arXiv subjects

Kim Page

Publications and source records attributed to Kim Page.

17 recordsLinked to original sources

arXiv2026

4th TDAMM Workshop White Paper

Time-Domain and Multi-Messenger Astrophysics (TDAMM) is entering a new era in which the rate and diversity of transient discoveries will grow rapidly across electromagnetic, gravitational-wave, neutrino, and cosmic-ray facilities. The scientific return from these investments will increasingly depend not on discovery alone, but on the ability to identify, prioritize, and coordinate follow-up observations across a heterogeneous and globally distributed network of observatories. This white paper summarizes the outcomes of the Fourth TDAMM Workshop and assesses the near-term discovery landscape, the infrastructure and tools that support coordinated observations, and the technical, policy, and capability gaps that may limit future progress. The workshop identified three principal challenges: insufficiently scalable and interoperable alert and coordination infrastructure, policies that impede rapid multi-facility observations and rare-event science, and the potential loss of critical high-energy, rapid-response, and spectroscopic capabilities. The white paper identifies the need for sustained support for alert distribution, brokers, standardized observatory metadata, cross-facility coordination platforms, and unified follow-up repositories; expanded joint observing opportunities and funding mechanisms for coordinated analysis; and strategic investment in future TDAMM facilities. The white paper also present a framework for community observing plans that would establish pre-coordinated responses to rare, high-impact events, supported by transparent governance, immediate public data release, and regular community revision. Science overviews and detailed observing strategies are provided for gamma-ray bursts, tidal disruption events, X-ray binaries, novae, supernovae, magnetars, compact binary mergers, and high-energy neutrino sources.

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arXiv2025

X-ray Observations of Nova Scorpii 2023 (V1716 Sco) in Outburst

Nova Scorpii 2023 was first detected as a luminous supersoft X-ray source (SSS) 93 days after outburst and continued emitting soft X-rays for over two months, until it was too close to the Sun to observe. The nova was monitored with the Swift X-ray Telescope (XRT) and the Neutron Star Interior Composition Explorer (NICER) on the International Space Station, and in long exposures with the Chandra High Resolution Camera (HRC) and Low Energy Transmission Grating (LETG) on days 128, 129, and 183-185 after optical maximum. Swift detected a rapidly decaying SSS when observations resumed, constraining the constant bolometric luminosity phase to 9 months. The SSS flux was irregularly variable. A nearly three-fold increase in flux was observed between August and October 2023 in the 15 to 35 Angstrom range, from 3.5 x 10^(-11) to 9.4 x 10^(-11) erg cm^(-2) s^(-1). The SSS duration and effective temperature derived from the October LETG spectra indicate a massive white dwarf with temperature fitting nova evolutionary tracks for a 1.2 solar mass WD; emission lines superimposed on the WD continuum are attributed to surrounding shocked ejecta. We present a timing study based on Chandra and archival NICER data. The irregular variability timescale was days, but a 77.9 second periodic modulation in the SSS flux with varying amplitude was measured in many observations. Our analysis shows that this period was stable; short drifts derived with NICER, but not in long, uninterrupted Chandra exposures, are artifacts of measuring variable amplitude modulation. We suggest the modulations are associated with the WD rotation.

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arXiv2024

Swift-BAT GUANO follow-up of gravitational-wave triggers in the third LIGO-Virgo-KAGRA observing run

We present results from a search for X-ray/gamma-ray counterparts of gravitational-wave (GW) candidates from the third observing run (O3) of the LIGO-Virgo-KAGRA (LVK) network using the Swift Burst Alert Telescope (Swift-BAT). The search includes 636 GW candidates received in low latency, 86 of which have been confirmed by the offline analysis and included in the third cumulative Gravitational-Wave Transient Catalogs (GWTC-3). Targeted searches were carried out on the entire GW sample using the maximum--likelihood NITRATES pipeline on the BAT data made available via the GUANO infrastructure. We do not detect any significant electromagnetic emission that is temporally and spatially coincident with any of the GW candidates. We report flux upper limits in the 15-350 keV band as a function of sky position for all the catalog candidates. For GW candidates where the Swift-BAT false alarm rate is less than 10$^{-3}$ Hz, we compute the GW--BAT joint false alarm rate. Finally, the derived Swift-BAT upper limits are used to infer constraints on the putative electromagnetic emission associated with binary black hole mergers.

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arXiv2024

Mixing of hot shocked plasma with cold gas in Nova YZ Ret 2020

The origin of bright X-ray emission lines that appear late in a nova eruption remains largely a puzzle. We present two high-resolution X-ray grating spectra of the classical nova YZ Ret, observed 77 and 115 days post-eruption, using XMM-Newton and Chandra , respectively. Both spectra feature resolved emission lines blueshifted by $v = -1500$ km s$^{-1}$ and broadened by $\sigma_v=500$ km s$^{-1}$. The two spectra are well described by a collisionally ionized plasma of $kT\sim 70$ eV that dimmed by a factor of $\sim40$ between the two exposures. The spectra also show narrow radiative recombination continua (RRCs) of C$^{+4}$, C$^{+5}$, and N$^{+5}$, indicating the interaction of the hot ionized plasma with cold electrons of $kT\sim 2$ eV. The high-$n$ Rydberg series of C$^{+4}$ is anomalously bright, allowing us to measure the electron density through continuum lowering, which is in agreement with the He-like N$^{+5}$ density diagnostic of $n_e=(1.7\pm0.4)\times10^{11}$ cm$^{-3}$. The high population of these high-$n$ levels constitutes the best evidence to date of charge exchange (CX) with neutral H in an astrophysical ionized plasma. The remarkable fact that the velocity and plasma temperature are the same after 38 days, despite the high density and decreasing flux is evidence for ongoing heating. We suggest the heating is due to a reverse shock in the nova ejecta, which forms a thin X-ray shell. The narrow RRCs and CX are attributed to direct mixing with cold gas, which overtakes the hot plasma either from the shock front, or through the contact discontinuity.

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arXiv2023

Low-redshift absorption in the Seyfert galaxy PG 1211+143 -- a distant inflow maintaining off-plane accretion or the gravitational redshift of matter orbiting the SMBH?

The detection of a high velocity (~ 0.3c) inflow of highly ionized matter during an extended XMM-Newton observation of the luminous Seyfert galaxy PG 1211+143 in 2014 provided the first direct evidence of a short-lived accretion event, and an explanation for the powerful winds (UFOs) now recognised as a common property of many luminous Seyfert galaxies. Although the ultra-fast inflow - observed at a redshift of 0.483 - was detected in only one of seven spacecraft orbits, weaker (lower column) but more persistent absorption is seen - at a redshift of 0.123 - in the high exposure, soft X-ray (RGS) spectra summed over all 7 individual spacecraft orbits. Similar stacking of the higher energy (pn camera) spectra reveals underlying absorption at a redshift of 0.148. Interpreted, conventionally, as a Doppler redshift, the RGS observation indicates a line-of-sight inflow velocity v ~ 0.038c and (free-fall) radial location at 1400 R_g, with the higher redshift and ionization in pn camera spectra perhaps detecting that inflow closer to the black hole. A very different explanation would be absorption in matter subject to the strong gravity close to the SMBH, an interpretation supported by the launch of a new UFO in the final spacecraft orbit.

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arXiv2023

Observing the launch of an Eddington wind in the luminous Seyfert galaxy PG1211+143

The luminous narrow line Seyfert galaxy PG1211+143 was the first non-BAL AGN to reveal a powerful ionized wind, based on early observations with ESA's XMM-Newton X-ray Observatory. Subsequent observations, mainly with XMM-Newton and the Japanese Suzaku Observatory, found such winds to be a common feature of luminous AGN. Typical outflow velocities of v ~ 0.1c and flow momenta mv ~ L_Edd /c are consistent with winds being launched by continuum driving from a disc when the local mass accretion rate is super-Eddington. Here we report the launch of a new, ultra-fast outflow component in PG1211+143, near the end of a 5-week XMM-Newton observing campaign, and discuss its origin in an ultra-fast {\it inflow} detected some 3 weeks earlier. We note that the inflow lasted for at least 3 days and delivered at least 10 Earth mass of fresh material into the innermost region of the source. While this mass by itself is insufficient to cause a complete inner disc restructuring - a prediction supported by lack of change in simultaneous UV fluxes - we suggest that a ring of matter at R ~ 20 R_g, located via its gravitational redshift (Pounds and Page 2024), was subsequently accreted, leading to the launch of a new outflow at a velocity of v ~ 0.27c.

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arXiv2023

Multiwavelength spectroscopic study of shock driven phenomena in explosive outbursts in symbiotic-like recurrent novae with emphasis on RS Ophiuchi

To detail the development of RS Ophiuchi and the other Galactic Symbiotic-like Recurrent Novae throughout their outburst and quiescence, with a particular emphasis on the propagation of the shock wave during the outburst of the binaries. The spectral analysis has been performed using archival data according to the features of the individual datasets. Swift grism spectra were reduced and extracted using a combination of the pre-existing UVOTPY Python routine and newly written pipelines in Matlab. Other datasets were directly available in reduced form, already corrected for instrumental or background contamination, calibrated in wavelength and flux or intensity. The work on these was done through pipelines suited for reading the data and elaborating them to extract quantities of interest for the analysis. We find striking similarities in different outbursts of the same object and for different novae. For example, RS Oph 2021 was almost identical to the 2006 outburst, despite having occurred at a different orbital phase with the observations made from a different line of sight through the red giant wind. Despite the intrinsically different properties of the binaries, striking similarities are found for different systems of the same class, for instance, that the trend of the electron density over time during outburst appears to follow a general temporal development.

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arXiv2022

A Cosmological Fireball with Sixteen-Percent Gamma-Ray Radiative Efficiency

Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. How efficiently the jet converts its energy to radiation is a long-standing problem and it is poorly constrained. The standard model invokes a relativistic fireball with a bright photosphere emission component. A definitive diagnosis of GRB radiation components and measurement of GRB radiative efficiency require prompt emission and afterglow data with high-resolution and wide-band coverage in time and energy. Here we report a comprehensive temporal and spectral analysis of the TeV-emitting bright GRB 190114C. Its fluence is one of the highest of all GRBs detected so far, which allows us to perform a high-resolution study of the prompt emission spectral properties and their temporal evolution down to a timescale of about 0.1 s. We observe that each of the initial pulses has a thermal component contributing $\sim20\%$ of the total energy, the corresponding temperature and the inferred Lorentz factor of the photosphere evolve following broken power-law shapes. From the observation of the non-thermal spectra and the light curve, the onset of afterglow corresponding to the deceleration of the fireball is considered at $\sim 6$~s. By incorporating the thermal and the non-thermal observations, as well as the photosphere and the synchrotron radiative mechanisms, we can directly derive the fireball energy budget with little dependence on hypothetical parameters and to measure a $\sim 16\%$ radiative efficiency for this GRB. With the fireball energy budget derived, the afterglow microphysics parameters can also be constrained directly from the data.

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arXiv2019

A Swift view of X-ray and UV radiation in the planet-forming T-Tauri system PDS 70

PDS 70 is a $\sim$5 Myr old star with a gas and dust disc in which several proto-planets have been discovered. We present the first UV detection of the system along with X-ray observations taken with the \textit{Neil Gehrels Swift Observatory} satellite. PDS 70 has an X-ray flux of 3.4$\times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ in the 0.3-10.0 keV range, and UV flux (U band) of 3.5$\times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ . At the distance of 113.4 pc determined from Gaia DR2 this gives luminosities of 5.2$\times 10^{29}$ erg s$^{-1}$ and 5.4$\times 10^{29}$ erg s$^{-1}$ respectively. The X-ray luminosity is consistent with coronal emission from a rapidly rotating star close to the log $\frac{L_{\mathrm{X}}}{L_{\mathrm{bol}}} \sim -3$ saturation limit. We find the UV luminosity is much lower than would be expected if the star were still accreting disc material and suggest that the observed UV emission is coronal in origin.

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arXiv2018

V1369 Cen high resolution panchromatic late nebular spectra in the context of a unified picture for nova ejecta

Nova Cen 2013 (V1369 Cen) is the fourth bright nova observed panchromatically through high resolution UV+optical multi epoch spectroscopy. It is also the nova with the richest set of spectra (both in terms of data quality and number of epochs) thanks to its exceptional brightness. Here, we use the late nebular spectra taken between day ~250 and day ~837 after outburst to derive the physical, geometrical and kinematical properties of the nova. We compare the results with those determined for the other panchromatic studies in this series: T Pyx, V339 Del (nova Del 2013), and V959 Mon (nova Mon 2012). From this we conclude that in all these novae the ejecta geometry and phenomenology can be consistently explained by clumpy gas expelled during a single, brief ejection episode and in ballistic expansion, and not by a wind. For V1369 Cen the ejecta mass (about 1E-4 solar masses) and filling factor (0.1<=f<=0.2) are consistent with those of classical novae but larger (by at least an order of magnitude) than those of T Pyx and the recurrent novae. V1369 Cen has an anomalously high relative to solar N/C ratio that is beyond the range currently predicted for a CO nova, and the Ne emission line strengths are dissimilar to those of typical ONe or CO white dwarfs.

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arXiv2016

A Very Bright, Very Hot, and Very Long Flaring Event from the M Dwarf Binary System DG CVn

On April 23, 2014, the Swift satellite responded to a hard X-ray transient detected by its Burst Alert Telescope, which turned out to be a stellar flare from a nearby, young M dwarf binary DG~CVn. We utilize observations at X-ray, UV, optical, and radio wavelengths to infer the properties of two large flares. The X-ray spectrum of the primary outburst can be described over the 0.3-100 keV bandpass by either a single very high temperature plasma or a nonthermal thick-target bremsstrahlung model, and we rule out the nonthermal model based on energetic grounds. The temperatures were the highest seen spectroscopically in a stellar flare, at T$_{X}$ of 290 MK. The first event was followed by a comparably energetic event almost a day later. We constrain the photospheric area involved in each of the two flares to be $>$10$^{20}$ cm$^{2}$, and find evidence from flux ratios in the second event of contributions to the white light flare emission in addition to the usual hot, T$\sim$10$^{4}$K blackbody emission seen in the impulsive phase of flares. The radiated energy in X-rays and white light reveal these events to be the two most energetic X-ray flares observed from an M dwarf, with X-ray radiated energies in the 0.3-10 keV bandpass of 4$\times$10$^{35}$ and 9$\times$10$^{35}$ erg, and optical flare energies at E$_{V}$ of 2.8$\times$10$^{34}$ and 5.2$\times$10$^{34}$ erg, respectively. The results presented here should be integrated into updated modelling of the astrophysical impact of large stellar flares on close-in exoplanetary atmospheres.

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arXiv2016

Demonstrating the likely neutron star nature of five M31 globular cluster sources with Swift-NuSTAR spectroscopy

We present the results of a joint Swift-NuSTAR spectroscopy campaign on M31. We focus on the five brightest globular cluster X-ray sources in our fields. Two of these had previously been argued to be black hole candidates on the basis of apparent hard-state spectra at luminosities above those for which neutron stars are in hard states. We show that these two sources are likely to be Z-sources (i.e. low magnetic field neutron stars accreting near their Eddington limits), or perhaps bright atoll sources (low magnetic field neutron stars which are just a bit fainter than this level) on the basis of simultaneous Swift and NuSTAR spectra which cover a broader range of energies. These new observations reveal spectral curvature above 6-8 keV that would be hard to detect without the broader energy coverage the NuSTAR data provide relative to Chandra and XMM-Newton. We show that the other three sources are also likely to be bright neutron star X-ray binaries, rather than black hole X-ray binaries. We discuss why it should already have been realized that it was unlikely that these objects were black holes on the basis of their being persistent sources, and we re-examine past work which suggested that tidal capture products would be persistently bright X-ray emitters. We discuss how this problem is likely due to neglecting disk winds in older work that predict which systems will be persistent and which will be transient.

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arXiv2008

Reprocessing of X-rays in the outer accretion disc of the black hole binary XTE J1817--330

We build a simple model of the optical/UV emission from irradiation of the outer disc by the inner disc and coronal emission in black hole binaries. We apply this to the broadband Swift data from the outburst of the black hole binary XTE J1817--330 to confirm previous results that the optical/UV emission in the soft state is consistent with a reprocessing a constant fraction of the bolometric X-ray luminosity. However, this is very surprising as the disc temperature drops by more than a factor 3 in the soft state, which should produce a marked change in the reprocessing efficiency. The easiest way to match the observed constant reprocessed fraction is for the disc skin to be highly ionized (as suggested 30 years ago by van Paradijs), so that the bulk of the disc flux is reflected and only the hardest X-rays heat the disc. The constant reprocessed fraction also favours direct illumination of the disc over a scattering origin as the optical depth/solid angle of any scattering material (wind/corona) over the disc should decrease as the source luminosity declines. By contrast, the reprocessed fraction increases very significantly (by a factor ~6) as the source enters the hard state. This dramatic change is not evident from X-ray/UV flux correlations as it is masked by bandpass effects. However, it does not necessarily signal a change in emission e.g. the emergence of the jet dominating the optical/UV flux as the reflection albedo must change with the dramatic change in spectral shape.

astro-ph↗

arXiv2008

X-ray irradiation in XTE J1817-330 and the inner radius of the truncated disc in the hard state

The key aspect of the very successful truncated disc model for the low/hard X-ray spectral state in black hole binaries is that the geometrically thin disc recedes back from the last stable orbit at the transition to this state. This has recently been challenged by direct observations of the low/hard state disc from CCD data. We reanalyze the Swift and RXTE campaign covering the 2006 outburst of XTE J1817-330 and show that these data actually strongly support the truncated disc model as the transition spectra unambiguously show that the disc begins to recede as the source leaves the disc dominated soft state. The disc radius inferred for the proper low/hard state is less clear-cut, but we show that the effect of irradiation from the energetically dominant hot plasma leads to an underestimate of the disc radius by a factor of 2-3 in this state. This may also produce the soft excess reported in some hard-state spectra. The inferred radius becomes still larger when the potential difference in stress at the inner boundary, increased colour temperature correction from incomplete thermalization of the irradiation, and loss of observable disc photons from Comptonization in the hot plasma are taken into account. We conclude that the inner disc radius in XTE J1817-330 in the low/hard spectral state is at least 6-8 times that seen in the disc dominated high/soft state, and that recession of the inner disc is the trigger for the soft--hard state transition, as predicted by the truncated disc models.

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arXiv2006

The Swift X-ray flaring afterglow of GRB 050607

The unique capability of the Swift satellite to perform a prompt and autonomous slew to a newly detected Gamma-Ray Burst (GRB) has yielded the discovery of interesting new properties of GRB X-ray afterglows, such as the steep early lightcurve decay and the frequent presence of flares detected up to a few hours after the GRB trigger. We present observations of GRB 050607, the fourth case of a GRB discovered by Swift with flares superimposed on the overall fading X-ray afterglow. The flares of GRB 050607 were not symmetric as in previously reported cases, showing a very steep rise and a shallower decay, similar to the Fast Rise, Exponential Decay that are frequently observed in the gamma-ray prompt emission. The brighter flare had a flux increase by a factor of approximately 25,peaking for 30 seconds at a count rate of approximately 30 counts s-1, and it presented hints of addition short time scale activity during the decay phase. There is evidence of spectral evolution during the flares. In particular, at the onset of the flares the observed emission was harder, with a gradual softening as each flare decayed. The very short time scale and the spectral variability during the flaring activity are indicators of possible extended periods of energy emission by the GRB central engine. The flares were followed by a phase of shallow decay, during which the forward shock was being refreshed by a long-lived central engine or by shells of lower Lorentz factors, and by a steepening after approximately 12 ks to a decay slope considered typical of X-ray afterglows.

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arXiv2005

Gamma-ray bursts: Restarting the Engine

Recent gamma-ray burst observations have revealed late-time, highly energetic events which deviate from the simplest expectations of the standard fireball picture. Instead they may indicate that the central engine is active or restarted at late times. We suggest that fragmentation and subsequent accretion during the collapse of a rapidly rotating stellar core offers a natural mechanism for this.

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arXiv2001

An XMM-Newton observation of the luminous Seyfert 1 galaxy Markarian 509

We present the spectral analysis of an early XMM-Newton observation of the luminous Seyfert 1 galaxy Markarian 509. We find the hard (2-10 keV) continuum slope, including reflection, to be somewhat flatter ($Γ=1.75$) than for a typical BLS1. The most obvious feature in the hard X-ray spectrum is a narrow emission line near 6.4 keV, with an equivalent width of 50 eV. The energy and strength of this line is consistent with fluorescence from `neutral' iron in the molecular torus, and we note the emerging ubiquity of this feature in XMM-Newton and Chandra observations of Seyfert 1 galaxies over a wide luminosity range. We also find evidence for a second emission line at 6.7-6.9 keV, which we attempt to model by reflection from a highly ionised disc. A `soft excess', evident as an upward curvature in the continuum flux below 1.5 keV, cannot be explained solely by enhanced reflection from the ionised disc. The RGS spectrum shows only weak discrete emission and absorption features in the soft X-ray spectrum, supporting our conclusion that the soft excess emission in Mkn 509 represents the high energy portion of optically thick, thermal emission from the inner accretion disc.

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