arXiv subjects

K. L. Page

Publications and source records attributed to K. L. Page.

At least 91 records · Page 5Linked to original sources

arXiv2012

The prompt-afterglow connection in Gamma-Ray Bursts: a comprehensive statistical analysis of Swift X-ray light-curves

We present a comprehensive statistical analysis of Swift X-ray light-curves of Gamma-Ray Bursts (GRBs) collecting data from more than 650 GRBs discovered by Swift and other facilities. The unprecedented sample size allows us to constrain the REST FRAME X-ray properties of GRBs from a statistical perspective, with particular reference to intrinsic time scales and the energetics of the different light-curve phases in a common rest-frame 0.3-30 keV energy band. Temporal variability episodes are also studied and their properties constrained. Two fundamental questions drive this effort: i) Does the X-ray emission retain any kind of "memory"of the prompt gamma-ray phase? ii) Where is the dividing line between long and short GRB X-ray properties? We show that short GRBs decay faster, are less luminous and less energetic than long GRBs in the X-rays, but are interestingly characterized by similar intrinsic absorption. We furthermore reveal the existence of a number of statistically significant relations that link the X-ray to prompt gamma-ray parameters in long GRBs; short GRBs are outliers of the majority of these 2-parameter relations. However and more importantly, we report on the existence of a universal 3-parameter scaling that links the X-ray and the gamma-ray energy to the prompt spectral peak energy of BOTH long and short GRBs: E_{X,iso}\propto E_{gamma,iso}^{1.00\pm 0.06}/E_{pk}^{0.60\pm 0.10}.

astro-ph.HE↗

arXiv2012

A search for thermal X-ray signatures in Gamma-Ray Bursts I: Swift bursts with optical supernovae

The X-ray spectra of Gamma-Ray Bursts can generally be described by an absorbed power law. The landmark discovery of thermal X-ray emission in addition to the power law in the unusual GRB 060218, followed by a similar discovery in GRB 100316D, showed that during the first thousand seconds after trigger the soft X-ray spectra can be complex. Both the origin and prevalence of such spectral components still evade understanding, particularly after the discovery of thermal X-ray emission in the classical GRB 090618. Possibly most importantly, these three objects are all associated with optical supernovae, begging the question of whether the thermal X-ray components could be a result of the GRB-SN connection, possibly in the shock breakout. We therefore performed a search for blackbody components in the early Swift X-ray spectra of 11 GRBs that have or may have associated optical supernovae, accurately recovering the thermal components reported in the literature for GRBs 060218, 090618 and 100316D. We present the discovery of a cooling blackbody in GRB 101219B/SN2010ma, and in four further GRB-SNe we find an improvement in the fit with a blackbody which we deem possible blackbody candidates due to case-specific caveats. All the possible new blackbody components we report lie at the high end of the luminosity and radius distribution. GRB 101219B appears to bridge the gap between the low-luminosity and the classical GRB-SNe with thermal emission, and following the blackbody evolution we derive an expansion velocity for this source of order 0.4c. We discuss potential origins for the thermal X-ray emission in our sample, including a cocoon model which we find can accommodate the more extreme physical parameters implied by many of our model fits.

astro-ph.HE↗

arXiv2012

CC Sculptoris: A superhumping intermediate polar

We present high speed optical, spectroscopic and Swift X-ray observations made during the dwarf nova superoutburst of CC Scl in November 2011. An orbital period of 1.383 h and superhump period of 1.443 h were measured, but the principal new finding is that CC Scl is a previously unrecognised intermediate polar, with a white dwarf spin period of 389.49 s which is seen in both optical and Swift X-ray light curves only during the outburst. In this it closely resembles the old nova GK Per, but unlike the latter has one of the shortest orbital periods among intermediate polars.

astro-ph.SR↗

arXiv2012

Infrared observations of the recurrent nova T Pyxidis: ancient dust basks in the warm glow of the 2011 outburst

We present Spitzer Space Telescope and Herschel Space Observatory infrared observations of the recurrent nova T Pyx during its 2011 eruption, complemented by ground-base optical-infrared photometry. We find that the eruption has heated dust in the pre-existing nebulosity associated with T Pyx. This is most likely interstellar dust swept up by T Pyx - either during previous eruptions or by a wind - rather than the accumulation of dust produced during eruptions.

astro-ph.SR↗

arXiv2012

Swift follow-up observations of unclassified ASCA sources

We present Swift follow-up observations of a sample of 35 unclassified faint X-ray sources drawn from the ASCA Galactic centre and plane surveys. Our short pointed XRT observations allow detections down to a limiting 0.3-10 keV flux of ~1E-13 erg cm-2 s-1, which translates into a luminosity of ~1E33 erg s-1 for an assumed distance of D=8 kpc. The brightest source in our sample reaches a maximum 0.3-10 keV luminosity of ~2E36 (D/8kpc)^2 erg s-1 during our observations. We detect 16 (46%) of the ASCA sources with the XRT, while 19 were not detected during our program. Since we are probing the faint end of the ASCA source populations, we expect a large fraction of the non-detections to be due to the Eddington bias. This is strengthened by the fact that we find the observed XRT count rates to be predominantly lower than expected based on the reported ASCA intensities. Investigation of the ASCA properties and long-term X-ray variability leads us to conclude that the non-detections likely include two spurious ASCA detections and three objects that are variable or transient X-ray sources. For the 16 XRT-detected sources we obtain positional accuracies of ~2-4", which significantly improves upon their ASCA uncertainties of ~1'. We use the X-ray spectra and variability to characterise these objects. Most appear to be faint, persistent X-ray emitters that have highly absorbed spectra. Based on their X-ray properties we identify three accreting compact objects: one confirmed (AX J1754.2-2754) and one candidate (AX J1538.3-5541) X-ray binary, and one possible magnetically accreting white dwarf (AX J1620.1-5002). Furthermore, we use the improved positions of XRT-detected sources to search for counterparts in simultaneously obtained Swift/UVOT images and possible associations with cataloged sources at various wavelengths. This reveals three possible main sequence stars amongst our sample.

astro-ph.HE↗

arXiv2011

Swift X-Ray Observations of Classical Novae. II. The Super Soft Source sample

The Swift GRB satellite is an excellent facility for studying novae. Its rapid response time and sensitive X-ray detector provides an unparalleled opportunity to investigate the previously poorly sampled evolution of novae in the X-ray regime. This paper presents Swift observations of 52 Galactic/Magellanic Cloud novae. We included the XRT (0.3-10 keV) X-ray instrument count rates and the UVOT (1700-8000 Angstroms) filter photometry. Also included in the analysis are the publicly available pointed observations of 10 additional novae the X-ray archives. This is the largest X-ray sample of Galactic/Magellanic Cloud novae yet assembled and consists of 26 novae with super soft X-ray emission, 19 from Swift observations. The data set shows that the faster novae have an early hard X-ray phase that is usually missing in slower novae. The Super Soft X-ray phase occurs earlier and does not last as long in fast novae compared to slower novae. All the Swift novae with sufficient observations show that novae are highly variable with rapid variability and different periodicities. In the majority of cases, nuclear burning ceases less than 3 years after the outburst begins. Previous relationships, such as the nuclear burning duration vs. t_2 or the expansion velocity of the eject and nuclear burning duration vs. the orbital period, are shown to be poorly correlated with the full sample indicating that additional factors beyond the white dwarf mass and binary separation play important roles in the evolution of a nova outburst. Finally, we confirm two optical phenomena that are correlated with strong, soft X-ray emission which can be used to further increase the efficiency of X-ray campaigns.

astro-ph.SR↗

arXiv2011

From X-ray dips to eclipse: Witnessing disk reformation in the recurrent nova USco

The 10th recorded outburst of the recurrent eclipsing nova USco was observed simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9 after outburst. Two full passages of the companion in front of the nova ejecta were observed, witnessing the reformation of the accretion disk. On day 22.9, we observed smooth eclipses in UV and optical but deep dips in the X-ray light curve which disappeared by day 34.9, then yielding clean eclipses in all bands. X-ray dips can be caused by clumpy absorbing material that intersects the line of sight while moving along highly elliptical trajectories. Cold material from the companion could explain the absence of dips in UV and optical light. The disappearance of X-ray dips before day 34.9 implies significant progress in the formation of the disk. The X-ray spectra contain photospheric continuum emission plus strong emission lines, but no clear absorption lines. Both continuum and emission lines in the X-ray spectra indicate a temperature increase from day 22.9 to day 34.9. We find clear evidence in the spectra and light curves for Thompson scattering of the photospheric emission from the white dwarf. Photospheric absorption lines can be smeared out during scattering in a plasma of fast electrons. We also find spectral signatures of resonant line scattering that lead to the observation of the strong emission lines. Their dominance could be a general phenomenon in high-inclination systems such as Cal87.

astro-ph.GA↗

arXiv2011

An unusual stellar death on Christmas Day

Long Gamma-Ray Bursts (GRBs) are the most dramatic examples of massive stellar deaths, usually as- sociated with supernovae (Woosley et al. 2006). They release ultra-relativistic jets producing non-thermal emission through synchrotron radiation as they interact with the surrounding medium (Zhang et al. 2004). Here we report observations of the peculiar GRB 101225A (the "Christmas burst"). Its gamma-ray emission was exceptionally long and followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling blackbody after which an additional component, consistent with a faint supernova, emerged. We determine its distance to 1.6 Gpc by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a helium star-neutron star merger that underwent a common envelope phase expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which gets thermalized by interacting with the dense, previously ejected material and thus creating the observed black-body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy (Campana et al. 2011).

astro-ph.HE↗

arXiv2011

Is CGCS 5926 a symbiotic X-ray binary?

We here report on multiwavelength (X-ray to optical) followup observations of carbon star CGCS 5926. These were motivated by the fact that this star is positionally coincident with a faint X-ray emitting object belonging to the ROSAT catalog of sources, thus suggesting a possible symbiotic X-ray binary (SyXB) nature for it. Our spectrophotometric optical data confirm the giant carbon star nature of the object and allow us to classify its spectral type as C(6,2). This classification places CGCS 5926 at a distance of about 5 kpc from Earth. BVRcIc photometry of the star shows that it displays a variability of about 0.3 mag on timescales of months, with the star getting bluer when its brightness increases. Our photometric data indicate a periodicity of 151 days, which we explain as due to radial pulsations of CGCS 5926 on the basis of its global characteristics. The source is not detected at X-rays with Swift/XRT down to a 0.3-10 keV band luminosity of around 3e32 erg/s. This nondetection is apparently in contrast with the ROSAT data; however we show that, even if the probability that CGCS 5926 can be a SyXB appears quite low, the present information does not completely rule out such a possibility, while it makes other interpretations even more unlikely if we assume that the ROSAT detection was real. This issue might thus be settled by future, more sensitive, observations at high energies.

astro-ph.SR↗

arXiv2011

The dark GRB080207 in an extremely red host and the implications for GRBs in highly obscured environments

[Abridged] We present comprehensive X-ray, optical, near- and mid-infrared, and sub-mm observations of GRB 080207 and its host galaxy. The afterglow was undetected in the optical and near-IR, implying an optical to X-ray index <0.3, identifying GRB 080207 as a dark burst. Swift X-ray observations show extreme absorption in the host, which is confirmed by the unusually large optical extinction found by modelling the X-ray to nIR afterglow spectral energy distribution. Our Chandra observations obtained 8 days post-burst allow us to place the afterglow on the sky to sub-arcsec accuracy, enabling us to pinpoint an extremely red galaxy (ERO). Follow-up host observations with HST, Spitzer, Gemini, Keck and the James Clerk Maxwell Telescope (JCMT) provide a photometric redshift solution of z ~1.74 (+0.05,-0.06) (1 sigma), 1.56 < z < 2.08 at 2 sigma) for the ERO host, and suggest that it is a massive and morphologically disturbed ultra-luminous infrared galaxy (ULIRG) system, with L_FIR ~ 2.4 x 10^12 L_solar. These results add to the growing evidence that GRBs originating in very red hosts always show some evidence of dust extinction in their afterglows (though the converse is not true -- some extinguished afterglows are found in blue hosts). This indicates that a poorly constrained fraction of GRBs occur in very dusty environments. By comparing the inferred stellar masses, and estimates of the gas phase metallicity in both GRB hosts and sub-mm galaxies we suggest that many GRB hosts, even at z>2 are at lower metallicity than the sub-mm galaxy population, offering a likely explanation for the dearth of sub-mm detected GRB hosts. However, we also show that the dark GRB hosts are systematically more massive than those hosting optically bright events, perhaps implying that previous host samples are severely biased by the exclusion of dark events.

astro-ph.CO↗

arXiv2011

Recovering Swift-XRT energy resolution through CCD charge trap mapping

The X-ray telescope on board the Swift satellite for gamma-ray burst astronomy has been exposed to the radiation of the space environment since launch in November 2004. Radiation causes damage to the detector, with the generation of dark current and charge trapping sites that result in the degradation of the spectral resolution and an increase of the instrumental background. The Swift team has a dedicated calibration program with the goal of recovering a significant proportion of the lost spectroscopic performance. Calibration observations of supernova remnants with strong emission lines are analysed to map the detector charge traps and to derive position-dependent corrections to the measured photon energies. We have achieved a substantial recovery in the XRT resolution by implementing these corrections in an updated version of the Swift XRT gain file and in corresponding improvements to the Swift XRT HEAsoft software. We provide illustrations of the impact of the enhanced energy resolution, and show that we have recovered most of the spectral resolution lost since launch.

astro-ph.IM↗

arXiv2011

Swift observations of the March 2011 outburst of the cataclysmic variable NSV 1436: a probable dwarf nova (Research Note)

The March 2011 outburst of the poorly-studied cataclysmic variable NSV 1436 offered an opportunity to decide between dwarf nova and recurrent nova classifications. We use seven daily observations in the X-ray and UV by the Swift satellite, together with AAVSO V photometry, to characterise the outburst and decline behaviour. The short optical outburst coincided with a faint and relatively soft X-ray state, whereas in decline to fainter optical magnitudes the X-ray source was harder and brighter. These attributes, and the modest optical outburst amplitude, indicate that this was a dwarf nova outburst and not a recurrent nova. The rapid optical fading suggests an orbital period below 2 hours.

astro-ph.HE↗

arXiv2011

Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: III. X-ray spectral modelling

Following the Swift X-ray observations of the 2006 outburst of the recurrent nova RS Ophiuchi, we developed hydrodynamical models of mass ejection from which the forward shock velocities were used to estimate the ejecta mass and velocity. In order to further constrain our model parameters, here we present synthetic X-ray spectra from our hydrodynamical calculations which we compare to the Swift data. An extensive set of simulations was carried out to find a model which best fits the spectra up to 100 days after outburst. We find a good fit at high energies but require additional absorption to match the low energy emission. We estimate the ejecta mass to be in the range (2-5) x 10^{-7} solar masses and the ejection velocity to be greater than 6000 km/s (and probably closer to 10,000 km/s). We also find that estimates of shock velocity derived from gas temperatures via standard model fits to the X-ray spectra are much lower than the true shock velocities.

astro-ph.HE↗

arXiv2011

Discovery of the Onset of Rapid Accretion by a Dormant Massive Black Hole

Massive black holes are believed to reside at the centres of most galaxies. They can be- come detectable by accretion of matter, either continuously from a large gas reservoir or impulsively from the tidal disruption of a passing star, and conversion of the gravitational energy of the infalling matter to light. Continuous accretion drives Active Galactic Nuclei (AGN), which are known to be variable but have never been observed to turn on or off. Tidal disruption of stars by dormant massive black holes has been inferred indirectly but the on- set of a tidal disruption event has never been observed. Here we report the first discovery of the onset of a relativistic accretion-powered jet in the new extragalactic transient, Swift J164449.3+573451. The behaviour of this new source differs from both theoretical models of tidal disruption events and observations of the jet-dominated AGN known as blazars. These differences may stem from transient effects associated with the onset of a powerful jet. Such an event in the massive black hole at the centre of our Milky Way galaxy could strongly ionize the upper atmosphere of the Earth, if beamed towards us.

astro-ph.HE↗

arXiv2011

XMM-Newton X-ray and UV observations of the fast nova V2491 Cyg during the supersoft source phase

Two XMM observations of the fast classical nova V2491Cyg were carried out on days 39.93 and 49.62 after discovery, during the supersoft source (SSS) phase, yielding simultaneous X-ray and UV light curves and high-resolution X-ray spectra. The first X-ray light curve is highly variable with periodic oscillations (37.2 min) after an extended dip of factor of three lasting ~3 hours. The cause of the dip is currently unexplained and could have the same origin as similar events in V4743Sgr and RSOph, as it occurred on the same time scale. The 37-min period is not present during the dip and also not in the second observation. The UV light curves are variable but contain no dips and no period. High-resolution X-ray spectra are presented for 4 intervals of different intensity. All spectra are atmospheric continua with absorption lines and absorption edges. Interstellar lines of OI and NI are seen at their rest wavelengths, and a large number of high-ionization absorption lines are found at blue shifts indicating an expansion velocity of 3000-3400 km/s, which does not change significantly during the epochs of observation. Comparisons with the slower nova V4743Sgr and the symbiotic recurrent nova RSOph are presented. The SSS spectrum of V4743Sgr is much softer with broader and more complex photospheric absorption lines. Meanwhile, the absorption lines in RSOph are as narrow as in V2491Cyg, but they are less blue shifted. A remarkable similarity in the continua of V2491Cyg and RSOph is found. The only differences are smaller line shifts and additional emission lines in RSOph that are related to a dense stellar wind from the evolved companion. Three unidentified absorption lines are present in the X-ray spectra of all three novae, with rest wavelengths 26.05AA, 29.45AA, and 30.0AA. No satisfactory spectral model is currently available for the soft X-ray spectra of novae in outburst.

astro-ph.HE↗

arXiv2010

The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst. I. The shock and its evolution

On 2010 Mar 10, V407 Cyg was discovered in outburst, eventually reaching V< 8 and detected by Fermi. Using medium and high resolution ground-based optical spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we describe the behavior of the high-velocity profile evolution for this nova during its first three months. The peak of the X-ray emission occurred at about day 40 with a broad maximum and decline after day 50. The main changes in the optical spectrum began at around that time. The He II 4686A line first appeared between days 7 and 14 and initially displayed a broad, symmetric profile that is characteristic of all species before day 60. Low-excitation lines remained comparatively narrow, with v(rad,max) of order 200-400 km/s. They were systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and He II, all of which showed a sequence of profile changes going from symmetric to a blue wing similar to that of the low ionization species but with a red wing extended to as high as 600 km/s . The Na I D doublet developed a broad component with similar velocity width to the other low-ionization species. The O VI Raman features were not detected. We interpret these variations as aspherical expansion of the ejecta within the Mira wind. The blue side is from the shock penetrating into the wind while the red wing is from the low-density periphery. The maximum radial velocities obey power laws, v(rad,max) t^{-n} with n ~ 1/3 for red wing and ~0.8 for the blue. (truncated)

astro-ph.SR↗

arXiv2010

Detecting emission lines with XMM-Newton in 4U 1538-52

Context. The properties of the X-ray emission lines are a fundamental tool for studying the nature of the matter surrounding the neutron star and the phenomena that produce these lines. Aims. The aim of this work is to analyze the X-ray spectrum of 4U 1538-52 obtained by the XMM-Newton observatory and to look for the presence of diagnostic lines in the energy range 0.3-11.5 keV. Methods. We used a 54 ks PN & MOS/XMM-Newton observation of the high mass X-ray binary 4U 1538-52 covering the orbital phase between 0.75 to 1.00 (the eclipse-ingress). We have modelled the 0.3-11.5 keV continuum emission with three absorbed power laws and looked for the emission lines. Results. We found previously unreported recombination lines, in this system, at 2.4 keV, 1.9 keV and 1.3 keV, consistent with the presence of highly ionized states of S XV He?, Si XIII He? and Mg K? or Mg XI He?. On the other hand, both out of eclipse and in eclipse we detect a fluorescence iron emission line at 6.4 keV which is resolved into two components: a narrow ($σ\leq$ 10 eV) fluorescence Fe K? line plus one hot line from highly photoionized Fe XXV. Conclusions. The detection of new recombination lines during eclipse-ingress in 4U 1538-52 indicates that there is an extended ionized region surrounding the neutron star.

astro-ph.HE↗

arXiv2010

The Super-Soft X-ray Phase of Nova RS Ophiuchi 2006

Swift X-ray observations of the ~60 day super-soft phase of the recurrent nova RS Ophiuchi 2006 show the progress of nuclear burning on the white dwarf in exquisite detail. First seen 26 days after the optical outburst, this phase started with extreme variability likely due to variable absorption, although intrinsic white dwarf variations are not excluded. About 32 days later, a steady decline in count-rate set in. NLTE model atmosphere spectral fits during the super-soft phase show that the effective temperature of the white dwarf increases from ~65 eV to ~90 eV during the extreme variability phase, falling slowly after about day 60 and more rapidly after day 80. The bolometric luminosity is seen to be approximately constant and close to Eddington from day 45 up to day 60, the subsequent decline possibly signalling the end of extensive nuclear burning. Before the decline, a multiply-periodic, ~35 s modulation of the soft X-rays was present and may be the signature of a nuclear fusion driven instability. Our measurements are consistent with a white dwarf mass near the Chandrasekhar limit; combined with a deduced accumulation of mass transferred from its binary companion, this leads us to suggest RS Oph is a strong candidate for a future supernova explosion. The main uncertainty now is whether the WD is the CO type necessary for a SN Ia. This may be confirmed by detailed abundance analyses of spectroscopic data from the outbursts.

astro-ph.HE↗