Seyfert galaxies with Swift: giant flares, rapid drops, and other surprises

Swift has initiated a new era of understanding the extremes of active galactic nuclei (AGN) variability, their drivers and underlying physics. This is based on its rapid response, high sensitivity, good spatial resolution, and its ability to collect simultaneously X--ray-to-optical SEDs. Here, we present results from our recent monitoring campaigns with Swift of highly variable AGN, including outbursts, deep low states, and unusual long-term trends in several Seyfert galaxies including Mrk 335, WPVS007, and RXJ2314.9+2243. We also report detection of a new X-ray and optical outburst of IC 3599 and our Swift follow-ups. IC 3599 was previously known as one of the AGN with the highest-amplitude outbursts. We briefly discuss implications of this second outburst of IC 3599 for emission scenarios including accretion-disk variability, repeat tidal disruption events, and the presence of a binary supermassive black hole.Comment: to appear in "Swift: 10 years of discovery", Proceedings of Scienc

The XMM-Newton slew survey in the 2-10 keV band

The XMM-Newton Slew Survey (XSS) covers a significant fraction of the sky in a broad X-ray bandpass. Although shallow by contemporary standards, in the `classical' 2-10 keV band of X-ray astronomy, the XSS provides significantly better sensitivity than any currently available all-sky survey. We investigate the source content of the XSS, focussing on detections in the 2-10 keV band down to a very low threshold (> 4 counts net of background). At the faint end, the survey reaches a flux sensitivity of roughly 3e-12 erg/cm2/s (2-10 keV). Our starting point was a sample of 487 sources detected in the XMMSL1d2 XSS at high galactic latitude in the hard band. Through cross-correlation with published source catalogues from surveys spanning the electromagnetic spectrum from radio to gamma-rays, we find that 45% of the sources have likely identifications with normal/active galaxies, 18% are associated with other classes of X-ray object (nearby coronally active stars, accreting binaries, clusters of galaxies), leaving 37% of the XSS sources with no current identification. We go on to define an XSS extragalactic hard band sample comprised of 219 galaxies and active galaxies. We investigate the properties of this extragalactic sample including its X-ray logN-logS distribution. We find that in the low-count limit, the XSS is strongly affected by Eddington bias. There is also a very strong bias in the XSS against the detection of extended sources, most notably clusters of galaxies. A significant fraction of the detections at and around the low-count limit may be spurious. Nevertheless, it is possible to use the XSS to extract a reasonably robust sample of extragalactic sources, excluding galaxy clusters. The differential logN-logS relation of these extragalactic sources matches very well to the HEAO-1 A2 all-sky survey measurements at bright fluxes and to the 2XMM source counts at the faint end.Comment: 16 pages, 13 figures, FITS table of XSS extragalactic sample available from http://www.star.le.ac.uk/~amr30/Slew

Dynamic Model Generation and Classification of Network Attacks

When attempting to read malicious network traffic, security analysts are challenged to determine what attacks are happening in the network at any given time. This need to analyze data and attempt to classify the data requires a large amount of manual time and knowledge to be successful. It can also be difficult for the analysts to determine new attacks if the data is unlike anything they have seen before. Because of the ever-changing nature of cyber-attacks, a need exists for an automated system that can read network traffic and determine the types of attacks present in a network. Many existing works for classification of network attacks exist and contain a very similar fundamental problem. This problem is the need either for labeled data, or batches of data. Real network traffic does not contain labels for attack types and is streaming packet by packet. This work proposes a system that reads in streaming malicious network data and classifies the data into attack models while dynamically generating and reevaluating attack models when needed. This research develops a system that contains three major components. The first is a dynamic Bayesian classifier that utilizes Bayes\u27 Theorem to classify the data into the proper attack models using dynamic priors and novel likelihood functions. The second component is the dynamic model generator. This component utilizes the concept of a cluster validity index to determine the proper time to generate new models. The third component is a model shuffler. This component redistributes misclassified data into attack models that more closely fit the behaviors of the data. Malicious packet captures obtained from two network attack and defense competitions are used to demonstrate the ability of the system to classify data, successfully and reasonably create new attack models, and shuffle the data into more closely related models

The Impact of Prior Experience Employees’ Perceptions and Beliefs about Workplace Policies and Practices

Domestic violence (DV) is associated with negative consequences for victims, children, families, and even national economies. More recently, research has demonstrated that DV also has a serious impact on workers and workplaces. Less is known about Canadians’ beliefs toward the impact DV has on workers or the extent to which individuals are able to identify co-workers’ experiences of DV. Using data from a pan-Canadian sample of 7,834 men and women, the current study examined: 1) how prior experiences with DV relates to beliefs toward the impact DV has on workers, 2) how gender and age relates to beliefs toward DV’s impact on workers, 3) the factors associated with identifying co-workers as DV victims and perpetrators. Overall, participants held positive beliefs that acknowledged DV’s impact on workers. Types of prior experiences with DV were found to have a significant relationship with how participants perceived the impact DV has on workers. There were also significant relationships found between gender and age on participants’ beliefs toward the impact DV has on workers. Additionally, the present study found age, gender, and certain types of prior DV experiences were associated with identifying a colleague as a victim or perpetrator of DV. These findings have implications for a how workplaces respond to DV and take into account the need to engage all employees

The XMM-Newton Slew Survey: Towards The Whole X-ray Sky and the Rarest X-ray Events

The data collected by XMM-Newton as it slews between pointings currently cover almost half the entire sky, and many familiar features and new sources are visible. The soft-band sensitivity limit of the Slew is close to that of the RASS, and a large-area Slew-RASS comparison now provides the best opportunity for discovering extremely rare high-variability objects.Comment: To appear in Proceedings of "X-ray Astronomy 2009: Present Status, Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin

Statistical evaluation of the flux cross-calibration of the XMM-Newton EPIC cameras

The second XMM-Newton serendipitous source catalogue, 2XMM, provides the ideal data base for performing a statistical evaluation of the flux cross-calibration of the XMM-Newton European Photon Imaging Cameras (EPIC). We aim to evaluate the status of the relative flux calibration of the EPIC cameras on board XMM-Newton (MOS1, MOS2, and pn) and investigate the dependence of the calibration on energy, position in the field of view of the X-ray detectors, and lifetime of the mission. We compiled the distribution of flux percentage differences for large samples of 'good quality' objects detected with at least two of the EPIC cameras. The mean offset of the fluxes and dispersion of the distributions was then found by Gaussian fitting. Count rate to flux conversion was performed with a fixed spectral model. The impact on the results of varying this model was investigated. Excellent agreement was found between the two EPIC MOS cameras to better than 4% from 0.2 keV to 12.0 keV. MOS cameras register 7-9% higher flux than pn below 4.5 keV and 10-13% flux excess above 4.5 keV. No evolution of the flux ratios is seen with time, except at energies below 0.5 keV, where we found a strong decrease in the MOS to pn flux ratio with time. This effect is known to be due to a gradually degrading MOS redistribution function. The flux ratios show some dependence on distance from the optical axis in the sense that the MOS to pn flux excess increases with off-axis angle. Furthermore, in the 4.5-12.0 keV band there is a strong dependence of the MOS to pn excess flux on the azimuthal-angle. These results strongly suggest that the calibration of the Reflection Grating Array (RGA) blocking factors is incorrect at high energies. Finally, we recommend ways to improve the calculation of fluxes in future versions of XMM-Newton source catalogues.Comment: 11 pages, 10 figures, 3 tables. Abridged Abstract. Accepted for publication in Astronomy and Astrophysic

Online containers for hypergraphs, with applications to linear equations

A set of containers for a hypergraph G is a collection CC of vertex subsets, such that for every independent (or, indeed, merely sparse) set I of G there is some C∈CC∈C with I⊂CI⊂C, no member of CC is large, and the collection CC is relatively small. Containers with useful properties have been exhibited by Balogh, Morris and Samotij [6] and by the authors [39]; [40] ; [41], along with several applications. Our purpose here is to give a simpler algorithm than the one used in [40], which nevertheless yields containers with all the properties needed for the main container theorem of [40] and its consequences. Moreover this algorithm produces containers having the so-called online property, allowing the colouring results of [40] to be extended to all, not just simple, hypergraphs. Most of the proof of the container theorem remains the same if this new algorithm is used, and we do not repeat all the details here, but describe only the changes that need to be made. However, for illustrative purposes, we do include a complete proof of a slightly weaker but simpler version of the theorem, which for many (perhaps most) applications is plenty. We also present applications to the number of solution-free sets of linear equations, including the number of Sidon sets, that were announced in [40]

Does Stakeholder Engagement Pay Off on Social Media? A Social Capital Perspective

Nonprofits use social media to pursue a broad range of mission-related outcomes. Given the centrality of user connections and social networks on these sites, attaining these outcomes is contingent on first generating a stock of online social capital through investing in online relationships. Yet, little is known empirically about this process. To better understand the return on social media, this study develops empirical measures of four key dimensions of social media–based social capital centering on the nature of nonprofits’ network positions and stakeholder ties. The study then tests a series of hypotheses relating the increase in social capital to different types of stakeholder engagement tactics. Using Twitter data on 198 community foundations, the study finds that content with multiple communication cues and intersectoral stakeholder targeting predict higher levels of social capital; communicative and stakeholder diversity, thus, appear to play a key role in the successful organizational use of social media