MAGIC long-term study of the distant TeV blazar PKS 1424+240 in a multiwavelength context (original) (raw)
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The Astrophysical …, 2010
Discovery of very high energy gamma rays from PKS 1424+240 1 and multiwavelength constraints on its redshift 2 VERITAS collaboration: V. A. Acciari v1 , E. Aliu v2 , T. Arlen v3 , T. Aune v4 , 3 M. Bautista v5 , M. Beilicke v6 , W. Benbow v1 , M. Böttcher v7 , D. Boltuch v2 , 4 S. M. Bradbury v8 , J. H. Buckley v6 , V. Bugaev v6 , K. Byrum v9 , A. Cannon v10 , 5 A. Cesarini v11 , Y. C. Chow v3 , L. Ciupik v12 , P. Cogan v5 , W. Cui v13 , C. Duke v14 , 6 A. Falcone v15 , J. P. Finley v13 , G. Finnegan v16 , L. Fortson v12 , A. Furniss v4, * , N. Galante v1 , 7 D. Gall v13 , G. H. Gillanders v11 , S. Godambe v16 , J. Grube v10 , R. Guenette v5 , G. Gyuk v12 , 8 D. Hanna v5 , J. Holder v2 , C. M. Hui v16 , T. B. Humensky v17 , P. Kaaret v18 , N. Karlsson v12 , 9 M. Kertzman v19 , D. Kieda v16 , A. Konopelko v20 , H. Krawczynski v6 , F. Krennrich v21 , 10 M. J. Lang v11 , S. LeBohec v16 , G. Maier v5 , S. McArthur v6 , A. McCann v5 , M. McCutcheon v5 , 11 J. Millis v13,v22 , P. Moriarty v23 , T. Nagai v21 , R. A. Ong v3 , A. N. Otte v4, * , D. Pandel v18 , 12 J. S. Perkins v1 , A. Pichel v24 , M. Pohl v21 , J. Quinn v10 , K. Ragan v5 , L. C. Reyes v25 , 13 P. T. Reynolds v26 , E. Roache v1 , H. J. Rose v8 , M. Schroedter v21 , G. H. Sembroski v13 , 14 G. Demet Senturk v27 , A. W. Smith v9 , D. Steele v12 , S. P. Swordy v17 , M. Theiling v1 , 15 S. Thibadeau v6 , A. Varlotta v13 , V. V. Vassiliev v3 , S. Vincent v16 , R. G. Wagner v9 , 16 S. P. Wakely v17 , J. E. Ward v10 , T. C. Weekes v1 , A. Weinstein v3 , T. Weisgarber v17 , 17 D. A. Williams v4 , S. Wissel v17 , M. Wood v3 , B. Zitzer v13 , 18 Fermi LAT collaboration: A.
2014
Aims. Among more than fifty blazars detected in very high energy (VHE, E>100GeV) γ-rays, only three belong to the subclass of Flat Spectrum Radio Quasars (FSRQs). The detection of FSRQs in the VHE range is challenging, mainly because of their soft spectra in the GeV-TeV regime. MAGIC observed PKS 1510-089 (z=0.36) starting 2012 February 3 until April 3 during a high activity state in the high energy (HE, E>100 MeV) γ-ray band observed by AGILE and Fermi. MAGIC observations result in the detection of a source with significance of 6.0 standard deviations (σ). We study the multifrequency behaviour of the source at the epoch of MAGIC observation, collecting quasi-simultaneous data at radio and optical (GASP-WEBT and F-Gamma collaborations, REM, Steward, Perkins, Liverpool, OVRO and VLBA telescopes), X-ray (Swift satellite) and HE γ-ray frequencies.
Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021)
OT 081 is a luminous blazar well known for its variability in many energy bands. The veryhigh-energy (VHE; > 100 GeV) gamma-ray emission from the source was discovered by MAGIC and H.E.S.S. during flaring activity in July 2016, after a trigger from the Large Area Telescope (LAT) onboard the Fermi satellite. By analysing the multiwavelength light curves and the broadband spectral energy distribution (SED), we study the activity of the source and investigate four individual states of activity in the window from MJD 57575 to 57602. The intrinsic gammaray spectrum can be described by a power law with spectral indices of 3.27 ± 0.44 (MAGIC) and 3.39 ± 0.58 (H.E.S.S.) over energy ranges 60-300 GeV and 120-500 GeV, respectively. The combined contemporaneous high-energy (HE; > 100 MeV) through VHE SED shows curvature and can be described by a log-parabola shape. A simple one-zone synchrotron self-Compton (SSC) model is not sufficient to describe the broadband SED. The presence of broad emission lines in the optical spectrum of the source challenges the categorisation of OT 081 as a BL Lac and, together with the emission scenarios tested, points to the possibility that the source is transitional in nature between a BL Lac and a flat-spectrum radio quasar.
Monthly Notices of the Royal Astronomical Society, 2015
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 cutoff 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 model gives a satisfactory description of the observed multiwavelength spectral energy distribution during the flare.
Monthly Notices of the Royal Astronomical Society, 2015
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 cutoff 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.
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 the 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 ). For the first time a VHE spectral shape compatible with an exponential decay has been found in a distant blazar (z > 0.2). The observed curvature is compatible with the extragalactic background light (EBL) imprint predicted by the current generation of EBL models assuming a redshift z ∼ 0.4. New constraints on the redshift were 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. 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.
On the origin of theγ-ray emission from the flaring blazar PKS 1222+216
Astronomy & Astrophysics, 2011
The flat-spectrum radio quasar PKS 1222+216 (4C+21.35, z = 0.432) was detected in the very high energy γ-ray band by MAGIC during a highly active γ-ray phase following an alert by the Large Area Telescope (LAT) onboard Fermi. Its relatively hard spectrum (70-400 GeV photon index Γ = 2.7± 0.3) without a cut off, together with its observed variability on a timescale of ∼10 min challenges standard emission models. In particular, if the emission originates in a portion of the relativistic jet located inside the broad line region (BLR), severe absorption of γ rays above a few tens of GeV is expected to be caused by the γγ → e ± process. These observations therefore imply that there is a very compact (R b ∼ 5 × 10 14 cm) and rapidly moving blob located far beyond the BLR radius (to avoid the gamma-ray absorption through pair production) that is responsible for the rapidly varying high energy flux. However, the long-term (day-week) coherent evolution of the GeV flux recorded by LAT indicates that there could also be a substantial contribution from another, larger emission region. We model the spectral energy distribution of PKS 1222+216 during the epoch of the MAGIC detection assuming three different scenarios, namely: (1) a one-zone model considering only the emission from a compact blob outside the BLR; (2) a two-zone model consisting of a compact blob plus an emitting region encompassing the whole jet cross-section located outside the BLR; and (3) a two-zone model with the jet emitting region inside the BLR. In all cases we find that the high-energy emission from the compact blob is dominated by the inverse Compton scattering of the infrared thermal radiation of the dusty torus. Furthermore, both regions are matter-dominated, with the Poynting flux providing a negligible contribution to the total jet power. These results do not support models in which the compact blob is the result of reconnection events inside the jet or "needles" of highenergy electrons accelerated close to the BH. The observational framework and our radiative models might instead be compatible with scenarios in which the jet is re-collimated and focussed at large distances from the central BH.
Discovery of TeV γ -ray emission from PKS 0447-439 and derivation of an upper limit on its redshift
Astronomy & Astrophysics, 2013
Very high-energy γ-ray emission from PKS 0447−439 was detected with the H.E.S.S. Cherenkov telescope array in December 2009. This blazar is one of the brightest extragalactic objects in the Fermi bright source list and has a hard spectrum in the MeV to GeV range. In the TeV range, a photon index of 3.89 ± 0.37 (stat) ±0.22 (sys) and a flux normalisation at 1 TeV, Φ 1 TeV = (3.5 ± 1.1(stat) ± 0.9(sys)) × 10 −13 cm −2 s −1 TeV −1 were found. The detection with H.E.S.S. triggered observations in the X-ray band with the Swift and RXTE telescopes. Simultaneous UV and optical data from Swift UVOT and data from the optical telescopes ATOM and ROTSE are also available. The spectrum and light curve measured with H.E.S.S. are presented and compared to the multi-wavelength data at lower energies. A rapid flare is seen in the Swift XRT and RXTE data, together with a flux variation in the UV band, at a time scale of the order of one day. A firm upper limit of z < 0.59 on the redshift of PKS 0447−439 is derived from the combined Fermi-LAT and H.E.S.S. data, given the assumptions that there is no upturn in the intrinsic spectrum above the Fermi-LAT energy range and that absorption on the extragalactic background light (EBL) is not weaker than the lower limit provided by current models. The spectral energy distribution is well described by a simple one-zone synchrotron self-Compton scenario, if the redshift of the source is less than z 0.4.
The Astrophysical Journal, 2015
The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5 σ using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability time scale is estimated to be 6.4 ± 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy.