Chandra Observations Research Articles

An X-Ray Census of Fast Radio Burst Host Galaxies: Constraints on Active Galactic Nuclei and X-Ray Counterparts

We present the first X-ray census of fast radio burst (FRB) host galaxies to conduct the deepest search for active galactic nuclei (AGN) and X-ray counterparts to date. Our sample includes seven well-localized FRBs with unambiguous host associations and existing deep Chandra observations, including two events for which we present new observations. We find evidence for AGN in two FRB host galaxies based on the presence of X-ray emission coincident with their centers, including the detection of a luminous (L X ≈ 5 × 1042 erg s−1) X-ray source at the nucleus of FRB 20190608B’s host, for which we infer an SMBH mass of M BH ∼ 108 M ⊙ and an Eddington ratio L bol/L Edd ≈ 0.02, characteristic of geometrically thin disks in Seyfert galaxies. We also report nebular emission-line fluxes for 24 highly secure FRB hosts (including 10 hosts for the first time), and assess their placement on a BPT diagram, finding that FRB hosts trace the underlying galaxy population. We further find that the hosts of repeating FRBs are not confined to the star-forming locus, contrary to previous findings. Finally, we place constraints on associated X-ray counterparts to FRBs in the context of ultraluminous X-ray sources (ULXs), and find that existing X-ray limits for FRBs rule out ULXs brighter than L X ≳ 1040 erg s−1. Leveraging the CHIME/FRB catalog and existing ULX catalogs, we search for spatially coincident ULX–FRB pairs. We identify a total of 28 ULXs spatially coincident with the localization regions for 17 FRBs, but find that the DM-inferred redshifts for the FRBs are inconsistent with the ULX redshifts, disfavoring an association between these specific ULX–FRB pairs.

A Chandra Study of the NGC 7618/UGC 12491 Major Group Merger at Apogee: Multiple Cold Fronts, Boxy Wings, Filaments, and Arc-shaped Slingshot Tails

Analyses of major group mergers are key to understanding the evolution of large-scale structure in the Universe and the microphysical properties of the hot gas in these systems. We present imaging and spectral analyses of deep Chandra observations of hot gas structures formed in the major merger of the NGC 7618 and UGC 12491 galaxy groups and compare the observed hot gas morphology, temperatures, and abundances with recent simulations. The morphology of the observed multiple cold front edges and boxy wings are consistent with those expected to be formed by Kelvin–Helmholtz instabilities and gas sloshing in inviscid gas. The arc-shaped slingshot tail morphologies seen in each galaxy suggest that the dominant galaxies are near their orbital apogee after having experienced at least one core passage at a large impact parameter.

The Chandra Cygnus OB2 Legacy Survey: Design and X-Ray Point-source Catalog

The Cygnus OB2 association is the largest concentration of young and massive stars within 2 kpc of the Sun, including an estimated ∼65 O-type stars and hundreds of OB stars. The Chandra Cygnus OB2 Legacy Survey is a large imaging program undertaken with the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. The survey has imaged the central 0.5 deg2 of the Cyg OB2 association with an effective exposure of ∼120 ks and an outer 0.35 deg2 area with an exposure of ∼60 ks. Here we describe the survey design and observations, discuss the data reduction and source detection, and present a catalog of ∼8000 X-ray point sources. The survey design employs a grid of 36 heavily (∼50%) overlapping pointings, a method that overcomes Chandra's low off-axis sensitivity and produces a highly uniform exposure over the inner 0.5 deg2. The full X-ray catalog is described here and is made available online.

The formation channels of multiphase gas in nearby early-type galaxies

ABSTRACT The processes responsible for the assembly of cold and warm gas in early-type galaxies (ETGs) are not well understood. We report on the multiwavelength properties of 15 non-central, nearby (z ≤ 0.008 89) ETGs primarily through Multi-Unit Spectroscopic Explorer (MUSE) and Chandra X-ray observations, to address the origin of their multiphase gas. The MUSE data reveal that 8/15 sources contain warm ionized gas traced by the H α emission line. The morphology of this gas is found to be filamentary in 3/8 sources: NGC 1266, NGC 4374, and NGC 4684, which is similar to that observed in many group and cluster-centred galaxies. All H α filamentary sources have X-ray luminosities exceeding the expected emission from the stellar population, suggesting the presence of diffuse hot gas, which likely cooled to form the cooler phases. The morphologies of the remaining 5/8 sources are rotating gas discs, not as commonly observed in higher mass systems. Chandra X-ray observations (when available) of the ETGs with rotating H α discs indicate that they are nearly void of hot gas. A mixture of stellar mass-loss and external accretion was likely the dominant channel for the cool gas in NGC 4526 and NGC 4710. These ETGs show full kinematic alignment between their stars and gas, and are fast rotators. The H α features within NGC 4191 (clumpy, potentially star-forming ring), NGC 4643, and NGC 5507 (extended structures) along with loosely overlapping stellar and gas populations allow us to attribute external accretion to be the primary formation channel of their cool gas.

New black hole spin values for Sagittarius A* obtained with the outflow method

ABSTRACT Six archival Chandra observations are matched with eight sets of radio data and studied in the context of the outflow method to measure and study the spin properties of $\rm {Sgr ~A^{*}}$. Three radio and X-ray data sets obtained simultaneously, or partially simultaneously, are identified as preferred for the purpose of measuring the spin properties of $\rm {Sgr ~A^{*}}$. Similar results are obtained with other data sets. Results obtained with the preferred data sets are combined and indicate weighted mean values of the spin function of $F = 0.62 \pm 0.10$ and dimensionless spin angular momentum of $a_* = 0.90 \pm 0.06$. The spin function translates into measurements of the black hole rotational mass, Mrot, irreducible mass, Mirr, and spin mass–energy available for extraction, Mspin, relative to the total black hole dynamical mass, Mdyn. Weighted mean values of (Mrot/Mdyn) = (0.53 ± 0.06), (Mirr/Mdyn) = (0.85 ± 0.04), (Mspin/Mdyn) = (0.15 ± 0.04), Mrot = (2.2 ± 0.3) × 106 M⊙, Mirr = (3.5 ± 0.2) × 106 M⊙, and Mspin = (6.2 ± 1.6) × 105 M⊙ are obtained; of course (Mrot/Mirr) = (0.62 ± 0.10) since (Mrot/Mirr) = F. Values obtained for $\rm {Sgr ~A^{*}}$ are compared with those obtained for M87 based on the published spin function, which indicate that M87 carries substantially more rotational energy and spin mass–energy relative to the total (i.e. dynamical) black hole mass, the irreducible black hole mass, and in absolute terms.

New Insights on 30 Dor B Revealed by High-quality Multiwavelength Observations

The supernova remnant (SNR) 30 Dor B is associated with the H ii region ionized by the OB association LH99. The complex interstellar environment has made it difficult to study the physical structure of this SNR. We have used Hubble Space Telescope Hα images to identify SNR shocks and deep Chandra X-ray observations to detect faint diffuse emission. We find that 30 Dor B hosts three zones with very different X-ray surface brightnesses and nebular kinematics that are characteristic of SNRs in different interstellar environments and/or evolutionary stages. The ASKAP 888 MHz map of 30 Dor B shows counterparts to all X-ray emission features except the faint halo. The ASKAP 888 and 1420 MHz observations are used to produce a spectral index map, but its interpretation is complicated by the background thermal emission and the pulsar PSR J0537−6910's flat spectral index. The stellar population in the vicinity of 30 Dor B indicates a continuous star formation in the past 8–10 Myr. The observed very massive stars in LH99 cannot be coeval with the progenitor of 30 Dor B’s pulsar. Adopting the pulsar’s spin-down timescale, 5000 yr, as the age of the SNR, the X-ray shell would be expanding at ∼4000 km s−1 and the post-shock temperature would be 1–2 orders of magnitude higher than that indicated by the X-ray spectra. Thus, the bright central region of 30 Dor B and the X-ray shell requires two separate SN events, and the faint diffuse X-ray halo perhaps other older SN events.

TCP J18224935-2408280: a symbiotic star identified during outburst

ABSTRACT TCP J18224935-2408280 was reported to be in outburst on 2021 May 19. Follow-up spectroscopic observations confirmed that the system was a symbiotic star. We present optical spectra obtained from the Himalayan Chandra Telescope during 2021–22. The early spectra were dominated by Balmer lines, He i lines and high ionization lines such as He ii. In the later observations, Raman scattered O vi was also identified. Outburst in the system started as a disc instability, and later the signature of enhanced shell burning and expansion of photospheric radius of the white dwarf was identified. Hence we suggest this outburst is of combination nova type. The post-outburst temperature of the hot component remains above 1.5 × 105 K indicating a stable shell burning in the system for a prolonged time after the outburst. Based on our analysis of archival multiband photometric data, we find that the system contains a cool giant of M1-2 III spectral type with a temperature of ∼3600 K and a radius of ∼69 R⊙. The pre- and post-outburst light curve shows a periodicity of 631.25 ± 2.93 d; we consider this as the orbital period.

Constraints on thermal conductivity in the merging cluster Abell 2146

ABSTRACT The cluster of galaxies Abell 2146 is undergoing a major merger and is an ideal cluster to study intracluster medium (ICM) physics, as it has a simple geometry with the merger axis in the plane of the sky, its distance allows us to resolve features across the relevant scales and its temperature lies within Chandra’s sensitivity. Gas from the cool core of the subcluster has been partially stripped into a tail of gas, which gives a unique opportunity to look at the survival of such gas and determine the rate of conduction in the ICM. We use deep 2.4-Ms Chandra observations of Abell 2146 to produce a high spatial resolution map of the temperature structure along a plume in the ram-pressure stripped tail, described by a partial cone, which is distinguishable from the hot ambient gas. Previous studies of conduction in the ICM typically rely on estimates of the survival time for key structures, such as cold fronts. Here we use detailed hydrodynamical simulations of Abell 2146 to determine the flow velocities along the stripped plume and measure the time-scale of the temperature increase along its length. We find that conduction must be highly suppressed by multiple orders of magnitude compared to the Spitzer rate, as the energy used is about 1 per cent of the energy available. We discuss magnetic draping around the core as a possible mechanism for suppressing conduction.

Dataset of Classified Chandra Sources in Globular Clusters

We present a collection of classified X-ray sources in Globular Clusters (GCs) observed by the Chandra X-ray Observatory, including active binaries, cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries. We cross-match the most accurate published positions from multiwavelength observations of these sources to the Chandra Source Catalog Release 2.1, and the HST UV Globular Cluster Survey to extract their multiwavelength properties. The data set can be accessed via an interactive website (https://home.gwu.edu/~kargaltsev/XCLASS_GC) and used as a training data set for machine-learning classification of unidentified X-ray sources in GCs.

AT2023fhn (the Finch): a luminous fast blue optical transient at a large offset from its host galaxy

ABSTRACT Luminous fast blue optical transients (LFBOTs) – the prototypical example being AT 2018cow – are a rare class of events whose origins are poorly understood. They are characterized by rapid evolution, featureless blue spectra at early times, and luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming host galaxies. We present Hubble Space Telescope, Gemini, Chandra, and Very Large Array observations of a new LFBOT, AT 2023fhn. The Hubble Space Telescope data reveal a large offset (>3.5 half-light radii) from the two closest galaxies, both at redshift z ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can occur in a range of galactic environments.

Chandra Observation of NGC 1559: Eight Ultraluminous X-Ray Sources Including a Compact Binary Candidate

Despite the 30 yr history of ultraluminous X-ray sources (ULXs) studies, issues such as the majority of their physical natures (i.e., neutron stars, stellar-mass black holes, or intermediate black holes) as well as the accretion mechanisms are still under debate. Expanding the ULX sample size in the literature is clearly a way to help. To this end, we investigated the X-ray source population, ULXs in particular, in the barred spiral galaxy NGC 1559 using a Chandra observation made in 2016. In this 45 ks exposure, 33 X-ray point sources were detected within the 2.′7 isophotal radius of the galaxy. Among them, eight ULXs were identified with the criterion of the X-ray luminosity L x > 1039 erg s−1 (0.3–7 keV). Both X-ray light curves and spectra of all the sources were examined. Except for some low-count spectra that only provide ambiguous spectral fitting results, all the X-ray sources were basically spectrally hard and therefore likely have nonthermal origins. While no strong X-ray variability was present in most of the sources owing to the relatively short exposure of the observation, we found an intriguing ULX, named X-24, exhibiting a periodicity of ∼7500 s with a detection significance of 2.7σ. We speculate that it is the orbital period of the system. Roche-lobe overflow and Roche limit are consistent with the speculation. Thus, we suggest that X-24 may be one of the rare compact binary ULXs, and hence, a good candidate as a stellar-mass black hole.

Investigating the outskirts of Abell 133 with Suzaku and Chandra observations

Context. Past observations and simulations have predicted an increasingly inhomogeneous gas distribution towards the outskirts of galaxy clusters. However, the exact properties of such gas clumping are not yet well known. The outskirts of Abell 133 can benefit from deep X-ray observations, with a 2.4 Ms ultra-deep Chandra exposure, as well as eight archival Suzaku pointings, making it a unique laboratory for studying the clumping of the intracluster medium (ICM). Aims. We searched for significant clump candidates with the specific aim of identifying ones that could represent genuine ICM inhomogeneity. To further understand how clumping biases the thermodynamic profiles, we compared the measurements including and excluding the clump candidates. Methods. We jointly analyzed Chandra and Suzaku observations of Abell 133. We selected clump candidates with at least 2σ significance based on the Chandra image and we discussed their origins further, using information from the DESI Legacy Imaging Surveys cluster catalog as well as the CFHT r-band image. We performed multiple rounds of Suzaku spectral analysis with different corrections for the underlying point sources and clump distribution and we compared the resulting thermodynamic profiles. Results. We detected 16 clump candidates using Chandra, most of which are identified as background clusters or galaxies – as opposed to intrinsic inhomogeneity. Even after the correction of the resolved clumps, the entropy profile approaching the outskirts still flattens, deviating from the power law model expected from self-similar evolution, which implies that unresolved clumping and other complex physics contribute to the entropy flattening in the outskirts.

AMUSE-Antlia. I. Nuclear X-Ray Properties of Early-type Galaxies in a Dynamically Young Galaxy Cluster

To understand the formation and growth of supermassive black holes (SMBHs) and their coevolution with host galaxies, it is essential to know the impact of environment on the activity of active galactic nuclei (AGNs). We present new Chandra X-ray observations of nuclear emission from member galaxies in the Antlia cluster, the nearest non-cool core and the nearest merging galaxy cluster, residing at D = 35.2 Mpc. Its inner region, centered on two dominant galaxies NGC 3268 and NGC 3258, has been mapped with three deep Chandra ACIS-I pointings. Nuclear X-ray sources are detected in 7/84 (8.3%) early-type galaxies (ETG) and 2/8 (25%) late-type galaxies with a median detection limit of 8 × 1038 erg s−1. All nuclear X-ray sources but one have a corresponding radio continuum source detected by MeerKAT at the L band. Nuclear X-ray sources detected in early-type galaxies are considered the genuine X-ray counterpart of low-luminosity AGN. When restricted to a detection limit of and a stellar mass of , six of 11 ETGs are found to contain an X-ray AGN in Antlia, exceeding the AGN occupation fraction of 7/39 (18.0%) and 2/12 (16.7%) in the more relaxed, cool core clusters, Virgo and Fornax, respectively, and rivaling that of the AMUSE-Field ETG of 27/49 (55.1%). Furthermore, more than half of the X-ray AGN in Antlia is hosted by its younger subcluster, centered on NGC 3258. We believe that this is because SMBH activity is enhanced in a dynamically young cluster compared to relatively relaxed clusters.

A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Centauri: a correlation between spider pulsar companion mass and X-ray luminosity

ABSTRACT Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs). In this work, we investigate 18 MSPs newly found in the GC Omega Centauri (ω Cen) and search for their X-ray counterparts using Chandra observations with a total exposure time of 290.9 ks. We identify confident X-ray counterparts for 11 of the MSPs, with 9 of them newly identified in this work based on their positions, spectral properties, and X-ray colours. The X-ray spectra of nine MSPs are well described by a neutron star hydrogen atmosphere model, while two MSPs are well fitted by a power-law model. The identified MSPs have X-ray luminosities ranging from 1.0 × 1030 to 1.4 × 1031 erg s−1. Additionally, for population comparison purposes, we study the X-ray counterpart to MSP E in the GC M71, and find its X-ray spectrum is well described by blackbody-like models with a luminosity of 1.9 × 1030 erg s−1. We investigate the empirical correlations between X-ray luminosities and minimum companion masses, as well as mass functions, of spider pulsars. Clear correlations are observed, with best-fitting functions of log10LX = (1.0 ± 0.1)log10Mc, min + (32.5 ± 0.2) and (0.35 ± 0.04)log10MF + (32.71 ± 0.20), respectively, with an intrinsic scatter of log10LX of ∼0.3, where LX is the 0.5–10 keV X-ray luminosity, Mc, min is the minimum companion mass, and MF represents the mass function, in solar masses.

CHANDRA X-Ray Observations of A119: Cold Fronts and a Shock in an Evolved Off-axis Merger

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.

Probing the nature of the X-ray source IGR J16327-4940 with Chandra

ABSTRACT We report on the results of a Chandra observation of the source IGR J16327-4940, suggested to be a high-mass X-ray binary hosting a luminous blue variable star (LBV). The source field was imaged by ACIS-I in 2023 to search for X-ray emission from the LBV star and eventually confirm this association. No X-ray emission is detected from the LBV star, with an upper limit on the X-ray luminosity of L$_{\rm 0.5-10 \,keV}\lt 2.9(^{+1.6} _{-1.1})\times 10^{32}$ erg s−1 (at the LBV distance d = 12.7$^{+3.2} _{-2.7}$ kpc). We detected 21 faint X-ray sources, 8 of which inside the INTEGRAL error circle. The brightest one is the best candidate soft X-ray counterpart of IGR J16327-4940, showing a hard power-law spectrum and a flux corrected for the absorption UF0.5–10 keV = 2.5 × 10−13 erg cm−2 s−1, implying a luminosity of 3.0 × 1033 d$_{10~{\rm kpc}}^2$ erg s−1. No optical/near-infrared counterparts have been found. Previous X–ray observations of the source field with Swift/XRT and ART-XC did not detect any source consistent with the INTEGRAL position. These findings exclude the proposed LBV star as the optical association, and pinpoint the most likely soft X-ray counterpart. In this case, the source properties suggest a low-mass X-ray binary, possibly a new member of the very faint X-ray transient class.

Asteroseismology and Spectropolarimetry of the Exoplanet Host Star λ Serpentis

The bright star λ Ser hosts a hot Neptune with a minimum mass of 13.6 M ⊕ and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system and constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite, and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and estimate the wind braking torque. We conclude that the remaining uncertainty on the stellar age currently prevents an unambiguous interpretation of the properties of λ Ser, and that the rate of angular momentum loss appears to be higher than for other stars with a similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.

Tracing the energetic outflows from galactic nuclei: observational evidence for a large-scale bipolar radio and X-ray-emitting bubble-like structure in M106

ABSTRACT The role of energetic outflows from galactic nuclei in shaping galaxy formation and evolution is still shrouded in uncertainty. In this study, we shed light on this complex phenomenon by presenting evidence for a large-scale bipolar radio/X-ray-emitting bubble-like structure emanating from the central region of the nearby disc galaxy M106 (NGC 4258). Our findings, based on Low-Frequency Array survey data and Chandra observations, provide a glimpse into the underlying physical processes driving this enigmatic structure. Similar to the eROSITA/Fermi bubbles in our own Galaxy, the M106 bubbles enclose diffuse hot plasma and are partially bounded by prominent radio/X-ray-emitting edges. We constrain the magnetic field and cosmic-ray properties of the structure. The analysis of the X-ray data gives an estimate of the thermal energy of the bubbles as ∼8 × 1056 erg. This energy can be supplied by the jets and perhaps by the wind from the accretion flow of the galaxy’s low-luminosity AGN, which most likely has been much more powerful in the recent past, with an average mechanical energy release rate of ∼4 × 1042 erg s−1 over the last ∼8 × 106 yr – the estimated age of the structure. We also show evidence for diffuse X-ray emission on larger scales, indicating the presence of a hot galactic corona. Our results provide a clear manifestation of galactic nuclear feedback regulating the gas content and energetics of the circumgalactic medium of disc galaxies similar to our own.

Progenitors and explosion properties of supernova remnants hosting central compact objects: II. A global systematic study with a comparison to nucleosynthesis models

ABSTRACT Core-collapse explosions of massive stars leave behind neutron stars, with a known diversity that includes the ‘Central Compact Objects’ (CCOs). Typified by the neutron star discovered near the centre of the Cas A supernova remnant (SNR), CCOs have been observed to shine only in X-rays. To address their supernova progenitors, we perform a systematic study of SNRs that contain a CCO and display X-ray emission from their shock-heated ejecta. We make use of X-ray data primarily using the Chandra X-ray observatory, complemented with XMM–Newton. This study uses a systematic approach to the analysis of each SNR aimed at addressing the supernova progenitor as well as the explosion properties (energy and ambient density). After fitting for the ejecta abundances estimated from a spatially resolved spectroscopic study, we compare the data to six nucleosynthesis models making predictions on supernova ejecta yields in core-collapse explosions. We find that the explosion models commonly used by the astrophysics community do not match the ejecta yields for any of the SNRs, suggesting additional physics, for example multidimensional explosion models or updated progenitor structures, are required. Overall we find low-mass (≤25 solar masses) progenitors among the massive stars population and low-energy explosions (<1051 ergs). We discuss degeneracies in our model fitting, particularly how altering the explosion energy affects the estimate of the progenitor mass. Our systematic study highlights the need for improving on the theoretical models for nucleosynthesis predictions as well as for sensitive, high-resolution spectroscopy observations to be acquired with next generation X-ray missions.

X-Ray Cavity Dynamics and Their Role in the Gas Precipitation in Planck Sunyaev–Zeldovich (SZ) Selected Clusters

We study active galactic nucleus (AGN) feedback in nearby (z < 0.35) galaxy clusters from the Planck Sunyaev–Zeldovich sample using Chandra observations. This nearly unbiased mass-selected sample includes both relaxed and disturbed clusters and may reflect the entire AGN feedback cycle. We find that relaxed clusters better follow the one-to-one relation of cavity power versus cooling luminosity, while disturbed clusters display higher cavity power for a given cooling luminosity, likely reflecting a difference in cooling and feedback efficiency. Disturbed clusters are also found to contain asymmetric cavities when compared to relaxed clusters, hinting toward the influence of the intracluster medium (ICM) “weather” on the distribution and morphology of the cavities. Disturbed clusters do not have fewer cavities than relaxed clusters, suggesting that cavities are difficult to disrupt. Thus, multiple cavities are a natural outcome of recurrent AGN outbursts. As in previous studies, we confirm that clusters with short central cooling times, t cool, and low central entropy values, K 0, contain warm ionized (10,000 K) or cold molecular (<100 K) gas, consistent with ICM cooling and a precipitation/chaotic cold accretion scenario. We analyzed archival Multi-Unit Spectroscopic Explorer observations that are available for 18 clusters. In 11/18 of the cases, the projected optical line emission filaments appear to be located beneath or around the cavity rims, indicating that AGN feedback plays an important role in forming the warm filaments by likely enhancing turbulence or uplift. In the remaining cases (7/18), the clusters either lack cavities or their association of filaments with cavities is vague, suggesting alternative turbulence-driven mechanisms (sloshing/mergers) or physical time delays are involved.