In this work we present data from observations with the MAGIC telescopes of SN 2014J detected on January 21 2014, the closest Type Ia supernova since Imaging Air Cherenkov Telescopes started to ...operate.Aims. We aim to probe the possibility of very-high-energy (VHE; E ≥ 100 GeV) gamma rays produced in the early stages of Type Ia supernova explosions.Methods. We performed follow-up observations after this supernova (SN) explosion for five days, between January 27 and February 2 2014. We searched for gamma-ray signals in the energy range between 100 GeV and several TeV from the location of SN 2014J using data from a total of ~5.5 h of observations. Prospects for observing gamma rays of hadronic origin from SN 2014J in the near future are also being addressed.Results. No significant excess was detected from the direction of SN 2014J. Upper limits at 95% confidence level on the integral flux, assuming a power-law spectrum, dF/dE ∝ E− Γ, with a spectral index of Γ = 2.6, for energies higher than 300 GeV and 700 GeV, are established at 1.3 × 10$^{-12}$ and 4.1 × 10$^{-13}$ photons cm$^{-2}$ s$^{-2}$, respectively.Conclusions. For the first time, upper limits on the VHE emission of a Type Ia supernova are established. The energy fraction isotropically emitted into TeV gamma rays during the first ~ 10 days after the supernova explosion for energies greater than 300 GeV is limited to 10$^{-6}$ of the total available energy budget (~1051 erg). Within the assumed theoretical scenario, the MAGIC upper limits on the VHE emission suggest that SN 2014J will not be detectable in the future by any current or planned generation of Imaging Atmospheric Cherenkov Telescopes.
Aims. We study the multi-band variability and correlations of the TeV blazar Mrk 421 on year timescales, which can bring additional insight on the processes responsible for its broadband ...emission.Methods. We observed Mrk 421 in the very high energy (VHE) γ-ray range with the Cherenkov telescope MAGIC-I from March 2007 to June 2009 for a total of 96 h of effective time after quality cuts. The VHE flux variability is quantified using several methods, including the Bayesian Block algorithm, which is applied to data from Cherenkov telescopes here for the first time. The 2.3 yr long MAGIC light curve is complemented with data from the Swift/BAT and RXTE/ASM satellites and the KVA, GASP-WEBT, OVRO, and Metsähovi telescopes from February 2007 to July 2009, allowing for an excellent characterisation of the multi-band variability and correlations over year timescales.Results. Mrk 421 was found in different γ-ray emission states during the 2.3 yr long observation period: The flux above 400 GeV spans from the minimum nightly value of (1.3 ± 0.4) × 10$^{-11}$ cm$^{-2}$ s$^{-1}$ to the maximum flux, that is about 24 times higher, at (3.1 ± 0.1) × 10$^{-10}$ cm$^{-2}$ s$^{-1}$. Flares and different levels of variability in the γ-ray light curve could be identified with the Bayesian Block algorithm. The same behaviour of a quiet and active emission was found in the X-ray light curves measured by Swift/BAT and the RXTE/ASM, with a direct correlation in time. The behaviour of the optical light curve of GASP-WEBT and the radio light curves by OVRO and Metsähovi are different as they show no coincident features with the higher energetic light curves and a less variable emission. Overall, the fractional variability increases with energy. The comparable variability in the X-ray and VHE bands and their direct correlation during both high- and low-activity periods spanning many months show that the electron populations radiating the X-ray and γ-ray photons are either the same, as expected in the synchrotron-self-Compton mechanism, or at least strongly correlated, as expected in electromagnetic cascades.
1ES 1011+496 (z = 0.212) was discovered in very high-energy (VHE, E> 100 GeV) γ rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of ...the broadband spectral energy distribution (SED).Aims. We study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum.Methods. We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and Metsähovi in addition to optical polarimetry data and radio maps from the Liverpool Telescope and MOJAVE.Results. The VHE spectrum was fit with a simple power law with a photon index of 3.69 ± 0.22 and a flux above 150 GeV of (1.46 ± 0.16) × 10$^{-11}$ ph cm$^{-2}$ s$^{-1}$. The source 1ES 1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8 ± 0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac.Conclusions. For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1 GeV to 1 TeV, which permitted a more reliable interpretation within the one-zone SSC scenario. The polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission.
QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components that are spatially indistinguishable by ...gamma-ray instruments, but separated by a 10–12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes.Aims. The spectral energy distribution of QSO B0218+357 can give information on the energetics of z ~ 1 very high energy gamma-ray sources. Moreover the gamma-ray emission can also be used as a probe of the extragalactic background light at z ~ 1.Methods. MAGIC performed observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data obtained by Fermi-LAT and MAGIC are used to set constraints on the extragalactic background light.Results. Very high energy gamma-ray emission was detected from the direction of QSO B0218+357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray source detected to date. The observed emission spans the energy range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broadband emission can be modeled in the framework of a two-zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.
The BL Lac object 1ES 1011+496 was discovered at very high energy (VHE, E > 100GeV) γ-rays by Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) in Spring 2007. Before that the source was little ...studied in different wavelengths. Therefore, a multiwavelength (MWL) campaign was organized in Spring 2008. Along MAGIC, the MWL campaign included the Metsähovi Radio Observatory, Bell and Kungliga Vetenskapsakademien (KVA) optical telescopes and the Swift and AGILE satellites. MAGIC observations span from 2008 March to May for a total of 27.9 h, of which 19.4 h remained after quality cuts. The light curve showed no significant variability yielding an integral flux above 200 GeV of (1.3 ± 0.3) × 10$^{−11}$ photons cm$^{−2}$ s$^{−1}$. The differential VHE spectrum could be described with a power-law function with a spectral index of 3.3 ± 0.4. Both results were similar to those obtained during the discovery. Swift X-ray Telescope observations revealed an X-ray flare, characterized by a harder-when-brighter trend, as is typical for high synchrotron peak BL Lac objects (HBL). Strong optical variability was found during the campaign, but no conclusion on the connection between the optical and VHE γ-ray bands could be drawn. The contemporaneous spectral energy distribution shows a synchrotron-dominated source, unlike concluded in previous work based on non-simultaneous data, and is well described by a standard one-zone synchrotron self-Compton model. We also performed a study on the source classification. While the optical and X-ray data taken during our campaign show typical characteristics of an HBL, we suggest, based on archival data, that 1ES 1011+496 is actually a borderline case between intermediate and high synchrotron peak frequency BL Lac objects.
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