X-Ray Eclipse Time Delays in 4U2129+47

4U 2129+47 was discovered in the early 80's and classified as an accretion disk corona source due to its broad and partial X-ray eclipses. The 5.24 hr binary orbital period was inferred from the X-ray and optical light curve modulation, implying a late K or M spectral type companion star. The source entered a low state in 1983, during which the optical modulation disappeared and an F8 IV star was revealed, suggesting that 4U 2129+47 might be part of a triple system. The nature of 4U 2129+47 has since been investigated, but no definitive conclusion has been reached. Here, we present timing and spectral analyses of two XMM-Newton observations of this source, carried out in May and June, 2005. We find evidence for a delay between two mid-eclipse epochs measured ~22 days apart, and we show that this delay can be naturally explained as being due to the orbital motion of the binary 4U 2129+47 around the center of mass of a triple system. This result thus provides further support in favor of the triple nature of 4U 2129+47.Comment: 6 pages, 5 figures, accepted by A&

Radio / X-ray correlation in the low/hard state of GX 339--4

We present the results of a long-term study of the black hole candidate GX 339-4 using simultaneous radio (from the Australia Telescope Compact Array) and X-ray (from the Rossi X-ray Timing Explorer and BeppoSAX) observations performed between 1997 and 2000. We find strong evidence for a correlation between these two emission regimes that extends over more than three decades in X-ray flux, down to the quiescence level of GX 339-4. This is the strongest evidence to date for such strong coupling between radio and X-ray emission. We discuss these results in light of a jet model that can explain the radio/X-ray correlation. This could indicate that a significant fraction of the X-ray flux that is observed in the low-hard state of black hole candidates may be due to optically thin synchrotron emission from the compact jet.Comment: 8 pages. Accepted for publication in Astronomy & Astrophysics, 200

Black Hole and Neutron Star Transients in Quiescence

We consider the X-ray luminosity difference between neutron star and black hole soft X-ray transients (NS and BH SXTs) in quiescence. The current observational data suggest that BH SXTs are significantly fainter than NS SXTs. The luminosities of quiescent BH SXTs are consistent with the predictions of binary evolution models for the mass transfer rate if (1) accretion occurs via an ADAF in these systems and (2) the accreting compact objects have event horizons. The luminosities of quiescent NS SXTs are not consistent with the predictions of ADAF models when combined with binary evolution models, unless most of the mass accreted in the ADAF is prevented from reaching the neutron star surface. We consider the possibility that mass accretion is reduced in quiescent NS SXTs because of an efficient propeller and develop a model of the propeller effect that accounts for the observed luminosities. We argue that modest winds from ADAFs are consistent with the observations while strong winds are probably not.Comment: LateX, 37 pages, 7 figures; Accepted for publication in The Astrophysical Journa

A Very Young Radio-loud Magnetar

The magnetar Swift J1818.0–1607 was discovered in 2020 March when Swift detected a 9 ms hard X-ray burst and a long-lived outburst. Prompt X-ray observations revealed a spin period of 1.36 s, soon confirmed by the discovery of radio pulsations. We report here on the analysis of the Swift burst and follow-up X-ray and radio observations. The burst average luminosity was L burst ~ 2 × 1039 erg s−1 (at 4.8 kpc). Simultaneous observations with XMM-Newton and NuSTAR three days after the burst provided a source spectrum well fit by an absorbed blackbody (${N}_{{\rm{H}}}$ = (1.13 ± 0.03) × 1023 cm−2 and kT = 1.16 ± 0.03 keV) plus a power law (Γ = 0.0 ± 1.3) in the 1–20 keV band, with a luminosity of ~8 × 1034 erg s−1, dominated by the blackbody emission. From our timing analysis, we derive a dipolar magnetic field B ~ 7 × 1014 G, spin-down luminosity ${\dot{E}}_{\mathrm{rot}}\sim 1.4\times {10}^{36}$ erg s−1, and characteristic age of 240 yr, the shortest currently known. Archival observations led to an upper limit on the quiescent luminosity <5.5 × 1033 erg s−1, lower than the value expected from magnetar cooling models at the source characteristic age. A 1 hr radio observation with the Sardinia Radio Telescope taken about 1 week after the X-ray burst detected a number of strong and short radio pulses at 1.5 GHz, in addition to regular pulsed emission; they were emitted at an average rate 0.9 min−1 and accounted for ~50% of the total pulsed radio fluence. We conclude that Swift J1818.0–1607 is a peculiar magnetar belonging to the small, diverse group of young neutron stars with properties straddling those of rotationally and magnetically powered pulsars. Future observations will make a better estimation of the age possible by measuring the spin-down rate in quiescence

Observation of an Excited Bc+ State

Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date

Observation of two new Ξb−\Xi_b^- baryon resonances

Two structures are observed close to the kinematic threshold in the $\Xi_b^0 \pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = \frac{1}{2}^+$ and $J^P=\frac{3}{2}^+$ states, denoted $\Xi_b^{\prime -}$ and $\Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(\Xi_b^{\prime -}) - m(\Xi_b^0) - m(\pi^{-}) = 3.653 \pm 0.018 \pm 0.006$ MeV$/c^2$, $m(\Xi_b^{*-}) - m(\Xi_b^0) - m(\pi^{-}) = 23.96 \pm 0.12 \pm 0.06$ MeV$/c^2$, $\Gamma(\Xi_b^{*-}) = 1.65 \pm 0.31 \pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $\Gamma(\Xi_b^{\prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.Comment: 17 pages, 2 figure

Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at √s=7 TeV

Bose-Einstein correlations of same-sign charged pions, produced in protonproton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the form of an enhancement of pairs of like-sign charged pions with small four-momentum difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source is investigated, determining both the correlation radius and the chaoticity parameter. The measured correlation radius is found to increase as a function of increasing charged-particle multiplicity, while the chaoticity parameter is seen to decreas

Measurement of the relative rate of prompt χc0, χc1 and χc2 production at √s=7TeV

Prompt production of charmonium χc0, χc1 and χc2 mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of √s=7TeV. The χc mesons are identified through their decay to J/ψγ, with J/ψ→μ+mu− using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of 1.0fb−1 collected by the LHCb detector, is used to measure the relative prompt production rate of χc1 and χc2 in the rapidity range 2.0<y<4.5 as a function of the J/ψ transverse momentum from 3 to 20 GeV/c. First evidence for χc0 meson production at a hadron collider is also presented

Study of charmonium production in b -hadron decays and first evidence for the decay Bs0

Using decays to φ-meson pairs, the inclusive production of charmonium states in b-hadron decays is studied with pp collision data corresponding to an integrated luminosity of 3.0 fb−1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Denoting byBC ≡ B(b → C X) × B(C → φφ) the inclusive branching fraction of a b hadron to a charmonium state C that decays into a pair of φ mesons, ratios RC1C2 ≡ BC1 /BC2 are determined as Rχc0ηc(1S) = 0.147 ± 0.023 ± 0.011, Rχc1ηc(1S) =0.073 ± 0.016 ± 0.006, Rχc2ηc(1S) = 0.081 ± 0.013 ± 0.005,Rχc1 χc0 = 0.50 ± 0.11 ± 0.01, Rχc2 χc0 = 0.56 ± 0.10 ± 0.01and Rηc(2S)ηc(1S) = 0.040 ± 0.011 ± 0.004. Here and below the first uncertainties are statistical and the second systematic.Upper limits at 90% confidence level for the inclusive production of X(3872), X(3915) and χc2(2P) states are obtained as RX(3872)χc1 < 0.34, RX(3915)χc0 < 0.12 andRχc2(2P)χc2 < 0.16. Differential cross-sections as a function of transverse momentum are measured for the ηc(1S) andχc states. The branching fraction of the decay B0s → φφφ is measured for the first time, B(B0s → φφφ) = (2.15±0.54±0.28±0.21B)×10−6. Here the third uncertainty is due to the branching fraction of the decay B0s → φφ, which is used for normalization. No evidence for intermediate resonances is seen. A preferentially transverse φ polarization is observed.The measurements allow the determination of the ratio of the branching fractions for the ηc(1S) decays to φφ and p p asB(ηc(1S)→ φφ)/B(ηc(1S)→ p p) = 1.79 ± 0.14 ± 0.32