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After the identification of a candidate $\gamma$-ray transient in the error region of the binary black hole (BBH) merger GW150914 by the \textit{Fermi} satellite, the question of whether BBH mergers can be associated to electromagnetic counterparts remains highly debated. Here, we present radio follow-up observations of GW170608, a BBH merger that occurred during the second observing run (O2) of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). Our radio follow up focused on a specific field contained in the GW170608 sky localization area, where a candidate high-energy transient was detected by the \textit{Fermi} Large Area Telescope (LAT). We make use of data collected at 1.4\,GHz with the Karl G. Jansky Very Large Array (VLA), as well as with the VLA Low-band Ionosphere and Transient Experiment (VLITE). Our analysis is sensitive to potential radio afterglows with luminosity densities $L_{\rm 1.4\,GHz}\gtrsim 6\times10^{28}$\,erg\,s$^{-1}$\,Hz$^{-1}$. In the most optimistic theoretical models, $\approx 20\%$ of BBH events occurring in massive hosts could be associated with outflows as radio luminous as this. Although we find no evidence for the presence of a radio counterpart associated with the LAT candidate in the GW170608 error region, our analysis demonstrates the feasibility of future radio follow-up observations of well localized BBHs. Comparing our radio upper-limits with theoretical expectations for the radio afterglows potentially associated with jets launched in BBH mergers, we find that for jets of energy $\approx 10^{49}$\,erg seen on-axis, only jet angles $\theta_{jet}\gtrsim 40^{\circ}$ are compatible with the observations., Comment: 8 pages, 1 figure, 3 tables; version update to match the published one

We present new radio and X-ray observations of Abell 262. The X-ray residual image provides the first evidence of an X-ray tunnel in this system while the radio data reveal that the central radio source is more than three times larger than previously known. We find that the well-known cluster-center S-shaped radio source B2 0149+35 is surrounded by extended emission to the east and south-west. The south-western extension is co-spatial with the X-ray tunnel seen in our new Chandra images while the eastern extension shows three clumps of emission with the innermost coincident with a faint X-ray cavity. The outer two eastern radio extensions are coincident with a newly detected X-ray depression. We use the projected separation of the emission regions to estimate a lower limit of tau_rep=28 Myr to the outburst repetition timescale of the central AGN. The total energy input into the cluster over multiple outburst episodes is estimated to be 2.2x 10^{58} ergs, more than an order of magnitude larger than previously thought. The total AGN energy output determined from our new observations shows that the source should be capable of offsetting radiative cooling over several outburst episodes.

We present an analysis of Chandra observations of the central regions of the cooling flow cluster Abell 2029. We find a number of X-ray filaments in the central 40 kpc, some of which appear to be associated with the currently active central radio galaxy. The outer southern lobe of the steep-spectrum radio source appears to be surrounded by a region of cool gas and is at least partially surrounded by a bright X-ray rim similar to that seen around radio sources in the cores of other cooling flow clusters. Spectroscopic fits show that the overall cluster emission is best fitted by either a two temperature gas (kT_high=7.47 keV, kT_low=0.11 keV), or a cooling flow model with gas cooling over the same temperature range. This large range of temperatures (over a factor of 50) is relatively unique to Abell 2029 and may suggest that this system is a very young cooling flow where the gas has only recently started cooling to low temperatures. The cooling flow model gives a mass deposition rate of Mdot=56 +16/-21 Msun/yr. In general, the cluster emission is elongated along a position angle of 22 degrees with an ellipticity of 0.26. The distribution of the X-ray emission in the central region of the cluster is asymmetric, however, with excess emission to the north-east and south-east compared to the south-west and north-west, respectively. Fitting and subtracting a smooth elliptical model from the X-ray data reveals a dipolar spiral excess extending in a clockwise direction from the cluster core to radii of ~150 kpc. We estimate a total mass of M_spiral ~6 x 10^12 Msun in the spiral excess. The most likely origins of the excess are either stripping of gas from a galaxy group or bare dark matter potential which has fallen into the cluster, or sloshing motions in the cluster core induced by a past merger., Comment: Astrophysical Journal, in press; 15 pages, including 11 figures and 3 tables

We have detected an X-ray absorption feature against the core of the galaxy cluster Abell 2029 (z=0.0767) which we identify with the foreground galaxy UZC J151054.6+054313 (z=0.0221). Optical observations (B, V, R, and I) indicate that it is an Scd galaxy seen nearly edge-on at an inclination of 87 \pm 3 degrees. HI observations give a rotation velocity of 108 kms and an atomic hydrogen mass of M_{HI} = 3.1 X 10^9 d_{90}^2 \msun, where d_{90} is the distance to the galaxy in units of 90 Mpc. X-ray spectral fits to the Chandra absorption feature yield a hydrogen column density of (2.0 \pm 0.4) X 10^{21} cm^{-2} assuming solar abundances. If the absorber is uniformly distributed over the disk of the galaxy, the implied hydrogen mass is M_H = (6.2 \pm 1.2) X 10^8 d_{90}^2 \msun. Since the absorbing gas in the galaxy is probably concentrated to the center of the galaxy and the middle of the disk, this is a lower limit to the total hydrogen mass. On the other hand, the absorption measurements imply that the dark matter in UZC J151054.6+054313 is not distributed in a relatively uniform diffuse gas.

On 2015 February 21, simultaneous observations of Jupiter's decametric radio emission between 10 and 33 MHz were carried out using three powerful low-frequency radio telescopes: Long Wavelength Array Station One (LWA1) in USA; Nan\c{c}ay Decameter Array (NDA) in France; and URAN2 telescope in Ukraine. We measure lag times of short-bursts (S-bursts) for 105-minutes of data over effective baselines up to 8460 km by using cross-correlation analysis of the spectrograms from each instrument. Of particular interest is the measurement of the beaming thickness of S-bursts, testing if either flashlight- or beacon-like beaming is emanating from Jupiter. We find that the lag times for all pairs drift slightly as time elapses, in agreement with expectations from the flashlight-like beaming model. This leads to a new constraint of the minimum beaming thickness of 2.66". Also, we find that most of the analyzed data abound with S-bursts, whose occurrence probability peaks at 17-18 MHz., Comment: This is an author-created, un-copyedited version of an article accepted for publication/published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi: 10.3847/0004-637X/826/2/176

We present a new Chandra X-ray observation of the intracluster medium in the galaxy cluster Abell 2443, hosting an ultra-steep spectrum radio source. The data reveal that the intracluster medium is highly disturbed. The thermal gas in the core is elongated along a northwest to southeast axis and there is a cool tail to the north. We also detect two X-ray surface brightness edges near the cluster core. The edges appear to be consistent with an inner cold front to the northeast of the core and an outer shock front to the southeast of the core. The southeastern edge is coincident with the location of the radio relic as expected for shock (re)acceleration or adiabatic compression of fossil relativistic electrons., Comment: 12 pages, 9 figures; Accepted for publication in The Astrophysical Journal

The search for diffuse non-thermal, inverse Compton (IC) emission from galaxy clusters at hard X-ray energies has been underway for many years, with most detections being either of low significance or controversial. In this work, we investigate 14-195 keV spectra from the Swift Burst Alert Telescope (BAT) all-sky survey for evidence of non-thermal excess emission above the exponentially decreasing tail of thermal emission in the flux-limited HIFLUGCS sample. To account for the thermal contribution at BAT energies, XMM-Newton EPIC spectra are extracted from coincident spatial regions so that both thermal and non-thermal spectral components can be determined simultaneously. We find marginally significant IC components in six clusters, though after closer inspection and consideration of systematic errors we are unable to claim a clear detection in any of them. The spectra of all clusters are also summed to enhance a cumulative non-thermal signal not quite detectable in individual clusters. After constructing a model based on single-temperature fits to the XMM-Newton data alone, we see no significant excess emission above that predicted by the thermal model determined at soft energies. This result also holds for the summed spectra of various subgroups, except for the subsample of clusters with diffuse radio emission. Formore » clusters hosting a diffuse radio halo, a relic, or a mini-halo, non-thermal emission is initially detected at the {approx}5{sigma} confidence level-driven by clusters with mini-halos-but modeling and systematic uncertainties ultimately degrade this significance. In individual clusters, the non-thermal pressure of relativistic electrons is limited to {approx}< 10% of the thermal electron pressure, with stricter limits for the more massive clusters, indicating that these electrons are likely not dynamically important in the central regions of clusters.« less

We present a Chandra X-ray observation and Very Large Array radio observations of the nearby (z = 0.11) galaxy cluster A562 and the wide angle tail (WAT) radio source 0647+693. The cluster displays signatures of an ongoing merger leading to the bending of the WAT source including an elongation of the X-ray surface brightness distribution along the line that bisects the WAT, an excess of displaced gas found between the radio lobes, and anisotropies within the intracluster medium projected temperature and abundance distributions. The most likely geometry of the ongoing interaction is a head-on merger occurring along the WAT bending axis. By combining observable properties of A562 and 0647+693 with common values for the conditions within merging clusters at the time of core crossing, we constrain the internal density ({rho}{sub j} = 0.001 {rho}{sub ICM}) of the jets and plasma flow velocity within the lobes (v{sub r} = 0.02c-0.03c) of the WAT source.

The Coma Cluster of galaxies hosts the brightest radio halo known and has therefore been the target of numerous searches for associated inverse Compton (IC) emission, particularly at hard X-ray energies where the IC signal must eventually dominate over thermal emission. The most recent search with the Suzaku Hard X-ray Detector failed to confirm previous IC detections with RXTE and BeppoSAX, instead setting an upper limit 2.5 times below their non-thermal flux. However, this discrepancy can be resolved if the IC emission is very extended, beyond the scale of the cluster radio halo. Using reconstructed sky images from the 58-month Swift Burst Alert Telescope (BAT) all-sky survey, the feasibility of such a solution is investigated. Building on Renaud et al., we test and implement a method for extracting the fluxes of extended sources, assuming specified spatial distributions. BAT spectra are jointly fit with an XMM-Newton EPIC-pn spectrum derived from mosaic observations. We find no evidence for large-scale IC emission at the level expected from the previously detected non-thermal fluxes. For all non-thermal spatial distributions considered, which span the gamut of physically reasonable IC models, we determine upper limits for which the largest (most conservative) limit is 4.2 ? 10?12 erg s?1 cm?2 (20-80 keV), which corresponds to a lower limit on the magnetic field B > 0.2 ? G. A nominal flux upper limit of 0.25 ? G, is derived for the most probable IC distribution given the size of the radio halo and likely magnetic field radial profile.