ABSTRACT
Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 1039 erg s−1
. The average number of ULXs per galaxy is still not well-constrained, ...especially given the uncertainty on the fraction of ULX transients. Here, we report the identification of a new transient ULX in the galaxy NGC 55 (which we label as ULX-2), thanks to recent XMM–Newton and the Neil Gehrels Swift Observatory observations. This object was previously classified as a transient X-ray source with a luminosity around a few 1038 erg s−1 in a 2010 XMM–Newton observation. Thanks to new and deeper observations (∼130 ks each), we show that the source reaches a luminosity peak >1.6 × 1039 erg s−1. The X-ray spectrum of ULX-2 is much softer than in previous observations and fits in the class of soft ULXs. It can be well-described using a model with two thermal components, as often found in ULXs. The time-scales of the X-ray variability are of the order of a month and are likely driven by small changes in the accretion rate or due to super-orbital modulations, attributed to precession of the accretion disc, which is similar to other ULXs.
The Swift X-ray telescope BURROWS, David N; HILL, J. E; CHINCARINI, G ...
Space science reviews,
10/2005, Volume:
120, Issue:
3-4
Journal Article
Peer reviewed
he Swift Gamma-Ray Explorer is designed to make prompt multiwavelength observations of gamma-ray bursts (GRBs) and GRB afterglows. The X-ray telescope (XRT) enables Swift to determine GRB positions ...with a few arcseconds accuracy within 100 s of the burst onset. The XRT utilizes a mirror set built for JET-X and an XMM-Newton/EPIC MOS CCD detector to provide a sensitive broad-band (0.2-10 keV) X-ray imager with effective area of > 120 cm^sup 2^ at 1.5 keV, field of view of 23.6 × 23.6 arcminutes, and angular resolution of 18 arcseconds (HPD). The detection sensitivity is 2×10^sup -14^ erg cm^sup -2^ s^sup -1^ in 10^sup 4^ s. The instrument is designed to provide automated source detection and position reporting within 5 s of target acquisition. It can also measure the redshifts of GRBs with Fe line emission or other spectral features. The XRT operates in an auto-exposure mode, adjusting the CCD readout mode automatically to optimize the science return for each frame as the source intensity fades. The XRT will measure spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and will follow each burst for days or weeks.PUBLICATION ABSTRACT
Context. The Swift satellite is a multi-wavelength observatory specifically designed for gamma-ray burst (GRB) astronomy that is operational since 2004. Swift is also a very flexible multi-purpose ...facility that supports a wide range of scientific fields such as active galactic nuclei, supernovae, cataclysmic variables, Galactic transients, active stars and comets. The Swift X-ray Telescope (XRT) has collected more than 150 Ms of observations in its first seven years of operations. Aims. The purpose of this work is to present to the scientific community the list of all the X-ray point sources detected in XRT imaging data taken in photon counting mode during the first seven years of Swift operations. All these point-like sources, excluding the GRB, will be stored in a catalog publicly available (1SWXRT). Methods. We considered all the XRT observations with exposure time longer than 500 s taken in the period 2005−2011. Data were reduced and analyzed with standard techniques and a list of detected sources for each observation was produced. A careful visual inspection was performed to remove extended, spurious and piled-up sources. Finally, positions, count rates, fluxes, and the corresponding uncertainties were computed. Results. We have analyzed more than 35 000 XRT fields, with exposures ranging between 500 s and 100 ks, for a total exposure time of almost 140 Ms. The catalog includes approximately 89 000 entries, of which almost 85 000 are not affected by pile-up and are not GRBs. Considering that many XRT fields were observed several times, we have a total of ~36 000 distinct celestial sources. We computed count rates in three energy bands: 0.3−10 keV (Full, or F), 0.3−3 keV (Soft, or S) and 2−10 keV (Hard, or H). Each entry has a detection in at least one of these bands. In particular, we detect ~80 000, ~70 000 and ~25 500 in the F, S and H band, respectively. Count rates were converted into fluxes in the 0.5−10, 0.5−2 and 2−10 keV bands. The flux interval sampled by the detected sources is 7.4 × 10-15 − 9.1 × 10-11, 3.1 × 10-15 − 1.1 × 10-11 and 1.3 × 10-14 − 9.1 × 10-11 erg cm-2 s-1 for the F, S and H band, respectively. Some possible scientific uses of the catalog are also highlighted.
The 22 Month Swift-BAT All-Sky Hard X-ray Survey Tueller, J; Baumgartner, W. H; Markwardt, C. B ...
The Astrophysical journal. Supplement series,
02/2010, Volume:
186, Issue:
2
Journal Article
We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) well observed by the Swift X-Ray Telescope (XRT). The early X-ray afterglows show a canonical ...behavior, where the light curve broadly consists of three distinct power-law segments: (1) an initial very steep decay (8t super(-a) with 3 a sub(1) 5), followed by (2) a very shallow decay (0.5 a sub(2) 1.0), and finally (3) a somewhat steeper decay (1 a sub(3) 1.5). These power-law segments are separated by two corresponding break times, t sub(break,1) 500 s and 10 super(3) s t sub(break,2) 10 super(4)s. On top of this canonical behavior, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long-lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (t sub(break,1)) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (a sub(2)) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (t sub(break,2))- This energy injection increases the energy of the afterglow shock by at least a factor of f 4 and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.
We present a detailed analysis of Swift multiwavelength observations of GRB 070110 and its remarkable afterglow. The early X-ray light curve, interpreted as the tail of the prompt emission, displays ...a spectral evolution already seen in other gamma-ray bursts. The optical afterglow shows a shallow decay up to similar to 2 days after the burst, which is not consistent with standard afterglow models. The most intriguing feature is a very steep decay in the X-ray flux at similar to 2 x 10 super(-1) s after the burst, ending an apparent plateau. The abrupt drop of the X-ray light curve rules out an external shock as the origin of the plateau in this burst and implies long-lasting activity of the central engine. The temporal and spectral properties of the plateau phase point toward a continuous central engine emission rather than the episodic emission of X-ray flares. We suggest that the observed X-ray plateau is powered by a spinning-down central engine, possibly a millisecond pulsar, which dissipates energy at an internal radius before depositing energy into the external shock.
OBJECTIVES
Thymectomy plays an important role in patients with myasthenia gravis (MG). This study aimed to explore predictors of postoperative myasthenic crisis (POMC) after thymectomy and to define ...a predictive score of respiratory failure.
METHODS
The clinical data of 177 patients with MG undergoing thymectomy from January 1995 to December 2011 were retrospectively reviewed. The following factors were analysed in relation to the occurrence of myasthenic crisis: gender, age, body mass index (BMI), anti-acetylcholine receptor-antibody level, bulbar symptoms, comorbidities, duration of symptoms, Osserman-stage, Myasthenia Gravis Foundation of America (MGFA) stage, history of myasthenic crisis, use of immoglobulins or plasmapheresis, kind of therapy, spirometric and blood gas parameters, histology, kind of surgery, non-myasthenic complications and duration of intubation.
RESULTS
Twenty-two patients experienced postoperative respiratory failure after thymectomy. Univariate analysis revealed a correlation with age >60 years (odds ratio (OR) = 1.79, 95% confidence interval (CI) = 1.04-6.78; P = 0.040); Osserman-stage (IIB- OR = 5.16, 95% CI = 1.10-24.18; P = 0.037, III-IV- OR = 8.75, 95% CI = 1.53-50.05; P = 0.015); bulbar symptoms (OR = 7.42, 95% CI = 1.67-32.84; P = 0.008); BMI >28 (OR = 3.99, 95% CI = 1.58-10.03; P = 0.003); preoperative plasmapheresis (OR = 2.97, 95% CI = 1.18-14.04; P = 0.021); duration of symptoms >2 years (OR = 4.00, 95% CI = 1.09-14.762; P = 0.036); extended surgery (OR = 2.52, 95% CI = 1.02-6.22; P = 0.045); lung (OR = 4.05, 95% CI = 1.44-11.42; P = 0.008), pericardial (OR = 3.78, 95% CI = 1.45-9.82; P = 0.006) or pleural resection (OR = 3.23, 95% CI = 1.30-8.03; P = 0.012); Vital Capacity % <80% (OR = 0.20, 95% CI = 0.05-0.82; P = 0.025) and PaCO2 >40 mmHg (OR = 3.76, 95% CI = 1.12-12.68; P = 0.032). Multivariate logistic regression analysis showed that Osserman-stage (IIB- OR = 5.69, 95% CI = 1.09-29.69; P = 0.039 (III-IV- OR = 11.33, 95% CI = 1.67-76.72; P = 0.013), BMI >28 (OR = 3.65, 95% CI = 1.10-12.15; P = 0.035), history of myasthenic crisis (OR = 24.10, 95% CI = 2.34-248.04; P = 0.007), duration of symptoms >2 years (OR = 5.94, 95% CI = 1.12-31.48; P = 0.036) and lung resection (OR = 8.48, 95% CI = 2.18-32.97; P = 0.002) independently predict POMC. Excluding history of preoperative myasthenic crisis (statistically associated with Osserman-stage), we built a scoring system according to the OR of Osserman-stage (I-IIA, IIB, III-IV), BMI (<28, ≥28), duration of symptoms (<1, 1-2, >2 years) and association with a pulmonary resection. This model helped in creating four classes with increasing risk of respiratory failure (Group I, 6%; Group II, 10%; Group III, 25%; Group IV, 50%).
CONCLUSIONS
Our model facilitates the stratification of patient risk and prediction of the occurrence of POMC. Moreover, it could help to guide the anaesthesiologist's decision on the duration of intubation. Further studies based on larger series are needed to confirm these preliminary data.
We present the first systematic investigation of the morphological and timing properties of flares in GRBs observed by Swift XRT. We consider a large sample drawn from all GRBs detected by Swift, ...INTEGRAL, and HETE-2 prior to 2006 January 31, which had an XRT follow-up and which showed significant flaring. Our sample of 33 GRBs includes long and short, at low and high redshift, and a total of 69 flares. The strongest flares occur in the early phases, with a clear anticorrelation between the flare peak intensity and the flare time of occurrence. Fitting each X-ray flare with a Gaussian model, we find that the mean ratio of the width and peak time is < Delta t/t> similar to 0.13 plus or minus 0.10, albeit with a large scatter. Late flares at times >2000 s have long durations, Delta t > 300 s, and can be very energetic compared to the underlying continuum. We further investigated whether there is a clear link between the number of pulses detected in the prompt phase by BAT and the number of X-ray flares detected by XRT, finding no correlation. However, we find that the distribution of intensity ratios between successive BAT prompt pulses and that between successive XRT flares is the same, an indication of a common origin for gamma-ray pulses and X-ray flares. All evidence indicates that flares are indeed related to the workings of the central engine and, in the standard fireball scenario, originate from internal shocks rather than external shocks. While all flares can be explained by long-lasting engine activity, 29/69 flares may also be explained by refreshed shocks. However, 10 can only be explained by prolonged activity of the central engine.
Context. IGR J18410-0535 is a supergiant fast X-ray transients. This subclass of supergiant X-ray binaries typically undergoes few-hour-long outbursts reaching luminosities of 1036–1037 erg s-1, the ...occurrence of which has been ascribed to the combined effect of the intense magnetic field and rotation of the compact object hosted in them and/or the presence of dense structures (“clumps”) in the wind of their supergiant companion. Aims. IGR J18410-0535 was observed for 45 ks by XMM-Newton as part of a program designed to study the quiescent emission of supergiant fast X-ray transients and clarify the origin of their peculiar X-ray variability. Methods. We carried out an in-depth spectral and timing analysis of these XMM-Newton data. Results. IGR J18410-0535 underwent a bright X-ray flare that started about 5 ks after the beginning of the observation and lasted for ~15 ks. Thanks to the capabilities of the instruments on-board XMM-Newton, the whole event could be followed in great detail. The results of our analysis provide strong convincing evidence that the flare was produced by the accretion of matter from a massive clump onto the compact object hosted in this system. Conclusions. By assuming that the clump is spherical and moves at the same velocity as the homogeneous stellar wind, we estimate a mass and radius of Mcl ≃ 1.4 × 1022 g and Rcl ≃ 8 × 1011 cm. These are in qualitative agreement with values expected from theoretical calculations. We found no evidence of pulsations at ~4.7 s after investigating coherent modulations in the range 3.5 ms–100 s. A reanalysis of the archival ASCA and Swift data of IGR J18410-0535, for which these pulsations were previously detected, revealed that they were likely to be due to a statistical fluctuation and an instrumental effect, respectively.
On 2020 February 24, during their third observing run ("O3"), the Laser Interferometer Gravitational-wave Observatory and Virgo Collaboration detected S200224ca: a candidate gravitational wave (GW) ...event produced by a binary black hole (BBH) merger. This event was one of the best-localized compact binary coalescences detected in O3 (with 50%/90% error regions of 13/72 deg2), and so the Neil Gehrels Swift Observatory performed rapid near-UV/X-ray follow-up observations. Swift-XRT and UVOT covered approximately 79.2% and 62.4% (respectively) of the GW error region, making S200224ca the BBH event most thoroughly followed-up in near-UV (u-band) and X-ray to date. No likely EM counterparts to the GW event were found by the Swift BAT, XRT, or UVOT, nor by other observatories. Here, we report on the results of our searches for an EM counterpart, both in the BAT data near the time of the merger, and in follow-up UVOT/XRT observations. We also discuss the upper limits we can place on EM radiation from S200224ca, as well as the implications these limits have on the physics of BBH mergers. Namely, we place a shallow upper limit on the dimensionless BH charge, , and an upper limit on the isotropic-equivalent energy of a blast wave E < 4.1 × 1051 erg (assuming typical GRB parameters).
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