195 research outputs found
Contribution to Galactic cosmic rays from young stellar clusters
The origin of Galactic cosmic rays (CR) is still a matter of debate.
Diffusive shock acceleration (DSA) applied to supernova remnant (SNR) shocks
provides the most reliable explanation. However, within the current
understanding of DSA several issues remain unsolved, like the CR maximum
energy, the chemical composition and the transition region between Galactic and
extra-Galactic CRs. These issues motivate the search for other possible
Galactic sources. Recently, several young stellar clusters (YSC) have been
detected in gamma rays, suggesting that such objects could be powerful sources
of Galactic CRs. The energy input could come from winds of massive stars hosted
in the clusters which is a function of the cluster total mass and initial mass
function of stars. In this work we evaluate the total CR flux produced by a
synthetic population of YSCs assuming that the CR acceleration occurs at the
termination shock of the collective wind resulting from the sum of cluster's
stellar winds. We show that the spectrum produced by YSC can significantly
contribute to energies TeV if the diffusion inside the wind-blown
bubble is Bohm-like and the spectral slope is harder than the one produced by
SNRs.Comment: Proceeding to the International Cosmic Ray Conference, ICRC 2023,
Nagoya, Japa
Searching for evidence of PeVatron activity from stellar clusters via gamma-ray and neutrino signatures
Young and massive stellar clusters are a promising source class for the acceleration of galactic cosmic rays to PeV energies. Supernova explosions of massive stars lead to semi-continuous injection of cosmic rays into the cluster environment. Collective stellar winds form a wind-blown bubble with a termination shock at which further particle acceleration may occur. Interactions of such energetic hadronic particles with target material - such as molecular clouds - will generate signature gamma-ray and neutrino emission. We apply a model of cosmic ray acceleration in stellar clusters to catalogues of known stellar clusters, identifying the most promising targets to search for evidence of PeVatron activity. Predictions for the secondary fluxes of gamma-ray and neutrino emission are derived based on particle acceleration at the collective wind termination shock. Our results are compared to data available from the H.E.S.S. Galactic Plane Survey, and we estimate the detection prospects for current and future generation neutrino experiments
Follow-up observations of GW170817 with the MAGIC telescopes
The discovery of the electromagnetic counterpart AT2017gfo and the GRB 170817A, associated to the binary neutron star merger GW170817, was one of the major advances in the study of gamma-ray bursts (GRBs) and the hallmark of the multi-messenger astronomy with gravitational waves. Another breakthrough in GRB physics is represented by the discovery of the highly energetic, teraelectronvolt (TeV) component in the GRB 190114C, possibly an universal component in all GRBs. This conclusion is also suggested by the hint of TeV emission in the short GRB 160821B and a few more events reported in the literature. The missing observational piece is the joint detection of TeV emission and gravitational waves from a short GRB and its progenitor. MAGIC observed the counterpart AT2017gfo as soon as the visibility conditions allowed it, namely from January to June 2018. These observations correspond to the maximum flux level observed in the radio and X-ray bands. The upper limits derived from TeV observations are compared with the modelling of the late non-thermal emission using the multi-frequency SED
First detection of VHE gamma-ray emission from TXS 1515-273, study of its X-ray variability and spectral energy distribution
We report here on the first multi-wavelength (MWL) campaign on the blazar TXS
1515-273, undertaken in 2019 and extending from radio to very-high-energy gamma
rays (VHE). Up until now, this blazar had not been the subject of any detailed
MWL observations. It has a rather hard photon index at GeV energies and was
considered a candidate extreme high-synchrotronpeaked source. MAGIC
observations resulted in the first-time detection of the source in VHE with a
statistical significance of 7.6. The average integral VHE flux of the
source is 6 1% of the Crab nebula flux above 400 GeV. X-ray coverage was
provided by Swift-XRT, XMMNewton, and NuSTAR. The long continuous X-ray
observations were separated by 9 h, both showing clear hour scale
flares. In the XMM-Newton data, both the rise and decay timescales are longer
in the soft X-ray than in the hard X-ray band, indicating the presence of a
particle cooling regime. The X-ray variability timescales were used to
constrain the size of the emission region and the strength of the magnetic
field. The data allowed us to determine the synchrotron peak frequency and
classify the source as a flaring high, but not extreme, synchrotron peaked
object. Considering the constraints and variability patterns from the X-ray
data, we model the broad-band spectral energy distribution. We applied a simple
one-zone model, which could not reproduce the radio emission and the shape of
the optical emission, and a two-component leptonic model with two interacting
components, enabling us to reproduce the emission from radio to VHE band
Probing extreme environments with the Cherenkov Telescope Array
The physics of the non-thermal Universe provides information on the
acceleration mechanisms in extreme environments, such as black holes and
relativistic jets, neutron stars, supernovae or clusters of galaxies. In the
presence of magnetic fields, particles can be accelerated towards relativistic
energies. As a consequence, radiation along the entire electromagnetic spectrum
can be observed, and extreme environments are also the most likely sources of
multi-messenger emission. The most energetic part of the electromagnetic
spectrum corresponds to the very-high-energy (VHE, E>100 GeV) gamma-ray regime,
which can be extensively studied with ground based Imaging Atmospheric
Cherenkov Telescopes (IACTs). The results obtained by the current generation of
IACTs, such as H.E.S.S., MAGIC, and VERITAS, demonstrate the crucial importance
of the VHE band in understanding the non-thermal emission of extreme
environments in our Universe. In some objects, the energy output in gamma rays
can even outshine the rest of the broadband spectrum. The Cherenkov Telescope
Array (CTA) is the next generation of IACTs, which, with cutting edge
technology and a strategic configuration of ~100 telescopes distributed in two
observing sites, in the northern and southern hemispheres, will reach better
sensitivity, angular and energy resolution, and broader energy coverage than
currently operational IACTs. With CTA we can probe the most extreme
environments and considerably boost our knowledge of the non-thermal Universe.Comment: Submitted as input to ASTRONET Science Vision and Infrastructure
roadmap on behalf of the CTA consortiu
MAGIC observations of the nearby short GRB 160821B
Gamma-ray bursts (GRBs), the most luminous explosions in the universe, have at least two types known. One of them, short GRBs, have been thought to originate from binary neutron star (BNS) mergers. The discovery of GW170817 together with a GRB was the first and only direct proof of the hypothesis, and thus the properties of the short GRBs are poorly known yet. Aiming to clarify the underlying physical mechanisms of the short GRBs, we analyzed GRB 160821B, one of the nearest short GRBs known at z=0.162, observed with the MAGIC telescopes. A hint of a gamma-ray signal is found above 0.5 TeV at a significance of >3 sigma during observations from 24 seconds until 4 hours after the burst, as presented in the past. Recently, multi-wavelength data of its afterglow emission revealed a well-sampled kilonova component from a BNS merger, and the importance of GRB 160821B increased concerning GRB-GW studies. Accordingly, we investigated GRB afterglow models again, using the revised multi-wavelength data. We found that the straightforward interpretation with one-zone synchrotron self-Compton model from the external forward shock is in tension with the observed TeV flux, contradicting the suggestion reported previously. In this contribution we discuss the implication from the TeV observation, including alternative scenarios where the TeV emission can be enhanced. We also give a brief outlook of future GeV-TeV observations of short GRBs with imaging atmospheric Cherenkov telescopes, which could shed more light on the GRB-BNS merger relation
Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES 2344+514
Aims. The BL Lac 1ES 2344+514 is known for temporary extreme properties characterised by a shift of the synchrotron spectral energy distribution (SED) peak energy νsynch;p above 1 keV. While those extreme states have only been observed during high flux levels thus far, additional multi-year observing campaigns are required to achieve a coherent picture. Here, we report the longest investigation of the source from radio to very high energy (VHE) performed so far, focussing on a systematic characterisation of the intermittent extreme states. Methods.We organised a monitoring campaign covering a 3-year period from 2019 to 2021.Morethan ten instruments participated in the observations in order to cover the emission from radio to VHE. In particular, sensitive X-ray measurements by XMM-Newton, NuSTAR, and AstroSat took place simultaneously with multi-hour MAGIC observations, providing an unprecedented constraint of the two SED components for this blazar. Results. While our results confirm that 1ES 2344+514 typically exhibits νsynch;p > 1 keV during elevated flux periods, we also find periods where the extreme state coincides with low flux activity. A strong spectral variability thus happens in the quiescent state, and is likely caused by an increase in the electron acceleration efficiency without a change in the electron injection luminosity. On the other hand, we also report a strong X-ray flare (among the brightest for 1ES 2344+514) without a significant shift of νsynch;p. During this particular flare, the X-ray spectrum is among the softest of the campaign. It unveils complexity in the spectral evolution, where the common harder-when-brighter trend observed in BL Lacs is violated. By combining Swift-XRT and Swift-UVOT measurements during a low and hard X-ray state, we find an excess of the UV flux with respect to an extrapolation of the X-ray spectrum to lower energies. This UV excess implies that at least two regions significantly contribute to the infrared/optical/ultraviolet/X-ray emission. Using the simultaneous MAGIC, XMM-Newton, NuSTAR, and AstroSat observations, we argue that a region possibly associated with the 10 GHz radio core may explain such an excess. Finally, we investigate a VHE flare, showing an absence of simultaneous variability in the 0.3-2 keV band. Using time-dependent leptonic modelling, we show that this behaviour, in contradiction to single-zone scenarios, can instead be explained by a two-component model
Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES~2344+514
The BL Lac 1ES 2344+514 is known for temporary extreme properties (e.g., a
shift of the synchrotron SED peak energy above 1keV). While
those extreme states were so far observed only during high flux levels,
additional multi-year observing campaigns are required to achieve a coherent
picture. Here, we report the longest investigation of the source from radio to
VHE performed so far, focusing on a systematic characterisation of the
intermittent extreme states. While our results confirm that 1ES 2344+514
typically exhibits 1keV during elevated flux periods, we also
find periods where the extreme state coincides with low flux activity. A strong
spectral variability thus happens in the quiescent state, and is likely caused
by an increase of the electron acceleration efficiency without a change in the
electron injection luminosity. We also report a strong X-ray flare (among the
brightest for 1ES 2344+514) without a significant shift of .
During this particular flare, the X-ray spectrum is among the softest of the
campaign. It unveils complexity in the spectral evolution, where the common
harder-when-brighter trend observed in BL Lacs is violated. During a low and
hard X-ray state, we find an excess of the UV flux with respect to an
extrapolation of the X-ray spectrum to lower energies. This UV excess implies
that at least two regions contribute significantly to the
infrared/optical/ultraviolet/X-ray emission. Using the simultaneous MAGIC,
XMM-Newton, NuSTAR, and AstroSat observations, we argue that a region possibly
associated with the 10 GHz radio core may explain such an excess. Finally, we
investigate a VHE flare, showing an absence of simultaneous variability in the
0.3-2keV band. Using a time-dependent leptonic modelling, we show that this
behaviour, in contradiction to single-zone scenarios, can instead be explained
by a two-component model.Comment: Accepted for publication in Astronomy & Astrophysic
Multiwavelength monitoring of the gravitationally lensed blazar QSO B0218+357 between 2016 and 2020
QSO B0218+357 is currently the only gravitationally lensed source from which very-high-energy (VHE, &100GeV) gamma-ray emission has been detected. We report the multiwavelength monitoring observations of this source performed between 2016 and 2020 in radio interferometry, optical, X-ray and gamma-ray bands. During the monitoring individual flares and hints of enhanced states in optical, X-ray and GeV bands have been observed, and the simultaneous data taken by the MAGIC telescopes allow us to search for the VHE gamma-ray emission associated with these events
- …