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Missing Gamma-Ray Halos and the Need for New Physics in the Gamma-Ray Sky

Broderick, Avery E. and Tiede, Paul and Chang, Philip and Lamberts, Astrid and Pfrommer, Christoph and Puchwein, Ewald and Shalaby, Mohamad and Werhahn, Maria (2018) Missing Gamma-Ray Halos and the Need for New Physics in the Gamma-Ray Sky. Astrophysical Journal, 868 (2). Art. No. 87. ISSN 1538-4357.

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An intergalactic magnetic field (IGMF) stronger than 3 × 10^(−13) G would explain the lack of a bright, extended degree-scale, GeV-energy inverse Compton component in the gamma-ray spectra of TeV blazars. A robustly predicted consequence of the presence of such a field is the existence of degree-scale GeV-energy gamma-ray halos (gamma-ray bow ties) about TeV-bright active galactic nuclei, corresponding to more than half of all radio galaxies. However, the emitting regions of these halos are confined to and aligned with the direction of the relativistic jets associated with gamma-ray sources. Based on the orientation of radio jets, we align and stack corresponding degree-scale gamma-ray images of isolated Fanaroff–Riley class I and II objects and exclude the existence of these halos at overwhelming confidence, limiting the intergalactic field strength to <10^(−15) G for large-scale fields and progressively larger in the diffusive regime when the correlation length of the field becomes small in comparison to 1 Mpc. When combined with prior limits on the strength of the IGMF, this excludes a purely magnetic explanation for the absence of halos. Thus, it requires the existence of novel physical processes that preempt the creation of halos, e.g., the presence of beam-plasma instabilities in the intergalactic medium or a drastic cutoff of the very high-energy spectrum of these sources.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Broderick, Avery E.0000-0002-3351-760X
Tiede, Paul0000-0003-3826-5648
Chang, Philip0000-0002-2137-2837
Lamberts, Astrid0000-0001-8740-0127
Pfrommer, Christoph0000-0002-7275-3998
Shalaby, Mohamad0000-0001-9625-5929
Werhahn, Maria0000-0003-4984-4389
Additional Information:© 2018 The American Astronomical Society. Received 2018 August 8; revised 2018 September 29; accepted 2018 October 1; published 2018 November 26. A.E.B., P.T., and M.S. receive financial support from the Perimeter Institute for Theoretical Physics and the Natural Sciences and Engineering Research Council of Canada through a Discovery Grant and through the Alexander Graham Bell scholarship (P.T.). Research at the Perimeter Institute is supported by the Government of Canada through Industry Canada and by the Province of Ontario through the Ministry of Research and Innovation. A.E.B. thanks the Delaney family for their generous financial support via the Delaney Family John A. Wheeler Chair at Perimeter Institute. C.P., M.S., and M.W. acknowledge support by the European Research Council under ERC-CoG grant CRAGSMAN-646955. P.C. gratefully acknowledges support from NSF grant AST-1255469. A.L. receives financial support from an Alfred P. Sloan Research Fellowship, NASA ATP grant NNX14AH35G, and NSF Collaborative Research Grant 411920 and CAREER grant 1455342. E.P. acknowledges support by the Kavli Foundation.
Funding AgencyGrant Number
Perimeter Institute for Theoretical PhysicsUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Alexander Graham Bell ScholarshipUNSPECIFIED
Industry CanadaUNSPECIFIED
Ontario Ministry of Research and InnovationUNSPECIFIED
Delaney Family John A. Wheeler ChairUNSPECIFIED
European Research Council (ERC)646955
Alfred P. Sloan FoundationUNSPECIFIED
Kavli FoundationUNSPECIFIED
Subject Keywords:BL Lacertae objects: general – gamma rays: diffuse background – gamma rays: general – infrared: diffuse background – plasmas – radiation mechanisms: nonthermal
Issue or Number:2
Record Number:CaltechAUTHORS:20181126-134840597
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Official Citation:Avery E. Broderick et al 2018 ApJ 868 87
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91181
Deposited By: Tony Diaz
Deposited On:26 Nov 2018 22:10
Last Modified:03 Oct 2019 20:32

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