CHARACTERIZATION OF THE INNER KNOT OF THE CRAB: THE SITE OF THE GAMMA-RAY FLARES?

Rudy A, Horns D, Deluca A, Kolodziejczak J, Tennant A, Yuan Y, Buehler R, Arons J, Blandford R, Caraveo P, Costa E, Funk S, Hays E, Lobanov A, Max C, Mayer M, Mignani R, O'Dell SL, Romani R, Tavani M, Weisskopf MC (2015)

Publication Type: Journal article

Publication year: 2015

Journal

Astrophysical Journal American Astronomical Society

Book Volume: 811

Journal Issue: 1

DOI: 10.1088/0004-637X/811/1/24

Abstract

A particularly intriguing recent result from gamma-ray astronomy missions is the detection of powerful flares from the Crab Nebula, which challenges the current understanding of pulsar wind nebulae and acceleration mechanisms. To search for the production site(s) of these flares, we conducted a multi-wavelength observing campaign using Keck, the Hubble Space Telescope (HST), and the Chandra X-ray Observatory. As the short timescales of the gamma-ray flares (less than or similar to 1 day) suggest a small emitting region, the Crab's inner knot (about 0.6 arcsec from the pulsar) is a candidate site for such flaring. This paper describes observations of the inner knot, seeking to understand its nature and possible relationship with gamma-ray flares. Using singular-value decomposition, analysis of the HST images yielded results consistent with traditional methods while substantially reducing some uncertainties. These analyses show that the knot's intrinsic properties (especially size and brightness) are correlated with its (projected) separation from the pulsar. This characterization of the inner knot helps in constraining standard shock model parameters, under the assumption that the knot lies near the shocked surface. While the standard shock model gives good agreement in several respects, two puzzles persist: (a) the observed angular size of the knot relative to the pulsar-knot separation is much smaller than expected; and (b) the variable high degree of polarization (reported by others) is difficult to reconcile with a highly relativistic downstream flow. However, the IR-optical flux of the inner knot is marginally consistent with the shock accelerating most of the Nebula's optical-emitting particles.

Authors with CRIS profile

Stefan Funk

Involved external institutions

University of California Santa Cruz US United States (USA) (US) National Aeronautics and Space Administration (NASA) US United States (USA) (US) National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF) IT Italy (IT) Deutsches Elektronen-Synchrotron DESY DE Germany (DE) University of California, Berkeley US United States (USA) (US) Stanford University US United States (USA) (US) Universität Hamburg (UHH) DE Germany (DE) Max-Planck-Institut für Radioastronomie / Max Planck Institute for Radio Astronomy DE Germany (DE) Università degli Studi di Roma 'Tor Vergata' IT Italy (IT)

How to cite

APA:

Rudy, A., Horns, D., Deluca, A., Kolodziejczak, J., Tennant, A., Yuan, Y.,... Weisskopf, M.C. (2015). CHARACTERIZATION OF THE INNER KNOT OF THE CRAB: THE SITE OF THE GAMMA-RAY FLARES? Astrophysical Journal, 811(1). https://doi.org/10.1088/0004-637X/811/1/24

MLA:

Rudy, Alexander, et al. "CHARACTERIZATION OF THE INNER KNOT OF THE CRAB: THE SITE OF THE GAMMA-RAY FLARES?" Astrophysical Journal 811.1 (2015).

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