Fig 4 - uploaded by Vadim Burwitz
Content may be subject to copyright.
Chandra LETG+HRC spectrum of RX J1856 binned to 0.5Å, derived with the effective area at wavelengths longwards of the carbon edge corrected to fit an abundance of carbon in the interstellar medium of a(C) = 245 − 400 ppm with 60% in dust grains. The twotemperature fit shown is for 320 ppm, with the upper level of the step indicated for 245 and 400 ppm, too. The fit has a χ 2 = 97.7 for 115 dof (see Sect. 4.5). The model parameters are quoted in Table 2.
Source publication
The absolute calibration of space-borne instruments in the soft X-ray regime
rests strongly on model spectra of hot white dwarfs.
We analyze the Chandra LETG+HRC-S observations of the white dwarfs HZ43 A and
Sirius B and of the neutron star RX J185635-3754 in order to resolve current
uncertainties in the soft X-ray spectral fluxes and photospheric...
Contexts in source publication
Context 1
... fit the summed model spectrum for the first to the sixth diffraction orders to the Chandra LETG+HRC-S count rate spectra of RX J1856 in the positive and negative disper- sion directions. Fig. 4 shows the corresponding summed pho- ton spectrum, which allows to judge the strength of the inter- stellar carbon absorption edge more clearly than the count rate spectrum with its superposed effective area structure. The pho- 6 Presently, the nature of the cool component is still disputed and so is the angular stellar radius derived ...
Context 2
... fac- tor applies within its error to both the negative and the posi- tive dispersion directions. Figure 4 shows the derived summed spectrum of both sides using effective areas A = α(λ) A 0 where the wavelength-dependent adjustment factor α is derived be- low and is forced to match α 1 between 44 to 48.5Å. Our photon spectrum is very similar to that presented by Drake et al. (2002, see their Fig. ...
Context 3
... HZ43 A does not help because the spectrum of Sirius B does not extend to 44Å where it could be tied down. 6. Photon spectra of RX J1856, HZ43 A, and Sirius B based on our analysis of the LETG+HRC-S observations (data points) and best fit model spectra with parameters as given in Table 2 (solid curves). The spectrum of RX J1856 is the same as in Fig. 4 with the two black- body components shown separately as dashed curves. Longwards of 78Å, we have included the EUVE spectra of the two white dwarfs (green/gray ...
Similar publications
We present the first evidence for the direct detection of nickel in the photosphere of the hot DO white dwarf REJ0503$-$289. While this element has been seen previously in the atmospheres of hot H-rich white dwarfs, this is one of the first similar discoveries in a He-rich object. Intriguingly, iron, which is observed to be more abundant than Ni in...
We present a BeppoSAX survey of five Be/X-ray binary candidates. We report on the identification of two of them, HD 110432 and HD 141926, as low luminosity Be/X-ray binaries. For HD 110432 we report on the detection of a pulsation period of ~14 ks. Because the luminosity of these sources is low and their spectra do not require non-thermal emission...
Citations
... The optical spectrum follows a −4 law, but it lies above the extrapolation of a single-temperature X-ray blackbody at low energies. The brightness, simple spectrum, and steadiness of its emission make J1856 an ideal target for the calibration of X-ray telescopes (Beuermann et al. 2006), and hence a very frequently observed object. In particular, XMM-Newton observed it about every six months, around April and October, since 2004 (with an earlier single observation in spring 2002). ...
The soft X-ray pulsar RX J1856.5−3754 is the brightest member of a small class of thermally-emitting, radio-silent, isolated neutron stars. Its X-ray spectrum is almost indistinguishable from a blackbody with kT∞ ≈ 60eV, but evidence of harder emission above ∼ 1 keV has been recently found. We report on a spectral and timing analysis of RX J1856.5−3754 based on the large amount of data collected by XMM-Newton in 2002–2022, complemented by a dense monitoring campaign carried out by NICER in 2019. Through a phase-coherent timing analysis we obtained an improved value of the spin-down rate $\dot{\nu }={-6.042(4)}\, times\, 10^{-16}Hz\, s^{-1}$, reducing by more than one order magnitude the uncertainty of the previous measurement, and yielding a characteristic spin-down field of 1.47 × 1013G. We also detect two spectral components above ∼1 keV: a blackbody-like one with kT∞ = 138 ± 13 eV and emitting radius $31_{-16}^{+8}\,$m, and a power law with photon index $\Gamma =1.4_{-0.4}^{+0.5}$. The power-law 2–8 keV flux, $(2.5_{-0.6}^{+0.7})\times 10^{-15}$erg cm−2s−1, corresponds to an efficiency of 10−3, in line with that seen in other pulsars. We also reveal a small difference between the 0.1–0.3 keV and 0.3–1.2 keV pulse profiles, as well as some evidence for a modulation above 1.2 keV. These results show that, notwithstanding its simple spectrum, RX J1856.5−3754 still has a non-trivial thermal surface distribution and features non-thermal emission as seen in other pulsars with higher spin-down power.
... The optical spectrum follows a −4 law, but it lies above the extrapolation of a single-temperature X-ray blackbody at low energies. The brightness, simple spectrum, and steadiness of its emission make J1856 an ideal target for the calibration of X-ray telescopes (Beuermann et al. 2006), and hence a very frequently observed object. In particular, XMM-Newton observed it about every six months, around April and October, since 2004 (with an earlier single observation in spring 2002). ...
The soft X-ray pulsar RX J1856.5-3754 is the brightest member of a small class of thermally-emitting, radio-silent, isolated neutron stars. Its X-ray spectrum is almost indistinguishable from a blackbody with $kT^\infty\approx 60$ eV, but evidence of harder emission above $\sim 1$ keV has been recently found. We report on a spectral and timing analysis of RX J1856.5-3754 based on the large amount of data collected by XMM-Newton in 2002--2022, complemented by a dense monitoring campaign carried out by NICER in 2019. Through a phase-coherent timing analysis we obtained an improved value of the spin-down rate $\dot{\nu}=-6.042(4)\times10^{-16}$ Hz s$^{-1}$, reducing by more than one order magnitude the uncertainty of the previous measurement, and yielding a characteristic spin-down field of $1.47\times10^{13}$ G. We also detect two spectral components above $\sim1$ keV: a blackbody-like one with $kT^\infty=138\pm13$ eV and emitting radius $31_{-16}^{+8}$ m, and a power law with photon index $\Gamma=1.4_{-0.4}^{+0.5}$. The power-law 2--8\,keV flux, $(2.5_{-0.6}^{+0.7})\times10{-15}$ erg cm$^{-2}$ s$^{-1}$, corresponds to an efficiency of $10^{-3}$, in line with that seen in other pulsars. We also reveal a small difference between the $0.1$--$0.3$ keV and $0.3$--$1.2$ keV pulse profiles, as well as some evidence for a modulation above $1.2$ keV. These results show that, notwithstanding its simple spectrum, \eighteen still has a non-trivial thermal surface distribution and features non-thermal emission as seen in other pulsars with higher spin-down power.
... An e xtensiv e discussion of the photoelectric cross-sections for soft X-ray fluxes is provided in Bonamente et al. ( 2002 ) and Bonamente, Lieu & Mittaz ( 2001a ). 1 The calibration and stability of the ROSAT PSPC detector are discussed in Snowden et al. ( 1994 ) and Snowden, Turner & Freyberg MNRAS 514, 416-426 (2022, including the calibration of the radial dependence of the detector efficiency with off-set angle. A study of the soft emission from white dwarfs and neutron stars by Beuermann, Burwitz & Rauch ( 2006 ) shows that the ROSAT PSPC soft X-ray fluxes are well calibrated within ≤10 per cent, as also indicated by Snowden et al. ( 1995 ). Moreo v er, the Bonamente et al. ( 2003 ) analysis excluded the portions of the detector shadowed by the 'wagon wheel' structure used to house the filters, in correspondence of which the response of the PSPC is significantly reduced. ...
This paper provides a new analysis of ROSAT observations of the Coma cluster, to determine the amount of soft X–ray radiation in excess of the contribution from the hot intra–cluster medium. The re–analysis is made possible by a high–resolution study of the hot intra–cluster medium with the XMM–Newton and Planck telescopes out to the cluster’s virial radius. The analysis confirms the original findings of a strong excess of soft X–ray radiation, which is likely to be of thermal origin. We find quantitative agreement between the detected soft excess and the physical characteristics of warm–hot intergalactic medium (WHIM) filaments seen in hydrodynamical simulations. We conclude that the most plausible explanation for the soft excess isthe presence of ∼10 Mpc–long filaments at log T(K) ≃ 6, with a baryon overdensity of ∼300, converging towards the Coma cluster. This interpretation therefore provides support for the identification of the missing low–redshift baryons with WHIM filaments, as predicted by numerical simulations.
... and white dwarfs such as Sirius B, GD153 or HZ43 exhibit a blackbody-like spectrum with an effective temperature in the range 30 to 70 × 10 5 K and low photoelectric absorption column densities (N H ≲ 10 20 cm −2 ), making them appropriate sources to calibrate the effective area in the soft x-ray band. 21 Extended long-term monitoring with all the major modern x-ray satellites confirmed that the x-ray emission of 1E0102-72 and RXJ1856-3754 is constant within a few percent over one decade, 15,17 at variance with Cas A. 22 In the 2 to 10 keV band, radio-loud AGN with relative featureless spectra, such as 3C273, H1426+128, and PKS2155-304, are still widely used for effective area calibration. Their x-ray emission is believed to be dominated by a relativistic jet seen at a very small angle from the line-of-sight, although the decomposition of the 3C273 spectrum might be more complex and a variable contribution from the thermal accretion disk cannot be ruled out. ...
We present an overview of the set of celestial sources used for in-flight calibration of X-ray detectors by past and operational missions. We show the rationale behind their choice as a guideline for future missions aiming at optimizing the critical early phases of their science operations. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE).
... Thus, Sirius (α CMa, HD 48915, HR 2491) was observed by Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) on 2012 October 7 and 2013 January 26. The hot WD companion, Sirius B, is 10 mag fainter at V and contributes <1% of the system flux, even at 1300 Å (Holberg et al. 1998;Beuermann et al. 2006). The HST flux system (R. C. Bohlin & K. D. Gordon 2014, in preparation) is based on the flux distribution of NLTE model atmospheres for the pure hydrogen white dwarfs (WDs) GD153 and GD71 and on an NLTE metal line-blanketed model of Rauch et al. (2013, RWBK) for G191B2B. ...
The Space Telescope Imaging Spectrograph (STIS) has measured the flux for Sirius from 0.17 to 1.01 μm on the Hubble Space Telescope (HST) White Dwarf scale. Because of the cool debris disk around Vega, Sirius is commonly recommended as the primary IR flux standard. The measured STIS flux agrees well with predictions of a special Kurucz model atmosphere, adding confidence to the modeled IR flux predictions. The IR flux agrees to 2%-3% with respect to the standard template of Cohen and to 2% with the Midcourse Space Experiment absolute flux measurements in the mid-IR. A weighted average of the independent visible and mid-IR absolute flux measures implies that the monochromatic flux at 5557.5 Å (5556 Å in air) for Sirius and Vega, respectively, is 1.35 × 10-8 and 3.44 × 10-9 erg cm-2 s-1 Å-1 with formal uncertainties of 0.5%. Contrary to previously published conclusions, the Hipparcos photometry offers no support for the variability of Vega. Pulse pileup severely affects the Hp photometry for the brightest stars.
... This issue was addressed by undertaking a recalibration of the LETGS spectra, as processed through the custom software (in IDL) utilized here. The approach is described in general terms by Ayres (2009) and has the heritage of Beuermann et al. (2006), who promoted the value of hot white dwarfs, like HZ 43, and the neutron star RXJ 1856.6−3754 (hereafter RXJ 1856) for calibrating the soft response of LETGS, and of Pollock (2004), who similarly advocated the value of power law active galactic nucleus sources for establishing the higher energy behavior of X-ray grating instruments. ...
... One can provide the p λ spectrum at the nominal wavelength-dependent LETGS resolution, to avoid having to introduce additional line-spread terms directly into R, but this is irrelevant for the calibrators used here, which all are smooth continuum sources. Beuermann et al. (2006) tabulated consensus SEDs for HZ 43 and RXJ 1856. The authors also provided a model for the latter based on a dominant T ∼ 32 eV blackbody plus a T ∼ 63 eV "hot spot," absorbed by an interstellar column, N H ∼ 1.1 × 10 20 cm −2 . ...
The following is a progress report on the long-term coronal (T ~ 1 MK) activity of α Centauri A (HD 128620: G2 V) and B (HD 128621: K1 V). Since 2005, Chandra
X-Ray Observatory has carried out semiannual pointings on AB, mainly with the High Resolution Camera, but also on two occasions with the Low-Energy Transmission Grating Spectrometer, fully resolving the close pair in all cases. During 2008-2013, Chandra captured the rise, peak, and initial decline of B's coronal luminosity. Together with previous high states documented by ROSAT and XMM-Newton, the long-term X-ray record suggests a period of 8.1 ± 0.2 yr, compared to 11 yr for the Sun, with a minimum-to-peak contrast of 4.5, about half the typical solar cycle amplitude. Meanwhile, the A component has been mired in a Maunder-Minimum-like low state since 2005, initially recognized by XMM-Newton. But now, A finally appears to be climbing out of the extended lull. If interpreted simply as an overlong cycle, the period would be 19.2 ± 0.7 yr, with a minimum-to-peak contrast of 3.4. The short X-ray cycle of B, and possibly long cycle of A, are not unusual compared with the diverse (albeit much lower amplitude) chromospheric variations recorded, for example, by the HK Project. Further, the deep low state of A also is not unusual, but instead is similar to the L
X/L
bol of the Sun during recent minima of the sunspot cycle.
... Spectra for Sirius B presented in e.g. Pease et al. (2000) and Beuermann et al. (2006) support this conclusion. O'Dwyer et al. (2003) list WD1631+78 as a source of " hard " (> 0.5 keV) X-rays, probably from its unresolved dM4e companion star. ...
The MESSENGER spacecraft conducted its first flyby of Mercury on 14th January
2008, followed by two subsequent encounters on 6th October 2008 and 29th
September 2009, prior to Mercury orbit insertion on 18th March 2011. We have
reviewed MESSENGER flight telemetry and X-ray Spectrometer observations from
the first two encounters, and correlate several prominent features in the data
with the presence of astrophysical X-ray sources in the instrument field of
view. We find that two X-ray peaks attributed in earlier work to the detection
of suprathermal electrons from the Mercury magnetosphere, are likely to contain
a significant number of events that are of astrophysical origin. The
intensities of these two peaks cannot be explained entirely on the basis of
astrophysical sources, and we support the previous suprathermal explanation but
suggest that the electron fluxes derived in those studies be revised to correct
for a significant astrophysical signal.
We describe a process for cross-calibrating the effective areas of X-ray telescopes that observe common targets. The targets are not assumed to be “standard candles” in the classic sense, in that we assume that the source fluxes have well-defined, but a priori unknown values. Using a technique developed by Chen et al. that involves a statistical method called shrinkage estimation , we determine effective area correction factors for each instrument that bring estimated fluxes into the best agreement, consistent with prior knowledge of their effective areas. We expand the technique to allow unique priors on systematic uncertainties in effective areas for each X-ray astronomy instrument and to allow correlations between effective areas in different energy bands. We demonstrate the method with several data sets from various X-ray telescopes.
Strongly magnetized isolated neutron stars (NSs) are categorized into two families according, mainly, to their magnetic field strength. The one with a higher magnetic field of 1014–1015 Gauss is called “magnetar,” and the other is the X‐ray isolated neutron star (XINS) with 1013 Gauss. Both magnetars and XINSs show thermal emission in X‐rays, whose spectra are different. The soft X‐ray spectrum (below 10 keV) of a magnetar is reproduced with a two‐temperature blackbody (2BB), whereas that of an XINS shows only a single‐temperature blackbody (1BB), and its temperature is even lower than that of magnetars. On the basis of the magnetic field and temperature, it is often speculated that XINSs may be old and cooled magnetars. However, no other strong observational evidence has yet been reported to support the speculation. Here, we report that all the seven known XINSs show high‐temperature emission, which should have a similar origin to that of magnetars. Analyzing all the XMM‐Newton data of the XINSs with the highest statistics ever achieved, we find that their X‐ray spectra are all reproduced with a 2BB model, similar to magnetars, as opposed to the traditional 1BB model. Their emission radii and temperature ratios are also similar to those of magnetars except for two XINSs, which show significantly smaller radii than the others. The remarkable similarity in the X‐ray spectra between XINSs and magnetars suggests that the origins of their emitting regions are also the same. The lower temperature in XINSs can be explained if XINSs are older than magnetars. Therefore, this result is another observational indication that supports the standard hypothesis of classification of highly magnetized NSs. This article is based on our paper Yoneyama et al. (2019; accepted to PASJ).
Strongly magnetized isolated neutron stars (NSs) are categorized into two families, according mainly to their magnetic field strength. The one with a higher magnetic field of $10^{14}$ - $10^{15}$ G is called magnetar, characterized with repeated short bursts, and the other is X-ray isolated neutron star (XINS) with $10^{13}$ G. Both magnetars and XINSs show thermal emission in X-rays, but it has been considered that the thermal spectrum of magnetars is reproduced with a two-temperature blackbody (2BB), while that of XINSs shows only a single-temperature blackbody (1BB) and the temperature is lower than that of magnetars. On the basis of the magnetic field and temperature, it is often speculated that XINSs may be old and cooled magnetars. Here we report that all the seven known XINSs show a high-energy component in addition to the 1BB model. Analyzing all the XMM-Newton data of the XINSs with the highest statistics ever achieved, we find that their X-ray spectra are all reproduced with a 2BB model, similar to magnetars. Their emission radii and temperature ratios are also similar to those of magnetars except for two XINSs, which show significantly smaller radii than the others. The remarkable similarity in the X-ray spectra between XINSs and magnetars suggests that their origins of the emission are also the same. The lower temperature in XINSs can be explained if XINSs are older than magnetars. Therefore, these results are the observational indication that supports the standard hypothesis on the classification of highly-magnetized NSs.
