62 research outputs found
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]
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
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]
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
Quantum gravity phenomenology at the dawn of the multi-messenger era -- A review
The exploration of the universe has recently entered a new era thanks to the
multi-messenger paradigm, characterized by a continuous increase in the
quantity and quality of experimental data that is obtained by the detection of
the various cosmic messengers (photons, neutrinos, cosmic rays and
gravitational waves) from numerous origins. They give us information about
their sources in the universe and the properties of the intergalactic medium.
Moreover, multi-messenger astronomy opens up the possibility to search for
phenomenological signatures of quantum gravity. On the one hand, the most
energetic events allow us to test our physical theories at energy regimes which
are not directly accessible in accelerators; on the other hand, tiny effects in
the propagation of very high energy particles could be amplified by
cosmological distances. After decades of merely theoretical investigations, the
possibility of obtaining phenomenological indications of Planck-scale effects
is a revolutionary step in the quest for a quantum theory of gravity, but it
requires cooperation between different communities of physicists (both
theoretical and experimental). This review is aimed at promoting this
cooperation by giving a state-of-the art account of the interdisciplinary
expertise that is needed in the effective search of quantum gravity footprints
in the production, propagation and detection of cosmic messengers
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
MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT081 for the first time: a deep multiwavelength study
https://pos.sissa.it/395/815/pdfPublished versio
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