X-ray sources and their optical counterparts in the globular cluster M 22

Using XMM-Newton EPIC imaging data, we have detected 50 low-luminosity X-ray sources in the field of view of M 22, where 5 +/- 3 of these sources are likely to be related to the cluster. Using differential optical photometry, we have identified probable counterparts to those sources belonging to the cluster. Using X-ray spectroscopic and timing studies, supported by the optical colours, we propose that the most central X-ray sources in the cluster are cataclysmic variables, millisecond pulsars, active binaries and a blue straggler. We also identify a cluster of galaxies behind this globular cluster.Comment: 11 pages, 7 figures, accepted for publication in A&

Constraints on the baryonic load of gamma-ray bursts using ultra-high energy cosmic rays

Ultra-high energy cosmic rays are the most extreme energetic particles detected on Earth, however, their acceleration sites are still mysterious. We explore the contribution of low-luminosity gamma-ray bursts to the ultra-high energy cosmic ray flux, since they form the bulk of the nearby population. We analyse a representative sample of these bursts detected by BeppoSAX, INTEGRAL and Swift between 1998-2016, and find they can produce a theoretical cosmic ray flux on Earth of at least $R_\text{UHECR} = 1.2 \times 10^{15}$ particles km$^{-2}$ century$^{-1}$ mol$^{-1}$. No suppression mechanisms can reconcile this value with the flux observed on Earth. Instead, we propose that the jet of low-luminosity gamma-ray bursts propels only the circumburst medium - which is accelerated to relativistic speeds - not the stellar matter. This has implications for the baryonic load of the jet: it should be negligible compared to the leptonic content.Comment: 5 pages, submitted to MNRA

Multi-wavelength analysis of the field of the dark burst GRB 031220

We have collected and analyzed data taken in different spectral bands (from X-ray to optical and infrared) of the field of GRB031220 and we present results of such multiband observations. Comparison between images taken at different epochs in the same filters did not reveal any strong variable source in the field of this burst. X-ray analysis shows that only two of the seven Chandra sources have a significant flux decrease and seem to be the most likely afterglow candidates. Both sources do not show the typical values of the R-K colour but they appear to be redder. However, only one source has an X-ray decay index (1.3 +/- 0.1) that is typical for observed afterglows. We assume that this source is the best afterglow candidate and we estimate a redshift of 1.90 +/- 0.30. Photometric analysis and redshift estimation for this object suggest that this GRB can be classified as a Dark Burst and that the obscuration is the result of dust extinction in the circum burst medium or inside the host galaxy.Comment: 7 pages, 5 figures, accepted for publication on A&

The CoNFIG Catalogue - II. Comparison of Space Densities in the FR Dichotomy

This paper focuses on a comparison of the space densities of FRI and FRII sources at different epochs, with a particular focus on FRI sources. First, we present the concluding steps in constructing the Combined NVSS-FIRST Galaxy catalogue (CoNFIG), including new VLA observations, optical identifications and redshift estimates. The final catalogue consists of 859 sources over 4 samples (CoNFIG-1, 2, 3 and 4 with flux density limits of S_1.4GHz = 1.3, 0.8, 0.2 and 0.05 Jy respectively). It is 95.7% complete in radio morphology classification and 74.3% of the sources have redshift data. Combining CoNFIG with complementary samples, the distribution and evolution of FRI and FRII sources are investigated. We find that FRI sources undergo mild evolution and that, at the same radio luminosity, FRI and FRII sources show similar space density enhancements in various redshift ranges, possibly implying a common evolution.Comment: 15 pages, 15 figures, 6 tables + appendix (80 pages). accepted in M.N.R.A.

GRB 130427A Afterglow: A Test for GRB Models

Gamma-ray Burst 130427A had the largest fluence for almost 30 years. With an isotropic energy output of 8.5×1053 erg and redshift of 0.34, it combined a very high energy release with a relative proximity to Earth in an unprecedented fashion. Sensitive X-ray facilities such as {\it XMM-Newton} and {\it Chandra} detected the afterglow of this event for a record-breaking baseline of 90 Ms. We show the X-ray light curve of GRB 130427A of this event over such an interval. The light curve shows an unbroken power law decay with a slope of α=1.31 over more than three decades in time. In this presentation, we investigate the consequences of this result for the scenarios proposed to interpret GRB 130427A and the implications in the context of the forward shock model (jet opening angle, energetics, surrounding medium). We also remark the chance of extending GRB afterglow observations for several hundreds of Ms with {\it Athena}

First XMM-Newton Observations of the Globular Cluster M22

We have examined preliminary data of the globular cluster, M22, from the EPIC MOS detectors on board XMM-Newton. We have detected 27 X-ray sources within the centre of the field of view, 24 of which are new detections. Three sources were found within the core of the cluster. From spectral analysis of the X-ray sources, it is possible that the object at the centre of the core is a quiescent X-ray transient and those lying further out are maybe cataclysmic variables.Comment: 6 pages, 3 figures, accepted to be published in Astronomy and Astrophysic

Multiwavelength chase of GRB 031220 afterglow

Several gamma ray bursts (GRBs) with X-ray afterglow do not show any optical-IR afterglow. The nature of this class of events, the so-called Dark Bursts, is still not clear. The optical absorption could be due to the interstellar dust or to the high redshift of the event. Or, more simply, the non-detection of the optical transient should be due to the delay in the observation or to the rapid energy decaying of these events. High spatial resolution X-ray observations are the most promising tool to investigate on such kind of events. We have collected and analyzed X-ray data and images taken in different spectral bands (optical and infrared) for GRB 031220 and we present the results of the analysis of multiband observations on the field of this burst. Comparison between images taken at different epochs in the same filters did not reveal any strongly variable sources. Photometric analysis and photometric redshift estimation of all possible afterglow candidates suggest that this GRB can be classifie d as a Dark Burst

An XMM-Newton observation of the globular cluster Omega Centauri

We report on a deep XMM-Newton EPIC observation of the globular cluster Omega Cen performed on August 13th, 2001. We have detected 11 and 27 faint X-ray sources in the core and half mass radii, searching down to a luminosity of 1.3 x 10^{31} erg s^{-1} in the 0.5-5 keV range. Most sources have bolometric X-ray luminosities between ~ 10^{31}-10^{32} erg s^{-1}. We present the color-color and hardness-intensity diagrams of the source sample, as well as high-quality EPIC spectra of the brightest objects of the field; including the two candidate Cataclysmic Variables (CVs) in the core and the quiescent neutron star low-mass X-ray binary candidate. The spectra of the latter objects fully support their previous classification. We show that the bulk of sources are hard and spectrally similar to CVs. The lack of soft faint sources might be related to the absence of millisecond pulsars in the cluster. The XMM-Newton observations reveal the presence of an excess of sources well outside the core of the cluster where several RS CVn binaries have already been found. We have also analyzed a publicly available Chandra ACIS-I observation performed on January 24-25th, 2000, to improve the XMM-Newton source positions and to search for source intensity variations between the two data sets. 63 XMM-Newton sources have a Chandra counterpart, and 15 sources within the half-mass radius have shown time variability. Overall, the general properties of the faint X-ray sources in Omega Cen suggest that they are predominantly CVs and active binaries (RS CVn or BY Dra).Comment: 21 pages, 2 color figures, 8 B&W figures. Accepted for publication in Astronomy and Astrophysic