86 research outputs found
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
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
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 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&
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
Multimessenger Characterization of Markarian 501 during Historically Low X-Ray and γ-Ray Activity
We study the broadband emission of Mrk 501 using multiwavelength observations from 2017 to 2020 performed with a multitude of instruments, involving, among others, MAGIC, Fermi's Large Area Telescope (LAT), NuSTAR, Swift, GASP-WEBT, and the Owens Valley Radio Observatory. Mrk 501 showed an extremely low broadband activity, which may help to unravel its baseline emission. Nonetheless, significant flux variations are detected at all wave bands, with the highest occurring at X-rays and very-high-energy (VHE) 3-rays. A significant correlation (>3σ) between X-rays and VHE 3-rays is measured, supporting leptonic scenarios to explain the variable parts of the emission, also during low activity. This is further supported when we extend our data from 2008 to 2020, and identify, for the first time, significant correlations between the Swift X-Ray Telescope and Fermi-LAT. We additionally find correlations between high-energy 3-rays and radio, with the radio lagging by more than 100 days, placing the 3-ray emission zone upstream of the radio-bright regions in the jet. Furthermore, Mrk 501 showed a historically low activity in X-rays and VHE 3-rays from mid-2017 to mid-2019 with a stable VHE flux (>0.2 TeV) of 5% the emission of the Crab Nebula. The broadband spectral energy distribution (SED) of this 2 yr long low state, the potential baseline emission of Mrk 501, can be characterized with one-zone leptonic models, and with (lepto)-hadronic models fulfilling neutrino flux constraints from IceCube. We explore the time evolution of the SED toward the low state, revealing that the stable baseline emission may be ascribed to a standing shock, and the variable emission to an additional expanding or traveling shock. © 2023. The Author(s). Published by the American Astronomical Society
Multiwavelength Observations of the Blazar VER J0521+211 during an Elevated TeV Gamma-Ray State
We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211 observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral flux above 200 GeV measured with the nightly binned light curve is (8.8 ± 0.4) × 10-7 photons m-2 s-1, or ∼37% of the Crab Nebula flux. Multiwavelength observations from X-ray, UV, and optical instruments are also presented. A moderate correlation between the X-ray and TeV gamma-ray fluxes was observed, and the X-ray spectrum appeared harder when the flux was higher. Using the gamma-ray spectrum and four models of the extragalactic background light (EBL), a conservative 95% confidence upper limit on the redshift of the source was found to be z ≤ 0.31. Unlike the gamma-ray and X-ray bands, the optical flux did not increase significantly during the studied period compared to the archival low-state flux. The spectral variability from optical to X-ray bands suggests that the synchrotron peak of the spectral energy distribution (SED) may become broader during flaring states, which can be adequately described with a one-zone synchrotron self-Compton model varying the high-energy end of the underlying particle spectrum. The synchrotron peak frequency of the SED and the radio morphology of the jet from the MOJAVE program are consistent with the source being an intermediate-frequency-peaked BL Lac object
Multi-messenger characterization of Mrk 501 during historically low X-ray and -ray activity
We study the broadband emission of Mrk 501 using multi-wavelength
observations from 2017 to 2020 performed with a multitude of instruments,
involving, among others, MAGIC, Fermi-LAT, NuSTAR, Swift, GASP-WEBT, and OVRO.
Mrk 501 showed an extremely low broadband activity, which may help to unravel
its baseline emission. Nonetheless, significant flux variations are detected at
all wavebands, with the highest occurring at X-rays and very-high-energy (VHE)
-rays. A significant correlation (3) between X-rays and VHE
-rays is measured, supporting leptonic scenarios to explain the
variable parts of the emission, also during low activity. This is further
supported when we extend our data from 2008 to 2020, and identify, for the
first time, significant correlations between Swift-XRT and Fermi-LAT. We
additionally find correlations between high-energy -rays and radio,
with the radio lagging by more than 100 days, placing the -ray emission
zone upstream of the radio-bright regions in the jet. Furthermore, Mrk 501
showed a historically low activity in X-rays and VHE -rays from
mid-2017 to mid-2019 with a stable VHE flux (0.2 TeV) of 5% the emission of
the Crab Nebula. The broadband spectral energy distribution (SED) of this
2-year-long low-state, the potential baseline emission of Mrk 501, can be
characterized with one-zone leptonic models, and with (lepto)-hadronic models
fulfilling neutrino flux constraints from IceCube. We explore the time
evolution of the SED towards the low-state, revealing that the stable baseline
emission may be ascribed to a standing shock, and the variable emission to an
additional expanding or traveling shock.Comment: 56 pages, 30 figures, 14 tables, submitted. Corresponding authors are
L. Heckmann, D. Paneque, S. Gasparyan, M. Cerruti, and N. Sahakya
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