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Register a new userDetection of very-high energy gamma-ray emission from NGC 1275 by the MAGIC telescopes
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MAGIC Collaboration: J. Aleksic
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We report on the detection of very-high energy (VHE, E>100 GeV) gamma-ray emission from NGC 1275, the central radio galaxy of the Perseus cluster of galaxies. The source has been detected by the MAGIC telescopes with a statistical significance of 6.6 sigma above 100 GeV in 46 hr of stereo observations carried out between August 2010 and February 2011. The measured differential energy spectrum between 70 GeV and 500 GeV can be described by a power law with a steep spectral index of Gamma=-4.1+/-0.7stat+/-0.3syst, and the average flux above 100 GeV is F_{gamma}=(1.3+/-0.2stat+/-0.3syst) x 10^-11 cm^-2 s^-1. These results, combined with the power-law spectrum measured in the first two years of observations by the Fermi-LAT above 100 MeV, with a spectral index of Gamma ~ -2.1, strongly suggest the presence of a break or cut-off around tens of GeV in the NGC 1275 spectrum. The light curve of the source above 100 GeV does not show hints of variability on a month time scale. Finally, we report on the nondetection in the present data of the radio galaxy IC 310, previously discovered by the Fermi-LAT and MAGIC. The derived flux upper limit F^{U.L.}_{gamma} (>300 GeV)=1.2 x 10^-12 cm^-2 s^-1 is a factor ~ 3 lower than the mean flux measured by MAGIC between October 2009 and February 2010, thus confirming the year time-scale variability of the source at VHE.
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The number of known very high energy (VHE) blazars is $sim,50$, which is very small in comparison to the number of blazars detected in other frequencies. This situation is a handicap for population studies of blazars, which emit about half of their luminosity in the $gamma$-ray domain. Moreover, VHE blazars, if distant, allow for the study of the environment that the high-energy $gamma$-rays traverse in their path towards the Earth, like the extragalactic background light (EBL) and the intergalactic magnetic field (IGMF), and hence they have a special interest for the astrophysics community. We present the first VHE detection of 1ES,0033+595 with a statistical significance of 5.5,$sigma$. The VHE emission of this object is constant throughout the MAGIC observations (2009 August and October), and can be parameterized with a power law with an integral flux above 150 GeV of $(7.1pm1.3)times 10^{-12} {mathrm{ph,cm^{-2},s^{-1}}}$ and a photon index of ($3.8pm0.7$). We model its spectral energy distribution (SED) as the result of inverse Compton scattering of synchrotron photons. For the study of the SED we used simultaneous optical R-band data from the KVA telescope, archival X-ray data by textit{Swift} as well as textit{INTEGRAL}, and simultaneous high energy (HE, $300$,MeV~--~$10$,GeV) $gamma$-ray data from the textit{Fermi} LAT observatory. Using the empirical approach of Prandini et al. (2010) and the textit{Fermi}-LAT and MAGIC spectra for this object, we estimate the redshift of this source to be $0.34pm0.08pm0.05$. This is a relevant result because this source is possibly one of the ten most distant VHE blazars known to date, and with further (simultaneous) observations could play an important role in blazar population studies, as well as future constraints on the EBL and IGMF.
We report on the detection with the MAGIC telescopes of very high energy gamma-rays from IC 310, a head-tail radio galaxy in the Perseus galaxy cluster, observed during the interval November 2008 to February 2010. The Fermi satellite has also detected this galaxy. The source is detected by MAGIC at a high statistical significance of 7.6sigma in 20.6 hr of stereo data. The observed spectral energy distribution is flat with a differential spectral index of -2.00 pm 0.14. The mean flux above 300 GeV, between October 2009 and February 2010, (3.1 pm 0.5)x10^{-12} cm^{-2} s^{-1}, corresponds to (2.5 pm 0.4)% of Crab Nebula units. Only an upper limit, of 1.9% of Crab Nebula units above 300 GeV, was obtained with the 2008 data. This, together with strong hints (>3sigma) of flares in the middle of October and November 2009, implies that the emission is variable. The MAGIC results favour a scenario with the very high energy emission originating from the inner jet close to the central engine. More complicated models than a simple one-zone SSC scenario, e.g. multi-zone SSC, external Compton or hadronic, may be required to explain the very flat spectrum and its extension over more than three orders of magnitude in energy.
Context. 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, 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 sources 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 broad band 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.
Motivated by the Costamante & Ghisellini (2002) predictions we investigated if the blazar 1ES 1727+502 (z=0.055) is emitting very high energy (VHE, E>100 GeV) gamma rays. We observed the BL Lac object 1ES 1727+502 in stereoscopic mode with the two MAGIC telescopes during 14 nights between May 6th and June 10th 2011, for a total effective observing time of 12.6 hours. For the study of the multiwavelength spectral energy distribution (SED) we use simultaneous optical R-band data from the KVA telescope, archival UV/optical and X-ray observations by instruments UVOT and XRT on board of the Swift satellite and high energy (HE, 0.1 GeV - 100 GeV) gamma-ray data from the Fermi-LAT instrument. We detect, for the first time, VHE gamma-ray emission from 1ES 1727+502 at a statistical significance of 5.5 sigma. The integral flux above 150 GeV is estimated to be (2.1pm0.4)% of the Crab Nebula flux and the de-absorbed VHE spectrum has a photon index of (2.7pm0.5). No significant short-term variability was found in any of the wavebands presented here. We model the SED using a one-zone synchrotron self-Compton model obtaining parameters typical for this class of sources.
The acceleration of particles up to GeV or higher energies in microquasars has been the subject of considerable theoretical and observational efforts in the past few years. Sco X-1 is a microquasar from which evidence of highly energetic particles in the jet has been found when it is in the so-called Horizontal Branch (HB), a state when the radio and hard X-ray fluxes are higher and a powerful relativistic jet is present. Here we present the first very high energy gamma-ray observations of Sco X-1 obtained with the MAGIC telescopes. An analysis of the whole dataset does not yield a significant signal, with 95% CL flux upper limits above 300 GeV at the level of 2.4x10^{-12} ph/cm^2/s. Simultaneous RXTE observations were conducted to search for TeV emission during particular X-ray states of the source. A selection of the gamma-ray data obtained during the HB based on the X-ray colors did not yield a signal either, with an upper limit of 3.4x10^{-12} ph/cm^2/s. These upper limits place a constraint on the maximum TeV luminosity to non-thermal X-ray luminosity of L_{VHE}/L_{ntX}<0.02, that can be related to a maximum TeV luminosity to jet power ratio of L_{VHE}/L_{j}<10^{-3}. Our upper limits indicate that the underlying high-energy emission physics in Sco X-1 must be inherently different from that of the hitherto detected gamma-ray binaries.
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