Several experiments in high-energy physics and astrophysics can be treated as on/off measurements, where an observation potentially containing a new source or effect ("on" measurement) is contrasted ...with a background-only observation free of the effect ("off" measurement). In counting experiments, the significance of the new source or effect can be estimated with a widely used formula from Li & Ma, which assumes that both measurements are Poisson random variables. In this paper we study three other cases: (i) the ideal case where the background measurement has no uncertainty, which can be used to study the maximum sensitivity that an instrument can achieve, (ii) the case where the background estimate b in the off measurement has an additional systematic uncertainty, and (iii) the case where b is a Gaussian random variable instead of a Poisson random variable. The latter case applies when b comes from a model fitted on archival or ancillary data, or from the interpolation of a function fitted on data surrounding the candidate new source/effect. Practitioners typically use a formula that is only valid when b is large and when its uncertainty is very small, while we derive a general formula that can be applied in all regimes. We also develop simple methods that can be used to assess how much an estimate of significance is sensitive to systematic uncertainties on the efficiency or on the background. Examples of applications include the detection of short gamma-ray bursts and of new X-ray or γ-ray sources. All the techniques presented in this paper are made available in a Python code that is ready to use.
ABSTRACT
Characterizing the sub-mm Galactic emission has become increasingly critical especially in identifying and removing its polarized contribution from the one emitted by the cosmic microwave ...background (CMB). In this work, we present a parametric foreground removal performed on to sub-patches identified in the celestial sphere by means of spectral clustering. Our approach takes into account efficiently both the geometrical affinity and the similarity induced by the measurements and the accompanying errors. The optimal partition is then used to parametrically separate the Galactic emission encoding thermal dust and synchrotron from the CMB one applied on two nominal observations of forthcoming experiments from the ground and from the space. Moreover, the clustering is performed on tracers that are different from the data used for component separation, e.g. the spectral index maps of dust and synchrotron. Performing the parametric fit singularly on each of the clustering derived regions results in an overall improvement: both controlling the bias and the uncertainties in the CMB B-mode recovered maps. We finally apply this technique using the map of the number of clouds along the line of sight, $\mathcal {N}_c$, as estimated from H i emission data and perform parametric fitting on to patches derived by clustering on this map. We show that adopting the $\mathcal {N}_c$ map as a tracer for the patches related to the thermal dust emission, results in reducing the B-mode residuals post-component separation. The code is made publicly available https://github.com/giuspugl/fgcluster.
Abstract
A bright burst, followed by an X-ray tail lasting ∼10 ks, was detected during an XMM–Newton observation of the magnetar 1E 1547.0−5408 carried out on 2009 February 3. The burst, also ...observed by Swift/BAT, had a spectrum well fitted by the sum of two blackbodies with temperatures of ∼4 and 10 keV and a fluence in the 0.3–150 keV energy range of ∼10−5 erg cm−2. The X-ray tail had a fluence of ∼4 × 10−8 erg cm−2. Thanks to the knowledge of the distances and relative optical depths of three dust clouds between us and 1E 1547.0−5408, we show that most of the X-rays in the tail can be explained by dust scattering of the burst emission, except for the first ∼20–30 s. We point out that other X-ray tails observed after strong magnetar bursts may contain a non-negligible contribution due to dust scattering.
During a search for X-ray transients in the XMM-Newton archive within the EXTraS project, we discovered a new X-ray source that is detected only during an ∼5 min interval of an ∼21 hr-long ...observation performed on 2011 June 21 (EXMM 023135.0-603743, probability of a random Poissonian fluctuation: ∼1.4 × 10−27). With dedicated follow-up observations, we found that its position is consistent with a star-forming galaxy (SFR = 1-2 M yr−1) at redshift z = 0.092 0.003 (d = 435 15 Mpc). At this redshift, the energy released during the transient event was 2.8 × 1046 erg in the 0.3-10 keV energy band (in the source rest frame). The luminosity of the transient, together with its spectral and timing properties, make EXMM 023135.0-603743 a gripping analog to the X-ray transient associated to SN 2008D, which was discovered during a Swift/XRT observation of the nearby (d = 27 Mpc) supernova-rich galaxy NGC 2770. We interpret the XMM-Newton event as a supernova shock break-out or an early cocoon, and show that our serendipitous discovery is broadly compatible with the rate of core-collapse supernovae derived from optical observations and much higher than that of tidal disruption events.
Galactic diffuse TeV gamma-ray emission is produced by the interaction of high-energy cosmic- ray particles with matter and radiation in our Galaxy. The measurement of Galactic diffuse TeV gamma-ray ...emission would provide strong constraints on the acceleration and propagation of Galactic cosmic rays. The High Altitude Water Cherenkov (HAWC) Observatory, located in central Mexico at 4100 m above sea level, is sensitive to gamma rays between a few hundreds GeV and ~100 TeV. Thanks to its large field of view of 2 steradians and excellent background estimation, HAWC has a unique capability to observe large extended sources such as Galactic diffuse emission. We present the analysis strategy to detect the Galactic diffuse emission with HAWC, including techniques to remove contaminations from localized sources.
Let \(E \subset \Omega\) be a local almost-minimizer of the relative perimeter in the open set \(\Omega \subset \mathbb{R}^{n}\). We prove a free-boundary monotonicity inequality for \(E\) at a point ...\(x\in \partial\Omega\), under a geometric property called ``visibility'', that \(\Omega\) is required to satisfy in a neighborhood of \(x\). Incidentally, the visibility property is satisfied by a considerably large class of Lipschitz and possibly non-smooth domains. Then, we prove the existence of the density of the relative perimeter of \(E\) at \(x\), as well as the fact that any blow-up of \(E\) at \(x\) is necessarily a perimeter-minimizing cone within the tangent cone to \(\Omega\) at \(x\).
Observations of Gamma-ray Bursts with the Fermi Large Area Telescope Longo, Francesco; Vianello, Giacomo; Omodei, Nicola ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2014, Letnik:
742
Journal Article
Recenzirano
The Fermi observatory, with its Gamma-ray Bursts Monitor (GBM) and Large Area Telescope (LAT), is observing Gamma-ray Bursts (GRBs) with a very large spectral coverage and unprecedented sensitivity, ...from ~10keV to >300GeV. In the first 3 years of the mission it observed emission above 100MeV from 35GRBs. In this paper we review the main results obtained on such a sample, highlighting also the relationships with the low-energy spectral and temporal features (as measured by the GBM). Some recent results on high energy photons from GRBs obtained with the preliminary Pass 8 new event-level reconstruction will be discussed.
Given a convex domain \(\Omega\subset \mathbb{R}^{3}\) and an almost-minimizer \(E\) of the relative perimeter in \(\Omega\), we prove that the closure of \(\partial E \cap \Omega\) does not contain ...vertices of \(\Omega\).
The age of multi-wavelength and multi-messenger astronomy has arrived and with it, new tools are needed to analyze data from multiple instruments properly and with ease. The Multi-Mission Maximum ...Likelihood framework (3ML) provides this functionality via the novel use of instrument plugins which allow for every instrument’s unique data to be treated independently with an appropriate likelihood. Under the 3ML framework, users can design plugins that handle instrument specific data routines transparently in the background. When multiple instruments are used together, their independent likelihoods are treated under a common minimization or Bayesian sampling framework. 3ML provides a multitude of minimization algorithm for maximum likelihood estimation (MLE) as well as several popular Bayesian posterior samplers. The entire framework is provided via a modern Python interface providing the user with a modern and easily transportable analysis framework well suited for modern astronomy. New models can be added easily. It is also possible to perform time-energy modeling. We present the framework and its main functionalities.
PDF
