Possible Detection of X-Ray Emitting Circumstellar Material in the Synchrotron-dominated Supernova Remnant RX J1713.7−3946

We report on a discovery of an X-ray emitting circumstellar material (CSM) knot inside the synchrotron dominant supernova remnant RX J1713.7−3946. This knot was previously thought to be a Wolf–Rayet star (WR 85), but we realized that it is in fact ∼40″ away from WR 85, indicating no relation to WR 85. We performed high-resolution X-ray spectroscopy with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. The RGS spectrum clearly resolves a number of emission lines, such as N Lyα, O Lyα, Fe xviii, Ne x, Mg xi, and Si xiii. The spectrum can be well represented by an absorbed thermal-emission model with a temperature of k B T e = 0.65 ± 0.02 keV. The elemental abundances are obtained to be N / H = 3.5 ± 0.8 N / H ⊙ , O / H = 0.5 ± 0.1 O / H ⊙ , Ne / H = 0.9 ± 0.1 Ne / H ⊙ , Mg / H = 1.0 ± 0.1 Mg / H ⊙ , Si / H = 1.0 ± 0.2 Si / H ⊙ , and Fe / H = 1.3 ± 0.1 Fe / H ⊙ . The enhanced N abundance with others being about the solar values allows us to infer that this knot is CSM ejected when the progenitor star evolved into a red supergiant. The abundance ratio of N to O is obtained to be N / O = 6.8 − 2.1 + 2.5 N / O ⊙ . By comparing this to those in outer layers of red supergiant stars expected from stellar evolution simulations, we estimate the initial mass of the progenitor star to be 15 M ⊙ ≲ M ≲ 20 M ⊙.

Variable oxygen emission from the accretion disk of Mrk 110

Six XMM-Newton observations of the bright narrow line Seyfert 1, Mrk 110, from 2004–2020, are presented. The analysis of the grating spectra from the Reflection Grating Spectrometer (RGS) reveals a broad component of the He-like Oxygen (O VII) line, with a full width at half maximum of 15 900 ± 1800 km s−1 measured in the mean spectrum. The broad O VII line in all six observations can be modelled with a face-on accretion disk profile, where from these profiles the inner radius of the line emission is inferred to lie between about 20–100 gravitational radii from the black hole. The derived inclination angle, of about 10 degrees, is consistent with studies of the optical Broad Line Region in Mrk 110. The line also appears variable and for the first time, a significant correlation is measured between the O VII flux and the continuum flux from both the RGS and EPIC-pn data. Thus the line responds to the continuum, being brightest when the continuum flux is highest, similar to the reported behaviour of the optical He II line. The density of the line emitting gas is estimated to be ne ∼ 1014 cm−3, consistent with an origin in the accretion disk.

Performance Testing of a Large-Format X-ray Reflection Grating Prototype for a Suborbital Rocket Payload

The soft X-ray grating spectrometer on board the Off-plane Grating Rocket Experiment (OGRE) hopes to achieve the highest resolution soft X-ray spectrum of an astrophysical object when it is launched via suborbital rocket. Paramount to the success of the spectrometer are the performance of the [Formula: see text] reflection gratings populating its reflection grating assembly. To test current grating fabrication capabilities, a grating prototype for the payload was fabricated via electron-beam lithography at The Pennsylvania State University’s Materials Research Institute and was subsequently tested for performance at Max Planck Institute for Extraterrestrial Physics’ PANTER X-ray Test Facility. Bayesian modeling of the resulting data via Markov chain Monte Carlo (MCMC) sampling indicated that the grating achieved the OGRE single-grating resolution requirement of [Formula: see text] at the 94% confidence level. The resulting [Formula: see text] posterior probability distribution suggests that this confidence level is likely a conservative estimate though, since only a finite [Formula: see text] parameter space was sampled and the model could not constrain the upper bound of [Formula: see text] to less than infinity. Raytrace simulations of the tested system found that the observed data can be reproduced with a grating performing at [Formula: see text]. It is therefore postulated that the behavior of the obtained [Formula: see text] posterior probability distribution can be explained by a finite measurement limit of the system and not a finite limit on [Formula: see text]. Implications of these results and improvements to the test setup are discussed.

The various accretion modes of AM Herculis: Clues from multi-wavelength observations in high accretion states

We report on XMM-Newton and NuSTAR X-ray observations of the prototypical polar, AM Herculis, supported by ground-based photometry and spectroscopy, all obtained in high accretion states. In 2005, AM Herculis was in its regular mode of accretion, showing a self-eclipse of the main accreting pole. X-ray emission during the self-eclipse was assigned to a second pole through its soft X-ray emission and not to scattering. In 2015, AM Herculis was in its reversed mode with strong soft blobby accretion at the far accretion region. The blobby acretion region was more luminous than the other, persistently accreting, therefore called main region. Hard X-rays from the main region did not show a self-eclipse indicating a pronounced migration of the accretion footpoint. Extended phases of soft X-ray extinction through absorption in interbinary matter were observed for the first time in AM Herculis. The spectral parameters of a large number of individual soft flares could be derived. Simultaneous NuSTAR observations in the reversed mode of accretion revealed clear evidence for Compton reflection of radiation from the main pole at the white dwarf surface. This picture is supported by the trace of the Fe resonance line at 6.4 keV through the whole orbit. Highly ionized oxygen lines observed with the Reflection Grating Spectrometer (RGS) were tentatively located at the bottom of the accretion column, although the implied densities are quite different from expectations. In the regular mode of accretion, the phase-dependent modulations in the ultraviolet (UV) are explained with projection effects of an accretion-heated spot at the prime pole. In the reversed mode projection effects cannot be recognized. The light curves reveal an extra source of UV radiation and extended UV absorbing dips. An Hα Doppler map obtained contemporaneously with the NuSTAR and XMM-Newton observations in 2015 lacks the typical narrow emission line from the donor star but reveals emission from an accretion curtain in all velocity quadrants, indicating widely dispersed matter in the magnetosphere.