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Zhang Y. | Zhang L. | Zhang J. | Zhang Wei | Zhang Yu | Zhang Z. P. | Zhang Jun | Zhang Lei | Zhang Rui | Zhang S.

W S. R. Juarez | W | W Aaron Sonabend | W B. | W Lee C. | W Lehnert. | W Medhat Shafaa. | W Rupert | W Shivaraj B | W Wei G.

C David J. Fernández | C David J Fernández | C Susanth | c Aleksandar Ili\' | c Marko Kosti\' | c Stevan Pilipovi\' | C Jiji | C Swathi | C | C Dharmani Bhaveshkumar

Search results

Identified particle spectra in Pb-Pb and p-Pb collisions with a modified Tsallis blast-wave model

Che G. R., Gu J. B., Zhang W. C.
28 Oct 2020 nucl-th hep-ph arxiv.org/abs/2010.14880

With the recipe of the Tsallis-blast wave (TBW) model, we propose a modified version (mTBW) in which the transverse velocity profile does not depend on the radius of the emitting source. A combined fit is performed to the transverse momentum spectra of identified hadrons at a given centrality in Pb-Pb (Pb-Pb, p-Pb) collisions at $\sqrt{s_{\rm NN}}=$ 2.76 (5.02, 5.02) TeV with this modified model. It is found that the mTBW model can describe the spectra well up to 3 GeV/c. Moreover, we observe that the transverse flow velocity increases while the non-extensive parameter decreases with centrality, indicating a more rapid expansion and less off-equilibrium of the system in central collisions. In addition, to check whether there is a possible early kinetic freeze-out of hadrons containing strange valence quarks at the LHC, the spectra are investigated by grouping them into strange and non-strange hadrons. We also extend our investigation to the spectra of deuterons and $^{3}\rm He$ in Pb-Pb (p-Pb) collisions at 2.76 (5.02) TeV. The combined fit can provide insight on the degree of non-equilibrium, the radial flow and the temperature of the system at the kinetic freeze-out. Its usefulness lies in the ability to compare the results at different energies in the same colliding system and the results in different colliding systems at the same energy.

A variable ionized disk wind in the black-hole candidate EXO 1846-031

Wang Yanan, Ji Long, Garcia Javier A., Dauser Thomas, Mendez Mariano, Mao Junjie, Tao L., Altamirano Diego, Maggi Pierre, Zhang S. N.
27 Oct 2020 astro-ph.HE arxiv.org/abs/2010.14662

After 34 years, the black-hole candidate EXO 1846-031 went into outburst again in 2019. We investigate its spectral properties in the hard intermediate and the soft states with NuSTAR and Insight-HXMT. A reflection component has been detected in the two spectral states but possibly originating from different illumination spectra: in the intermediate state, the illuminating source is attributed to a hard coronal component, which has been commonly observed in other X-ray binaries, whereas in the soft state the reflection is probably produced by the disk self-irradiation. Both cases support EXO 1846-031 as a low inclination system of ~40 degrees. An absorption line is clearly detected at ~7.2 keV in the hard intermediate state, corresponding to a highly ionized disk wind (log {\xi} > 6.1) with a velocity up to 0.06c. Meanwhile, quasi-simultaneous radio emissions have been detected before and after the X-rays, implying the co-existence of disk winds and jets in this system. Additionally, the observed wind in this source is potentially driven by magnetic forces. The absorption line disappeared in the soft state and a narrow emission line appeared at ~6.7 keV on top of the reflection component, which may be evidence for disk winds, but data with the higher spectral resolution are required to examine this.

Constraining the transient high-energy activity of FRB180916.J0158+65 with Insight-HXMT followup observations

Guidorzi C., Orlandini M., Frontera F., Nicastro L., Xiong S. L., Liao J. Y., Li G., Zhang S. N., Amati L., Virgilli E.
27 Aug 2020 astro-ph.HE arxiv.org/abs/2008.11965

A link between magnetars and fast radio burst (FRB) sources has finally been established. In this context, one of the open issues is whether/which sources of extra galactic FRBs exhibit X/gamma-ray outbursts and whether it is correlated with radio activity. We aim to constrain possible X/gamma-ray burst activity from one of the nearest extragalactic FRB sources currently known over a broad energy range, by looking for bursts over a range of timescales and energies that are compatible with being powerful flares from extragalactic magnetars. We followed up the as-yet nearest extragalactic FRB source at a mere 149 Mpc distance, the periodic repeater FRB180916.J0158+65, during the active phase on February 4-7, 2020, with the Insight-Hard X-ray Modulation Telescope (HXMT). Taking advantage of the combination of broad band, large effective area, and several independent detectors available, we searched for bursts over a set of timescales from 1 ms to 1.024 s with a sensitive algorithm, that had previously been characterised and optimised. Moreover, through simulations we studied the sensitivity of our technique in the released energy-duration phase space for a set of synthetic flares and assuming different energy spectra. We constrain the possible occurrence of flares in the 1-100 keV energy band to E<10^46 erg for durations <0.1 s over several tens of ks exposure. We can rule out the occurrence of giant flares similar to the ones that were observed in the few cases of Galactic magnetars. The absence of reported radio activity during our observations does not allow us to make any statements on the possible simultaneous high-energy emission.

Insight-HXMT firm detection of the highest energy fundamental cyclotron resonance scattering feature in the spectrum of GRO J1008-57

Ge M. Y., Ji L., Zhang S. N., Santangelo A., Liu C. Z., Doroshenko V., Staubert R., Qu J. L., Zhang S., Lu F. J.
04 Aug 2020 astro-ph.HE arxiv.org/abs/2008.01797

We report on the observation of the accreting pulsar GRO J1008-57 performed by Insight-HXMT at the peak of the source's 2017 outburst. Pulsations are detected with a spin period of 93.283(1) s. The pulse profile shows double peaks at soft X-rays, and only one peak above 20 keV. The spectrum is well described by the phenomenological models of X-ray pulsars. A cyclotron resonant scattering feature is detected with very high statistical significance at a centroid energy of $E_{\rm cyc}=90.32_{-0.28}^{+0.32}$ keV, for the reference continuum and line models, HIGHECUT and GABS respectively. Detection is very robust with respect to different continuum models. The line energy is significantly higher than what suggested from previous observations, which provided very marginal evidence for the line. This establishes a new record for the centroid energy of a fundamental cyclotron resonant scattering feature observed in accreting pulsars. We also discuss the accretion regime of the source during the Insight-HXMT observation.

Search for $CP$ violation in $\Xi_c^+\rightarrow pK^-\pi^+$ decays using model-independent techniques

LHCb collaboration , Aaij R., , Ackernley T., Adeva B., Adinolfi M., Afsharnia H., Aidala C. A., Aiola S., Ajaltouni Z.
04 Jun 2020 hep-ex arxiv.org/abs/2006.03145

A first search for $CP$ violation in the Cabibbo-suppressed $\Xi_c^+\rightarrow pK^-\pi^+$ decay is performed using both a binned and an unbinned model-independent technique in the Dalitz plot. The studies are based on a sample of proton-proton collision data, corresponding to an integrated luminosity of $3.0~{\rm fb^{-1}}$, and collected by the LHCb experiment at centre-of-mass energies of $7$ and $8~\rm TeV$. The data are consistent with the hypothesis of no $CP$ violation.

Identification of a non-thermal X-ray burst with the Galactic magnetar SGR 1935+2154 and a fast radio burst with Insight-HXMT

Li C. K., Lin L., Xiong S. L., Ge M. Y., Li X. B., Li T. P., Lu F. J., Zhang S. N., Tuo Y. L., Nang Y.
22 May 2020 astro-ph.HE astro-ph.IM arxiv.org/abs/2005.11071

Fast radio bursts (FRBs) are short pulses observed in radio band from cosmological distances, some of which emit repeating bursts. The physical origins of these mysterious events have been subject to wide speculations and heated debates. One class of models invoke soft gamma-ray repeaters (SGRs), or magnetars, as the sources of FRBs. Magnetars are rotating neutron stars with extremely strong magnetic field and can sporadically emit bursts from X-ray ($\sim$keV) to soft gamma-ray ($\sim$sub-MeV) with duration from $10^{-2}$~s to $10^2$~s. However, even though some bright radio bursts have been observed from some magnetars, no FRB-like events had been detected to be associated with any magnetar burst, including one giant flare, and no radio burst has been associated with any X-ray event from any magnetar. Therefore, there is still no observational evidence for magnetar-FRB association up to today. Recently, a pair of FRB-like bursts (FRB~200428 hereafter) separated by 30 milliseconds (ms) were detected from the general direction of the Galactic magnetar SGR~J1935+2154. Here we report the detection of a non-thermal X-ray burst in the 1-250 keV energy band with the Insight-HXMT satellite, which we identify as emitted from SGR~J1935+2154. The burst showed two hard peaks with a separation of $\sim30$ ms, consistent with the separation between the two bursts in FRB~200428. The delay time between the double radio and X-ray peaks is $\sim8.57$ s, fully consistent with the dispersion delay of FRB~200428. We thus identify the non-thermal X-ray burst is associated with FRB~200428 whose high energy counterpart is the two hard peaks in X-ray. Our results suggest that the non-thermal X-ray burst and FRB~200428 share the same physical origin in an explosive event from SGR~J1935+2154.

Insight-HXMT insight into switch of the accretion mode: the case of the X-ray pulsar 4U 1901+03

Tuo Y. L., Ji L., Tsygankov S. S., Mihara T., Song L. M., Ge M. Y., Nabizadeh A., Tao L., Qu J. L., Zhang Y.
28 Apr 2020 astro-ph.HE arxiv.org/abs/2004.13307

We use the In data collected during the 2019 outburst from X-ray pulsar 4U 1901+03 to complement the orbital parameters reported by Fermi/GBM. Using the Insight-HXMT, we examine the correlation between the derivative of the intrinsic spin frequency and bolometric flux based on accretion torque models. It was found that the pulse profiles significantly evolve during the outburst. The existence of two types of the profile's pattern discovered in the Insight-HXMT data indicates that this source experienced transition between a super-critical and a sub-critical accretion regime during its 2019 outburst. Based on the evolution of the pulse profiles and the torque model, we derive the distance to 4U 1901+03 as 12.4+-0.2 kpc.

The evolution of the broadband temporal features observed in the black-hole transient MAXI J1820+070 with Insight-HXMT

Wang Yanan, Ji Long, Zhang S. N., , Qu J. L., Maggi Pierre, Ge M. Y., Qiao Erlin, Tao L., Zhang S.
27 Apr 2020 astro-ph.HE arxiv.org/abs/2004.12946

We study the evolution of the temporal properties of MAXI 1820+070 during the 2018 outburst in its hard state from MJD 58190 to 58289 with Insight-HXMT in a broad energy band 1-150 keV. We find different behaviors of the hardness ratio, the fractional rms and time lag before and after MJD 58257, suggesting a transition occurred at around this point. The observed time lags between the soft photons in the 1-5 keV band and the hard photons in higher energy bands, up to 150 keV, are frequency-dependent: the time lags in the low-frequency range, 2-10 mHz, are both soft and hard lags with a timescale of dozens of seconds but without a clear trend along the outburst; the time lags in the high-frequency range, 1-10 Hz, are only hard lags with a timescale of tens of milliseconds; first increase until around MJD 58257 and decrease after this date. The high-frequency time lags are significantly correlated to the photon index derived from the fit to the quasi-simultaneous NICER spectrum in the 1-10 keV band. This result is qualitatively consistent with a model in which the high-frequency time lags are produced by Comptonization in a jet.

Precision measurement of the $B_{c}^{+}$ meson mass

LHCb collaboration , Aaij R., , Ackernley T., Adeva B., Adinolfi M., Afsharnia H., Aidala C. A., Aiola S., Ajaltouni Z.
17 Apr 2020 hep-ex arxiv.org/abs/2004.08163

A precision measurement of the $B_{c}^{+}$ meson mass is performed using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of $7, 8$ and $13$ TeV, corresponding to a total integrated luminosity of $9.0 \,{\rm fb}^{-1}$. The $B_{c}^{+}$ mesons are reconstructed via the decays $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu \pi^+ \pi^- \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu p \bar{p} \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu D_{s}^{+}$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu D^{0} K^{+}$ and $B_{c}^{+} \rightarrow B_{s}^{0} \pi^{+}$. Combining the results of the individual decay channels, the $B_{c}^{+}$ mass is measured to be $6274.47 \pm 0.27 \,({\rm stat}) \pm 0.17 \,({\rm syst}) \mathrm{\,Me\kern -0.1em V}/c^{2}$. This is the most precise measurement of the $B_{c}^{+}$ mass to date. The difference between the $B_{c}^{+}$ and $B_{s}^{0}$ meson masses is measured to be $907.75 \pm 0.37 \,({\rm stat}) \pm 0.27 \,({\rm syst}) \mathrm{\,Me\kern -0.1em V}/c^{2}$.

Nuclear modification factor in Pb-Pb and p-Pb collisions using Boltzmann transport equation

Qiao L., Che G., Gu J., Zheng H., Zhang W. C.
06 Apr 2020 nucl-th arxiv.org/abs/2004.03081

We investigate the nuclear modification factor ($R_{AA}$) of identified particles as a function of transverse momentum ($p_{\rm T}$) in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=$ 2.76 and 5.02 TeV, as well as p-Pb collision at 5.02 TeV in the framework of Boltzmann transport equation with relaxation time approximation. In this framework, the initial distribution of particles is chosen as the Tsallis distribution and the local equilibrium distribution as the Boltzmann-Gibbs blast-wave distribution. The non-extensive parameter $q_{pp}$, the Tsallis temperature $T_{pp}$ and the equilibrium temperature $T_{eq}$ are set to be in common for all particles, while the ratio of kinetic freeze-out time to relaxation time $t_{f}/\tau$ is different for different particles when we performed a combined fit to the $R_{AA}$ spectra of different particles at a given centrality. We observe that the fitted curves describe the spectra well up to $p_{\rm T}\approx$ 3 GeV/c. $q_{pp}$ and $T_{eq}$ ($t_{f}/\tau$) decrease (increases) with centrality nonlinearly, while $T_{pp}$ is almost independent of centrality. The dependence of the rate at which $q_{pp}$, $T_{eq}$ or $t_{f}/\tau$ changes with centrality on the energy and the size of the colliding system is discussed.