MAGIC upper limits on the GRB 090102 afterglow

Indications of a GeV component in the emission from gamma-ray bursts (GRBs) are known since the Energetic Gamma-Ray Experiment Telescope observations during the 1990s and they have been confirmed by the data of the Fermi satellite. These results have, however, shown that our understanding of GRB physics is still unsatisfactory. The new generation of Cherenkov observatories and in particular the MAGIC telescope, allow for the first time the possibility to extend the measurement of GRBs from several tens up to hundreds of GeV energy range. Both leptonic and hadronic processes have been suggested to explain the possible GeV/TeV counterpart of GRBs. Observations with ground-based telescopes of very high energy (VHE) photons (E &gt; 30 GeV) from these sources are going to play a key role in discriminating among the different proposed emission mechanisms, which are barely distinguishable at lower energies. MAGIC telescope observations of the GRB 090102 (z = 1.547) field and Fermi Large Area Telescope data in the same time interval are analysed to derive upper limits of the GeV/TeV emission. We compare these results to the expected emissions evaluated for different processes in the framework of a relativistic blastwave model for the afterglow. Simultaneous upper limits with Fermi and a Cherenkov telescope have been derived for this GRB observation. The results we obtained are compatible with the expected emission although the difficulties in predicting the HE and VHE emission for the afterglow of this event makes it difficult to draw firmer conclusions. Nonetheless, MAGIC sensitivity in the energy range of overlap with space-based instruments (above about 40 GeV) is about one order of magnitude better with respect to Fermi. This makes evident the constraining power of ground-based observations and shows that the MAGIC telescope has reached the required performance to make possible GRB multiwavelength studies in the VHE range.</p

Multifrequency studies of the peculiar quasar 4C+21.35 during the 2010 flaring activity

The discovery of rapidly variable Very High Energy ( VHE; E &gt; 100 GeV). - ray emission from 4C + 21.35 ( PKS 1222+ 216) by MAGIC on 2010 June 17, triggered by the high activity detected by the Fermi Large Area Telescope ( LAT) in high energy ( HE; E &gt; 100 MeV). - rays, poses intriguing questions on the location of the. - ray emitting region in this flat spectrum radio quasar. We present multifrequency data of 4C + 21.35 collected from centimeter to VHE during 2010 to investigate the properties of this source and discuss a possible emission model. The first hint of detection at VHE was observed by MAGIC on 2010 May 3, soon after a gamma- ray flare detected by Fermi-LAT that peaked on April 29. The same emission mechanism may therefore be responsible for both the HE and VHE emission during the 2010 flaring episodes. Two optical peaks were detected on 2010 April 20 and June 30, close in time but not simultaneous with the two gamma- ray peaks, while no clear connection was observed between the X-ray and gamma- ray emission. An increasing flux density was observed in radio and mm bands from the beginning of 2009, in accordance with the increasing gamma- ray activity observed by Fermi-LAT, and peaking on 2011 January 27 in the mm regime ( 230 GHz). We model the spectral energy distributions ( SEDs) of 4C + 21.35 for the two periods of the VHE detection and a quiescent state, using a one-zone model with the emission coming from a very compact region outside the broad line region. The three SEDs can be fit with a combination of synchrotron self-Compton and external Compton emission of seed photons from a dust torus, changing only the electron distribution parameters between the epochs. The fit of the optical/UV part of the spectrum for 2010 April 29 seems to favor an inner disk radius of &lt; six gravitational radii, as one would expect from a prograde-rotating Kerr black hole.</p

Performance of the Cherenkov Telescope Array in the presence of clouds

The Cherenkov Telescope Array (CTA) is the future ground-based observatory for gamma-ray astronomy at very high energies. The atmosphere is an integral part of every Cherenkov telescope. Different atmospheric conditions, such as clouds, can reduce the fraction of Cherenkov photons produced in air showers that reach ground-based telescopes, which may affect the performance. Decreased sensitivity of the telescopes may lead to misconstructed energies and spectra. This study presents the impact of various atmospheric conditions on CTA performance. The atmospheric transmission in a cloudy atmosphere in the wavelength range from 203 nm to 1000 nm was simulated for different cloud bases and different optical depths using the MODerate resolution atmospheric TRANsmission (MODTRAN) code. MODTRAN output files were used as inputs for generic Monte Carlo simulations. The analysis was performed using the MAGIC Analysis and Reconstruction Software (MARS) adapted for CTA. As expected, the effects of clouds are most evident at low energies, near the energy threshold. Even in the presence of dense clouds, high-energy gamma rays may still trigger the telescopes if the first interaction occurs lower in the atmosphere, below the cloud base. A method to analyze very high-energy data obtained in the presence of clouds is presented. The systematic uncertainties of the method are evaluated. These studies help to gain more precise knowledge about the CTA response to cloudy conditions and give insights on how to proceed with data obtained in such conditions. This may prove crucial for alert-based observations and time-critical studies of transient phenomena

Observation of the black widow B1957+20 millisecond pulsar binary system with the MAGIC telescopes

B1957+20 is a millisecond pulsar located in a black-widow-type compact binary system with a low-mass stellar companion. The interaction of the pulsar wind with the companion star wind and/or the interstellar plasma is expected to create plausible conditions for acceleration of electrons to TeV energies and subsequent production of very high-energy gamma-rays in the inverse Compton process. We performed extensive observations with the Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC) telescopes of B1957+20. We interpret results in the framework of a few different models, namely emission from the vicinity of the millisecond pulsar, the interaction of the pulsar and stellar companion wind region or bow shock nebula. No significant steady very high-energy gamma-ray emission was found. We derived a 95 per cent confidence level upper limit of 3.0 x 10(-12) cm(-2) s(-1) on the average gamma-ray emission from the binary system above 200 GeV. The upper limits obtained with the MAGIC constrain, for the first time, different models of the high-energy emission in B1957+20. In particular, in the inner mixed wind nebula model with mono-energetic injection of electrons, the acceleration efficiency of electrons is constrained to be below similar to 2-10 per cent of the pulsar spin-down power. For the pulsar emission, the obtained upper limits for each emission peak are well above the exponential cut-off fits to the Fermi-LAT data, extrapolated to energies above 50 GeV. The MAGIC upper limits can rule out a simple power-law tail extension through the sub-TeV energy range for the main peak seen at radio frequencies

Search for very high-energy gamma-ray emission from the microquasar Cygnus X-1 with the MAGIC telescopes

The microquasar Cygnus X-1 displays the two typical soft and hard X-ray states of a black hole transient. During the latter, Cygnus X-1 shows a one-sided relativistic radio-jet. Recent detection of the system in the high energy (HE; E greater than or similar to 60 MeV) gamma-ray range with FermiLAT associates this emission with the outflow. Former MAGIC observations revealed a hint of flaring activity in the very high-energy (VHE; E greater than or similar to 100 GeV) regime during this X-ray state. We analyse similar to 97 h of Cygnus X-1 data taken with the MAGIC telescopes between July 2007 and October 2014. To shed light on the correlation between hard X-ray and VHE gamma rays as previously suggested, we study each main X-ray state separately. We perform an orbital phase-folded analysis to look for variability in the VHE band. Additionally, to place this variability behaviour in a multiwavelength context, we compare our results with Fermi-LAT, AGILE, Swift-BAT, MAXI, RXTE-ASM, AMI and RATAN-600 data. We do not detect Cygnus X-1 in the VHE regime. We establish upper limits for each X-ray state, assuming a power-law distribution with photon index Gamma = 3.2. For steady emission in the hard and soft X-ray states, we set integral upper limits at 95 per cent confidence level for energies above 200 GeV at 2.6 x 10(-12) photons cm(-2) s(-1) and 1.0 x 10(-11) photons cm(-2) s(-1), respectively. We rule out steady VHE gamma-ray emission above this energy range, at the level of theMAGIC sensitivity, originating in the interaction between the relativistic jet and the surrounding medium, while the emission above this flux level produced inside the binary still remains a valid possibility

MAGIC observations of the microquasar V404 Cygni during the 2015 outburst

The microquasar V404 Cygni underwent a series of outbursts in 2015, June 15-31, during which its flux in hard X-rays (20-40 keV) reached about 40 times the Crab nebula flux. Because of the exceptional interest of the flaring activity from this source, observations at several wavelengths were conducted. The MAGIC telescopes, triggered by the INTEGRAL alerts, followed-up the flaring source for several nights during the period June 18-27, for more than 10 h. One hour of observation was simultaneously conducted on a giant 22 GHz radio flare and a hint of signal at GeV energies seen by Fermi-LAT. The MAGIC observations did not show significant emission in any of the analysed time intervals. The derived flux upper limit, in the energy range 200-1250 GeV, is 4.8 x 10(-12) photons cm(-2) s(-1). We estimate the gamma-ray opacity during the flaring period, which along with our non-detection points to an inefficient acceleration in the V404 Cyg jets if a very high energy emitter is located further than 1 x 10(10) cm from the compact object

Constraining Lorentz Invariance Violation Using the Crab Pulsar Emission Observed up to TeV Energies by MAGIC

Spontaneous breaking of Lorentz symmetry at energies on the order of the Planck energy or lower is predicted by many quantum gravity theories, implying non-trivial dispersion relations for the photon in vacuum. Consequently, gamma-rays of different energies, emitted simultaneously from astrophysical sources, could accumulate measurable differences in their time of flight until they reach the Earth. Such tests have been carried out in the past using fast variations of gamma-ray flux from pulsars, and more recently from active galactic nuclei and gamma-ray bursts. We present new constraints studying the gamma-ray emission of the galactic Crab Pulsar, recently observed up to TeV energies by the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) collaboration. A profile likelihood analysis of pulsar events reconstructed for energies above 400. GeV finds no significant variation in arrival time as their energy increases.. Ninety-five percent CL limits are obtained on the effective Lorentz invariance violating energy scale at the level of E-QG1 > 5.5 x 10(17) GeV (4.5 x 10(17) GeV) for a linear, and E-QG2 > 5.9 x 10(10) GeV (5.3 x 10(10) GeV) for a quadratic scenario, for the subluminal and the superluminal cases, respectively. A substantial part of this study is dedicated to calibration of the test statistic, with respect to bias and coverage properties. Moreover, the limits take into account systematic uncertainties, which are found to worsen the statistical limits by about 36%-42%. Our constraints would have been much more stringent if the intrinsic pulse shape of the pulsar between 200 GeV and 400 GeV was understood in sufficient detail and allowed inclusion of events well below 400 GeV

Observations of Sagittarius A* during the pericenter passage of the G2 object with MAGIC

Context. We present the results of a multi-year monitoring campaign of the Galactic center (GC) with the MAGIC telescopes. These observations were primarily motivated by reports that a putative gas cloud (G2) would be passing in close proximity to the super-massive black hole (SMBH), associated with Sagittarius A*, located at the center of our galaxy. This event was expected to give astronomers a unique chance to study the effect of in-falling matter on the broad-band emission of a SMBH.Aims. We search for potential flaring emission of very-high-energy (VHE; >= 100 GeV) gamma rays from the direction of the SMBH at the GC due to the passage of the G2 object. Using these data we also study the morphology of this complex region.Methods. We observed the GC region with the MAGIC Imaging Atmospheric Cherenkov Telescopes during the period 2012-2015, collecting 67 h of good-quality data. In addition to a search for variability in the flux and spectral shape of the GC gamma-ray source, we use a point-source subtraction technique to remove the known gamma-ray emitters located around the GC in order to reveal the TeV morphology of the extended emission inside that region.Results. No effect of the G2 object on the VHE gamma-ray emission from the GC was detected during the 4 yr observation campaign. We confirm previous measurements of the VHE spectrum of Sagittarius A*, and do not detect any significant variability of the emission from the source. Furthermore, the known VHE gamma-ray emitter at the location of the supernova remnant G0.9+0.1 was detected, as well as the recently discovered VHE source close to the GG radio arc

First multi-wavelength campaign on the gamma-ray-loud active galaxy IC 310

Context. The extragalactic very-high-energy gamma-ray sky is rich in blazars. These are jetted active galactic nuclei that are viewed at a small angle to the line-of-sight. Only a handful of objects viewed at a larger angle are so far known to emit above 100 GeV. Multi-wavelength studies of such objects up to the highest energies provide new insights into the particle and radiation processes of active galactic nuclei.Aims. We aim to report the results from the first multi-wavelength campaign observing the TeV detected nucleus of the active galaxy IC 310, whose jet is observed at a moderate viewing angle of 10 degrees-20 degrees.Methods. The multi-instrument campaign was conducted between 2012 November and 2013 January, and involved observations with MAGIC, Fermi, INTEGRAL, Swift, OVRO, MOJAVE and EVN. These observations were complemented with archival data from the AllWISE and 2MASS catalogs. A one-zone synchrotron self-Compton model was applied to describe the broadband spectral energy distribution.Results. IC 310 showed an extraordinary TeV flare at the beginning of the campaign, followed by a low, but still detectable TeV flux. Compared to previous measurements in this energy range, the spectral shape was found to be steeper during the low emission state. Simultaneous observations in the soft X-ray band showed an enhanced energy flux state and a harder-when-brighter spectral shape behavior. No strong correlated flux variability was found in other frequency regimes. The broadband spectral energy distribution obtained from these observations supports the hypothesis of a double-hump structure.Conclusions. The harder-when-brighter trend in the X-ray and VHE emission, observed for the first time during this campaign, is consistent with the behavior expected from a synchrotron self-Compton scenario. The contemporaneous broadband spectral energy distribution is well described with a one-zone synchrotron self-Compton model using parameters that are comparable to those found for other gamma-ray-emitting misaligned blazars

Broadband characterisation of the very intense TeV flares of the blazar 1ES 1959+650 in 2016

1ES 1959+650 is a bright TeV high-frequency-peaked BL Lac object exhibiting interesting features like "orphan" TeV flares and broad emission in the high-energy regime that are difficult to interpret using conventional one-zone Synchrotron Self-Compton (SSC) scenarios. We report the results from the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observations in 2016 along with the multi-wavelength data from the Fermi Large Area Telescope (LAT) and Swift instruments. MAGIC observed 1ES 1959+650 with different emission levels in the very-high-energy (VHE, E> 100 GeV) gamma -ray band during 2016. In the long-term data, the X-ray spectrum becomes harder with increasing flux and a hint of a similar trend is also visible in the VHE band. An exceptionally high VHE flux reaching similar to 3 times the Crab Nebula flux was measured by MAGIC on the 13 and 14 of June, and 1 July 2016 (the highest flux observed since 2002). During these flares, the high-energy peak of the spectral energy distribution (SED) lies in the VHE domain and extends up to several TeV. The spectrum in the gamma -ray (both Fermi-LAT and VHE bands) and the X-ray bands are quite hard. On 13 June and 1 July 2016, the source showed rapid variations in the VHE flux within timescales of less than an hour. A simple one-zone SSC model can describe the data during the flares requiring moderate to large values of the Doppler factors (delta >= 30-60). Alternatively, the high-energy peak of the SED can be explained by a purely hadronic model attributed to proton-synchrotron radiation with jet power L-jet similar to 10(46) erg s(-1) and under high values of the magnetic field strength (similar to 100 G) and maximum proton energy (similar to few EeV). Mixed lepto-hadronic models require super-Eddington values of the jet power. We conclude that it is difficult to get detectable neutrino emission from the source during the extreme VHE flaring period of 2016