The isolated neutron star X-ray pulsars RX J0420.0–5022   and RX J0806.4–4123: New X-ray and optical observations

Haberl, F.; Motch, C.; Zavlin, V. E.; Reinsch, K.; Gänsicke, B. T.; Cropper, Mark; Schwope, A. D.; Turolla, R.; Zane, S.

doi:10.1051/0004-6361:20040440

Cited by 84 publications

(109 citation statements)

References 35 publications

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“…The first optical observations of the field performed with the New Technology Telescope (NTT) soon after the discovery of the X-ray source (Haberl et al 1999) did not reveal any candidate counterpart brighter than B ∼ 25.2 and R ∼ 25.2. More recently, thanks to the updated Chandra position, a possible optical identification was proposed by Haberl et al (2004b) with a faint object (B = 26.6 ± 0.3, V ≥ 25.5) tentatively detected in archival Very Large Telescope (VLT) images. However, the identification has not been confirmed so far.…”

Section: Introductionmentioning

confidence: 99%

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VLT optical observations of the isolated neutron star RX J0420.0-5022

Mignani¹,

Motch

Haberl

et al. 2009

A&A

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Context. X-ray observations performed with the Röntgen Satellite (ROSAT) led to the discovery of seven radio-silent isolated neutron stars (INSs) which are detected only through the relatively dim and purely thermal X-ray emission from the cooling star surface. A few of these INSs (X-ray Dim INSs, or XDINSs) have been also detected at optical wavelengths where they seem to feature thermal spectra. Optical studies of XDINSs thus play a crucial role in mapping the temperature distribution on the neutron star surface and in investigating the existence of an atmosphere around the neutron star. Aims. The aim of this work is to investigate the optical identification of the XDINS RX J0420.0−5022, tentatively proposed in the literature based on Very Large Telescope (VLT) observations. Methods. We re-analysed the original VLT observations of the proposed counterpart to assess its detection significance and we performed deeper VLT observations aiming at a higher confidence detection. Results. With a ∼2σ detection significance and a re-computed flux of B = 27.52 ± 0.61, we cannot rule out that the proposed counterpart was spurious and produced by the halo of a very bright nearby star. While we could not detect the proposed counterpart in our deeper VLT observations, we found evidence for a marginally significant (∼3.9σ) detection of a similarly faint object (B = 27.5 ± 0.3), ≈0. 5 north of it and coincident with the updated Chandra position of RX J0420.0−5022. Interestingly, the angular separation is consistent with the upper limit on the RX J0420.0−5022 proper motion, which suggests that we might have actually detected the originally proposed counterpart. From the flux of the putative RX J0420.0−5022 counterpart we can rule out a >7 optical excess with respect to the extrapolation of the XMM-Newton spectrum. Conclusions. High spatial resolution observations with the refurbished Hubble Space Telescope (HST) are the only way to confirm the detection of the putative candidate counterpart and to validate its identification with RX J0420.0−5022.

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Section: Introductionmentioning

confidence: 99%

“…In this paper we re-analyze the original VLT observations of RX J0420.0−5022 presented by Haberl et al (2004b) and we report follow-up, longer optical observations of the candidate counterpart, performed by our team with the VLT. Observations and data analysis are described in Sect.…”

Section: Introductionmentioning

confidence: 99%

VLT optical observations of the isolated neutron star RX J0420.0-5022

Mignani¹,

Motch

Haberl

et al. 2009

A&A

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“…With 230 eV and 460 eV the line energies are a factor of two apart. Also, in the case of RX J0806.4-4123 a simple absorbed blackbody model yields an unacceptable fit to the EPIC-pn spectra (Haberl et al 2004a). A model with one line results in χ 2 red = 1.39 which is formally acceptable.…”

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confidence: 98%

The magnificent seven: magnetic fields and surface temperature distributions

Haberl

2007

Astrophys Space Sci

284

302

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Presently seven nearby radio-quiet isolated neutron stars discovered in ROSAT data and characterized by thermal X-ray spectra are known. They exhibit very similar properties and despite intensive searches their number remained constant since 2001 which led to their name "The Magnificent Seven". Five of the stars exhibit pulsations in their X-ray flux with periods in the range of 3.4 s to 11.4 s. XMM-Newton observations revealed broad absorption lines in the X-ray spectra which are interpreted as cyclotron resonance absorption lines by protons or heavy ions and / or atomic transitions shifted to X-ray energies by strong magnetic fields of the order of 10 13 G. New XMM-Newton observations indicate more complex X-ray spectra with multiple absorption lines. Pulse-phase spectroscopy of the best studied pulsars RX J0720.4-3125 and RBS 1223 reveals variations in derived emission temperature and absorption line depth with pulse phase. Moreover, RX J0720.4-3125 shows long-term spectral changes which are interpreted as due to free precession of the neutron star. Modeling of the pulse profiles of RX J0720.4-3125 and RBS 1223 provides information about the surface temperature distribution of the neutron stars indicating hot polar caps which have different temperatures, different sizes and are probably not located in antipodal positions.

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“…For example, while for most radio pulsars the optical and near IR flux is thought to be dominated by magnetospheric emission, several middle-aged pulsars (PSR B0656+14, PSR B0950+08 and Geminga) also exhibit a surface optical component (e.g., Mignani, de Luca & Caraveo 2004;Kargaltsev et al 2005, Mignani et al 2006. The optical emission detected in several thermally emitting, isolated neutron stars mostly likely has a surface origin (e.g., Kaplan et al 2003;Haberl et al 2004;Haberl 2005;van KerKwijk & Kaplan 2006). Finally, the optical/IR emission detected from a number of magnetars may originate from a hot corona near the stellar surface (Beloborodov & Thompson 2006).…”

Section: Introductionmentioning

confidence: 99%

Wave Modes in the Magnetospheres of Pulsars and Magnetars

Wang

Lai

2009

Astrophysics and Space Science Proceedings

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We study the wave propagation modes in the relativistic streaming pair plasma of the magnetospheres of pulsars and magnetars, focusing on the effect of vacuum polarization. We show that the combined plasma and vacuum polarization effects give rise to a vacuum resonance, where "avoided mode crossing" occurs between the extraordinary mode and the (superluminous) ordinary mode. When a photon propagates from the vacuum-polarization-dominated region at small radii to the plasma-dominated region at large radii, its polarization state may undergo significant change across the vacuum resonance. We map out the parameter regimes (e.g., field strength, plasma density and Lorentz factor) under which the vacuum resonance occurs and examine how wave propagation is affected by the resonance. Some possible applications of our results are discussed, including high-frequency radio emission from pulsars and possibly magnetars, and optical/IR emission from neutron star surfaces and inner magnetospheres.

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The isolated neutron star X-ray pulsars RX J0420.0–5022 and RX J0806.4–4123: New X-ray and optical observations

Cited by 84 publications

References 35 publications

VLT optical observations of the isolated neutron star RX J0420.0-5022

VLT optical observations of the isolated neutron star RX J0420.0-5022

The magnificent seven: magnetic fields and surface temperature distributions

Wave Modes in the Magnetospheres of Pulsars and Magnetars

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