Constraining blazar distances with combined Fermi and TeV data: an empirical approach

We discuss a method to constrain the distance of blazars with unknown redshift using combined observations in the GeV and TeV regimes. We assume that the VHE spectrum corrected for the absorption through the interaction with the Extragalactic Background Light can not be harder than the spectrum in the Fermi/LAT band. Starting from the observed VHE spectral data we derive the EBL-corrected spectra as a function of the redshift z and fit them with power laws to be compared with power law fits to the LAT data. We apply the method to all TeV blazars detected by LAT with known distance and derive an empirical law describing the relation between the upper limits and the true redshifts that can be used to estimate the distance of unknown redshift blazars. Using different EBL models leads to systematic changes in the derived upper limits. Finally, we use this relation to infer the distance of the unknown redshift blazar PKS 1424+240.Comment: 5 pages, 4 figures, accepted for publication in MNRAS, minor revisio

The experimental challenge of detecting solar axion-like particles to test cosmological ALP-photon oscillation hypothesis

We consider possible experimental tests of recent hypotheses suggesting that TeV photons survive the pair production interaction with extragalactic background light over cosmological distances by converting to axion-like particles (ALPs) in galactic magnetic fields. We show that proposed giant ultra-low background scintillation detectors will even have a difficult time reaching the present CAST sensitivity, which is one to two orders of magnitude less sensitive than necessary for a meaningful test of the ALP-photon oscillation hypothesis. Potential alternative tests are briefly discussed.Comment: 4 pages, no figure

Examination of the macroeconomic implicit tax rate on labour derived by the European Commission

All tax indicator estimates, whether based on aggregate- or micro data, need to be corroborated by other information and preferably also other tax indicators before policy conclusions can reasonably be drawn. The purpose of this paper is to describe the way the (macroeconomic implicit tax rate on labour income is calculated in the European Commission Structures of the Taxation Systems in the EU? publication, to show its relationship to the widely recognised (microeconomic) tax wedge indicator for an average production worker from the "Taxing Wages" approach of the OECD, and to illustrate its use. It appears from the European Commission report that evidence from the implicit tax ratio at the macro level in a single year cannot simply be projected to observations for an average worker at the micro level, and conversely. With a few exemptions, however, both the macroeconomic and the microeconomic indicator appear to have comparable informative content as regards to general increasing or decreasing trends over time. It should be noted that the changes in the macroeconomic implicit tax rate may reflect structural changes in the entire economy, such as changes in the distribution of wage income. The implicit tax rate relates to actual tax revenue data and it could be, for example, that the revenue effect of targeted reductions in personal income tax, at say, the lower end of the income scale, has been offset by increases in wage income at the top of the wage scale. The two indicators could then be considered complementary instruments for evaluating tax policy.European Union, Tax indicators, Effective tax rates, Taxes on labour, Non-wage labour costs

VHE Gamma-Ray Induced Pair Cascades in Blazars and Radio Galaxies: Application to NGC 1275

Recent blazar detections by HESS, MAGIC, and VERITAS suggest that very-high-energy (VHE, E > 100 GeV) gamma-rays may be produced in most, if not all, types of blazars, including those that possess intense circumnuclear radiation fields. In this paper, we investigate the interaction of nuclear VHE gamma-rays with the circumnuclear radiation fields through gamma-gamma absorption and pair production, and the subsequent Compton-supported pair cascades. We have developed a Monte-Carlo code to follow the spatial development of the cascade in full 3-dimensional geometry, and calculate the radiative output due to the cascade as a function of viewing angle with respect to the primary VHE gamma-ray beam (presumably the jet axis of the blazar). We show that even for relatively weak magnetic fields, the cascades can be efficiently isotropized, leading to substantial off-axis cascade emission peaking in the Fermi energy range at detectable levels for nearby radio galaxies. We demonstrate that this scenario can explain the Fermi flux and spectrum of the radio galaxy NGC 1275.Comment: Accepted for publication in The Astrophysical Journa

Unveiling the super-orbital modulation of LS I +61 303 in X-rays

From the longest monitoring of LS I +61 303 done to date by the Rossi X-ray Timing Explorer (RXTE) we found evidence for the long-sought, years- long modulation in the X-ray emission of the source. The time evolution of the modulated fraction in the orbital lightcurves can be well fitted with a sinusoidal function having a super-orbital period of 1667 days, the same as the one reported in non-contemporaneous radio measurements. However, we have found a 281.8 \pm 44.6 days shift between the super-orbital variability found at radio frequencies extrapolated to the observation time of our campaign and what we found in the super-orbital modulation of the modulated fraction of our X-ray data. We also find a super-orbital modulation in the maximum count rate of the orbital lightcurves, compatible with the former results, including the shift.Comment: 11 pages, 3 figures, 1 table, Accepted to ApJ Letter

Constraining Extragalactic Background Light From TeV Blazars

Our goal is to research the upper limits on the extragalactic background light (EBL). The upper limits on the extragalactic background light (EBL), using the Fermi and very high energy (VHE) spectra recently observed in TeV blazars, are presented. We use an assumption that the VHE intrinsic photon index cannot be harder than the Fermi index measured by the Fermi-LAT. Totally, these upper limits on the EBL are compatible with ones given by most of EBL models. However, the models of high EBL density are denied by TeV blazars.Comment: 4 pages, 2 figures, accepted by A&

Who is worth being called a ‘worker’? Domestic workers’ struggle for recognition in Brazil

The rights of domestic workers have recently been at the centre of public debate in Brazil, with issues such as prejudice, the remnants of an ideology of slavery and mistreatment of workers being discussed openly in the media. In this post, Louisa Acciari argues that the intersection of gender, race and class in the Brazilian context works to devalue domestic workers, positioning them as unskilled cheap labour

Does the hard pomeron obey Regge factorisation?

While data for the proton structure function demand the presence of a hard-pomeron contribution even at quite small Q^2, previous fits to the pp and p\bar p total cross sections have found that in these there is little or no room for such a contribution. We re-analyse the data and show that itmay indeed be present and that, further, it probably obeys Regge factorisation: sigma^{gamma p}(s,Q_1^2)sigma^{gamma p}(s,Q_2^2)= sigma^{pp}(s)sigma^{gamma gamma}(s,Q_1^2,Q_2^2) for all values of Q_1^2 and Q_2^2.Comment: 11 pages, 10 figure

A compulsory heteronormative university? The regulation of sexualities and identities in the UK higher education system

It is often believed that universities are open and progressive places where everyone can and express themselves. However, several studies highlight the ongoing discriminations against oppressed groups such as women, Black and LGBT people. The particular experience of LGBT students is quite difficult to capture as there is no consistent data collection and monitoring. It also represents an epistemological challenge around the use of the category ‘LGBT’. By using it as opposed to ‘heterosexuality’ we risk reinforcing the idea that one is the norm while the other represents the deviation (Phellas 2012)

Recognising religious women as feminist subjects: The case of Catholic feminists in Brazil

In this post, Louisa Acciari analyses the use of religious norms by a feminist group in Brazil, and calls for the recognition of religious women by feminist movement and theory. She argues that religion can play an important role in structuring collective action and gives legitimacy to feminist claims in the Brazilian context