We simulate the spectral behaviour of the non-transient gamma-ray binaries using archival observations as a reference. With this we test the CTA capability to measure the sources' spectral parameters ...and detect variability on various time scales. We review the known properties of gamma-ray binaries and the theoretical models that have been used to describe their spectral and timing characteristics. We show that CTA is capable of studying these sources on time scales comparable to their characteristic variability time scales. For most of the binaries, the unprecedented sensitivity of CTA will allow the spectral evolution to be studied on a time scale as short as 30 min. This will enable a direct comparison of the TeV and lower energy (radio to GeV) properties of these sources from simultaneous observations. We also review the source-specific questions that can be addressed with such high-accuracy CTA measurements.
We report the detection of pulsed gamma-ray emission from the Geminga pulsar (PSR J0633+1746) between \(15\,\)GeV and \(75\,\)GeV. This is the first time a middle-aged pulsar has been detected up to ...these energies. Observations were carried out with the MAGIC telescopes between 2017 and 2019 using the low-energy threshold Sum-Trigger-II system. After quality selection cuts, \(\sim 80\,\)hours of observational data were used for this analysis. To compare with the emission at lower energies below the sensitivity range of MAGIC, \(11\) years of Fermi-LAT data above \(100\,\)MeV were also analysed. From the two pulses per rotation seen by Fermi-LAT, only the second one, P2, is detected in the MAGIC energy range, with a significance of \(6.3\,\sigma\). The spectrum measured by MAGIC is well-represented by a simple power law of spectral index \(\Gamma= 5.62\pm0.54\), which smoothly extends the Fermi-LAT spectrum. A joint fit to MAGIC and Fermi-LAT data rules out the existence of a sub-exponential cut-off in the combined energy range at the \(3.6\,\sigma\) significance level. The power-law tail emission detected by MAGIC is interpreted as the transition from curvature radiation to Inverse Compton Scattering of particles accelerated in the northern outer gap.
We report a characterization of the multi-band flux variability and
correlations of the nearby (z=0.031) blazar Markarian 421 (Mrk 421) using data
from Mets\"{a}hovi, Swift, Fermi-LAT, MAGIC, FACT ...and other collaborations and
instruments from November 2014 till June 2016. Mrk 421 did not show any
prominent flaring activity, but exhibited periods of historically low activity
above 1 TeV (F$_{>1\mathrm{TeV}}<$ 1.7$\times$10$^{-12}$ ph cm$^{-2}$ s$^{-1}$)
and in the 2-10 keV (X-ray) band (F$_{2-10 \mathrm{keV}}<$3.6$\times$10$^{-11}$
erg cm$^{-2}$ s$^{-1}$), during which the Swift-BAT data suggests an additional
spectral component beyond the regular synchrotron emission. The highest flux
variability occurs in X-rays and very-high-energy (E$>$0.1 TeV) $\gamma$-rays,
which, despite the low activity, show a significant positive correlation with
no time lag. The HR$_\mathrm{keV}$ and HR$_\mathrm{TeV}$ show the
harder-when-brighter trend observed in many blazars, but the trend flattens at
the highest fluxes, which suggests a change in the processes dominating the
blazar variability. Enlarging our data set with data from years 2007 to 2014,
we measured a positive correlation between the optical and the GeV emission
over a range of about 60 days centered at time lag zero, and a positive
correlation between the optical/GeV and the radio emission over a range of
about 60 days centered at a time lag of $43^{+9}_{-6}$ days.This observation is
consistent with the radio-bright zone being located about 0.2 parsec downstream
from the optical/GeV emission regions of the jet. The flux distributions are
better described with a LogNormal function in most of the energy bands probed,
indicating that the variability in Mrk 421 is likely produced by a
multiplicative process.
Extreme high-frequency peaked BL Lac objects (EHBLs) are blazars which exhibit extremely energetic synchrotron emission. They also feature non-thermal gamma-ray emission whose peak lies in the very ...high-energy (VHE, E > 100 GeV) range, and in some sources exceeds 1TeV: this is the case of hard-TeV EHBLs such as 1ES 0229+200. With the aim of increasing the EHBL population, ten targets were observed with the MAGIC telescopes from 2010 to 2017, for a total of 262 h of good quality data. The data were complemented by coordinated Swift observations. The X-ray data analysis confirms that all the sources but two are EHBLs. The sources show only a modest variability and a harder-when-brighter behavior, typical for this class of objects. At VHE gamma rays, three new sources were detected and a hint of signal was found for another new source. In each case the intrinsic spectrum is compatible with the hypothesis of a hard-TeV nature of these EHBLs. The broadband spectral energy distributions (SEDs) of all sources are built and modeled in the framework of a single-zone purely leptonic model. The VHE gamma-ray detected sources were also interpreted with a spine-layer and a proton synchrotron models. The three models provide a good description of the SEDs. However, the resulting parameters differ substantially in the three scenarios, in particular the magnetization parameter. This work presents a first mini-catalog of VHE gamma-ray and multi-wavelength observations of EHBLs.
M87 is one of the closest (z=0.00436) extragalactic sources emitting at very-high-energies (VHE, E > 100 GeV). The aim of this work is to locate the region of the VHE gamma-ray emission and to ...describe the observed broadband spectral energy distribution (SED) during the low VHE gamma-ray state. The data from M87 collected between 2012 and 2015 as part of a MAGIC monitoring programme are analysed and combined with multi-wavelength data from Fermi-LAT, Chandra, HST, EVN, VLBA and the Liverpool Telescope. The averaged VHE gamma-ray spectrum can be fitted from 100GeV to 10TeV with a simple power law with a photon index of (-2.41 \(\pm\) 0.07), while the integral flux above 300GeV is \((1.44 \pm 0.13) \times 10^{-12} cm^{-2} s^{-1}\). During the campaign between 2012 and 2015, M87 is generally found in a low emission state at all observed wavelengths. The VHE gamma-ray flux from the present 2012-2015 M87 campaign is consistent with a constant flux with some hint of variability (\(\sim3\sigma\)) on a daily timescale in 2013. The low-state gamma-ray emission likely originates from the same region as the flare-state emission. Given the broadband SED, both a leptonic synchrotron self Compton and a hybrid photo-hadronic model reproduce the available data well, even if the latter is preferred. We note, however, that the energy stored in the magnetic field in the leptonic scenario is very low suggesting a matter dominated emission region.
MWC 656 is the first known Be/black hole (BH) binary system. Be/BH binaries are important in the context of binary system evolution and sources of detectable gravitational waves because they are ...possible precursors of coalescing neutron star/BH binaries. X-ray observations conducted in 2013 revealed that MWC 656 is a quiescent high-mass X-ray binary (HMXB), opening the possibility to explore X-ray/radio correlations and the accretion/ejection coupling down to low luminosities for BH HMXBs. Here we report on a deep joint Chandra/VLA observation of MWC 656 (and contemporaneous optical data) conducted in 2015 July that has allowed us to unambiguously identify the X-ray counterpart of the source. The X-ray spectrum can be fitted with a power law with \(\Gamma\sim2\), providing a flux of \(\simeq4\times10^{-15}\) erg cm\(^{-2}\) s\(^{-1}\) in the 0.5-8 keV energy range and a luminosity of \(L_{\rm X}\simeq3\times10^{30}\) erg s\(^{-1}\) at a 2.6 kpc distance. For a 5 M\(_\odot\) BH this translates into \(\simeq5\times10^{-9}\) \(L_{\rm Edd}\). These results imply that MWC 656 is about 7 times fainter in X-rays than it was two years before and reaches the faintest X-ray luminosities ever detected in stellar-mass BHs. The radio data provide a detection with a peak flux density of \(3.5\pm1.1\) \(\mu\)Jy beam\(^{-1}\). The obtained X-ray/radio luminosities for this quiescent BH HMXB are fully compatible with those of the X-ray/radio correlations derived from quiescent BH low-mass X-ray binaries. These results show that the accretion/ejection coupling in stellar-mass BHs is independent of the nature of the donor star.
On January 14, 2019, the Major Atmospheric Gamma Imaging Cherenkov telescopes detected GRB 190114C above 0.2 TeV, recording the most energetic photons ever observed from a gamma-ray burst. We use ...this unique observation to probe an energy dependence of the speed of light in vacuo for photons as predicted by several quantum gravity models. Based on a set of assumptions on the possible intrinsic spectral and temporal evolution, we obtain competitive lower limits on the quadratic leading order of speed of light modification.
We investigate the physical nature and origin of the gamma-ray emission from the extended source HESS J1841-055 observed at TeV and GeV energies. We observed HESS J1841-055 at TeV energies for a ...total effective time of 43 hours with the MAGIC telescopes, in 2012 and 2013. Additionally, we analysed the GeV counterpart making use of about 10 years of Fermi-LAT data. Using both Fermi-LAT and MAGIC, we study both the spectral and energy-dependent morphology of the source for almost four decades of energy. The origin of the gamma-ray emission from this region is investigated using multi-waveband information on sources present in this region, suggested to be associated with this unidentified gamma-ray source. We find that the extended emission at GeV-TeV energies is best described by more than one source model. We also perform the first energy-dependent analysis of the HESS J1841-055 region at GeV-TeV. We find that the emission at lower energies comes from a diffuse or extended component, while the major contribution of gamma rays above 1 TeV arises from the southern part of the source. Moreover, we find that a significant curvature is present in the combined observed spectrum of MAGIC and Fermi-LAT. The first multi-wavelength spectral energy distribution of this unidentified source shows that the emission at GeV-TeV energies can be well explained with both leptonic and hadronic models. For the leptonic scenario, bremsstrahlung is the dominant emission compared to inverse Compton. On the other hand, for the hadronic model, gamma-ray resulting from the decay of neutral pions (\(\pi^0\)) can explain the observed spectrum. The presence of dense molecular clouds overlapping with HESS J1841-055 makes both bremsstrahlung and \(\pi^0\)-decay processes the dominant emission mechanisms for the source.
We present the first results from very-high-energy observations of the dwarf spheroidal satellite candidate Triangulum II with the MAGIC telescopes from 62.4 hours of good-quality data taken between ...August 2016 and August 2017. We find no gamma-ray excess in the direction of Triangulum II, and upper limits on both the differential and integral gamma-ray flux are presented. Currently, the kinematics of Triangulum II are affected by large uncertainties leading to a bias in the determination of the properties of its dark matter halo. Using a scaling relation between the annihilation J-factor and heliocentric distance of well-known dwarf spheroidal galaxies, we estimate an annihilation J-factor for Triangulum II for WIMP dark matter of \(\logJ_{\text{ann}}({0.5^{\circ}})/\) GeV\(^{2}\) cm\(^{-5} = 19.35 \pm 0.37\). We also derive a dark matter density profile for the object relying on results from resolved simulations of Milky Way sized dark matter halos. We obtain 95% confidence-level limits on the thermally averaged annihilation cross section for WIMP annihilation into various Standard Model channels. The most stringent limits are obtained in the \(\tau^{+}\tau^{-}\) final state, where a cross section for annihilation down to \(\langle \sigma_{\text{ann}} v \rangle = 3.05 \times 10^{-24}\) cm\(^{3}\) s\(^{-1}\) is excluded.
Aims: We aim to measure the Crab Nebula gamma-ray spectral energy distribution in the ~100 TeV energy domain and test the validity of existing leptonic emission models at these high energies. ...Methods: We use the novel very large zenith angle observations with the MAGIC telescope system to increase the collection area above 10 TeV. We also develop an auxiliary procedure of monitoring atmospheric transmission in order to assure proper calibration of the accumulated data. This employs recording of optical images of the stellar field next to the source position, which provides a better than 10% accuracy for the transmission measurements. Results: We demonstrate that MAGIC very large zenith angle observations yield a collection area larger than a square kilometer. In only ~56 hr of observations, we detect the gamma-ray emission from the Crab Nebula up to 100 TeV, thus providing the highest energy measurement of this source to date with Imaging Atmospheric Cherenkov Telescopes. Comparing accumulated and archival MAGIC and Fermi/LAT data with some of the existing emission models, we find that none of them provides an accurate description of the 1 GeV to 100 TeV gamma-ray signal.
