Cross-spectral modelling of the black hole X-ray binary XTEJ1550-564: challenges to the propagating fluctuations paradigm [HEAP]

Timing properties of black hole X-ray binaries in outburst can be modeled with mass accretion rate fluctuations propagating towards the black hole. Such models predict time lags between energy bands due to propagation delays. First application of a propagating fluctuations model to black hole power spectra showed good agreement with the data. Indeed, hard lags observed from these systems appear to be in agreement with this generic prediction. Our PROPFLUC code allows to simultaneously predict power spectra, time lags, and coherence of the variability as a function of energy. This was successfully applied to Swift data on the black hole MAXIJ1659-152, fitting jointly the power spectra in two energy bands and the cross-spectrum between these two bands. In the current work, we attempt to to model two high signal to noise Rossi X-ray Timing Explorer (RXTE) observations of the black hole XTE J1550-564. We find that neither observation can be adequately explained by the model even when considering, additionally to previous PROPFLUC versions, different propagation speeds of the fluctuations. After extensive exploration of model extensions, we tentatively conclude that the quantitative and qualitative discrepancy between model predictions and data is generic to the propagating fluctuations paradigm. This result encourages further investigation of the fundamental hypotheses of the propagating fluctuations model. We discuss some of these hypotheses with an eye to future works.

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S. Rapisarda, A. Ingram and M. Klis
Wed, 26 Apr 17

Comments: 14 pages, 12 figures, accepted for publication in MNRAS

On the Radio Emitting Particles of the Crab Nebula: Stochastic Acceleration Model [HEAP]

The broadband emission of Pulsar Wind Nebulae (PWNe) is well described by non-thermal emissions from accelerated electrons and positrons. However, the standard shock acceleration model of PWNe does not account for the hard spectrum in radio wavelengths. The origin of the radio-emitting particles is also important to determine the pair production efficiency in the pulsar magnetosphere. Here, we propose a possible resolution for the particle energy distribution in PWNe; the radio-emitting particles are not accelerated at the pulsar wind termination shock but are stochastically accelerated by turbulence inside PWNe. We upgrade our past one-zone spectral evolution model including the energy diffusion, i.e., the stochastic acceleration, and apply to the Crab Nebula. A fairly simple form of the energy diffusion coefficient is assumed for this demonstrative study. For a particle injection to the stochastic acceleration process, we consider the continuous injection from the supernova ejecta or the impulsive injection associated with supernova explosion. The observed broadband spectrum and the decay of the radio flux are reproduced by tuning the amount of the particle injected to the stochastic acceleration process. The acceleration time-scale and the duration of the acceleration are required to be a few decades and a few hundred years, respectively. Our results imply that some unveiled mechanisms, such as back reaction to the turbulence, are required to make the energies of stochastically and shock accelerated particles comparable.

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S. Tanaka and K. Asano
Tue, 25 Apr 17

Comments: Accepted for publication in ApJ, 11 pages, 4 figures

The Auger Engineering Radio Array and multi-hybrid cosmic ray detection (TAUP 2015) [HEAP]

The Auger Engineering Radio Array (AERA) aims at the detection of air showers induced by high-energy cosmic rays. As an extension of the Pierre Auger Observatory, it measures complementary information to the particle detectors, fluorescence telescopes and to the muon scintillators of the Auger Muons and Infill for the Ground Array (AMIGA). AERA is sensitive to all fundamental parameters of an extensive air shower such as the arrival direction, energy and depth of shower maximum. Since the radio emission is induced purely by the electromagnetic component of the shower, in combination with the AMIGA muon counters, AERA is perfect for separate measurements of the electrons and muons in the shower, if combined with a muon counting detector like AMIGA. In addition to the depth of the shower maximum, the ratio of the electron and muon number serves as a measure of the primary particle mass.

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E. Holt
Tue, 25 Apr 17

Comments: Published in the proceedings of the TAUP 2015 conference, Torino, Italy; 5 pages, 3 figures

Magnetar Powered Ordinary Type IIP Supernovae [HEAP]

We investigate the properties of Type IIP supernovae that are dominantly powered by the rotational kinetic energy of the newly born neutron star. While the spin-down of a magnetar has previously been proposed as a viable energy source in the context of super-luminous supernovae, we show that a similar mechanism could produce both normal and peculiar Type IIP supernova light curves from red supergiant progenitors for a range of initial spin periods and equivalent dipole magnetic field strengths. Although the formation channel for such magnetars in a typical red supergiant progenitor is unknown, it is tantalizing that this proof of concept model is capable of producing ordinary Type IIP lightcurve properties, perhaps implying that rotation rate and magnetic field strength may play important roles in some ordinary looking Type IIP supernova explosions.

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T. Sukhbold and T. Thompson
Tue, 25 Apr 17

Comments: 7 pages, 4 figures, submitted to MNRAS

Black-Hole Growth is Mainly Linked to Host-Galaxy Stellar Mass rather than Star Formation Rate [HEAP]

We investigate the dependence of black-hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass ($M_$) in the CANDELS/GOODS-South field in the redshift range of $0.5\leq z < 2.0$. Our sample consists of $\approx 18000$ galaxies, allowing us to probe galaxies with $0.1 \lesssim \mathrm{SFR} \lesssim 100\ M_\odot\ \mathrm{yr}^{-1}$ and/or $10^8 \lesssim M_ \lesssim 10^{11}\ M_{\odot}$. We use sample-mean BHAR to approximate long-term average BHAR. Our sample-mean BHARs are derived from the $Chandra$ Deep Field-South 7 Ms observations, while the SFRs and $M_$ have been estimated by the CANDELS team through SED fitting. The average BHAR is correlated positively with both SFR and $M_$, and the BHAR-SFR and BHAR-$M_$ relations can both be described acceptably by linear models with a slope of unity. However, BHAR appears to be correlated more strongly with $M_$ than SFR. This result indicates that $M_$ is the primary host-galaxy property related to black-hole growth, and the apparent BHAR-SFR relation is largely a secondary effect due to the star-forming main sequence. Among our sources, massive galaxies ($M_ \gtrsim 10^{10} M_{\odot}$) have significantly higher BHAR/SFR ratios than less-massive galaxies, indicating the former have higher black-hole fueling efficiency and/or higher SMBH occupation fraction than the latter. Our results can naturally explain the observed proportionality between $M_{\rm BH}$ and $M_$ for local giant ellipticals, and suggest their $M_{\rm BH}/M_$ is higher than that of local star-forming galaxies. Among local star-forming galaxies, massive systems might have higher $M_{\rm BH}/M_*$ compared to dwarfs.

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G. Yang, C. Chen, F. Vito, et. al.
Tue, 25 Apr 17

Comments: 18 pages, 11 figures, 3 tables; post revision based on referee report

Cosmic-ray electron+positron spectrum from 7 GeV to 2 TeV with the Fermi Large Area Telescope [HEAP]

We present a measurement of the cosmic-ray electron+positron spectrum between 7 GeV and 2 TeV performed with almost seven years of data collected with the Fermi Large Area Telescope. We find that the spectrum is well fit by a broken power law with a break energy at about 50 GeV. Above 50 GeV, the spectrum is well described by a single power law with a spectral index of $3.07 \pm 0.02 \; (\text{stat+syst}) \pm 0.04 \; (\text{energy measurement})$. An exponential cutoff lower than 1.8 TeV is excluded at 95\% CL.

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Fermi-LAT Collaboration for the Fermi-LAT Collaboration et al.
Tue, 25 Apr 17

Comments: N/A

The Physics of UHECRs: Spectra, Composition and the Transition Galactic-Extragalactic [HEAP]

We review the experimental evidences about flux and mass composition of ultra high energy cosmic rays in connection with theoretical scenarios concerning astrophysical sources. In this context, we also address the discussion about the expected transition between cosmic rays produced inside the Galaxy and those coming from the intergalactic space.

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R. Aloisio
Tue, 25 Apr 17

Comments: 6 pages, 10 figures, invited talk given at the “2016 International Conference on Ultra-High Energy Cosmic Rays (UHECR2016)”, Kyoto (Japan), 11-14 October 2016