An Off-Axis Galaxy Cluster Merger: Abell 0141

We present structural analysis results of Abell 0141 ($z$ = 0.23) based on X-ray data. The X-ray luminosity map demonstrates that Abell 0141 (A0141) is a bimodal galaxy cluster, which is separated on the sky by $\sim$ 0.65 Mpc with an elongation along the north-south direction. The optical galaxy density map also demonstrates this bimodality. We estimate sub-cluster ICM temperatures of 5.17$^{+0.20}_{-0.19}$ keV for A0141N and 5.23$^{+0.24}_{-0.23}$ keV for A0141S. We obtain X-ray morphological parameters w = 0.034$\pm{0.004}$, c = 0.113$\pm{0.004}$ and w = 0.039$\pm{0.004}$, c = 0.104$\pm{0.005}$ for A0141N and A0141S, respectively. The resulting X-ray morphological parameters indicate that both sub-clusters are moderately disturbed non-cool core structures. We find a slight brightness jump in the bridge region, and yet, there is still an absence of strong X-ray emitting gas between sub-clusters. We discover a significantly hotspot ($\sim$ 10 keV) between sub-clusters, and a Mach number $\textit{M}$ = 1.69$^{+0.40}_{-0.37}$ is obtained by using the temperature jump condition. However, we did not find direct evidence for shock-heating between sub-clusters. We estimate the sub-clusters' central entropies as $K_{0}$ > 100 keV cm$^{2}$, which indicates that the sub-clusters are not cool cores. We find some evidence that the system undergoes an off-axis collision; however, the cores of each sub-clusters have not yet been destroyed. Due to the orientation of X-ray tails of sub-clusters, we suggest that the northern sub-cluster moves through the south-west direction, and the southern cluster moves through the north-east direction. In conclusion, we are witnessing an earlier phase of close core passage between sub-clusters.Comment: 9 pages, 4 figure

XMM-Newton view of X-ray overdensities from nearby galaxy clusters: the environmental dependencies

In this work, we studied ten nearby ($z$$\leq$0.038) galaxy clusters to understand possible interactions between hot plasma and member galaxies. A multi-band source detection was applied to detect point-like structures within the intra-cluster medium. We examined spectral properties of a total of 391 X-ray point sources within cluster's potential well. Log $N$ - Log $S$ was studied in the energy range of 2-10 keV to measure X-ray overdensities. Optical overdensities were also calculated to solve suppression/triggering phenomena for nearby galaxy clusters. Both X-ray to optical flux/luminosity properties, ($X/O$, $L_{X}$/$L_{B}$, $L_{X}$/$L_{K}$), were investigated for optically identified member galaxies. X-ray luminosity values of our point sources are found to be faint (40.08 $\leq$ log($L_{X}$) $\leq$ 42.39 erg s$^{-1}$). The luminosity range of point sources reveals possible contributions to X-ray emission from LLAGNs, X-ray Binaries and star formation. We estimated $\sim$ 2 times higher X-ray overdensities from galaxies within galaxy clusters compared to fields. Our results demonstrate that optical overdensities are much higher than X-ray overdensities at the cluster's centre, whereas X-ray overdensities increase through the outskirts of clusters. We conclude that high pressure from the cluster's centre affects the balance of galaxies and they lose a significant amount of their fuels; as a result, clustering process quenches X-ray emission of the member galaxies. We also find evidence that the existence of X-ray bright sources within cluster environment can be explained by two main phenomena: contributions from off-nuclear sources and/or AGN triggering caused by galaxy interactions rather than AGN fuelling.Comment: 17 pages, 6 figures. Accepted for publication in the Monthly Notices of the Royal Astronomical Societ

A Pre-Merger Stage Galaxy Cluster: Abell 3733

The galaxy cluster Abell 3733 (A3733) is a very suitable candidate in addressing dynamical processes throughout galaxy cluster mergers. This study shows structural analysis results of A3733 (z = 0.038) based on X-ray and optical data. According to X-ray luminosity map, A3733 hosts two sub-structures separated in the sky by $\sim$ 0.25 Mpc, and the two distinct clumps are located in the East (A3733E) and the West (A3733W) directions. Both sub-structures are centred on two different brightest cluster galaxies (BCGs), and the X-ray and optical centroids of both BCGs substantially coincide with each other. The intracluster medium (ICM) temperatures of the sub-structures are estimated to be 2.79 keV for A3733E and 3.28 keV for A3733W. Both sub-structures are found to be hosting cool central gas (kT $\sim$ 1.5-2.5 keV) surrounded by hotter gas (kT $\sim$ 3.0-3.5 keV). Besides, the X-ray concentration parameters are found to be c $\sim$ 0.3 for each sub-structure. These results indicate the existence of cool centres for both sub-structures. The optical density map reveals a crowded galaxy population within the vicinity of A3733W. The high probable (% 88.2) dynamical binding model of A3733 suggests that the cores of sub-structures have a 3D separation of 0.27 Mpc and will collide in 0.14 Gyr with the relative in-falling velocity of 1936 km s$^{-1}$. As a conclusion, this study demonstrates some evidence suggesting that the A3733 system is in the pre-merger state.Comment: 9 pages, 7 Figures, published by MNRA

An Approach to Help End Users Become Aware of Privacy Risks in Home Automation

Smart home devices, such as voice assistants, smart lights, and smart video doorbells have become a part of end users' daily lives. Many of these devices combine their features with other services and smart devices to create a simple and efficient user experience. This is partly because of the contribution of end-user programming platforms, like If This Then That (IFTTT). IFTTT provides trigger and action events to end users to connect two or more smart home devices via easy-to-create applets. However, these applets rarely highlight underlying risks related to confidentiality (leakage of sensitive information) or integrity (authorized access) violations. Prior work has shown that providing users with violation scenarios makes them aware of the risks associated with these specific applets. However, these works have not investigated if end users can identify potential risks from the applet descriptions and change their behavior. This thesis closes this gap by (1) presenting end users with “consequences” of using IFTTT applets to understand if end users could find the possible violations and their reasoning, and (2) evaluating whether end users’ behavior changes when applets are presented with the consequences. In this work, we conducted a user study with 20 participants to evaluate our approach of including consequences in applet description. Our results show that adding potential consequences into the basic IFTTT applet description can help end users discover integrity and confidentiality violations and related factors impacting their applet usage decisions. Finally, we suggest a framework to automatically nudge end users when they want to use applets through end-user programming platforms. In this way, end users can have a comprehensive understanding of using applets in different contexts

BASS XXXIX: Swift-BAT AGN with changing-look optical spectra

Changing-look (CL) AGN are unique probes of accretion onto supermassive black holes (SMBHs), especially when simultaneous observations in complementary wavebands allow investigations into the properties of their accretion flows. We present the results of a search for CL behaviour in 412 Swift-BAT detected AGN with multiple epochs of optical spectroscopy from the BAT AGN Spectroscopic Survey (BASS). 125 of these AGN also have 14-195 keV ultra-hard X-ray light-curves from Swift-BAT which are contemporaneous with the epochs of optical spectroscopy. Eight CL events are presented for the first time, where the appearance or disappearance of broad Balmer line emission leads to a change in the observed Seyfert type classification. Combining with known events from the literature, 21 AGN from BASS are now known to display CL behaviour. Nine CL events have 14-195 keV data available, and five of these CL events can be associated with significant changes in their 14-195 keV flux from BAT. The ultra-hard X-ray flux is less affected by obscuration and so these changes in the 14-195 keV band suggest that the majority of our CL events are not due to changes in line-of-sight obscuration. We derive a CL rate of 0.7-6.2 per cent on 10-25 year time-scales, and show that many transitions happen within at most a few years. Our results motivate further multi-wavelength observations with higher cadence to better understand the variability physics of accretion onto SMBHs.Comment: 14 pages, 7 figures, plus appendix. v2: updated references. Published in MNRA

BASS-XL: X-ray variability properties of unobscured active galactic nuclei

We investigate the X-ray variability properties of Seyfert 1 Galaxies belonging to the BAT AGN Spectroscopic Survey (BASS). The sample includes 151 unobscured (N-H < 10(22) cm(-2)) AGNs observed with XMM-Newton for a total exposure time of similar to 27 ms, representing the deepest variability study done so far with high signal-to-noise XMM-Newton observations, almost doubling the number of observations analysed in previous works. We constrain the relation between the normalized excess variance and the 2-10 keV AGN luminosities, black hole masses, and Eddington ratios. We find a highly significant correlation between sigma(2)(NXS) and M-BH, with a scatter of similar to 0.85 dex. For sources with high L2-10 this correlation has a lower normalization, confirming that more luminous (higher mass) AGNs show less variability. We explored the sigma(2)(NXS) versus M-BH relation for the sub-sample of sources with M-BH estimated via the 'reverberation mapping' technique, finding a tighter anticorrelation, with a scatter of similar to 0.65 dex. We examine how the sigma(2)(NXS) changes with energy by studying the relation between the variability in the hard (3-10 keV) and the soft (0.2-1 keV)/medium (1-3 keV) energy bands, finding that the spectral components dominating the hard energy band are more variable than the spectral components dominating in softer energy bands, on time-scales shorter than 10 ks

BASS. XXV. DR2 Broad-line-based Black Hole Mass Estimates and Biases from Obscuration

We present measurements of broad emission lines and virial estimates of supermassive black hole masses (M BH) for a large sample of ultrahard X-ray-selected active galactic nuclei (AGNs) as part of the second data release of the BAT AGN Spectroscopic Survey (BASS/DR2). Our catalog includes M BH estimates for a total of 689 AGNs, determined from the Hα, Hβ, Mg ii λ2798, and/or C iv λ1549 broad emission lines. The core sample includes a total of 512 AGNs drawn from the 70 month Swift/BAT all-sky catalog. We also provide measurements for 177 additional AGNs that are drawn from deeper Swift/BAT survey data. We study the links between M BH estimates and line-of-sight obscuration measured from X-ray spectral analysis. We find that broad Hα emission lines in obscured AGNs ( log(NH/cm−2)>22.0 ) are on average a factor of 8.0−2.4+4.1 weaker relative to ultrahard X-ray emission and about 35−12+7 % narrower than those in unobscured sources (i.e., log(NH/cm−2)1 dex) masses for Type 1.9 sources (AGNs with broad Hα but no broad Hβ) and/or sources with log(NH/cm−2)≳22.0 . We provide simple multiplicative corrections for the observed luminosity and width of the broad Hα component (L[bHα] and FWHM[bHα]) in such sources to account for this effect and to (partially) remedy M BH estimates for Type 1.9 objects. As a key ingredient of BASS/DR2, our work provides the community with the data needed to further study powerful AGNs in the low-redshift universe

Probing the Structure and Evolution of BASS AGN through Eddington Ratios

We constrain the intrinsic Eddington ratio (\lamEdd ) distribution function for local AGN in bins of low and high obscuration (log NH <= 22 and 22 < log NH < 25), using the Swift-BAT 70-month/BASS DR2 survey. We interpret the fraction of obscured AGN in terms of circum-nuclear geometry and temporal evolution. Specifically, at low Eddington ratios (log lamEdd < -2), obscured AGN outnumber unobscured ones by a factor of ~4, reflecting the covering factor of the circum-nuclear material (0.8, or a torus opening angle of ~ 34 degrees). At high Eddington ratios (\log lamEdd > -1), the trend is reversed, with < 30% of AGN having log NH > 22, which we suggest is mainly due to the small fraction of time spent in a highly obscured state. Considering the Eddington ratio distribution function of narrow-line and broad-line AGN from our prior work, we see a qualitatively similar picture. To disentangle temporal and geometric effects at high lamEdd, we explore plausible clearing scenarios such that the time-weighted covering factors agree with the observed population ratio. We find that the low fraction of obscured AGN at high lamEdd is primarily due to the fact that the covering factor drops very rapidly, with more than half the time is spent with < 10% covering factor. We also find that nearly all obscured AGN at high-lamEdd exhibit some broad-lines. We suggest that this is because the height of the depleted torus falls below the height of the broad-line region, making the latter visible from all lines of sight.Comment: Accepted by ApJ

Dynamical history of a binary cluster: Abell 3653

We study the dynamical structure of a bimodal galaxy cluster Abell 3653 at z=0.1089 by using combined optical and X-ray data. Observations include archival data from Anglo-Australian Telescope and X-ray observatories of XMM-Newton and Chandra. We draw a global picture for A3653 using galaxy density, X-ray luminosity and temperature maps. Galaxy distribution has a regular morphological shape at the 3 Mpc size. Galaxy density map shows an elongation EW direction, which perfectly aligns with the extended diffuse X-ray emission. We detect two dominant grouping around two brightest cluster galaxies (BCGs). The BCG1 (z=0.1099) can be associated with the main cluster A3653E, and a foreground subcluster A3563W concentrated at the BCG2 (z=0.1075). Both X-ray peaks are dislocated from BCGs by ($\sim$35 kpc), which suggest an ongoing merger process. We measure the subclusters' gas temperatures 4.67 and 3.66 keV, respectively. Two-body dynamical analysis shows that A3653E & A3653W are very likely (93.5% probability) gravitationally bound. The highly favoured scenario suggests that two subclusters with the mass ratio of 1.4 are colliding close to the plane of sky ($\alpha$=17$^\circ$.61) with 2400 km $s^{-1}$, and will undergo core passage in 380 Myr. Temperature map also significantly shows a shock-heated gas (6.16 keV) in between the subclusters, which confirms the supersonic infalling scenario.Comment: 10 pages, 7 figure