High‐ResolutionChandraHETGS andRossi X‐Ray Timing ExplorerObservations of GRS 1915+105: A Hot Disk Atmosphere and Cold Gas Enriched in Iron and Silicon

Abstract

The time-averaged 30 ks Chandra AO1 High Energy Transmission Grating Spectrometer observation of the microquasar GRS 1915]105 in the low hard state reveals for the Ðrst time in this source neutral K absorption edges from iron, silicon, magnesium, and sulphur. Ionized resonance (r) absorption from H-and He-like species of Fe (XXV, XXVI) and possibly Ca XX are also seen as well as possible emission from neutral Fe Ka and ionized Fe XXV (forbidden or the resonance emission component of a P Cygni proÐle). We report the tentative detection of the Ðrst astrophysical signature of X-ray absorption Ðne structure 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 and illustrate the importance of high-resolution X-ray measurements for assessing material that surrounds bright X-ray sources, especially if depletion onto grains plays a prominent role. Scenarios for which the anomalous abundances can be attributed to surrounding cold material associated with GRS 1915]105 and/or for which 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. Based on H-and He-like Fe (XXV, XXVI), we estimate constraints on the ionization parameter temperature (T [ 2.4 ] 106 K), and hydrogen equivalent number (log m Z 4.15), density cm~3) for this region. Variability studies with the simultaneous RXT E data show that (n Z 1012 the light-curve count rate tracks the changes in the disk blackbody as well as the power-law Ñux, with the most signiÐcant variations observed in the former. The Chandra data show spectral changes that also track the behavior of the light curve and may point to changes in both the ionizing Ñux and density of the absorber. A 3.69 Hz quasi-periodic oscillation and weak Ðrst harmonic are seen in the RXT E data.

Limits on pair production and multizone Comptonization: the broad-band X/γ-ray spectrum of XTE J1550–564 revisited

“…Observations of similar strong absorption lines have been reported in several high inclination Galactic binary systems and are believed to represent iron K resonance at 6.7 and 7.0 keV from outflowing material (e.g. Ueda et al 1998;Lee et al 2002;Ueda et al 2004;Kubota et al 2007). A P-Cygni profile from strong wind surrounding a black hole has only been reported for the Cygnus X-3 system, a WR-binary (Vilhu We caution however that our lines may simply represent corrections to the still not perfect model for reflection.…”

On the optical extinction and distance of GRS 1915+105

“…Assuming solar abundances, Chandra spectral observation leaded to an H column density derived from silicon and iron K-edges ((8.4 +0.1 −0.2 ) × 10 22 cm −2 and (9.3 +1.6 −1.3 ) × 10 22 cm −2 respectively) substantially higher than the values derived from sulphur and magnesium K-edges ((3.2 +0.1 −0.6 ) × 10 22 cm −2 and (3.1 +0.3 −0.3 ) × 10 22 cm −2 respectively) (Lee et al 2002). The last two values are both consistent with our calculated N H as well as the one from ASCA (Ebisawa et al 1998).…”

“…Meanwhile, another team evaluated the optical extinction to GRS 1915+105 to A v = 18−24 mag (Castro-Tirado et al 1996) with the help of the X-ray hydrogen absorption column density and the pioneering work of Gorenstein (1975) relating the optical extinction to the total hydrogen column density. Moreover, we have to note that the hydrogen column density derived from Si and Fe edges (X-ray observations with Chandra) is substantially higher than 5 × 10 22 cm −2 (leading to an extinction of 28 mag) and should imply additional local absorption (Lee et al 2002) although the Mg and S edges lead to consistent values of N H with the one of Ebisawa et al (1998). An overestimate of the extinction would allow higher dereddened fluxes in K bands and flat spectrum from radio to IR (Fuchs et al 2003).…”

“…The last two values are both consistent with our calculated N H as well as the one from ASCA (Ebisawa et al 1998). Based on the values of N H inferred from Si and Fe edges, it was suggested that either a highly unusual supernova or external supernova activity local to the binary could explain the overabundance in iron and silicon (Lee et al 2002). Indeed, it seems that a 10 52 erg kinetic energy SNe with high mixing, helped by a small mass cut and/or asphericity in explosion can provide high amounts of ejected 56 Ni, and thus ejected iron after 56 Ni decay A λ (mag) 30.8 ± 2.8 26.2 ± 2.3 19.6 ± 1.7 14.7 ± 1.3 9.4 ± 0.8 5.5 ± 0.5 3.7 ± 0.4 2.2 ± 0.3 1.1 ± 0.1 (Nomoto et al 2003).…”

Discovery of narrow X-ray absorption features from the dipping low-mass X-ray binary X 1624-490 with XMM-Newton

“…Narrow X-ray absorption lines were first detected from the superluminal jet sources GRO J1655−40 (Ueda et al 1998;Yamaoka et al 2001) and GRS 1915+105 (Kotani et al 2000;Lee et al 2002). ASCA observations of GRO J1655−40 revealed the presence of absorption features due to Fe xxv and Fe xxvi which did not show any obvious dependence of their EWs on orbital phase.…”