Abstract
We present deep X-ray and radio observations of the fast blue optical transient (FBOT) AT 2020xnd/ZTF 20acigmel at
z
= 0.2433 from 13 days to 269 days after explosion. AT 2020xnd belongs to ...the category of optically luminous FBOTs with similarities to the archetypal event AT 2018cow. AT 2020xnd shows luminous radio emission reaching
L
ν
≈ 8 × 10
29
erg s
−1
Hz
−1
at 20 GHz and 75 days post-explosion, accompanied by luminous and rapidly fading soft X-ray emission peaking at
L
X
≈ 6 × 10
42
erg s
−1
. Interpreting the radio emission in the context of synchrotron radiation from the explosion’s shock interaction with the environment, we find that AT 2020xnd launched a high-velocity outflow (
v
∼ 0.1
c
–0.2
c
) propagating into a dense circumstellar medium (effective
M
̇
≈
10
−
3
M
⊙
yr
−1
for an assumed wind velocity of
v
w
= 1000 km s
−1
). Similar to AT 2018cow, the detected X-ray emission is in excess compared to the extrapolated synchrotron spectrum and constitutes a different emission component, possibly powered by accretion onto a newly formed black hole or neutron star. These properties make AT 2020xnd a high-redshift analog to AT 2018cow, and establish AT 2020xnd as the fourth member of the class of optically luminous FBOTs with luminous multiwavelength counterparts.
Abstract
We present Chandra X-ray observations of the dynamically complex galaxy cluster A119 (
z
= 0.044). A119 is host to two narrow-angle-tail (NAT) radio sources (0053-015 and 0053-016), whose ...tails are oriented parallel to each other, despite orthogonally oriented jet axes. Imaging and spectral analysis reveal X-ray emission elongated along the NE–SW axis, along with the presence of complex structures, including surface brightness discontinuities, which suggest possible merger activity along this axis. From radial profiles of the X-ray surface brightness, temperature, pressure, and density, we identify two surface brightness edges that are found to be cold fronts, possibly associated with large-scale sloshing of intracluster medium gas. We also identify a brightness edge to the S that is found to be a shock front with Mach number
M
= 1.21 ± 0.11, consistent with a merger shock. In addition, previous optical studies show the alignment of optical substructures along the N–S direction. The elongated X-ray emission, orientations of the NAT tails, and alignment of the optical substructure all suggest recent or ongoing merger activity in the NE–SW direction.
Abstract In this paper, we present the results of a blind survey for compact sources in 243 Galaxy clusters that were identified using the thermal Sunyaev–Zel'dovich effect (tSZ). The survey was ...carried out at 90 GHz using MUSTANG2 on the Green Bank Telescope and achieved a 5 σ detection limit of 1 mJy in the center of each cluster. We detected 24 discrete sources. The majority (18) of these correspond to known radio sources, and of these, five show signs of significant variability, either with time or in spectral index. The remaining sources have no clear counterparts at other wavelengths. Searches for galaxy clusters via the tSZ strongly rely on observations at 90 GHz, and the sources found have the potential to bias mass estimates of clusters. We compare our results to the Websky simulation that can be used to estimate the source contamination in galaxy cluster catalogs. While the simulation shows a good match to our observations at the clusters’ centers, it does not match our source distribution further out. Sources over 104″ from a cluster’s center bias the tSZ signal high, for some of the sources found, by over 50%. When averaged over the whole cluster population, the effect is smaller but still at a level of 1%–2%. We also discovered that unlike previous measurements and simulations, we see an enhancement of source counts in the outer regions of the clusters and fewer sources than expected in the centers of this tSZ-selected sample.
Abstract
We present deep Chandra observations of the pre-merger galaxy cluster Abell 98 (A98). A98 is a complex merging system. While the northern (A98N) and central subclusters (A98S) are merging ...along the north–south direction, A98S is undergoing a separate late-stage merger, with two distinct X-ray cores. We report the detection of a gas sloshing spiral and two cold front edges in A98N. We find two more surface brightness edges along the east direction of the eastern core and west direction of the western core of A98S. By measuring the gas temperatures and densities across those edges, we confirm that the eastern edge appears to be a cold front while the western edge is a shock front with a Mach number
≈ 1.5. We detect a spiral structure and a “tail” of X-ray emission associated with the eastern core of A98S. Our measurement indicates that the tail is cooler than the surrounding gas at a 4.2
σ
level. This may suggest that the tail and the spiral structures are the results of ram-pressure stripping, as the eastern core orbits in the main cluster’s gravitational potential.
Abstract
The impact of feedback from active galactic nuclei (AGNs) on the cosmological evolution of the large-scale structure is a long-studied problem. However, it is still not well understood how ...the feedback energy couples to the ambient medium to influence the properties of AGN host galaxies and dark matter halos. In this work we investigate different modes of AGN feedback and their effect on the surrounding medium by probing the diffuse X-ray emission from the hot gas inside galaxy groups and clusters. For this purpose, we use the cosmological hydrodynamic simulation SIMBA to theoretically calculate the X-ray emission from simulated galaxy clusters/groups with the help of the Astrophysical Plasma Emission Code. We also perform synthetic observations of these systems with the Chandra X-ray telescope using the ray-tracing simulator Model of AXAF Response to X-rays. Our results show that in addition to the radiative wind mode of feedback from the AGNs, jet and X-ray modes of feedback play significant roles in suppressing the X-ray emission from the diffuse gas in the vicinity of the black hole. Our mock observational maps suggest that the signatures of AGN feedback from high-redshift objects may not be detected with the instrumental resolution of current X-ray telescopes like Chandra, but provide promising prospects for detection of these features with potential X-ray missions such as Lynx.
ABSTRACT We present results from recent Suzaku and Chandra X-ray and Multiple Mirrior Telescope optical observations of the strongly merging "double cluster" A1750 out to its virial radius, both ...along and perpendicular to a putative large-scale structure filament. Some previous studies of individual clusters have found evidence for ICM entropy profiles that flatten at large cluster radii, as compared with the self-similar prediction based on purely gravitational models of hierarchical cluster formation, and gas fractions that rise above the mean cosmic value. Weakening accretion shocks and the presence of unresolved cool gas clumps, both of which are expected to correlate with large-scale structure filaments, have been invoked to explain these results. In the outskirts of A1750, we find entropy profiles that are consistent with self-similar expectations, and gas fractions that are consistent with the mean cosmic value, both along and perpendicular to the putative large-scale filament. Thus, we find no evidence for gas clumping in the outskirts of A1750, in either direction. This may indicate that gas clumping is less common in lower temperature (kT 4 keV), less massive systems, consistent with some (but not all) previous studies of low-mass clusters and groups. Cluster mass may, therefore, play a more important role in gas clumping than dynamical state. Finally, we find evidence for diffuse, cool (<1 keV) gas at large cluster radii (R200) along the filament, which is consistent with the expected properties of the denser, hotter phase of the warm-hot intergalactic medium.
We have measured half-light radii, r sub(h), for thousands of globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC ...4697. An analysis of the dependencies of the measured half-light radii on both the properties of the GCs themselves and their host galaxies reveals that, in analogy with GCs in the Galaxy but in a milder fashion, the average half-light radius increases with increasing galactocentric distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average half-light radius decreases with the host galaxy color. We also show that there is no evidence for a variation of r sub(h) with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average r sub(h) depends on the color of GCs, with red GCs being 617% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed by Jordan. We discuss these findings in light of two simple pictures for the origin of the r sub(h) of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies on galaxy color, galactocentric radius, and underlying surface brightness, we show that the average GC half-light radii <r sub(h)> can be successfully used as a standard ruler for distance estimation. We outline the methodology, provide a calibration for its use, and discuss the prospects for this distance estimator with future observing facilities. We find <r sub(h)> = 2.7 c 0.35 pc for GCs with (g - z) = 1.2 mag in a galaxy with color (g - z) sub(gal) = 1.5 mag and at an underlying surface z-band brightness of k sub(z) = 21 mag arcsec super(-2). Using this technique, we place an upper limit of 3.4 Mpc on the 1s line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the r sub(h) distribution for our sample galaxies and provide an analytic expression that successfully describes this distribution.
A3667 is the archetype of a merging cluster with radio relics. The northwest (NW) radio relic is the brightest cluster relic or halo known and is believed to be due to a strong merger shock. We have ...observed the NW relic for {approx}40 ks of net XMM-Newton time. We observe a global decline of temperature across the relic from 6 to 1 keV, similar to the Suzaku results. Our new observations reveal a sharp change of both temperature and surface brightness near the position of the relic. The increased X-ray emission on the relic can be equivalently well described by either a thermal or nonthermal spectral model. The parameters of the thermal model are consistent with a Mach number M{approx}2 shock and a shock speed of {approx}1200 km s{sup -1}. The energy content of the relativistic particles in the radio relic can be explained if they are (re)-accelerated by the shock with an efficiency of {approx}0.2%. Comparing the limit on the inverse Compton X-ray emission with the measured radio synchrotron emission, we set a lower limit to the magnetic field in the relic of 3 {mu}G. If the emission from the relic is nonthermal, this lower limit is in fact the required magnetic field.
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