S. Vaughan

XMM-Newton discovery of a sharp spectral feature at ~ 7 keV in the narrow-line Seyfert 1 galaxy 1H 0707-495

We report the first detection of a sharp spectral feature in a narrow-line Seyfert 1 galaxy. Using XMM-Newton we have observed 1H 0707 - 495 and find a drop in flux by a factor of more than 2 at a rest-frame energy of ∼ 7keV without any detectable narrow Fe Ka line emission. The energy of this feature suggests a connection with the neutral iron K photoelectric edge, but the lack of any obvious absorption in the spectrum at lower energies makes the interpretation challenging. We explore two alternative explanations for this unusual spectral feature: (i) partial-covering absorption by clouds of neutral material; and (ii) ionized disc reflection with lines and edges from different ionization stages of iron blurred together by relativistic effects. We note that both models require an iron overabundance to explain the depth of the feature. The X-ray light curve shows strong and rapid variability, changing by a factor of 4 during the observation. The source displays modest spectral variability which is uncorrelated with flux.

SPACE TELESCOPE AND OPTICAL REVERBERATION MAPPING PROJECT. II. SWIFT AND HST REVERBERATION MAPPING OF THE ACCRETION DISK OF NGC 5548

Recent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and the X-rays. This is the densest extended active galactic nucleus (AGN) UV/optical continuum sampling ever obtained, with a mean sampling rate <0.5 day. Approximately daily Hubble Space Telescope UV sampling was also obtained. The UV/optical light curves show strong correlations (r max =0.57-0.90) and the clearest measurement to date of interband lags. These lags are well-fit by a τ ∝ λ4/3 wavelength dependence, with a normalization that indicates an unexpectedly large disk radius of ∼0.35 ± 0.05 lt-day at 1367 A, assuming a simple face-on model. The U band shows a marginally larger lag than expected from the fit and surrounding bands, which could be due to Balmer continuum emission from the broad-line region as suggested by Korista and Goad. The UV/X-ray correlation is weaker (rm < 0.45) and less consistent over time. This indicates that while Swift is beginning to measure UV/optical lags in general agreement with accretion disk theory (although the derived size is larger than predicted), the relationship with X-ray variability is less well understood. Combining this accretion disk size estimate with those from quasar microlensing studies suggests that AGN disk sizes scale approximately linearly with central black hole mass over a wide range of masses.

Long-term spectral changes in the partial-covering candidate narrow-line Seyfert 1 galaxy 1H 0707-495

We compare two XMM-Newton observations of the Narrow-Line Seyfert 1 galaxy 1H 0707–495 separated by two years, and discuss the results in terms of the partialcovering phenomenon. The second longer observation once again displays a sharp (< 200 eV) spectral drop above 7 keV; however, in comparison to the first observation, the edge depth and energy have changed significantly. In addition to changes in the edge parameters, the high-energy spectrum appears steeper. The changes in the highenergy continuum can be adequately explained in terms of a partial-covering absorber outflowing from the central region. The low-energy spectrum also shows significant long-term spectral variability, including: a substantial increase in the disc temperature; detection of a � 0.9 keV emission feature; and the presence of warm absorption that was also detected during the ASCA mission, but not seen during the first XMMNewton observation. The large increase in disc temperature, and more modest rise in luminosity, can be understood if we consider the slim-disc model for 1H 0707–495. In addition, the higher disc luminosity could be the driving force behind the outflow scenario and the re-appearance of a warm medium during the second XMM-Newton observation.

The Discovery of an Evolving Dust-scattered X-Ray Halo around GRB 031203

We report the first detection of a time-dependent dust-scattered X-ray halo around a gamma-ray burst (GRB). GRB 031203 was observed by XMM-Newton starting 6 hr after the burst. The halo appeared as concentric ringlike structures centered on the GRB location. The radii of these structures increased with time as t1/2, consistent with small-angle X-ray scattering caused by a large column of dust along the line of sight to a cosmologically distant GRB. The rings are due to dust concentrated in two distinct slabs in the Galaxy located at distances of 880 and 1390 pc, consistent with known Galactic features. The halo brightness implies an initial soft X-ray pulse consistent with the observed GRB.

Discovery of an Afterglow Extension of the Prompt Phase of Two Gamma Ray Bursts Observed by Swift

Contemporaneous BAT and XRT observations of two recent well-covered GRBs observed by Swift, GRB 050315 and GRB 050319, show clearly a prompt component of the afterglow emission. The rapid slewing capability of the spacecraft enables X-ray observations immediately after the burst, typically approximately 100 s following the initiation of the prompt gamma-ray phase. By fitting a power law form to the gamma-ray spectrum, we extrapolate the time dependent fluxes measured by the BAT, in the energy band 15 - 350 keV, into the spectral regime observed by the XRT, 0.2 - 10 keV, and examine the functional form of the rate of decay of the two light curves. We find that the BAT and XRT light curves merge to form a unified curve. There is a period of steep decay up to approximately 300 s, followed by a flatter decay. The duration of the steep decay, approximately 100 s in the source frame after correcting for cosmological time dilation, agrees with a theoretical estimate for the deceleration time of the relativistic ejecta as it interacts with circumstellar material. For GRB 050315, the steep decay can be characterized by an exponential form, where T(sub e),(BAT)approximately equal to 24 plus or minus 2 s, and T(sub e)(XRT) approximately equal to 35 plus or minus 2 s. For GRB 050319 a power law decay -d lnf/d lnt = n, where n approximately equal to 3, provides a reasonable fit. The early time X-ray fluxes are consistent with representing the lower energy tail of the prompt emission, and provide our first quantitative measure of the decay of the prompt gamma-ray emission over a large dynamic range. The initial steep decay is expected from the high latitude emission from a curved shell of relativistic plasma illuminated only for a short interval. The overall conclusion is that the prompt phase of GRBs lasts for hundreds of seconds longer than previously thought.

Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing

NASA [NNX13AC26G, NNX13AC63G, NNX13AE99G, NNH13CH61C]; NSF [AST-1412693, AST-1253702, AST-1211916, AST-1009571, AST-1210311, AST-1412315]; STFC [ST/M001296/1]; National Research Foundation (NRF) of South Africa; UK Space Agency; TABASGO Foundation; Christopher R. Redlich Fund; Packard Foundation; Danish Council for Independent Research [DFF 4002-00275]

Extensive X-ray variability studies of NGC 7314 using long XMM–Newton observations

DE and IMM acknowledge the Science and Technology Facilities Council (STFC) for support under grant ST/G003084/1. SV acknowledges the STFC for support under grant ST/K001000/1. DE is grateful to Dr Abdu Zoghbi who provided all the necessary information about the analysis methods used in ZO13 during the workshop ‘The X-ray Spectral-Timing Revolution’ in 2016 February, Leiden, the Netherlands. This research has made use of NASA’s Astrophysics Data System Bibliographic Services.