On the Adjudication of Conflicting Claims: An Experimental Study

This paper reports an experimental study on three well-known solutions for problems of adjudicating conflicting claims: the constrained equal awards, the proportional, and the constrained equal losses rules. We first let subjects play three games designed such that the unique equilibrium allocation coincides with the recommendation of one of these three rules. In addition, we let subjects play an additional game, that has the property that all (and only) strategy profiles in which players coordinate on the same rule constitute a strict Nash equilibrium. While in the first three games subjects’ play easily converges to the unique equilibrium rule, in the last game the proportional rule overwhelmingly prevails as a coordination device, especially when we frame the game as an hypothetical bankruptcy situation. We also administered a questionnaire to a different group of students, asking them to act as impartial arbitrators to solve (among others) the same problems played in the lab. Also in this case, respondents were sensitive to the framing of the questions, but the proportional rule was selected by the vast majority of respondents.Claims problems, Proportional rule, Experimental Economics

The truncated and evolving inner accretion disc of the black hole GX 339-4

The nature of accretion onto stellar mass black holes in the low/hard state remains unresolved, with some evidence suggesting that the inner accretion disc is truncated and replaced by a hot flow. However, the detection of relativistic broadened Fe emission lines, even at relatively low luminosities, seems to require an accretion disc extending fully to its innermost stable circular orbit. Modelling such features is however highly susceptible to degeneracies, which could easily bias any interpretation. We present the first systematic study of the Fe line region to track how the inner accretion disc evolves in the low/hard state of the black hole GX 339$-$4. Our four observations display increased broadening of the Fe line over two magnitudes in luminosity, which we use to track any variation of the disc inner radius. We find that the disc extends closer to the black hole at higher luminosities, but is consistent with being truncated throughout the entire low/hard state, a result which renders black hole spin estimates inaccurate at these stages of the outburst. Furthermore, we show that the evolution of our spectral inner disc radius estimates corresponds very closely to the trend of the break frequency in Fourier power spectra, supporting the interpretation of a truncated and evolving disc in the hard state.Comment: Accepted for publication in A&A. Some typos corrected from version

Revealing accretion onto black holes: X-ray reflection throughout three outbursts of GX 339-4

Understanding the dynamics behind black hole state transitions and the changes they reflect in outbursts has become long-standing problem. The X-ray reflection spectrum describes the interaction between the hard X-ray source (the power-law continuum) and the cool accretion disc it illuminates, and thus permits an indirect view of how the two evolve. We present a systematic analysis of the reflection spectrum throughout three outbursts (500+ observations) of the black hole binary GX 339-4, representing the largest study applying a self-consistent treatment of reflection to date. Particular attention is payed to the coincident evolution of the power-law and reflection, which can be used to determine the accretion geometry. The hard state is found to be distinctly reflection weak, however the ratio of reflection to power-law gradually increases as the source luminosity rises. In contrast the reflection is found dominate the power-law throughout most of the soft state, with increasing supremacy as the source decays. We discuss potential dynamics driving this, favouring inner disc truncation and decreasing coronal height for the hard and soft states respectively. Evolution of the ionisation parameter, power-law slope and high-energy cut-off also agree with this interpretation.Comment: Accepted for publication in MNRA

On the Adjudication of Conflicting Claims: An Experimental Study

This paper reports an experimental study on three well-known solutions for problems of adjudicating conflicting claims: the constrained equal awards, the proportional, and the constrained equal losses rules. We first let subjects play three games designed such that the unique equilibrium allocation coincides with the recommendation of one of these three rules. In addition, we let subjects play an additional game, that has the property that all (and only) strategy profiles in which players coordinate on the same rule constitute a strict Nash equilibrium. While in the first three games subjectsÕ play easily converges to the unique equilibrium rule, in the last game the proportional rule overwhelmingly prevails as a coordination device, especially when we frame the game as an hypothetical bankruptcy situation. We also administered a questionnaire to a different group of students, asking them to act as impartial arbitrators to solve (among others) the same problems played in the lab. Also in this case, respondents were sensitive to the framing of the questions, but the proportional rule was selected by the vast majority of respondents.Claims problems, Proportional rule, Experimental Economics

The peculiar Galactic center neutron star X-ray binary XMM J174457-2850.3

The recent discovery of a milli-second radio pulsar experiencing an accretion outburst similar to those seen in low mass X-ray binaries, has opened up a new opportunity to investigate the evolutionary link between these two different neutron star manifestations. The remarkable X-ray variability and hard X-ray spectrum of this object can potentially serve as a template to search for other X-ray binary/radio pulsar transitional objects. Here we demonstrate that the transient X-ray source XMM J174457-2850.3 near the Galactic center displays similar X-ray properties. We report on the detection of an energetic thermonuclear burst with an estimated duration of ~2 hr and a radiated energy output of ~5E40 erg, which unambiguously demonstrates that the source harbors an accreting neutron star. It has a quiescent X-ray luminosity of Lx~5E32 erg/s and exhibits occasional accretion outbursts during which it brightens to Lx~1E35-1E36 erg/s for a few weeks (2-10 keV). However, the source often lingers in between outburst and quiescence at Lx~1E33-1E34 erg/s. This unusual X-ray flux behavior and its relatively hard X-ray spectrum, a power law with an index of ~1.4, could possibly be explained in terms of the interaction between the accretion flow and the magnetic field of the neutron star.Comment: 10 pages, 3 figures, 2 tables, accepted to ApJ after minor revision (provided a more detailed description of the long-term X-ray behavior in Section 3.1 and Figure 1

Evaluation of the masonry and timber structures of San Francisco Church in Santiago de Cuba through nondestructive diagnostic methods

Recently, due to a renewed interest in the religious architectural heritage of the Caribbean island of Cuba, some important interventions for the restoration and reinforcement of the colonial churches of the island were carried out. The authors, collaborating with the Archdiocese of Santiago de Cuba in a project concerning the protection of Cuban churches, applied some nondestructive and noninvasive destructive tests for an in-depth study of the main characteristics of those structures. The diagnostic method, developed mainly for the historical buildings or monuments of Europe and North America, was used to study some peculiarities of the building construction traditions of this area. The proposed techniques revealed the existence of several original solutions, for example, defenses for seismic mitigation, developed to resist the earthquakes that frequently affect the area

NuSTAR + XMM-Newton monitoring of the neutron star transient AX J1745.6-2901

AX J1745.6-2901 is a high-inclination (eclipsing) transient neutron star (NS) Low Mass X-ray Binary (LMXB) showcasing intense ionised Fe K absorption. We present here the analysis of 11 XMM-Newton and 15 NuSTAR new data-sets (obtained between 2013-2016), therefore tripling the number of observations of AX J1745.6-2901 in outburst. Thanks to simultaneous XMM-Newton and NuSTAR spectra, we greatly improve on the fitting of the X-ray continuum. During the soft state the emission can be described by a disk black body ($kT\sim1.1-1.2$ keV and inner disc radius $r_{DBB}\sim14$ km), plus hot ($kT\sim2.2-3.0$ keV) black body radiation with a small emitting radius ($r_{BB}\sim0.5-0.8$ km) likely associated with the boundary layer or NS surface, plus a faint Comptonisation component. Imprinted on the spectra are clear absorption features created by both neutral and ionised matter. Additionally, positive residuals suggestive of an emission Fe K$\alpha$ disc line and consistent with relativistic ionised reflection are present during the soft state, while such residuals are not significant during the hard state. The hard state spectra are characterised by a hard ($\Gamma\sim1.9-2.1$) power law, showing no evidence for a high energy cut off ($kT_e>60-140$ keV) and implying a small optical depth ($\tau<1.6$). The new observations confirm the previously witnessed trend of exhibiting strong Fe K absorption in the soft state, that significantly weakens during the hard state. Optical (GROND) and radio (GMRT) observations suggest for AX J1745.6-2901 a standard broad band SED as typically observed in accreting neutron stars.Comment: Accepted for publication in MNRA

The X-ray outburst of the Galactic Centre magnetar SGR J1745-2900 during the first 1.5 year

In 2013 April a new magnetar, SGR 1745-2900, was discovered as it entered an outburst, at only 2.4 arcsec angular distance from the supermassive black hole at the Centre of the Milky Way, Sagittarius A*. SGR 1745-2900 has a surface dipolar magnetic field of ~ 2x10^{14} G, and it is the neutron star closest to a black hole ever observed. The new source was detected both in the radio and X-ray bands, with a peak X-ray luminosity L_X ~ 5x10^{35} erg s^{-1}. Here we report on the long-term Chandra (25 observations) and XMM-Newton (8 observations) X-ray monitoring campaign of SGR 1745-2900, from the onset of the outburst in April 2013 until September 2014. This unprecedented dataset allows us to refine the timing properties of the source, as well as to study the outburst spectral evolution as a function of time and rotational phase. Our timing analysis confirms the increase in the spin period derivative by a factor of ~2 around June 2013, and reveals that a further increase occurred between 2013 Oct 30 and 2014 Feb 21. We find that the period derivative changed from 6.6x10^{-12} s s^{-1} to 3.3x10^{-11} s s^{-1} in 1.5 yr. On the other hand, this magnetar shows a slow flux decay compared to other magnetars and a rather inefficient surface cooling. In particular, starquake-induced crustal cooling models alone have difficulty in explaining the high luminosity of the source for the first ~200 days of its outburst, and additional heating of the star surface from currents flowing in a twisted magnetic bundle is probably playing an important role in the outburst evolution.Comment: 16 pages, 12 figures; accepted for publication on MNRA

AGN X-ray variability in the XMM-COSMOS survey

We took advantage of the observations carried out by XMM in the COSMOS field during 3.5 years, to study the long term variability of a large sample of AGN (638 sources), in a wide range of redshift (0.1<z<3.5) and X-ray luminosity ($10^{41}<$L(2-10)$<10^{45.5}$). Both a simple statistical method to asses the significance of variability, and the Normalized Excess Variance ($\sigma^{2}_{rms}$) parameter, where used to obtain a quantitative measurement of the variability. Variability is found to be prevalent in most AGN, whenever we have good statistic to measure it, and no significant differences between type-1 and type-2 AGN were found. A flat (slope -0.23+/-0.03) anti-correlation between $\sigma^{2}_{rms}$ and X-ray luminosity is found, when significantly variable sources are considered all together. When divided in three redshift bins, the anti-correlation becomes stronger and evolving with z, with higher redshift AGN being more variable. We prove however that this effect is due to the pre-selection of variable sources: considering all the sources with available $\sigma^{2}_{rms}$ measurement, the evolution in redshift disappears. For the first time we were also able to study the long term X-ray variability as a function of $M_{\rm BH}$ and Eddington ratio, for a large sample of AGN spanning a wide range of redshift. An anti-correlation between $\sigma^{2}_{rms}$ and $M_{\rm BH}$ is found, with the same slope of the anti-correlation between $\sigma^{2}_{rms}$ and X-ray luminosity, suggesting that the latter can be a byproduct of the former one. No clear correlation is found between $\sigma^{2}_{rms}$ and the Eddington ratio in our sample. Finally, no correlation is found between the X-ray $\sigma^{2}_{rms}$ and the optical variability.Comment: 14 Pages, 13 figures. Accepted to the Astrophysical Journal on December 6, 201

Prospective randomized comparison of laparoscopic versus open adrenalectomy for sporadic pheochromocytoma.

BACKGROUND: Laparoscopic adrenalectomy for pheochromocytoma remains subject of debate, owing to the systemic consequences of pneumoperitoneum in patients with catecholamine-secreting tumors. METHODS: A prospective randomized study was conducted (2000-2006), evaluating cardiovascular instability during open (n = 9, group A) or laparoscopic (n = 13, group B) adrenalectomy for pheochromocytoma. Haemodynamic parameters were recorded by invasive monitoring. RESULTS: Haemodynamic instability was observed in 3/9 (group A) and 6/13 patients (group B), with a mean of 1.8 and 2.2 hypertensive peaks per patient (p = n.s.). Blood loss (164 +/- 94 cc versus 48 +/- 36 cc, p < 0.05) and operative time (180 +/- 40 versus 158 +/- 45 min, p = n.s.) favored laparoscopic procedures. Postoperative morbidity and mortality were nil. Hospital stay was shorter in group B (p < 0.05). Long-term follow-up was always normal. CONCLUSIONS: Laparoscopic approach for pheochromocytoma can be as safe as open surgery; intraoperative haemodynamic instability, although usually controlled with success, remains a source of concern