Contreras González, José Luis

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First Name
José Luis
Last Name
Contreras González
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Estructura de la Materia, Física Térmica y Electrónica
Física Atómica, Molecular y Nuclear
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Now showing 1 - 10 of 210
  • Publication
    Search for very high energy gamma-rays from the z=0.896 quasar 4C+55.17 with the MAGIC telescopes
    (Wiley, 2014-05) Antoranz Canales, Pedro; Barrio Uña, Juan Abel; Contreras González, José Luis; Fonseca González, Mª Victoria; López Moya, Marcos; Miranda Pantoja, José Miguel; Satalecka, Konstanzja; Scapin, Valeria
    The bright gamma-ray quasar 4C +55.17 is a distant source (z = 0.896) with a hard spectrum at GeV energies as observed by the Large Area Telescope (LAT) on board the Fermi satellite. This source is identified as a good source candidate for very high energy (VHE; > 30 GeV) gamma-rays. In general, VHE gamma-rays from distant sources provide a unique opportunity to study the extragalactic background light (EBL) and underlying astrophysics. The flux intensity of this source in the VHE range is investigated. Then, constraints on the EBL are derived from the attenuation of gamma-ray photons coming from the distant blazar. We searched for a gamma-ray signal from this object using the 35 h observations taken by the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes between 2010 November and 2011 January. No significant VHE gamma-ray signal was detected. We computed the upper limits of the integrated gamma-ray flux at the 95 per cent confidence level of 9.4 x 10(-12) and 2.5 x 10(-12) cm(-2) s(-1) above 100 and 200 GeV, respectively. The differential upper limits in four energy bins in the range from 80 to 500 GeV are also derived. The upper limits are consistent with the attenuation predicted by low-flux EBL models on the assumption of a simple power-law spectrum extrapolated from LAT data.
  • Publication
    Search for VHE gamma-ray emission from the globular cluster M13 with the Magic telescope
    (IOP Publishing, 2009-09-01) Antoranz Canales, Pedro; Barrio Uña, Juan Abel; Contreras González, José Luis; Fonseca González, Mª Victoria; Miranda Pantoja, José Miguel; Nieto, Daniel
    Based on MAGIC observations from 2007 June to July, we have obtained an integral upper limit to the VHE energy emission of the globular cluster M13 of F (E > 200 GeV) < 5.1 x 10(-12) cm(-2) s(-1), and differential upper limits for E > 140 GeV. Those limits allow us to constrain the population of millisecond pulsars within M13 and to test models for acceleration of leptons inside their magnetospheres and surrounding. We conclude that in M13 either millisecond pulsars are fewer than expected or they accelerate leptons less efficiently than predicted.
  • Publication
    Very high energy gamma-ray radiation from the stellar mass black hole binary Cygnus X-1
    (IOP Publishing, 2007-08-10) Antoranz Canales, Pedro; Barrio Uña, Juan Abel; Contreras González, José Luis; Fonseca González, Mª Victoria; López Moya, Marcos; Miranda Pantoja, José Miguel; Nieto, Daniel
    We report on the results from the observations in the very high energy band ( VHE; GeV) of the black E = 100 g hole X- ray binary ( BHXB) Cygnus X- 1. The observations were performed with the MAGIC telescope, for a total of 40 hr during 26 nights, spanning the period between 2006 June and November. Searches for steady gamma - ray signals yielded no positive result, and upper limits to the integral flux ranging between 1% and 2% of the Crab Nebula flux, depending on the energy, have been established. We also analyzed each observation night independently, obtaining evidence of gamma- ray signals at the 4.0 j significance level ( 3.2 j after trial correction) for 154 minutes of effective on- time ( EOT) on September 24 between 20: 58 and 23: 41 UTC, coinciding with an X- ray flare seen by RXTE, Swift, and INTEGRAL. A search for faster- varying signals within a night resulted in an excess with a significance of 4.9 j ( 4.1 j after trial correction) for 79 minutes EOT between 22: 17 and 23: 41 UTC. The measured excess is compatible with a pointlike source at the position of Cygnus X- 1 and excludes the nearby radio nebula powered by its relativistic jet. The differential energy spectrum is well fitted by an unbroken power law described as dN/(dA dt dE) = ( 2.3 +/- 0.6)* 10 ( E/1TeV). This is the first experimental evidence of VHE emission from a stellar mass black hole and therefore from a confirmed accreting X- ray binary.
  • Publication
    The june 2008 flare of Markarian 421 from optical to TeV energies
    (IOP Publishing, 2009-01-20) Antoranz Canales, Pedro; Barrio Uña, Juan Abel; Contreras González, José Luis; Fonseca González, Mª Victoria; Miranda Pantoja, José Miguel; Nieto, Daniel
    We present optical, X-ray, high-energy ((sic) 30 GeV) and very high energy ((sic) 100 GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high-energy gamma-ray signal was detected by AGILE with root TS = 4.5 between June 9 and 15, with F(E > 100 MeV) = 42(-12)(+14) x 10(-8) photons cm(-2) s(-1). This flaring state is brighter than the average flux observed by EGRET by a factor of similar to 3, but still consistent with the highest EGRET flux. In hard X-rays (20-60 keV) SuperAGILE resolved a five-day flare (June 9-15) peaking at similar to 55 mCrab. SuperAGILE, RXTE/ASM and Swift/BAT data show a correlated flaring structure between soft and hard X-rays. Hints of the same flaring behavior are also detected in the simultaneous optical data provided by the GASP-WEBT. A Swift/XRT observation near the flaring maximum revealed the highest 2-10 keV flux ever observed from this source, of 2.6 x 10(-9) erg cm(-2) s(-1) (i.e. > 100 mCrab). A peak synchrotron energy of similar to 3 keV was derived, higher than typical values of similar to 0.5-1 keV. VHE observations with MAGIC and VERITAS between June 6 and 8 showed the flux peaking in a bright state, well correlated with the X-rays. This extraordinary set of simultaneous data, covering a 12-decade spectral range, allowed for a deep analysis of the spectral energy distribution as well as of correlated light curves. The gamma-ray flare can be interpreted within the framework of the synchrotron self-Compton model in terms of a rapid acceleration of leptons in the jet.
  • Publication
    An intermittent extreme BL Lac: MWL study of 1ES 2344+514 in an enhanced state
    (Wiley, 2020-08) Barrio Uña, Juan Abel; Contreras González, José Luis; Fonseca González, Mª Victoria; Hoang, Kim Dinh; López Moya, Marcos; Miener, Tjark; Miranda Pantoja, José Miguel; Morcuende, D.; Peñil del Campo, Pablo; Saha, Lab; otros, ...
    Extreme high-frequency BL Lacs (EHBL) feature their synchrotron peak of the broad-band spectral energy distribution (SED) at nu(s) >= 10(17) Hz. The BL Lac object 1ES 2344+514 was included in the EHBL family because of its impressive shift of the synchrotron peak in 1996. During the following years, the source appeared to be in a low state without showing any extreme behaviours. In 2016 August, 1ES 2344+514 was detected with the groundbased gamma-ray telescope FACT during a high gamma-ray state, triggering multiwavelength (MWL) observations. We studied the MWL light curves of 1ES 2344+514 during the 2016 flaring state, using data from radio to very-high-energy (VHE) gamma-rays taken with OVRO, KAIT, KVA, NOT, some telescopes of the GASP-WEBT collaboration at the Teide, Crimean, and St. Petersburg observatories, Swift-UVOT, Swift-XRT, Fermi-LAT, FACT, and MAGIC. With simultaneous observations of the flare, we built the broad-band SED and studied it in the framework of a leptonic and a hadronic model. The VHE gamma-ray observations show a flux level of 55 per cent of the Crab Nebula flux above 300 GeV, similar to the historical maximum of 1995. The combination of MAGIC and Fermi-LAT spectra provides an unprecedented characterization of the inverse-Compton peak for this object during a flaring episode. The Gamma index of the intrinsic spectrum in the VHE gamma-ray band is 2.04 +/- 0.12(stat) +/- 0.15(sys). We find the source in an extreme state with a shift of the position of the synchrotron peak to frequencies above or equal to 1018 Hz.
  • Publication
    Detection of the Geminga pulsar with MAGIC hints at a power-law tail emission beyond 15 GeV
    (EDP Sciencies, 2020-11-20) Baquero Larriva, Orlando Andrés; Barrio Uña, Juan Abel; Contreras González, José Luis; Fonseca González, Mª Victoria; Hoang, Kim Dinh; López Moya, Marcos; Miener, Tjark; Morcuende, D.; Peñil del Campo, Pablo; Saha, Lab
    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, similar to 80 h 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 +/- 0.54, 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.
  • Publication
    The relevance of fluorescence radiation in Cherenkov telescopes
    (IOP Publishing Ltd, 2019) Arqueros Martínez, Fernando; Rosado Vélez, Jaime; Morcuende Parrilla, Daniel; Contreras González, José Luis
    Cherenkov telescopes are also sensitive to the atmospheric fluorescence produced by the extensive air showers. However this contribution is neglected by the reconstruction algorithms of imaging air Cherenkov telescopes IACTs and wide-angle Cherenkov detectors WACDs. In this paper we evaluate the fluorescence contamination in the Cherenkov signals from MC simulations in both kinds of Cherenkov telescopes and for some typical observational situations. Results for an observation level of 2200 m a.s.l. are shown. In addition, the feasibility and capabilities of IACTs working as fluorescence telescopes are discussed with the assistance of some geometrical calculations.
  • Publication
    Constraining very-high-energy and optical emission from FRB 121102 with the MAGIC telescopes
    (Oxford Univ Press, 2018-12) Barrio Uña, Juan Abel; Contreras González, José Luis; Domínguez Díaz, Alberto; Carreto Fidalgo, David Friedrich; Fonseca Gonzáez, Victoria; Hoang, Kim Dinh; López Moya, Marcos; Nievas Rosillo, Mireia; Peñil del Campo, Pablo; Saha, Lab; otros, ...
    Fast radio bursts (FRBs) are bright flashes observed typically at GHz frequencies with millisecond duration, whose origin is likely extragalactic. Their nature remains mysterious, motivating searches for counterparts at other wavelengths. FRB 121102 is so far the only source known to repeatedly emit FRBs and is associated with a host galaxy at redshift z similar or equal to 0.193. We conducted simultaneous observations of FRB 121102 with the Arecibo and MAGIC telescopes during several epochs in 2016-2017. This allowed searches for millisecond time-scale burst emission in very-high-energy (VHE) gamma-rays as well as the optical band. While a total of five FRBs were detected during these observations, no VHE emission was detected, neither of a persistent nature nor burst-like associated with the FRBs. The average integral flux upper limits above 100 GeV at 95 percent confidence level are 6.6 x 10(-12) photons cm(-2) s(-1) (corresponding to luminosity L-VHE < 10 (45) erg s(-1)) over the entire observation period, and 1.2 x 10(-7) photons cm(-2) s(-1 )(L-VHE < 10 (49) erg s( -1)) over the total duration of the five FRBs. We constrain the optical U-band flux to be below 8.6 mJy at 5 sigma level for 1-ms intervals around the FRB arrival times. A bright burst with U-band flux 29 mJy and duration similar to 12 ms was detected 4.3 s before the arrival of one FRB. However, the probability of spuriously detecting such a signal within the sampled time space is 1.5 percent (2.2, post-trial), i.e. consistent with the expected background. We discuss the implications of the obtained upper limits for constraining FRB models.
  • Publication
    Probing the very high energy gamma-ray spectral curvature in the blazar PG 1553+113 with the MAGIC telescopes
    (Oxford University Press, 2015-07-11) Antoranz Canales, Pedro; Barrio Uña, Juan Abel; Bonnefoy, Simon Francois Albert; Contreras González, José Luis; Fonseca González, Mª Victoria; López Moya, Marcos; Miranda Pantoja, José Miguel; Satalecka, Konstanzja; Scapin, Valeria
    PG 1553+113 is a very-high-energy (VHE, E > 100 GeV) γ-ray emitter classified as a BL Lac object. Its redshift is constrained by intergalactic absorption lines in the range 0.4 < z < 0.58. The MAGIC telescopes have monitored the source’s activity since 2005. In early 2012, PG 1553+113 was found in a high-state, and later, in April of the same year, the source reached its highest VHE flux state detected so far. Simultaneous observations carried out in X-rays during 2012 April show similar flaring behaviour. In contrast, the γ-ray flux at E < 100 GeV observed by Fermi-LAT is compatible with steady emission. In this paper, a detailed study of the flaring state is presented. The VHE spectrum shows clear curvature, being well fitted either by a power law with an exponential cut-off or by a log-parabola. A simple power-law fit hypothesis for the observed shape of the PG 1553+113 VHE γ-ray spectrum is rejected with a high significance (fit probability P=2.6 ×10−6). The observed curvature is compatible with the extragalactic background light (EBL) imprint predicted by current generation EBL models assuming a redshift z ∼ 0.4. New constraints on the redshift are derived from the VHE spectrum. These constraints are compatible with previous limits and suggest that the source is most likely located around the optical lower limit, z = 0.4, based on the detection of Lyα absorption. Finally, we find that the synchrotron self-Compton (SSC) model gives a satisfactory description of the observed multi-wavelength spectral energy distribution during the flare.
  • Publication
    Gamma-Ray excess from a stacked sample of high- and intermediate-frequency peaked blazars observed with the MAGIC telescope
    (IOP Publishing, 2011-03-10) Antoranz Canales, Pedro; Barrio Uña, Juan Abel; Contreras González, José Luis; Fonseca González, Mª Victoria; Miranda Pantoja, José Miguel; Nieto, Daniel
    Between 2004 and 2009, a sample of 28 X-ray selected high-and intermediate-frequency peaked blazars with an X-ray flux larger than 2 mu Jy at 1 keV in the redshift range from 0.018 to 0.361 was observed with the MAGIC telescope at energies above 100 GeV. Seven among them were detected and the results of these observations are discussed elsewhere. Here we concentrate on the remaining 21 blazars which were not detected during this observation campaign and present the 3 sigma (99.7%) confidence upper limits on their flux. The individual flux upper limits lie between 1.6% and 13.6% of the integral flux from the Crab Nebula. Applying a stacking method to the sample of non-detections with a total of 394.1 hr exposure time, we find evidence for an excess with a cumulative significance of 4.9 standard deviations. It is not dominated by individual objects or flares, but increases linearly with the observation time as for a constant source with an integral flux level of similar to 1.5% of that observed from the Crab Nebula above 150 GeV.