Context. Diffusive shock acceleration (DSA) is the most promising mechanism that accelerates Galactic cosmic rays (CRs) in the shocks of supernova remnants (SNRs). It is based on particles scattering ...caused by turbulence ahead and behind the shock. The turbulence upstream is supposedly generated by the CRs, but this process is not well understood. The dominant mechanism may depend on the evolutionary state of the shock and can be studied via the CRs escaping upstream into the interstellar medium (ISM). Aims. Previous observations of the γ Cygni SNR showed a difference in morphology between GeV and TeV energies. Since this SNR has the right age and is at the evolutionary stage for a significant fraction of CRs to escape, our aim is to understand γ-ray emission in the vicinity of the γ Cygni SNR. Methods. We observed the region of the γ Cygni SNR with the MAGIC Imaging Atmospheric Cherenkov telescopes between 2015 May and 2017 September recording 87 h of good-quality data. Additionally, we analysed Fermi-LAT data to study the energy dependence of the morphology as well as the energy spectrum in the GeV to TeV range. The energy spectra and morphology were compared against theoretical predictions, which include a detailed derivation of the CR escape process and their γ-ray generation. Results. The MAGIC and Fermi-LAT data allowed us to identify three emission regions that can be associated with the SNR and that dominate at different energies. Our hadronic emission model accounts well for the morphology and energy spectrum of all source components. It constrains the time-dependence of the maximum energy of the CRs at the shock, the time-dependence of the level of turbulence, and the diffusion coefficient immediately outside the SNR shock. While in agreement with the standard picture of DSA, the time-dependence of the maximum energy was found to be steeper than predicted, and the level of turbulence was found to change over the lifetime of the SNR.
PG 1553+113 is a very high energy (VHE, E > 100...GeV) γ-ray emitter classified as a BL Lac object. Its redshift is constrained by intergalactic absorption lines in the range 0.4 < z < 0.58. The ...MAGIC telescopes have monitored the source's activity since 2005. In early 2012, PG 1553+113 was found in a high state, and later, in April of the same year, the source reached its highest VHE flux state detected so far. Simultaneous observations carried out in X-rays during 2012 April show similar flaring behaviour. In contrast, the γ-ray flux at E < 100...GeV observed by Fermi-LAT is compatible with steady emission. In this paper, a detailed study of the flaring state is presented. The VHE spectrum shows clear curvature, being well fitted either by a power law with an exponential cut-off or by a log-parabola. A simple power-law fit hypothesis for the observed shape of the PG 1553+113 VHE γ-ray spectrum is rejected with a high significance (fit probability P = 2.6 x 10...). The observed curvature is compatible with the extragalactic background light (EBL) imprint predicted by current generation EBL models assuming a redshift z ~ 0.4. New constraints on the redshift are derived from the VHE spectrum. These constraints are compatible with previous limits and suggest that the source is most likely located around the optical lower limit, z = 0.4, based on the detection of Lyα absorption. Finally, we find that the synchrotron self-Compton model gives a satisfactory description of the observed multiwavelength spectral energy distribution during the flare. (ProQuest: ... denotes formulae/symbols omitted.)
The number of known very high energy (VHE) blazars is ~50, which is very small in comparison to the number of blazars detected in other frequencies. This situation is a handicap for population ...studies of blazars, which emit about half of their luminosity in the ...-ray domain. Moreover, VHE blazars, if distant, allow for the study of the environment that the high-energy ...-rays traverse in their path towards the Earth, like the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF), and hence they have a special interest for the astrophysics community. We present the first VHE detection of 1ES 0033+595 with a statistical significance of 5.5... The VHE emission of this object is constant throughout the MAGIC observations (2009 August and October), and can be parametrized with a power law with an integral flux above 150 GeV of (7.1 ± 1.3) x 10... photons cm... s... and a photon index of (3.8 ± 0.7). We model its spectral energy distribution (SED) as the result of inverse Compton scattering of synchrotron photons. For the study of the SED, we used simultaneous optical R-band data from the KVA telescope, archival X-ray data by Swift as well as INTEGRAL, and simultaneous high-energy (HE, 300 MeV-10 GeV) ...-ray data from the Fermi Large Area Telescope (LAT) observatory. Using the empirical approach of Prandini et al. (2010) and the Fermi LAT and MAGIC spectra for this object, we estimate the redshift of this source to be 0.34 ± 0.08 ± 0.05. This is a relevant result because this source is possibly one of the 10 most distant VHE blazars known to date, and with further (simultaneous) observations could play an important role in blazar population studies, as well as future constraints on the EBL and IGMF. (ProQuest: ... denotes formulae/symbols omitted.)
Supermassive black holes with masses of millions to billions of solar masses are commonly found in the centers of galaxies. Astronomers seek to image jet formation using radio interferometry but ...still suffer from insufficient angular resolution. An alternative method to resolve small structures is to measure the time variability of their emission. Here we report on gamma-ray observations of the radio galaxy IC 310 obtained with the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes, revealing variability with doubling time scales faster than 4.8 min. Causality constrains the size of the emission region to be smaller than 20% of the gravitational radius of its central black hole. We suggest that the emission is associated with pulsar-like particle acceleration by the electric field across a magnetospheric gap at the base of the radio jet.
The first Large Size Telescope (LST-1) of the Cherenkov Telescope Array has been operational since October 2018 at La Palma, Spain. We report on the results obtained during the camera commissioning. ...The noise level of the readout is determined as a 0.2 p.e. level. The gain of PMTs are well equalized within 2\% variation, using the calibration flash system. The effect of the night sky background on the signal readout noise as well as the PMT gain estimation are also well evaluated. Trigger thresholds are optimized for the lowest possible gamma-ray energy threshold and the trigger distribution synchronization has been achieved within 1~ns precision. Automatic rate control realizes the stable observation with 1.5\% rate variation over 3 hours. The performance of the novel DAQ system demonstrates a less than 10\% dead time for 15 kHz trigger rate even with sophisticated online data correction.
We present the first Fermi Large Area Telescope (LAT) catalog of long-term \(\gamma\)-ray transient sources (1FLT). This comprises sources that were detected on monthly time intervals during the ...first decade of Fermi-LAT operations. The monthly time scale allows us to identify transient and variable sources that were not yet reported in other Fermi-LAT catalogs. The monthly datasets were analyzed using a wavelet-based source detection algorithm that provided the candidate new transient sources. The search was limited to the extragalactic regions of the sky to avoid the dominance of the Galactic diffuse emission at low Galactic latitudes. The transient candidates were then analyzed using the standard Fermi-LAT Maximum Likelihood analysis method. All sources detected with a statistical significance above 4\(\sigma\) in at least one monthly bin were listed in the final catalog. The 1FLT catalog contains 142 transient \(\gamma\)-ray sources that are not included in the 4FGL-DR2 catalog. Many of these sources (102) have been confidently associated with Active Galactic Nuclei (AGN): 24 are associated with Flat Spectrum Radio Quasars; 1 with a BL Lac object; 70 with Blazars of Uncertain Type; 3 with Radio Galaxies; 1 with a Compact Steep Spectrum radio source; 1 with a Steep Spectrum Radio Quasar; 2 with AGN of other types. The remaining 40 sources have no candidate counterparts at other wavelengths. The median \(\gamma\)-ray spectral index of the 1FLT-AGN sources is softer than that reported in the latest Fermi-LAT AGN general catalog. This result is consistent with the hypothesis that detection of the softest \(\gamma\)-ray emitters is less efficient when the data are integrated over year-long intervals.
A&A 670, A8 (2023) Context. Diffusive shock acceleration (DSA) is the most promising mechanism
to accelerate Galactic cosmic rays (CRs) in the shocks of supernova remnants
(SNRs). The turbulence ...upstream is supposedly generated by the CRs, but this
process is not well understood. The dominant mechanism may depend on the
evolutionary state of the shock and can be studied via the CRs escaping
upstream into the interstellar medium (ISM). Aims. Previous observations of the
$\gamma$-Cygni SNR showed a difference in morphology between GeV and TeV
energies. Since this SNR has the right age and is at the evolutionary stage for
a significant fraction of CRs to escape, we aim to understand $\gamma$-ray
emission in the vicinity of the $\gamma$-Cygni SNR. Methods. We observed the
region of the $\gamma$-Cygni SNR with the MAGIC Imaging Atmospheric Cherenkov
telescopes between May 2015 and September 2017 recording 87 h of good-quality
data. Additionally we analysed Fermi-LAT data to study the energy dependence of
the morphology as well as the energy spectrum in the GeV to TeV range. The
energy spectra and morphology were compared against theoretical predictions,
which include a detailed derivation of the CR escape process and their
$\gamma$-ray generation. Results. The MAGIC and Fermi-LAT data allowed us to
identify three emission regions, which can be associated with the SNR and
dominate at different energies. Our hadronic emission model accounts well for
the morphology and energy spectrum of all source components. It constrains the
time-dependence of the maximum energy of the CRs at the shock, the
time-dependence of the level of turbulence, and the diffusion coefficient
immediately outside the SNR shock. While in agreement with the standard picture
of DSA, the time-dependence of the maximum energy was found to be steeper than
predicted and the level of turbulence was found to change over the lifetime of
the SNR.
Nature 575 (2019) 455-458 Gamma-ray bursts (GRBs) of the long-duration class are the most luminous
sources of electromagnetic radiation known in the Universe. They are generated
by outflows of plasma ...ejected at near the speed of light by newly formed
neutron stars or black holes of stellar mass at cosmological distances. Prompt
flashes of MeV gamma rays are followed by longer-lasting afterglow emission
from radio waves to GeV gamma rays, due to synchrotron radiation by energetic
electrons in accompanying shock waves. Although emission of gamma rays at even
higher, TeV energies by other radiation mechanisms had been theoretically
predicted, it had never been detected previously. Here we report the clear
detection of GRB 190114C in the TeV band, achieved after many years of
dedicated searches for TeV emission from GRBs. Gamma rays in the energy range
0.2--1 TeV are observed from about 1 minute after the burst (at more than 50
standard deviations in the first 20 minutes). This unambiguously reveals a new
emission component in the afterglow of a GRB, whose power is comparable to that
of the synchrotron component. The observed similarity in the radiated power and
temporal behaviour of the TeV and X-ray bands points to processes such as
inverse Compton radiation as the mechanism of the TeV emission, while processes
such as synchrotron emission by ultrahigh-energy protons are disfavoured due to
their low radiative efficiency.
A&A 642, A190 (2020) Aims: $\gamma$ rays can be used as a tracer in the search of sources of
Galactic cosmic rays (CRs). We present deep observations of the Galactic Centre
(GC) region with the MAGIC ...telescopes, which we use for inferring the
underlying CR distribution. Methods: We observed the GC region for
${\approx}100$ hours with the MAGIC telescopes from 2012 to 2017, at high
zenith angles (58-70~deg). This implies a larger energy threshold, but also an
increased effective collection area compared to low zenith observations. Using
new software, we derive instrument response and background models, enabling us
to study the diffuse emission in the region. We use pre-existing data of the
gas distribution in the GC region to derive the underlying distribution of CRs.
Results: We obtain a significant detection for all four model components used
to fit our data (Sgr~A*, ``Arc'', G0.9+0.1, and an extended component for the
Galactic Ridge). We find that the diffuse component is best described as a
power-law with index 2 and an exponential cut-off at around 20~TeV with the
significance of the cut-off being only 2~$\sigma$. The derived cosmic-ray
profile hints to a peak at the GC position, with a measured profile index of
$1.2 \pm 0.3$, supporting the hypothesis of a CR accelerator at the GC. We
argue that the measurements of this profile are presently limited by our
knowledge of the gas distribution in the GC vicinity.
We report on the observations of gamma-ray burst (GRB) 190114C by the Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Observatory. The early-time observations reveal multiple emission ...components that evolve independently, with a delayed power-law component that exhibits significant spectral attenuation above 40 MeV in the first few seconds of the burst. This power-law component transitions to a harder spectrum that is consistent with the afterglow emission observed at later times. This afterglow component is clearly identifiable in the GBM and BAT light curves as a slowly fading emission component on which the rest of the prompt emission is superimposed. As a result, we are able to constrain the transition from internal shock to external shock dominated emission. We find that the temporal and spectral evolution of the broadband afterglow emission can be well modeled as synchrotron emission from a forward shock propagating into a wind-like circumstellar environment and find that high-energy photons observed by Fermi LAT are in tension with the theoretical maximum energy that can be achieved through synchrotron emission from a shock. These violations of the maximum synchrotron energy are further compounded by the detection of very high energy (VHE) emission above 300 GeV by MAGIC concurrent with our observations. We conclude that the observations of VHE photons from GRB 190114C necessitates either an additional emission mechanism at very high energies that is hidden in the synchrotron component in the LAT energy range, an acceleration mechanism that imparts energy to the particles at a rate that is faster than the electron synchrotron energy loss rate, or revisions of the fundamental assumptions used in estimating the maximum photon energy attainable through the synchrotron process.
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