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High resolution Chandra HETG and RXTE observations of GRS 1915+105 : A hot disk atmosphere & cold gas enriched in Iron and Silicon

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 نشر من قبل Julia Lee
 تاريخ النشر 2001
  مجال البحث فيزياء
والبحث باللغة English
 تأليف J.C. Lee




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The time-averaged 30 ks Chandra HETGS observation of the micro-quasar GRS 1915+105 in the low hard state reveals for the first time in this source neutral K absorption edges from Fe, Si, Mg, & S. Ionized resonance absorption from H-, and He-like Fe (XXV, XXVI), Ca XX and possibly emission from neutral Fe Kalpha and ionized Fe XXV (forbidden, or the resonance emission component of a P-Cygni profile) are also seen. We report the tentative detection of the first astrophysical signature of XAFS in the photoelectric edge of Si (and possibly Fe and Mg), attributed to material in grains. The large column densities measured from the neutral edges reveal anomalous Si and Fe abundances. Scenarios for which the anomalous abundances can be attributed to surrounding cold material associated with GRS 1915+105 and/or that the enrichment may signify either a highly unusual supernova/hypernova, or external supernova activity local to the binary are discussed. We attribute the ionized features to a hot disk, disk-wind, or corona environment. These features allow for constraints on the ionization parameter (log xi > 4.15), temperature (T > 2.4 x 10^6 K), and hydrogen equivalent number density (n > 10^{12} cm^{-3}) for this region. Variability studies with simultaneous RXTE data show that the light curve count rate tracks changes in the disk blackbody and the power-law flux. Spectral changes in the Chandra data also track the behavior of the light curve, and may point to changes in both the ionizing flux and density of the absorber. A 3.69 Hz QPO and weak first harmonic is seen in the RXTE data.



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163 - J.C. Lee 2002
The Chandra AO1 HETGS observation of the micro-quasar GRS 1915+105 in the low hard state reveals (1) neutral K absorption edges from Fe, Si, Mg, and S in cold gas, and (2) highly ionized (Fe XXV and Fe XXVI) absorption attributed to a hot disk, disk wind, or corona. The neutral edges reveal anomalous Si and Fe abundances which we attribute to surrounding cold material in/near the environment of GRS 1915+105. We also point out the exciting possibility for the first astrophysical detection of XAFS attributed to material in interstellar grains. We place constraints on the ionization parameter, temperature, and hydrogen equivalent number density of the absorber near the accretion disk based on the detection of the H- and He-like Fe absorption. Observed spectral changes in the ionized lines which track the light curve point to changes in both the ionizing flux and density of the absorber, supporting the presence of a flow. Details can be found in Lee et al., 2002, ApJ., 567, 1102
The radio emitting X-ray binary GRS 1915+105 shows a wide variety of X-ray and radio states. We present a decade of monitoring observations, with the RXTE-ASM and the Ryle Telescope, in conjunction with high-resolution radio observations using MERLIN and the VLBA. Linear polarisation at 1.4 and 1.6 GHz has been spatially resolved in the radio jets, on a scale of ~150 mas and at flux densities of a few mJy. Depolarisation of the core occurs during radio flaring, associated with the ejection of relativistic knots of emission. We have identified the ejection at four epochs of X-ray flaring. Assuming no deceleration, proper motions of 16.5 to 27 mas per day have been observed, supporting the hypothesis of a varying angle to the line-of-sight per ejection, perhaps in a precessing jet.
We report on the analysis of 100 ks INTEGRAL observations of the Galactic microquasar GRS 1915+105. We focus on INTEGRAL Revolution number 48 when the source was found to exhibit a new type of variability as preliminarily reported in Hannikainen et a l. (2003). The variability pattern, which we name $xi$, is characterized by a pulsing behaviour, consisting of a main pulse and a shorter, softer, and smaller amplitude precursor pulse, on a timescale of 5 minutes in the JEM-X 3-35 keV lightcurve. We also present simultaneous RXTE data. From a study of the individual RXTE/PCA pulse profiles we find that the rising phase is shorter and harder than the declining phase, which is opposite to what has been observed in other otherwise similar variability classes in this source. The position in the colour-colour diagram throughout the revolution corresponds to State A (Belloni et al. 2000) but not to any previously known variability class. We separated the INTEGRAL data into two subsets covering the maxima and minima of the pulses and fitted the resulting two broadband spectra with a hybrid thermal--non-thermal Comptonization model. The fits show the source to be in a soft state characterized by a strong disc component below ~6 keV and Comptonization by both thermal and non-thermal electrons at higher energies.
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