X-Ray Observations of the Supernova Remnant CTB 87 (G74.9+1.2): An Evolved Pulsar Wind Nebula

Abstract

Pulsar wind nebulae (PWNe) studies with the Chandra X-ray Observatory have opened a new window to address the physics of pulsar winds, zoom on their interaction with their hosting supernova remnant (SNR) and interstellar medium, and identify their powering engines. We here present a new 70 ks, plus an archived 18 ks, Chandra ACIS observation of the SNR CTB 87 (G74.9+1.2), classified as a PWN with unusual radio properties and poorly studied in X-rays.We find that the peak of the X-ray emission is clearly offset from the peak of the radio emission by ∼100 ′′ and located at the southeastern edge of the radio nebula. We detect a point source -the putative pulsar -at the peak of the Xray emission and study its spectrum separately from the PWN. This new point source, CXOU J201609.2+371110, is surrounded by a compact nebula displaying a torus-like structure and possibly a jet. A more extended diffuse nebula is offset from the radio nebula, extending from the point source to the northwest for ∼250 ′′ . The spectra of the point source, compact nebula and extended diffuse nebula are all well described by a power law model with a photon index of 1.1 (0.7−1.6), 1.2 (0.9−1.4) and 1.7 (1.5−1.8), respectively, for a column density N H = 1.38 (1.21−1.57) × 10 22 cm −2 (90% confidence). The total X-ray luminosity of the source is ∼1.6 × 10 34 erg s −1 at an assumed distance of 6.1 kpc, with ∼ 2% and 6% contribution from the point source and compact nebula, respectively. The observed properties suggest that CTB 87 is an evolved (∼5−28 kyr) PWN, with the extended radio emission likely a 'relic' PWN, as in Vela-X and G327.1−1.1.To date, however, there is no evidence for thermal X-ray emission from this SNR, and the SNR shell is still missing, suggesting expansion into a low-density medium (n 0 < 0.2 D −1/2 6.1 cm −3 ), likely caused by a stellar wind bubble blown by the progenitor star.Subject headings: ISM: individual (CTB 87, CXOU J201609.2+371110) -ISM: supernova remnants -X-rays: ISM

The counterpart/s of IGR J20159+3713/SWIFT J2015.9+3715: dissecting a complex region with emission from keV to TeV

“…5 of Hapern et al 2001) is that of a cataclysmic variable, probably of the magnetic type since its He II j4686 emission line is as strong Notes. (a) The position reported here coincides, within uncertainties, with that of the bright spot detected by Chandra within the SNR/PWN diffuse emission and is associated with the X-ray source CXOU J201609.2+371110, firstly detected by Matheson et al (2013). Notes.…”

“…The first source (A) is extended and the position of its brightest spot is compatible with the peak of the X-ray emission associated with the PWN recently discovered in CTB 87 (Safi-Harb 2012; Matheson et al 2013). The source morphology is similar, although less detailed, to what is evident in a Chandra image of the region where both a compact nebula (with a torus/jet-like structure) and a diffuse nebula (with a cometary-like morphology) are clearly visible (Safi-Harb 2012; Matheson et al 2013).…”

“…The source morphology is similar, although less detailed, to what is evident in a Chandra image of the region where both a compact nebula (with a torus/jet-like structure) and a diffuse nebula (with a cometary-like morphology) are clearly visible (Safi-Harb 2012; Matheson et al 2013).…”

“…For the sake of completeness, we have also performed the spectral analysis of the X-ray emission associated with CTB 87, which has recently been studied in details by Matheson et al (2013) exploiting Chandra observations. Also in this case all XRT data have been added together to study the average X-ray spectrum of this source.…”

“…Close by there is also a newly discovered TeV/VERITAS object (VER J2016+372), whose position is compatible with that of CTB 87 a supernova remnant (SNR)/pulsar wind nebula (PWN) located at 6 kpc in the Perseus arm, but in the line of sight of Cyg OB1 (Aliu et al 2011). The properties and energetics of the underlying pulsar are poorly known although, recently, some information have been obtained by means of Chandra observations (Matheson et al 2013). The association between the VERITAS and Fermi source seems to be excluded at the 99% confidence level (c.l.)…”