The Evolution of Temperature and Bolometric Luminosity in Type-II Supernovae [HEAP]

In this work we present a uniform analysis of the temperature evolution and bolometric luminosity of a sample of 29 type-II supernovae (SNe), by fitting a black body model to their multi-band photometry. Our sample includes only SNe with high quality multi-band data and relatively well sampled time coverage. Most of the SNe in our sample were detected less than a week after explosion so their light curves cover the evolution both before and after recombination starts playing a role. We use this sample to study the signature of hydrogen recombination, which is expected to appear once the observed temperature drops to $\approx 7,000$K. Theory predicts that before recombination starts affecting the light curve, both the luminosity and the temperature should drop relatively fast, following a power-law in time. Once the recombination front reaches inner parts of the outflow, it sets the observed temperature to be nearly constant, and slows the decline of the luminosity (or even leads to a re-brightening). We compare our data to analytic studies and find strong evidence for the signature of recombination. We also find that the onset of the optical plateau in a given filter, is effectively the time at which the black body peak reaches the central wavelength of the filter, as it cools, and it does not correspond to the time at which recombination starts affecting the emission.

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T. Faran, E. Nakar and D. Poznanski
Wed, 26 Jul 17

Comments: Submitted to MNRAS, after reviewer comments

The correlation between radio power and Mach number for radio relics in galaxy clusters [HEAP]

We discuss a new technique to constrain models for the origin of radio relics in galaxy clusters using the correlation between the shock Mach number and the radio power of relics. This analysis is carried out using a sample of relics with information on both the Mach numbers derived from X-ray observation, $\mathcal{M}X$, and using spectral information from radio observations of the peak and the average values of the spectral index along the relic, $\mathcal{M}_R$. We find that there is a lack of correlation between $\mathcal{M}_X$ and $\mathcal{M}_R$; this result is an indication that the spectral index of the relic is likely not due to the acceleration of particles operated by the shock but it is related to the properties of a fossil electrons population. We also find that the available data on the correlation between the radio power $P{1.4}$ and Mach numbers ($\mathcal{M}R$ and $\mathcal{M}_X$) in relics indicate that neither the DSA nor the adiabatic compression can simply reproduce the observed $P{1.4}-\mathcal{M}$ correlations. Furthermore, we find that the radio power is not correlated with $\mathcal{M}_X$, whereas it is not possible to exclude a correlation with $\mathcal{M}_R$. This also indicates that the relic power is mainly determined by the properties of a fossil electron population rather than by the properties of the shock. Our results require either to consider models of shock (re)acceleration that go beyond the proposed scenarios of DSA and adiabatic compression at shocks, or to reconsider the origin of radio relics in terms of other physical scenarios.

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S. Colafrancesco, P. Marchegiani and C. Paulo
Wed, 26 Jul 17

Comments: 14 pages, 8 figures. MNRAS, in press

On the Possibility of Fast Radio Bursts from Inside Supernovae: The Case of SN 1986J [HEAP]

We discuss the possibility of obtaining Fast Radio Bursts (FRBs) from the interior of supernovae, in particular SN 1986J. Neutron stars are involved in many of the possible scenarios for the origin of FRBs, and it has been suggested that the high dispersion measures observed in FRBs might be produced by the ionized material in the ejecta of supernovae. Using VLA and VLBI measurements of the Type IIn SN 1986J, which has a central compact component not so far seen in other supernovae, we can directly observe for the first time radio signals which originate in the interior of a young (~30 yr old) supernova. We show that at age 30 yr, any FRB signal at ~1 GHz would still be largely absorbed by the ejecta. By the time the ejecta have expanded so that a 1-GHz signal would be visible, the internal dispersion measure due to the SN ejecta would be below the values typically seen for FRBs. The high dispersion measures seen for the FRBs detected so far could of course be due to propagation through the intergalactic medium provided that the FRBs are at distances much larger than that of SN 1986J, which is 10 Mpc. We conclude that if FRBs originate in Type II SNe/SNRs, they would likely not become visible till 60 ~ 200 yr after the SN explosion.

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M. Bietenholz and N. Bartel
Wed, 26 Jul 17

Comments: 8 pages, 3 figures

On the two main classes of Active Galactic Nuclei [GA]

Active Galactic Nuclei (AGN) are traditionally divided empirically into two main classes: “radio-loud” and “radio-quiet” sources. These labels, which are more than fifty years old, are obsolete, misleading, and wrong. I argue that AGN should be classified based on a fundamentally physical rather than just an observational difference, namely the presence (or lack) of strong relativistic jets, and that we should use the terms “jetted” and “non-jetted” AGN instead.

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P. Padovani
Wed, 26 Jul 17

Comments: Author’s version of Nature Astronomy Comment. 5 pages, 1 figure. See this https URL

Astrophysical neutrinos flavored with Beyond the Standard Model physics [CL]

We systematically study the allowed parameter space for the flavor composition of astrophysical neutrinos measured at Earth, including beyond the Standard Model theories at production, during propagation, and at detection. One motivation is to illustrate the discrimination power of the next-generation neutrino telescopes such as IceCube-Gen2. We identify several examples that lead to potential deviations from the standard neutrino mixing expectation such as significant sterile neutrino production at the source, effective operators modifying the neutrino propagation at high energies, dark matter interactions in neutrino propagation, or non-standard interactions in Earth matter. IceCube-Gen2 can exclude about 90% of the allowed parameter space in these cases, and hence will allow to efficiently test and discriminate models. More detailed information can be obtained from additional observables such as the energy-dependence of the effect, fraction of electron antineutrinos at the Glashow resonance, or number of tau neutrino events.

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R. Rasmussen, L. Lechner, M. Ackermann, et. al.
Wed, 26 Jul 17

Comments: 21 pages, 9 figures, 3 tables

A Spatially Resolved Study of the GRB 020903 Host Complex [HEAP]

GRB 020903 is a long-duration gamma ray burst (LGRB) with a host galaxy close enough and extended enough for spatially-resolved observations, making it one of less than a dozen GRBs where such host studies are possible. GRB 020903 lies in a galaxy host complex that appears to consist of four interacting components. Here we present the results of spatially-resolved spectroscopic observations of the GRB 020903 host. By taking observations at two different position angles we were able to obtain optical spectra (3600-9000{\AA}) of multiple regions in the host complex. After examining the data we conclude that the GRB 020903 host is not, as previously believed, composed of four interacting regions – two are star-forming regions at the same redshift as the GRB explosion site (z=0.251), while two others appear to comprise a background star-forming galaxy at z=0.662. We also measure the metallicities of the two regions at the redshift of GRB 020903, and find that the explosion site and the nearby star-forming region both have metallicities of log(O/H)+12 ~ 8.1 +/- 0.2. We conclude that, in agreement with past spatially-resolved studies of GRBs, the GRB explosion site is representative of the host galaxy as a whole rather than localized in a metal-poor region of the galaxy.

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M. Thorp and E. Levesque
Wed, 26 Jul 17

Comments: 6 pages, 4 figures, to be submitted to AJ

The impact of neutron star spin on X-ray spectra [HEAP]

We investigate whether the intrinsic spin of neutron stars leaves an observable imprint on the spectral properties of X-ray binaries. To evaluate this we consider a sample of nine NSs for which the spins have been measured that are not accreting pulsars (for which the accretion geometry will be different). For each source, we perform spectroscopy on a majority of RXTE hard state observations. Our sample of sources and observations spans the range of the Eddington ratios Lx/Ledd ~0.005-0.100. We find a clear trend between key Comptonization properties and the NS spin for a given accretion rate. Specifically, at a given Lx/Ledd, for more rapidly rotating NSs we find lower seed photon temperatures and a general increase in Comptonization strength, as parametrised by the Comptonization y parameter and amplification factor A. This is in good agreement with the theoretical scenario whereby less energy is liberated in a boundary layer for more rapidly spinning NSs, resulting in a lower seed photon luminosity and, consequently, less Compton cooling in the corona. This effect in extremis results in the hard states of the most rapidly spinning sources encroaching upon the regime of Comptonization properties occupied by BHs.

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M. Burke, M. Gilfanov and R. Sunyaev
Wed, 26 Jul 17

Comments: 11 pages, 4 figures, 3 tables Submitted to MNRAS