApJ 699, 976) triggered a multi-wavelength campaign between March and July 2009. Given its high compactness (Doi et al. 2006, PASJ 58, 829), inverted spectrum, and 0 declination, the source was an ideal target to observe at 22 GHz with a Global VLBI array extending from Europe to East Asia and Australia. In order to deliver prompt results to be analysed in combination with the other instruments participating in the campaign, the observations were carried out with real time VLBI, for the first time on a Global scale. Indeed, the main results have been published just a few months after the campaign (Abdo et al. 2009, ApJ 707, 727). Here we present additional details about the e-VLBI observations
A gamma-ray pulsar timing array constrains the nanohertz gravitational wave background
No full textAfter large galaxies merge, their central supermassive black holes are expected to form binary systems. Their orbital motion should generate a gravitational wave background (GWB) at nanohertz frequencies. Searches for this background use pulsar timing arrays, which perform long-term monitoring of millisecond pulsars at radio wavelengths. We used 12.5 years of Fermi Large Area Telescope data to form a gamma-ray pulsar timing array. Results from 35 bright gamma-ray pulsars place a 95% credible limit on the GWB characteristic strain of 1.0 × 10 −14 at a frequency of 1 year –1 . The sensitivity is expected to scale with t obs , the observing time span, as t obs − 13 / 6 . This direct measurement provides an independent probe of the GWB while offering a check on radio noise models.A gamma-ray pulsar timing array After galaxies merge, the supermassive black holes (SMBHs) at their centers are expected to form binaries that emit gravitational waves at nanohertz frequencies. Numerous SMBH binaries throughout the Universe should combine to produce a gravitational wave background. Existing searches for this signal use radio observations of pulsars as sensitive clocks and look for small shifts in the pulse timings. The Fermi-LAT Collaboration implemented a pulsar timing array using gamma rays and achieved a sensitivity close to that of the radio approaches. The results set an independent upper limit on the gravitational wave background, which is subject to different noise sources. —KTSA pulsar timing array is implemented using gamma rays, setting a limit on the nanohertz gravitational wave background
High-energy emission from GRBs: 10 years with Fermi-LAT
Get PDFIn 2018, the Fermi mission celebrated its first decade of operation. In this
time, the Large Area Telescope (LAT) has been very successful in detecting the
high-energy emission (>100 MeV) from Gamma-Ray Bursts (GRBs). The analysis of
particularly remarkable events - such as GRB 080916C, GRB 090510 and GRB
130427A - has been presented in dedicated publications. Here we present the
results of a new systematic search for high-energy emission from the full
sample of GRBs detected in 10 years by the Fermi Gamma-Ray Burst Monitor, as
well as Swift, AGILE, Integral and IPN bursts, featuring a detection efficiency
more than 50% better than previous works, and returning 186 detections during
10 years of LAT observations. This milestone marks a vast improvement from the
35 events contained in the first LAT GRB catalog (covering the first 3 years of
Fermi operations). We assess the characteristics of the GRB population at high
energy with unprecedented sensitivity, covering aspects such as temporal
properties, energetics and spectral index of the high-energy emission. Finally,
we show how the LAT observations can be used to inform theory, in particular
the prospects for very high-energy emission
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