The Dragonfly nebula is a Vela-like Pulsar Wind Nebula (PWN) in the Cygnus region powered by the spin down of PSR J2021+3651. In X-rays, the inner nebula is a few arcseconds across, whereas at TeV energies VERITAS and HAWC has observed extended emission much larger than the extension in X-rays. The TeV gamma-ray source HAWC J2019+368 was originally discovered in 2007 by the Milagro Observatory and has been associated with this pulsar. Recent work has shown hints of energy dependent morphology for the source at TeV energies, supporting the interpretation of the gamma-ray emission being due to Inverse Compton scattering of electrons and positrons from interstellar radiation fields and cosmic microwave background photons. The hard spectral index and spectral softening above 30 TeV of the source are consistent with Klein- Nishina suppression of the electron-photon cross-section at high energies. We will present our most recent studies in modeling and analysis of HAWC J2019+368, explaining the X-ray and TeV emission up to the highest energies using the latest data from the HAWC Observatory

Brisbois, Chad

Joshi, V.

English

Michigan Technological University

Michigan Technological University Digital Commons @ Michigan Tech Michigan Tech Publications 2019 Electron spectrum of the dragonfly pulsar wind nebula from X-ray to TeV Chad Brisbois Michigan Technological University, cbrisboi@mtu.edu V. Joshi Erlangen Centre for Astroparticle Physics Follow this and additional works at: https://digitalcommons.mtu.edu/michigantech-p  Part of the Physics Commons Recommended Citation Brisbois, C., & Joshi, V. (2019). Electron spectrum of the dragonfly pulsar wind nebula from X-ray to TeV. Proceedings of Science, 358. Retrieved from: https://digitalcommons.mtu.edu/michigantech-p/783 Follow this and additional works at: https://digitalcommons.mtu.edu/michigantech-p  Part of the Physics Commons PoS(ICRC2019)639Electron Spectrum of the Dragonfly Pulsar WindNebula from X-ray to TeVChad Brisbois∗Michigan Technological University, Houghton, Michigan, USAE-mail: cbrisboi@mtu.eduVikas JoshiFriedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen Centre for Astroparticle Physics,Erlangen, GermanyE-mail: vikas.joshi@fau.deFor the HAWC CollaborationFull author list and acknowledgements:https://www.hawc-observatory.org/collaboration/icrc2019.phpSee also PoS(ICRC2019)1177The Dragonfly nebula is a Vela-like Pulsar Wind Nebula (PWN) in the Cygnus region poweredby the spin down of PSR J2021+3651. In X-rays, the inner nebula is a few arcseconds across,whereas at TeV energies VERITAS and HAWC has observed extended emission much largerthan the extension in X-rays. The TeV gamma-ray source HAWC J2019+368 was originallydiscovered in 2007 by the Milagro Observatory and has been associated with this pulsar. Recentwork has shown hints of energy dependent morphology for the source at TeV energies, supportingthe interpretation of the gamma-ray emission being due to Inverse Compton scattering of electronsand positrons from interstellar radiation fields and cosmic microwave background photons. Thehard spectral index and spectral softening above 30 TeV of the source are consistent with Klein-Nishina suppression of the electron-photon cross-section at high energies. We will present ourmost recent studies in modeling and analysis of HAWC J2019+368, explaining the X-ray andTeV emission up to the highest energies using the latest data from the HAWC Observatory.36th International Cosmic Ray Conference -ICRC2019-July 24th - August 1st, 2019Madison, WI, U.S.A.∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). http://pos.sissa.it/PoS(ICRC2019)639Electron Spectrum of the Dragonfly PWN Chad Brisbois1. IntroductionPSR J2021+3651 was originally discovered in 2002 as a followup to an EGRET source [1].Soon after, its X-ray PWN was discovered and found to have a double torus structure, a featureonly previously found in the Vela PWN [2, 3]. Milagro first observed extended TeV emissionin this region, tentatively associating MGRO J2019+37 with PSR J2021+3651, but the measuredmorphology was too extended and angular resolution too wide to make firm conclusions [4]. VERI-TAS observed this region and discovered two sources, VER J2019+368 and VER J2016+371 [5, 6].VER J2019+368 is coincident with PSR J2021+3651 and Sh 2-104 (an HII region), although fol-lowup observations show that Sh 2-104 is unlikely to contribute significantly to the observed TeVemission [7]. Two publications by the VERITAS collaboration show that VER J2019+368 has anextended, asymmetric morphology [5, 6]. The VERITAS collaboration has reported a power lawenergy spectrum up to ∼ 40 TeV for VER J2019+368, with spectral softening at higher energiesnot being significantly preferred [6]. Previous publications by the VERITAS Collaboration haveassociated VER J2016+371 with the supernova remnant CTB 87, although it is also possible thatthere is some contribution from the BL Lac object QSO J2015+371[6]. The ARGO-YBJ exper-iment saw no significant excess coincident with VER J2016+371 [8]. The HAWC Collaborationhas recently developed energy estimation techniques, which allow for the measurement of γ-rayenergies in excess of 100 TeV [9]. HAWC J2019+368 is currently one of the only detected sourcesin the sky with emitting significant flux in γ-rays above 100 TeV [10]. Understanding the physi-cal processes giving rise to this γ-ray emission is important to understanding the limits of particleacceleration in pulsar powered systems.2. Analysis and Description of the RegionOriginally reported as a single source 2HWC J2019+367[11], this dedicated analysis has iden-tified two sources, HAWC J2019+368 and HAWC J2016+371. A significance map of the regionassuming an α = −2.7 spectrum with the nearby TeVCat sources and ROI labeled can be seenin Figure 1. The dataset analyzed included 1038 days of data using the ground parameter energyestimator (more details in [9]).The analysis was performed in a 3◦ Region Of Interest (ROI) centered at RA, Dec = 304.8690◦,36.7710◦. The fit was performed using the hawc_hal plugin for 3ML [12]. The nominal modelconsists of two physical sources, and one background source which accounts for sources leakinginto the ROI. HAWC J2019+368 is the primary focus of this work, and HAWC J2016+371 wasfound in the course of the analysis. HAWC J2019+368 is modeled as an asymmetric Gaussiansource with a log parabola energy spectrum. HAWC J2016+371 is modeled as a point source witha power law energy spectrum. The optimized morphological parameters for HAWC J2019+368 aresimilar to what the VERITAS collaboration has reported [5, 6]. The energy spectrum of HAWCJ2019+368 is given in Figure 4. We scale the flux measured by VERITAS [6] up to the size of themorphology measured by VERITAS, rather than the extraction region of 0.23◦in Figure 4.Prior to its inclusion in this analysis, HAWC J2016+371 was first seen as significant excessin the residual map after subtracting HAWC J2019+368. Its inclusion in the model significantly1PoS(ICRC2019)639Electron Spectrum of the Dragonfly PWN Chad BrisboisFigure 1: Significance map of the Cygnus region as seen by HAWC with TeV sources labeled. This pointsource map is produced by fitting the flux normalization to a power law spectrum with a fixed index ofα =−2.7 at each pixel on the sky. The ROI for the analysis detailed here is indicated by the green contour.improved the description of the ROI (∆T S = 35). After including the uniform background, thesignificance is T S = 27 and T S = 984 for HAWC J2016+371 and HAWC J2019+368, respectively.2.1 Energy Dependent MorphologyWe searched for energy dependent morphology in the HAWC data. Energy dependent mor-phology is a signature of leptonic origin for γ-ray emission, because of electrons relatively fastcooling time relative to hadrons [13]. Considering longitudinal profiles along the major axis ofHAWC J2019+368, there are hints of decreasing extent with increasing energy (See Figure 3). Theprofiles can be seen in Figure 2, using the position of PSR J2021+3651 as the zero point. In Figure3, we see a trend of decreasing size with increasing energy, but it is not statistically significant.3. Modeling of Electron spectrumAssuming the γ-ray emission is due to inverse compton scattering, we use the naima package[14, 15]. The electron spectrum was assumed to follow a broken power law with an exponentialcutoff following the work in [16]. We fit the normalization and cutoff energies, but left the indices (-2.1 and -3.1) and break energy (80 TeV) fixed to maintain consistency with the X-ray measurementsfrom Suzaku [16]. The inverse Compton (IC) band in Figure 4 represents the 68% containment2PoS(ICRC2019)639Electron Spectrum of the Dragonfly PWN Chad BrisboisPSF' [degree]1− 0.5− 0 0.5 1051015Distance to the PSR J2021+3651 [degree]2− 0 2051015 56.2 to 316.2 TeV PSF' [degree]1− 0.5− 0 0.5 10204060Distance to the PSR J2021+3651 [degree]2− 0 20204060 10.0 to 56.2 TeV PSF' [degree]1− 0.5− 0 0.5 150−050100Distance to the PSR J2021+3651 [degree]2− 0 250−0501001.7 to 10.0 TeV PSF' [degree]1− 0.5− 0 0.5 1200−0200Distance to the PSR J2021+3651 [degree]2− 0 2# Excess Counts200−02000.3 to 1.7 TeVPreliminaryFigure 2: Longitudinal profile plot along the major axis of HAWC J2019+368. The profile is 0.7◦×6◦with 40 bins. The Point Spread Function (PSF’) in each energy band is given on the right side in blue, forcomparison to the fit in red on the profile. It is the width(σ ) of a 1D Gaussian from the longitudinal profileof that point source about an arbitrary axis. It is obtained from a simulated point source with a spectral indexof −2.2. Note the different scales for excess counts in each energy band.region of the inverse Compton spectrum for the present-day electron spectrum to HAWC data.The interstellar radiation fields included were the Cosmic Microwave Background and a 30 Kblackbody field with an energy density of 0.3 eV cm−3. Alternative spectral models for the presentday electron spectrum are under study. This fit also allows for the calculation of the energy in theelectrons (calculated above 1 MeV) emitted by PSR J2021+3651. The total energy of the electronsin the spectrum predicts ∼ 18% of the pulsar’s spindown power has gone into the production ofelectrons and positrons under the assumption of constant Ė over the characteristic age of the pulsar.Accounting for time dependence will decrease this fraction.4. DiscussionThis work is the first detailed multi-source analysis using HAWC data up to the highest ener-gies of the source region containing 2HWC J2019+367. The morphology for HAWC J2019+3683PoS(ICRC2019)639Electron Spectrum of the Dragonfly PWN Chad Brisbois2 3 4Energy Band0.00.10.20.30.40.5size [degree]PSF(Simulations)Fit2Fit2PSFPreliminaryFigure 3: The measured width compared to the PSF in each energy band from Figure 2. A trend is seen, butgiven the number of data points and uncertainties, it is not statistically significant. The width of the PSF isplotted in blue.Figure 4: The spectral energy distribution of HAWC J2019+368 measured by HAWC in the latest data set.VERITAS flux points are taken from [6]. The grey band represents the 68% containment for the inverseCompton (IC) spectrum obtained from naima [15] using the same functional form as [16].4PoS(ICRC2019)639Electron Spectrum of the Dragonfly PWN Chad BrisboisFigure 5: The spectral energy distribution of HAWC J2016+371 measured by HAWC. Both sources aremodeled as point sources in their respective analysis, and no scaling of the flux is performed. VERITAS fluxpoints and fit taken from [6].is found to be very similar to VER J2019+368, with an asymmetric Gaussian morphology beingsignificantly preferred over symmetric models. The spectrum for HAWC J2019+368 agrees withthe scaled VERITAS measurements, confirming that the result is consistent with previously pub-lished results. This is the highest energy flux measurements ever observed from this region of thesky, and this emission appears consistent with a model of electrons developed to explain X-ray andTeV data from Suzaku and VERITAS [7]. We are working on an ab initio γ-ray spectrum from anelectron source using GAMERA [17] and a more detailed interstellar radiation field.This study is the first work to observe a TeV source coincident with VER J2016+371. As-suming that VER J2016+371 and HAWC J2016+371 are the same source (positional differenceof 0.09◦, within uncertainties), the spectrum has been measured to extend up to tens of TeV, withsimilar flux and index as reported by VERITAS [6]. More data will be required to test for cur-vature in the spectrum at higher energies. The new techniques developed in [9], combined withHAWC’s unparalleled uptime will allow for new multi-source studies of the form presented here tobe performed in other areas of the sky, potentially leading to many new discoveries.5PoS(ICRC2019)639Electron Spectrum of the Dragonfly PWN Chad BrisboisReferences[1] M. S. E. Roberts, J. W. T. Hessels, S. M. Ransom, et al., Astrophys. J. 577 (2002) L19–L22.[2] J. W. T. Hessels, M. S. E. Roberts, S. M. Ransom, et al., Astrophys. J. 612 (2004) 389–397.[3] A. Van Etten, R. W. Romani, and C. Ng, Astrophys. J. 680 (2008) 1417–1425.[4] A. A. Abdo, U. Abeysekara, B. T. Allen, et al., Astrophys. J. 753 (2012) 159.[5] E. Aliu, T. Aune, B. Behera, et al., Astrophys. J. 788 (2014) 78.[6] A. U. Abeysekara, A. Archer, T. Aune, et al., Astrophys. J. 861 (2018) 134.[7] E. V. Gotthelf, K. Mori, E. Aliu, et al., Astrophys. J. 826 (2016) 25.[8] B. Bartoli, P. Bernardini, X. J. Bi, et al., Astrophys. J. 745 (2012) L22.[9] HAWC Collaboration, A. U. Abeysekara, A. Albert, et al., arXiv e-prints (2019) arXiv:1905.12518.[10] K. Malone, PoS(ICRC2019)734 (2019).[11] A. U. Abeysekara, A. Albert, R. Alfaro, et al., Astrophys. J. 843 (2017) 40.[12] G. Vianello, R. J. Lauer, P. Younk, et al., arXiv:1507.08343.[13] J. Hinton and W. Hofmann, Annu. Rev. Astron. Astrophys. 47 (2009) 523–565.[14] D. Khangulyan, F. A. Aharonian, and S. R. Kelner, Astrophys. J. 783 (2014) 100.[15] V. Zabalza, Naima: a Python package for inference of particle distribution properties fromnonthermal spectra, in 34th Int. Cosm. Ray Conf., p. 922, 2015.[16] T. Mizuno, N. Tanaka, H. Takahashi, et al., Astrophys. J. 841 (2017) 104.[17] J. Hahn, GAMERA - a new modeling package for non-thermal spectral modeling, in 34thInternational Cosmic Ray Conference (ICRC2015), vol. 34 of International Cosmic Ray Conference,p. 917, 2015.6

Electron spectrum of the dragonfly pulsar wind nebula from X-ray to TeV

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Electron spectrum of the dragonfly pulsar wind nebula from X-ray to TeV

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