X-Ray Studies of HESS J1809-193 with Suzaku

📝 Abstract

Suzaku observed the region including HESS J1809-193, one of the TeV unidentified (unID) sources, and confirmed existence of the extended hard X-ray emission previously reported by ASCA, as well as hard X-ray emission from the pulsar PSR J1809-1917 in the region. One-dimensional profile of the diffuse emission is represented with a Gaussian model with the best-fit sigma of 7+-1 arcmin. The diffuse emission extends for at least 21 pc (at the 3sigma level, assuming the distance of 3.5 kpc), and has a hard spectrum with the photon index of Gamma ~1.7. The hard spectrum suggests the pulsar wind nebula (PWN) origin, which is also strengthened by the hard X-ray emission from PSR J1809-1917 itself. Thanks to the low background of Suzaku XIS, we were able to investigate spatial variation of the energy spectrum, but no systematic spectral change in the extended emission is found. These results imply that the X-ray emitting pulsar wind electrons can travel up to 21 pc from the pulsar without noticeable energy loss via synchrotron emission.

💡 Analysis

Suzaku observed the region including HESS J1809-193, one of the TeV unidentified (unID) sources, and confirmed existence of the extended hard X-ray emission previously reported by ASCA, as well as hard X-ray emission from the pulsar PSR J1809-1917 in the region. One-dimensional profile of the diffuse emission is represented with a Gaussian model with the best-fit sigma of 7+-1 arcmin. The diffuse emission extends for at least 21 pc (at the 3sigma level, assuming the distance of 3.5 kpc), and has a hard spectrum with the photon index of Gamma ~1.7. The hard spectrum suggests the pulsar wind nebula (PWN) origin, which is also strengthened by the hard X-ray emission from PSR J1809-1917 itself. Thanks to the low background of Suzaku XIS, we were able to investigate spatial variation of the energy spectrum, but no systematic spectral change in the extended emission is found. These results imply that the X-ray emitting pulsar wind electrons can travel up to 21 pc from the pulsar without noticeable energy loss via synchrotron emission.

📄 Content

arXiv:0912.1931v1 [astro-ph.HE] 10 Dec 2009 X-Ray Studies of HESS J1809–193 with Suzaku Takayasu Anada1, Aya Bamba2,1,∗, Ken Ebisawa1, and Tadayasu Dotani1 1Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 2School of Cosmic Physics, Dublin Institute for Advanced Studies 31 Fitzwilliam Place, Dublin 2, Ireland (Received ; accepted ) Abstract Suzaku observed the region including HESS J1809−193, one of the TeV uniden- tified (unID) sources, and confirmed existence of the extended hard X-ray emis- sion previously reported by ASCA, as well as hard X-ray emission from the pulsar PSR J1809−1917 in the region. One-dimensional profile of the diffuse emission is represented with a Gaussian model with the best-fit σ of 7 ± 1 arcmin. The diffuse emission extends for at least 21 pc (at the 3σ level, assuming the distance of 3.5 kpc), and has a hard spectrum with the photon index of Γ ∼1.7. The hard spectrum suggests the pulsar wind nebula (PWN) origin, which is also strengthened by the hard X-ray emission from PSR J1809−1917 itself. Thanks to the low background of Suzaku XIS, we were able to investigate spatial variation of the energy spectrum, but no systematic spectral change in the extended emission is found. These results imply that the X-ray emitting pulasr wind electrons can travel up to 21 pc from the pulsar without noticable energy loss via synchrotron emission. Key words: gamma rays: observations — ISM: individual (HESS J1809−193) — stars: pulsars: individual (PSR J1809−1917) — X-rays: ISM 1. Introduction Galactic plane survey with the H.E.S.S. Cherenkov telescope system revealed dozens of the new very-high-energy (VHE) γ-ray sources (Aharonian et al. 2005a; Aharonian et al. 2006a). Many of them have no counterparts in other wave-lengths, thus called “unidentified (unID) TeV sources”. Today, about 40 such unidentified TeV sources are known on the Galactic plane (Hinton 2007). Most of them are located within a height of ± 1 degree from the Galactic plane, and some are intrinsically extended. Despite a large number of intensive studies in the last several years, their origin is unclear (Hinton 2007). X-ray follow-up observations of the unID TeV sources are now on-going. Although supernova remnants (SNRs) or hypernova remnants were suggested to be major counterpart ∗ Corresponding author: abamba@cp.dias.ie 1 candidates of these TeV unID sources (Yamazaki et al. 2006; Ioka & Meszaros 2009), only a few sources have been actually identified as SNRs (Nakamura et al. 2009; Aharonian et al. 2008). On the other hand, rather surprisingly, several unID TeV sources have been identified as pulsar wind nebulae (PWNe) (Anada et al. 2009; Uchiyama et al. 2009, for example). They seem to be rather old, previously unknown PWNe, compared to the PWNe already identified and well studied in X-rays. The first HESS observations of the region around PSR J1809–1917 were made from May through June 2004 as part of the systematic survey of the inner Galaxy (Aharonian et al. 2005a; Aharonian et al. 2006a). Because marginal VHE γ-ray signals were detected, HESS J1809–193 was observed again in 2004 and 2005, and significant γ-ray emission was confirmed (Aharonian et al. 2007). Recent study of this source by HESS was reported by Renaud et al. (2008). Fitting the excess map with a 2-D symmetric Gaussian, the best fit position and intrinsic source extension (in rms) were determined as (RA, Dec) = (18h09m52s, −19◦23′42′′) and 0◦.25 ± 0◦.02, respectively. PSR J1809–1917 is a radio pulsar discovered by the Parkes Multibeam Pulsar Survey (Morris et al. 2002). The pulsar is located at the position of (RA, Dec) = (18h09m43.s1, −19◦17′38′′) with a pulse period of P = 82.7 ms and the period derivative of ˙P = 2.55 × 10−14 s s−1. The distance to the source was estimated to be d = 3.5 kpc from the pulsar’s dispersion measure using the NE2001 Galactic electron-density model (Cordes & Lazio 2002). The characteristic age and the spin-down luminosity are τc = 51 kyr and ˙E = 1.8×1036 ergs s−1, respectively. The γ-ray spectral analysis performed by Komin et al. (2007) indicated that the spectral slope is different between the regions near the pulsar and far from the pulsar. This is the second case that spatial variation of the spectral slope is revealed in the VHE γ-ray emission. The first case is HESS J1825–137 (Aharonian et al. 2006b), which is largely extended in both VHE γ-ray and X-ray bands (Uchiyama et al. 2009). ASCA observation revealed diffuse, non-thermal emission in the vicinity of PSR J1809– 1917 (Bamba et al. 2003a). Kargaltsev & Pavlov (2007) detected a bright point X-ray source which was positionally consistent with the pulsar PSR J1809−1917, and resolved the surround- ing compact PWN utilizing the very high angular resolution of Chandra. The PWN has a “head-tail” profile, consisting of the southern-head, which is coincident to the pulsar, and the northern-tail. Kargaltsev & Pavlov (2007) claimed that this comet

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