The multiwavelength observation of the nearby radio galaxy M87 provides a unique opportunity to study in detail processes occurring in Active Galactic Nuclei from radio waves to TeV gamma-rays. Here ...we report the detection of gamma-ray emission above 250 GeV from M87 in spring 2007 with the VERITAS atmospheric Cherenkov telescope array and discuss its correlation with the X-ray emission. The gamma-ray emission is measured to be point-like with an intrinsic source radius less than 4.5 arcmin. The differential energy spectrum is fitted well by a power-law function: dPhi/dE=(7.4+-1.3_{stat}+-1.5_{sys})(E/TeV)^{-2.31+-0.17_{stat}+-0.2_{sys}} 10^{-9}m^{-2}s^{-1}TeV^{-1}. We show strong evidence for a year-scale correlation between the gamma-ray flux reported by TeV experiments and the X-ray emission measured by the ASM/RXTE observatory, and discuss the possible short-time-scale variability. These results imply that the gamma-ray emission from M87 is more likely associated with the core of the galaxy than with other bright X-ray features in the jet.
The mechanisms producing fast variability of the γ-ray emission in active galactic nuclei (AGNs) are under debate. The MAGIC telescopes detected a fast, very-high-energy (VHE, E > 100 GeV) γ-ray ...flare from BL Lacertae on 2015 June 15. The flare had a maximum flux of (1.5 ± 0.3) × 10−10 photons cm−2 s−1 and halving time of 26 ± 8 min. The MAGIC observations were triggered by a high state in the optical and high-energy (HE, E > 100 MeV) γ-ray bands. In this paper we present the MAGIC VHE γ-ray data together with multi-wavelength data from radio, optical, X-rays, and HE γ rays from 2015 May 1 to July 31. Well-sampled multi-wavelength data allow us to study the variability in detail and compare it to the other epochs when fast, VHE γ-ray flares have been detected from this source. Interestingly, we find that the behaviour in radio, optical, X-rays, and HE γ-rays is very similar to two other observed VHE γ-ray flares. In particular, also during this flare there was an indication of rotation of the optical polarization angle and of activity at the 43 GHz core. These repeating patterns indicate a connection between the three events. We also test modelling of the spectral energy distribution based on constraints from the light curves and VLBA observations, with two different geometrical setups of two-zone inverse Compton models. In addition we model the γ-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE γ-ray flare, but all have some tension with the multi-wavelength observations.Key words: BL Lacertae objects: individual: BL Lacertae / gamma rays: galaxies⋆ MAGIC and multiwavelength data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A175⋆⋆ Corresponding authors: E. Lindfors, e-mail: elilin@utu.fi; M. Vazquez Acosta, e-mail: monicava@iac.es; S. Tsujimoto, e-mail: shimpei.tsujimoto@gmail.com
The mechanisms producing fast variability of the \(\gamma\)-ray emission in active galactic nuclei are under debate. The MAGIC telescopes detected a fast very high energy (VHE, E\(>100\) GeV) ...\(\gamma\)-ray flare from BL Lacertae on 2015 June 15. The flare had a maximum flux of \((1.5\pm 0.3)\times 10^{-10}\) photons cm\(^{-2}\) s\(^{-1}\) and halving time of \(26\pm8\) minutes. The MAGIC observations were triggered by a high state in the optical and high energy (HE, E\(>100\) MeV) \(\gamma\)-ray bands. In this paper we present the MAGIC VHE \(\gamma\)-ray data together with multiwavelength data from radio, optical, X-rays, and HE \(\gamma\) rays from 2015 May 1 to July 31. Well-sampled multiwavelength data allow us to study the variability in detail and compare it to the other epochs when fast VHE \(\gamma\)-ray flares have been detected from this source. Interestingly, we find that the behaviour in radio, optical, X-rays and HE \(\gamma\)-rays is very similar to two other observed VHE \(\gamma\)-ray flares. In particular, also during this flare there was an indication of rotation of the optical polarization angle and of activity at the 43\,GHz core. These repeating patterns indicate a connection between the three events. We also test modelling of the spectral energy distribution, based on constraints from the light curves and VLBA observations, with two different geometrical setups of two-zone inverse Compton models. In addition we model the \(\gamma\)-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE \(\gamma\)-ray flare, but all have some tension with the multiwavelength observations.
We report on observations of the pulsar/Be star binary system PSR J2032+4127/MT91 213 in the energy range between $100\,\mathrm{GeV}$ and $20\,\mathrm{TeV}$ with the Very Energetic Radiation Imaging ...Telescope Array and Major Atmospheric Gamma Imaging Cherenkov telescope arrays. The binary orbit has a period of approximately 50 years, with the most recent periastron occurring on 2017 November 13. Our observations span from 18 months prior to periastron to one month after. A new point-like gamma-ray source is detected, coincident with the location of PSR J2032+4127/MT91 213. The gamma-ray light curve and spectrum are well characterized over the periastron passage. The flux is variable over at least an order of magnitude, peaking at periastron, thus providing a firm association of the TeV source with the pulsar/Be star system. Observations prior to periastron show a cutoff in the spectrum at an energy around $0.5\,\mathrm{TeV}$. This result adds a new member to the small population of known TeV binaries, and it identifies only the second source of this class in which the nature and properties of the compact object are firmly established. We compare the gamma-ray results with the light curve measured with the X-ray Telescope on board the Neil Gehrels Swift Observatory and with the predictions of recent theoretical models of the system. We conclude that significant revision of the models is required to explain the details of the emission that we have observed, and we discuss the relationship between the binary system and the overlapping steady extended source, TeV J2032+4130.
SNR G24.7+0.6 is a 9.5 kyrs radio and \(\gamma\)-ray supernova remnant evolving in a dense medium. In the GeV regime, SNR G24.7+0.6 (3FHL\,J1834.1--0706e/FGES\,J1834.1--0706) shows a hard spectral ...index ($\Gamma$$\sim\(2) up to \)200\(\,GeV, which makes it a good candidate to be observed with Cherenkov telescopes such as MAGIC. We observed the field of view of \snr\ with the MAGIC telescopes for a total of 31 hours. We detect very high energy \)\gamma\(-ray emission from an extended source located 0.34\degr\ away from the center of the radio SNR. The new source, named \mgc\ is detected up to 5\,TeV, and its spectrum is well-represented by a power-law function with spectral index of \)2.74 \pm 0.08\(. The complexity of the region makes the identification of the origin of the very-high energy emission difficult, however the spectral agreement with the LAT source and overlapping position at less than 1.5\)\sigma\( point to a common origin. We analysed 8 years of \fermi-LAT data to extend the spectrum of the source down to 60\,MeV. \fermi-LAT and MAGIC spectra overlap within errors and the global broad band spectrum is described by a power-law with exponential cutoff at \)1.9\pm0.5\(\,TeV. The detected \)\gamma$-ray emission can be interpreted as the results of proton-proton interaction between the supernova and the CO-rich surrounding.
We report the discovery of very high energy gamma-ray emission from the
direction of the SNR G54.1+0.3 using the VERITAS ground-based gamma-ray
observatory. The TeV signal has an overall significance ...of 6.8$\sigma$ and
appears point-like given the 5$^{arcminute}$ resolution of the instrument. The
integral flux above 1 TeV is 2.5% of the Crab Nebula flux and significant
emission is measured between 250 GeV and 4 TeV, well described by a power-law
energy spectrum dN/dE $\sim$ E$^{-\Gamma}$ with a photon index $\Gamma=
2.39\pm0.23_{stat}\pm0.30_{sys}$. We find no evidence of time variability among
observations spanning almost two years. Based on the location, the morphology,
the measured spectrum, the lack of variability and a comparison with similar
systems previously detected in the TeV band, the most likely counterpart of
this new VHE gamma-ray source is the PWN in the SNR G54.1+0.3. The measured
X-ray to VHE gamma-ray luminosity ratio is the lowest among all the nebulae
supposedly driven by young rotation-powered pulsars, which could indicate a
particle-dominated PWN.
We report the discovery of very high energy gamma-ray emission from the direction of the SNR G54.1+0.3 using the VERITAS ground-based gamma-ray observatory. The TeV signal has an overall significance ...of 6.8\(\sigma\) and appears point-like given the 5\(^{arcminute}\) resolution of the instrument. The integral flux above 1 TeV is 2.5% of the Crab Nebula flux and significant emission is measured between 250 GeV and 4 TeV, well described by a power-law energy spectrum dN/dE \(\sim\) E\(^{-\Gamma}\) with a photon index \(\Gamma= 2.39\pm0.23_{stat}\pm0.30_{sys}\). We find no evidence of time variability among observations spanning almost two years. Based on the location, the morphology, the measured spectrum, the lack of variability and a comparison with similar systems previously detected in the TeV band, the most likely counterpart of this new VHE gamma-ray source is the PWN in the SNR G54.1+0.3. The measured X-ray to VHE gamma-ray luminosity ratio is the lowest among all the nebulae supposedly driven by young rotation-powered pulsars, which could indicate a particle-dominated PWN.
The high-frequency-peaked BL-Lacertae object \objectname{1ES 0806+524}, at redshift z=0.138, was observed in the very-high-energy (VHE) gamma-ray regime by VERITAS between November 2006 and April ...2008. These data encompass the two-, and three-telescope commissioning phases, as well as observations with the full four-telescope array. \objectname{1ES 0806+524} is detected with a statistical significance of 6.3 standard deviations from 245 excess events. Little or no measurable variability on monthly time scales is found. The photon spectrum for the period November 2007 to April 2008 can be characterized by a power law with photon index \(3.6 \pm 1.0_{\mathrm{stat}} \pm 0.3_{\mathrm{sys}}\) between \(\sim\)300 GeV and \(\sim\)700 GeV. The integral flux above 300 GeV is \((2.2\pm0.5_{\mathrm{stat}}\pm0.4_{\mathrm{sys}})\times10^{-12}\:\mathrm{cm}^{2}\:\mathrm{s}^{-1}\) which corresponds to 1.8% of the Crab Nebula flux. Non contemporaneous multiwavelength observations are combined with the VHE data to produce a broadband spectral energy distribution that can be reasonably described using a synchrotron-self Compton model.
