180 research outputs found
Measurement of the Extragalactic Background Light using MAGIC and Fermi-LAT gamma-ray observations of blazars up to z = 1
We present a measurement of the extragalactic background light (EBL) based on
a joint likelihood analysis of 32 gamma-ray spectra for 12 blazars in the
redshift range z = 0.03 to 0.944, obtained by the MAGIC telescopes and
Fermi-LAT. The EBL is the part of the diffuse extragalactic radiation spanning
the ultraviolet, visible and infrared bands. Major contributors to the EBL are
the light emitted by stars through the history of the universe, and the
fraction of it which was absorbed by dust in galaxies and re-emitted at longer
wavelengths. The EBL can be studied indirectly through its effect on very-high
energy photons that are emitted by cosmic sources and absorbed via
photon-photon interactions during their propagation across cosmological
distances. We obtain estimates of the EBL density in good agreement with
state-of-the-art models of the EBL production and evolution. The 1-sigma upper
bounds, including systematic uncertainties, are between 13% and 23% above the
nominal EBL density in the models. No anomaly in the expected transparency of
the universe to gamma rays is observed in any range of optical depth.We also
perform a wavelength-resolved EBL determination, which results in a hint of an
excess of EBL in the 0.18 - 0.62 m range relative to the studied models,
yet compatible with them within systematics.Comment: Accepted by MNRA
Study of the GeV to TeV morphology of the γ Cygni SNR (G 78.2+2.1) with MAGIC and Fermi-LAT: Evidence for cosmic ray escape
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. © 2023 EDP Sciences. All rights reserved
Periastron Observations of TeV Gamma-Ray Emission from a Binary System with a 50-year Period
We report on observations of the pulsar / Be star binary system PSR J2032+4127 / MT91 213 in the energy range between 100 GeV and 20 TeV with the VERITAS and MAGIC imaging atmospheric Cherenkov telescope arrays. The binary orbit has a period of approximately 50 years, with the most recent periastron occurring on 2017 November 13. Our observations span from 18 months prior to periastron to one month after. A new, point-like, gamma-ray source is detected, coincident with the location of PSR J2032+4127 / MT91 213. The gamma-ray light curve and spectrum are well-characterized over the periastron passage. The flux is variable over at least an order of magnitude, peaking at periastron, thus providing a firm association of the TeV source with the pulsar / Be star system. Observations prior to periastron show a cutoff in the spectrum at an energy around 0.5 TeV. This result adds a new member to the small population of known TeV binaries, and it identifies only the second source of this class in which the nature and properties of the compact object are firmly established. We compare the gamma-ray results with the light curve measured with the X-ray Telescope (XRT) on board the Neil Gehrels Swift Observatory and with the predictions of recent theoretical models of the system. We conclude that significant revision of the models is required to explain the details of the emission we have observed, and we discuss the relationship between the binary system and the overlapping steady extended source, TeV J2032+4130
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
The Great Markarian 421 Flare of 2010 February: Multiwavelength Variability and Correlation Studies
We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab Units above 1 TeV was measured in very high energy (VHE) γ-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsahovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (δ ⪆ 33) and the size of the emission region (δ-1RB≲ 3.8 × 1013cm) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model
A lower bound on intergalactic magnetic fields from time variability of 1ES 0229+200 from MAGIC and Fermi/LAT observations
Extended and delayed emission around distant TeV sources induced by the
effects of propagation of gamma rays through the intergalactic medium can be
used for the measurement of the intergalactic magnetic field (IGMF). We search
for delayed GeV emission from the hard-spectrum TeV blazar 1ES 0229+200 with
the goal to detect or constrain the IGMF-dependent secondary flux generated
during the propagation of TeV gamma rays through the intergalactic medium. We
analyze the most recent MAGIC observations over a 5 year time span and
complement them with historic data of the H.E.S.S. and VERITAS telescopes along
with a 12-year long exposure of the Fermi/LAT telescope. We use them to trace
source evolution in the GeV-TeV band over one-and-a-half decade in time. We use
Monte Carlo simulations to predict the delayed secondary gamma-ray flux,
modulated by the source variability, as revealed by TeV-band observations. We
then compare these predictions for various assumed IGMF strengths to all
available measurements of the gamma-ray flux evolution. We find that the source
flux in the energy range above 200 GeV experiences variations around its
average on the 14 years time span of observations. No evidence for the flux
variability is found in 1-100 GeV energy range accessible to Fermi/LAT.
Non-detection of variability due to delayed emission from electromagnetic
cascade developing in the intergalactic medium imposes a lower bound of
B>1.8e-17 G for long correlation length IGMF and B>1e-14 G for an IGMF of the
cosmological origin. Though weaker than the one previously derived from the
analysis of Fermi/LAT data, this bound is more robust, being based on a
conservative intrinsic source spectrum estimate and accounting for the details
of source variability in the TeV energy band. We discuss implications of this
bound for cosmological magnetic fields which might explain the baryon asymmetry
of the Universe.Comment: 10 pages, 5 figures, accepted to A&A. Corresponding authors: Ievgen
Vovk, Paolo Da Vela (mailto:[email protected]) and Andrii Neronov
(mailto:[email protected]
Long-term multi-wavelength study of 1ES 0647+250
The BL Lac object 1ES 0647+250 is one of the few distant -ray
emitting blazars detected at very high energies (VHE, 100 GeV) during
a non-flaring state. It was detected with the MAGIC telescopes during its low
activity in the years 2009-2011, as well as during three flaring activities in
the years 2014, 2019 and 2020, with the highest VHE flux in the latter epoch.
An extensive multi-instrument data set was collected within several coordinated
observing campaigns throughout these years. We aim to characterise the
long-term multi-band flux variability of 1ES 0647+250, as well as its broadband
spectral energy distribution (SED) during four distinct activity states
selected in four different epochs, in order to constrain the physical
parameters of the blazar emission region under certain assumptions. We evaluate
the variability and correlation of the emission in the different energy bands
with the fractional variability and the Z-transformed Discrete Correlation
Function, as well as its spectral evolution in X-rays and rays. Owing
to the controversy in the redshift measurements of 1ES 0647+250 reported in the
literature, we also estimate its distance in an indirect manner through the
comparison of the GeV and TeV spectra from simultaneous observations with
Fermi-LAT and MAGIC during the strongest flaring activity detected to date.
Moreover, we interpret the SEDs from the four distinct activity states within
the framework of one-component and two-component leptonic models, proposing
specific scenarios that are able to reproduce the available multi-instrument
data.Comment: 20 pages, 7 figures. Accepted in A&A. Corresponding authors: Jorge
Otero-Santos; Daniel Morcuende; Vandad Fallah Ramazani; Daniela Dorner; David
Paneque (mailto: [email protected]
MAGIC observations provide compelling evidence of hadronic multi-TeV emission from the putative PeVatron SNR G106.3+2.7
Context. Certain types of supernova remnants (SNRs) in our Galaxy are assumed to be PeVatrons, capable of accelerating cosmic rays (CRs) to ∼ PeV energies. However, conclusive observational evidence for this has not yet been found. The SNR G106.3+2.7, detected at 1- 100 TeV energies by different γ-ray facilities, is one of the most promising PeVatron candidates. This SNR has a cometary shape, which can be divided into a head and a tail region with different physical conditions. However, in which region the 100 TeV emission is produced has not yet been identified because of the limited position accuracy and/or angular resolution of existing observational data. Additionally, it remains unclear as to whether the origin of the γ-ray emission is leptonic or hadronic. Aims. With the better angular resolution provided by new MAGIC data compared to earlier γ-ray datasets, we aim to reveal the acceleration site of PeV particles and the emission mechanism by resolving the SNR G106.3+2.7 with 0.1 resolution at TeV energies. Methods. We observed the SNR G106.3+2.7 using the MAGIC telescopes for 121.7 h in total - after quality cuts - between May 2017 and August 2019. The analysis energy threshold is ∼0.2 TeV, and the angular resolution is 0.07-0.1. We examined the γ-ray spectra of different parts of the emission, whilst benefitting from the unprecedented statistics and angular resolution at these energies provided by our new data. We also used measurements at other wavelengths such as radio, X-rays, GeV γ-rays, and 10 TeV γ-rays to model the emission mechanism precisely. Results. We detect extended γ-ray emission spatially coincident with the radio continuum emission at the head and tail of SNR G106.3+2.7. The fact that we detect a significant γ-ray emission with energies above 6.0 TeV from only the tail region suggests that the emissions above 10 TeV detected with air shower experiments (Milagro, HAWC, Tibet ASγ and LHAASO) are emitted only from the SNR tail. Under this assumption, the multi-wavelength spectrum of the head region can be explained with either hadronic or leptonic models, while the leptonic model for the tail region is in contradiction with the emission above 10 TeV and X-rays. In contrast, the hadronic model could reproduce the observed spectrum at the tail by assuming a proton spectrum with a cutoff energy of ∼1 PeV for that region. Such high-energy emission in this middle-aged SNR (4-10 kyr) can be explained by considering a scenario where protons escaping from the SNR in the past interact with surrounding dense gases at present. Conclusions. The γ-ray emission region detected with the MAGIC telescopes in the SNR G106.3+2.7 is extended and spatially coincident with the radio continuum morphology. The multi-wavelength spectrum of the emission from the tail region suggests proton acceleration up to ∼PeV, while the emission mechanism of the head region could either be hadronic or leptonic
Investigating the blazar TXS 0506+056 through sharp multi-wavelength eyes during 2017-2019
The blazar TXS 0506+056 got into the spotlight of the astrophysical community
in September 2017, when a high-energy neutrino detected by IceCube
(IceCube-170922A) was associated at the 3 level to a -ray
flare from this source. This multi-messenger photon-neutrino association
remains, as per today, the most significant one ever observed. TXS 0506+056 was
a poorly studied object before the IceCube-170922A event. To better
characterize its broad-band emission, we organized a multi-wavelength campaign
lasting 16 months (November 2017 to February 2019), covering the radio-band
(Mets\"ahovi, OVRO), the optical/UV (ASAS-SN, KVA, REM, Swift/UVOT), the X-rays
(Swift/XRT, NuSTAR), the high-energy rays (Fermi/LAT) and the
very-high-energy (VHE) rays (MAGIC). In rays, the behaviour
of the source was significantly different from the 2017 one: MAGIC observations
show the presence of flaring activity during December 2018, while the source
only shows an excess at the 4 level during the rest of the campaign (74
hours of accumulated exposure); Fermi/LAT observations show several short
(days-to-week timescale) flares, different from the long-term brightening of
2017. No significant flares are detected at lower energies. The radio light
curve shows an increasing flux trend, not seen in other wavelengths. We model
the multi-wavelength spectral energy distributions in a lepto-hadronic
scenario, in which the hadronic emission emerges as Bethe-Heitler and
pion-decay cascade in the X-rays and VHE rays. According to the model
presented here, the December 2018 -ray flare was connected to a
neutrino emission that was too brief and not bright enough to be detected by
current neutrino instruments.Comment: 18 pages, 6 figures; in press in Ap
MAGIC observations provide compelling evidence of the hadronic multi-TeV emission from the putative PeVatron SNR G106.3+2.7
The SNR G106.3+2.7, detected at 1--100 TeV energies by different -ray
facilities, is one of the most promising PeVatron candidates. This SNR has a
cometary shape which can be divided into a head and a tail region with
different physical conditions. However, it is not identified in which region
the 100 TeV emission is produced due to the limited position accuracy and/or
angular resolution of existing observational data. Additionally, it remains
unclear whether the origin of the -ray emission is leptonic or
hadronic. With the better angular resolution provided by these new MAGIC data
compared to earlier -ray datasets, we aim to reveal the acceleration
site of PeV particles and the emission mechanism by resolving the SNR
G106.3+2.7 with 0.1 resolution at TeV energies. We detected extended
-ray emission spatially coincident with the radio continuum emission at
the head and tail of SNR G106.3+2.7. The fact that we detected a significant
-ray emission with energies above 6.0 TeV from the tail region only
suggests that the emissions above 10 TeV, detected with air shower experiments
(Milagro, HAWC, Tibet AS and LHAASO), are emitted only from the SNR
tail. Under this assumption, the multi-wavelength spectrum of the head region
can be explained with either hadronic or leptonic models, while the leptonic
model for the tail region is in contradiction with the emission above 10 TeV
and X-rays. In contrast, the hadronic model could reproduce the observed
spectrum at the tail by assuming a proton spectrum with a cutoff energy of
PeV for the tail region. Such a high energy emission in this
middle-aged SNR (4--10 kyr) can be explained by considering the scenario that
protons escaping from the SNR in the past interact with surrounding dense gases
at present.Comment: 13 pages, 7 figures, Accepted for publication in A&
- …