One of the most exciting near-term prospects in physics is the potential discovery of gravitational waves by the Advanced LIGO and Virgo detectors. To maximize both the confidence of the detection ...and the science return, it is essential to identify an electromagnetic counterpart. This is not trivial, as the events are expected to be poorly localized, particularly in the near-term, with error regions covering hundreds or even thousands of square degrees. In this paper, we discuss the prospects for finding an X-ray counterpart to a gravitational wave trigger with the Swift X-ray Telescope, using the assumption that the trigger is caused by a binary neutron star merger which also produces a short gamma-ray burst. We show that it is beneficial to target galaxies within the GW error region, highlighting the need for substantially complete galaxy catalogues out to distances of 300 Mpc. We also show that nearby, on-axis short GRBs are either extremely rare, or are systematically less luminous than those detected to date. We consider the prospects for detecting afterglow emission from an off-axis GRB which triggered the GW facilities, finding that the detectability, and the best time to look, are strongly dependent on the characteristics of the burst such as circumburst density and our viewing angle.
THESEUS, one of the two space mission concepts being studied by ESA as candidates for next M5 mission within its Comsic Vision programme, aims at fully exploiting Gamma-Ray Bursts (GRB) to solve key ...questions about the early Universe, as well as becoming a cornerstone of multi-messenger and time-domain astrophysics. By investigating the first billion years of the Universe through high-redshift GRBs, THESEUS will shed light on the main open issues in modern cosmology, such as the population of primordial low mass and luminosity galaxies, sources and evolution of cosmic re-ionization, SFR and metallicity evolution up to the “cosmic dawn” and across Pop-III stars. At the same time, the mission will provide a substantial advancement of multi-messenger and time-domain astrophysics by enabling the identification, accurate localisation and study of electromagnetic counterparts to sources of gravitational waves and neutrinos, which will be routinely detected in the late ‘20s and early ‘30s by the second and third generation Gravitational Wave (GW) interferometers and future neutrino detectors, as well as of all kinds of GRBs and most classes of other X/gamma-ray transient sources. Under all these respects, THESEUS will provide great synergies with future large observing facilities in the multi-messenger domain. A Guest Observer programme, comprising Target of Opportunity (ToO) observations, will expand the science return of the mission, to include, e.g., solar system minor bodies, exoplanets, and AGN.
ABSTRACT
On 2021 August 8, the recurrent nova RS Ophiuchi (RS Oph) erupted again, after an interval of 15.5 yr. Regular monitoring by the Neil Gehrels Swift Observatory began promptly, on August 9.9 ...(0.37 d after the optical peak), and continued until the source passed behind the Sun at the start of November, 86 d later. Observations then restarted on day 197, once RS Oph emerged from the Sun constraint. This makes RS Oph the first Galactic recurrent nova to have been monitored by Swift throughout two eruptions. Here we investigate the extensive X-ray data sets between 2006 and 2021, as well as the more limited data collected by the European X-ray Observatory Satellite (EXOSAT) in 1985. The hard X-rays arising from shock interactions between the nova ejecta and red giant wind are similar following the last two eruptions. In contrast, the early supersoft source (SSS) in 2021 was both less variable and significantly fainter than in 2006. However, 0.3–1 keV light curves from 2021 reveal a 35 s quasi-periodic oscillation consistent in frequency with the 2006 data. The Swift X-ray spectra from 2021 are featureless, with the soft emission typically being well parametrized by a simple blackbody, while the 2006 spectra showed much stronger evidence for superimposed ionized absorption edges. Considering the data after day 60 following each eruption, during the supersoft phase the 2021 spectra are hotter, with smaller effective radii and lower wind absorption, leading to an apparently reduced bolometric luminosity. We explore possible explanations for the gross differences in observed SSS behaviour between the 2006 and 2021 outbursts.
We report the Swift discovery of the nearby long, soft gamma-ray burst GRB 100316D, and the subsequent unveiling of its low-redshift host galaxy and associated supernova. We derive the redshift of ...the event to be z= 0.0591 ± 0.0001 and provide accurate astrometry for the gamma-ray burst (GRB) supernova (SN). We study the extremely unusual prompt emission with time-resolved γ-ray to X-ray spectroscopy and find that the spectrum is best modelled with a thermal component in addition to a synchrotron emission component with a low peak energy. The X-ray light curve has a remarkably shallow decay out to at least 800 s. The host is a bright, blue galaxy with a highly disturbed morphology and we use Gemini-South, Very Large Telescope and Hubble Space Telescope observations to measure some of the basic host galaxy properties. We compare and contrast the X-ray emission and host galaxy of GRB 100316D to a subsample of GRB-SNe. GRB 100316D is unlike the majority of GRB-SNe in its X-ray evolution, but resembles rather GRB 060218, and we find that these two events have remarkably similar high energy prompt emission properties. Comparison of the host galaxies of GRB-SNe demonstrates, however, that there is a great diversity in the environments in which GRB-SNe can be found. GRB 100316D is an important addition to the currently sparse sample of spectroscopically confirmed GRB-SNe, from which a better understanding of long GRB progenitors and the GRB-SN connection can be gleaned.
Context. Transient short-period (<100 s) oscillations have been found in the X-ray light curves of three novae during their super-soft source (SSS) phase and in one persistent SSS. Aims. We pursue an ...observational approach to determine possible driving mechanisms and relations to fundamental system parameters such as the white dwarf mass. Methods. We performed a systematic search for short-period oscillations in all available XMM-Newton and Chandra X-ray light curves of persistent SSS and novae during their SSS phase. To study time evolution, we divided each light curve into short time-segments and computed power spectra. We then constructed a dynamic power spectrum from which we identified transient periodic signals even when only present for a short time. We base our confidence levels on simulations of false-alarm probability for the chosen oversampling rate of 16, corrected for multiple testing based on the number of time segments. From all time segments of each system, we computed fractions of time when periodic signals were detected. Results. In addition to the previously known systems with short-period oscillations, RS Oph (35 s), KT Eri (35 s), V339 Del (54 s), and Cal 83 (67 s), we found one additional system, LMC 2009a (33 s), and also confirm the 35 s period from Chandra data of KT Eri. The oscillation amplitudes are of about <15% of the respective count rates and vary without any clear dependence on the X-ray count rate. The fractions of the time when the respective periods were detected at 2σ significance (duty cycle) are 11.3%, 38.8%, 16.9%, 49.2%, and 18.7% for LMC 2009a, RS Oph, KT Eri, V339 Del, and Cal 83, respectively. The respective highest duty cycles found in a single observation are 38.1%, 74.5%, 61.4%, 67.8%, and 61.8%. Conclusions. Since fast rotation periods of the white dwarfs as origin of these transient oscillations are speculative, we concentrate on pulsation mechanisms. We present initial considerations predicting the oscillation period to scale linearly with the white dwarf radius (and thus mass), weakly with the pressure at the base, and luminosity. Estimates of the size of the white dwarf could be useful for determining whether these systems are more massive than typical white dwarfs, and thus whether they are growing from accretion over time. Signs of such mass growth may have implications for whether some of these systems are attractive as Type Ia supernova progenitors.
We have derived an X-ray luminosity function using parallax-based distance measurements of a set of 12 dwarf novae, consisting of Suzaku, XMM–Newton and ASCA observations. The shape of the X-ray ...luminosity function obtained is the most accurate to date, and the luminosities of our sample are concentrated between ∼1030 and 1031 erg s−1, lower than previous measurements of X-ray luminosity functions of dwarf novae. Based on the integrated X-ray luminosity function, the sample becomes more incomplete below ∼3 × 1030 erg s−1 than it is above this luminosity limit, and the sample is dominated by X-ray bright dwarf novae. The total integrated luminosity within a radius of 200 pc is 1.48 × 1032 erg s−1 over the luminosity range of 1 × 1028 erg s−1 and the maximum luminosity of the sample (1.50 × 1032 erg s−1). The total absolute lower limit for the normalized luminosity per solar mass is 1.81 × 1026 erg s−1 M−1⊙ which accounts for ∼16 per cent of the total X-ray emissivity of cataclysmic variables as estimated by Sazonov et al.
Since its discovery in 2008, the Andromeda galaxy nova M31N 2008-12a has been observed in eruption every single year. This unprecedented frequency indicates an extreme object, with a massive white ...dwarf and a high accretion rate, which is the most promising candidate for the single-degenerate progenitor of a Type Ia supernova known to date. The previous three eruptions of M31N 2008-12a have displayed remarkably homogeneous multiwavelength properties: (i) from a faint peak, the optical light curve declined rapidly by two magnitudes in less than two days, (ii) early spectra showed initial high velocities that slowed down significantly within days and displayed clear He/N lines throughout, and (iii) the supersoft X-ray source (SSS) phase of the nova began extremely early, six days after eruption, and only lasted for about two weeks. In contrast, the peculiar 2016 eruption was clearly different. Here we report (i) the considerable delay in the 2016 eruption date, (ii) the significantly shorter SSS phase, and (iii) the brighter optical peak magnitude (with a hitherto unobserved cusp shape). Early theoretical models suggest that these three different effects can be consistently understood as caused by a lower quiescence mass accretion rate. The corresponding higher ignition mass caused a brighter peak in the free-free emission model. The less massive accretion disk experienced greater disruption, consequently delaying the re-establishment of effective accretion. Without the early refueling, the SSS phase was shortened. Observing the next few eruptions will determine whether the properties of the 2016 outburst make it a genuine outlier in the evolution of M31N 2008-12a.
In an age of advancing endoscopic and lithotripsy technologies, the management of urolithiasis poses a unique opportunity to advance compassionate veterinary care, not only for patients with ...urolithiasis but for those with other urinary diseases as well. The following are consensus‐derived, research and experience‐supported, patient‐centered recommendations for the treatment and prevention of uroliths in dogs and cats utilizing contemporary strategies. Ultimately, we hope that these recommendations will serve as a foundation for ongoing and future clinical research and inspiration for innovative problem solving.
ABSTRACT We report the discovery of Swift J221951−484240 (hereafter: J221951), a luminous slow-evolving blue transient that was detected by the Neil Gehrels Swift Observatory Ultraviolet/Optical ...Telescope (Swift/UVOT) during the follow-up of gravitational wave alert S190930t, to which it is unrelated. Swift/UVOT photometry shows the UV spectral energy distribution of the transient to be well modelled by a slowly shrinking blackbody with an approximately constant temperature of T ∼ 2.5 × 104 K. At a redshift z = 0.5205, J221951 had a peak absolute magnitude of Mu,AB = −23 mag, peak bolometric luminosity $L_{max}=1.1\times 10^{45}~{\rm erg\, s}^{-1}$ and a total radiated energy of E > 2.6 × 1052 erg. The archival Wide-field Infrared Survey Explorer IR photometry shows a slow rise prior to a peak near the discovery date. Spectroscopic UV observations display broad absorption lines in N v and O vi, pointing towards an outflow at coronal temperatures. The lack of emission in the higher H α lines, N i and other neutral lines is consistent with a viewing angle close to the plane of the accretion or debris disc. The origin of J221951 cannot be determined with certainty but has properties consistent with a tidal disruption event and the turn-on of an active galactic nucleus.
Until recently, X-ray flares during the afterglow of gamma-ray bursts (GRBs) were a rarely detected phenomenon; thus, their nature is unclear. During the afterglow of GRB 050502B, the largest X-ray ...flare ever recorded rose rapidly above the afterglow light curve detected by the Swift X-Ray Telescope. The peak flux of the flare was >500 times that of the underlying afterglow, and it occurred >12 minutes after the nominal prompt burst emission. The fluence of this X-ray flare, (1.0 c 0.05) x 10 super(-6) ergs cm super(-2) in the 0.2-10.0 keV energy band, exceeded the fluence of the nominal prompt burst. The spectra during the flare were significantly harder than those measured before and after the flare. Later in time, there were additional flux increases detected above the underlying afterglow, as well as a break in the afterglow light curve. All evidence presented below, including spectral and, particularly, timing information during and around the giant flare, suggests that this giant flare was the result of internal dissipation of energy due to late central engine activity, rather than an afterglow-related effect. We also find that the data are consistent with a second central engine activity episode, in which the ejecta is moving slower than that of the initial episode, causing the giant flare and then proceeding to overtake and refresh the afterglow shock, thus causing additional activity at even later times in the light curve.
PDF
