The radio-loud quasar SDSS J114657.79+403708.6 at a redshift z = 5.0 is one of the most distant radio-loud objects. The IR-optical luminosity and spectrum suggest that its black hole has a very large ...mass: M = (5 ± 1) × 109 M. The radio-loudness (ratio of the radio to optical flux) of the source is large (around 100), suggesting that the source is viewed at small angles from the jet axis, and could be a blazar. The X-ray observations fully confirm this hypothesis, due to the high level and hardness of the flux. This makes SDSS J114657.79+403708.6 the third most distant blazar known, after Q0906+693 (z = 5.47) and B2 1023+25 (z = 5.3). Among those, SDSS J114657.79+403708.6 has the largest black hole mass, setting interesting constraints on the mass function of heavy (>109 M) black holes at high redshifts.
ABSTRACT
Much of what is known of the chemical composition of the universe is based on emission line spectra from star-forming galaxies. Emission-based inferences are, nevertheless, model-dependent ...and they are dominated by light from luminous star-forming regions. An alternative and sensitive probe of the metallicity of galaxies is through absorption lines imprinted on the luminous afterglow spectra of long gamma ray bursts (GRBs) from neutral material within their host galaxy. We present results from a JWST/NIRSpec programme to investigate for the first time the relation between the metallicity of neutral gas probed in absorption by GRB afterglows and the metallicity of the star-forming regions for the same host galaxy sample. Using an initial sample of eight GRB host galaxies at z = 2.1–4.7, we find a tight relation between absorption and emission line metallicities when using the recently proposed $\hat{R}$ metallicity diagnostic (±0.2 dex). This agreement implies a relatively chemically homogeneous multiphase interstellar medium and indicates that absorption and emission line probes can be directly compared. However, the relation is less clear when using other diagnostics, such as R23 and R3. We also find possible evidence of an elevated N/O ratio in the host galaxy of GRB 090323 at z = 4.7, consistent with what has been seen in other z > 4 galaxies. Ultimate confirmation of an enhanced N/O ratio and of the relation between absorption and emission line metallicities will require a more direct determination of the emission line metallicity via the detection of temperature-sensitive auroral lines in our GRB host galaxy sample.
Objectives
Switching from tenofovir (TDF) to tenofovir alafenamide (TAF) affects lipid profile. The aim of this study was to evaluate whether this results in an increased frequency of patients with ...low‐density lipoprotein (LDL) above their cardiovascular‐related target.
Methods
All HIV patients switching from TDF to TAF, with no changes of the anchor drug, and with plasma lipids available within 6 months before and after the switch, were included. Demographic, HIV‐related parameters, cardiovascular (CV) risk factors and lipid profile on both TDF and TAF were collected. The CV risk score and the relative target of LDL for each patient were calculated according to 2016 European Society of Cardiology/European Atherosclerosis Society (ESC/EAS) guidelines for the management of dyslipidaemias. Modifications in lipid profiles and in the prevalence of patients with LDL above their CV‐related target were evaluated after switch to TAF.
Results
Overall, 221 HIV patients were included, according to CV risk: 55% at low risk, 34% at moderate risk, and 11% at high/very high risk. By analysing lipid profiles according to CV risk, 38% of patients on TDF had LDL above their CV target; this prevalence increases to 60% after switching to TAF (P < 0.0001). The presence of cobicistat in the combination antiretroviral therapy (cART) regimen was associated with an increased risk of LDL above the CV‐related target after switch to TAF adjusted odds ratio (aOR) = 2.4, 95% confidence interval (CI): 1–5.1, P = 0.03) and with an increased prescription of lifestyle/therapeutic intervention (OR = 3.0, 95% CI: 1.7–5.3, P < 0.0001).
Discussion
Switching from TDF to TAF affects lipid parameters, and data from real life suggest a clinical relevance of this worsening that often leads clinicians to implement lifestyle/therapeutic interventions.
Context. Blazars are the most luminous and variable active galactic nuclei (AGNs). They are thus excellent probes of accretion and emission processes close to the central engine. Aims. We concentrate ...here on PKS 1510–089 (z = 0.36), a blazar belonging to the flat-spectrum radio quasar subclass, an extremely powerful gamma-ray source and one of the brightest in the Fermi-LAT catalog. We aim to study the complex variability of this blazar’s bright multiwavelength spectrum, to identify the physical parameters responsible for the variations and the timescales of possible recurrence and quasi-periodicity at high energies. Methods. The blazar PKS 1510–089 was observed twice in hard X-rays with the IBIS instrument onboard INTEGRAL during the flares of Jan. 2009 and Jan. 2010, and simultaneously with Swift and the Nordic Optical Telescope (NOT), in addition to the constant Fermi monitoring. We also measured the optical polarization in several bands on 18 Jan. 2010 at the NOT.Using these and archival data we constructed historical light curves at gamma-to-radio wavelengths covering nearly 20 yr and applied tests of fractional and correlated variability. We assembled spectral energy distributions (SEDs) based on these data and compared them with those at two previous epochs, by applying a model based on synchrotron and inverse Compton radiation from blazars. Results. The modeling of the SEDs suggests that the physical quantities that undergo the largest variations are the total power injected into the emitting region and the random Lorentz factor of the electron distribution cooling break, that are higher in the higher gamma-ray states. This suggests a correlation of the injected power with enhanced activity of the acceleration mechanism. The cooling likely takes place at a distance of ~1000 Schwarzschild radii(~0.03 pc) from the central engine – a distance muchsmaller than the broad line region (BLR) radius.The emission at a few hundred GeV can be reproduced with inverse Compton scattering of highly relativistic electrons off far-infrared photons if these are located much farther than the BLR, that is, around 0.2 pc from the AGN, presumably in a dusty torus. We determine a luminosity of the thermal component due to the inner accretion disk of Ld ≃ 5.9 × 1045 erg s-1, a BLR luminosity of LBLR ≃ 5.3 × 1044 erg s-1, and a mass of the central black hole of MBH ≃ 3 × 108 M⊙.The fractional variability as a function of wavelength follows the trend expected if X- and gamma-rays are produced by the same electrons as radio and optical photons, respectively.Discrete correlation function (DCF) analysis between the long-term Steward observatory optical V-band and gamma-ray Fermi-LAT light curves yields a good correlation with no measurable delay. Marginal correlation where X-ray photons lag both optical and gamma-ray ones by time lags between 50 and 300 days is found with the DCF.Our time analysis of the RXTE PCA and Fermi-LAT light curves reveals no obvious (quasi-)periodicities, at least up to the maximum timescale (a few years) probed by the light curves, which are severely affected by red noise.
We study the properties of the population of optically dark events present in a carefully selected complete sample of bright Swift long gamma-ray bursts. The high level of completeness in redshift of ...our sample (52 objects out of 58) allows us to establish the existence of a genuine dark population, and we are able to estimate the maximum fraction of dark burst events (∼30 per cent) expected for the whole class of long gamma-ray burst. The redshift distribution of this population of dark bursts is similar to that of the whole sample. Interestingly, the rest-frame X-ray luminosity (and the de-absorbed X-ray flux) of the subclass of dark bursts is slightly higher than the average luminosity of the non-dark events. At the same time, the prompt properties do not differ and the optical flux of dark events is at the lower tail of the optical flux distribution, corrected for Galactic absorption. All these properties suggest that dark bursts events generate in much denser environments with respect to normal bright events. We can therefore exclude the high-z and the low-density scenarios and conclude that the major cause of the origin of optically dark events is the dust extinction.
High-redshift Fermi blazars Ghisellini, G.; Tagliaferri, G.; Foschini, L. ...
Monthly notices of the Royal Astronomical Society,
02/2011, Volume:
411, Issue:
2
Journal Article
Peer reviewed
Open access
With the release of the first-year Fermi catalogue, the number of blazars detected above 100 MeV lying at high redshift has been largely increased. There are 28 blazars at z > 2 in the 'clean' ...sample. All of them are flat spectrum radio quasars. We study and model their overall spectral energy distribution in order to find the physical parameters of the jet-emitting region, and for all of them, we estimate their black hole masses and accretion rates. We then compare the jet with the accretion disc properties, setting these sources in the broader context of all the other bright γ-ray or hard X-ray blazars. We confirm that the jet power correlates with the accretion luminosity. We find that the high-energy emission peak shifts to smaller frequencies as the observed luminosity increases, according to the blazar sequence, making the hard X-ray band the most suitable for searching the most-luminous and distant blazars.
The Early X-Ray Emission from GRBs O’Brien, P. T; Willingale, R; Osborne, J ...
The Astrophysical journal,
08/2006, Volume:
647, Issue:
2
Journal Article
Peer reviewed
Open access
We present observations of the early X-ray emission for a sample of 40 gamma-ray bursts (GRBs) obtained using the Swift satellite, for which the narrow-field instruments were pointed at the burst ...within 10 minutes of the trigger. Using data from the Burst Alert Telescope and the X-Ray Telescope, we show that the X-ray light curve can be well described by an exponential that relaxes into a power law, often with flares superimposed. The transition time between the exponential and the power law provides a physically defined timescale for the burst duration. In most bursts, the power law breaks to a shallower decay within the first hour, and a late emission "hump" is observed, which can last for many hours. In other GRBs the hump is weak or absent. The observed variety in the shape of the early X-ray light curve can be explained as a combination of three components: prompt emission from the central engine, afterglow, and the late hump. In this scenario, afterglow emission begins during or soon after the burst, and the observed shape of the X-ray light curve depends on the relative strengths of the emission due to the central engine and that of the afterglow. There is a strong correlation such that those GRBs with stronger afterglow components have brighter early optical emission. The late emission hump can have a total fluence equivalent to that of the prompt phase. GRBs with the strongest late humps have weak or no X-ray flares.
GRB observations with Swift produced the initially surprising result that many bursts have large, late-time X-ray flares. The flares were sometimes intense, had rapid rise and decay phases, and ...occurred late relative to the prompt phase. Many GRBs have had several flares, which were sometimes overlapping. The origin of the flares can be investigated by comparing the spectra during the flares to those of the afterglow and the initial prompt emission. In this work we have analyzed all significant X-ray flares from the first 110 GRBs observed by Swift. Significant X-ray flares (>3 sigma ) were found in 33 of these GRBs, with 77 flares detected. A variety of spectral models have been fit to each flare. We find that the spectral fits sometimes favor a Band function model, which is more akin to the prompt emission than to that of the afterglow. While some flares are approximately as energetic as the prompt GRB emission, we find that the average fluence of the flares is approximately 10 times below the average prompt GRB fluence. We also find that the peak energy of the observed flares is typically in the soft X-ray band, as one might expect due to the X-ray selection of the sample. These results, when combined with those presented in the companion paper on temporal properties of flares, support the hypothesis that many X-ray flares are from late-time activity of the internal engine that spawned the initial GRB, not from an afterglow-related effect.
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.
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