List of Approved CCT Projects

PI: Marcel Agueros

Title: Measurements of Coronal Emission in the Hyades: We need more!


As the closest and one of the oldest accessible open clusters (47 pc and 625 Myr), the Hyades is a benchmark in any number of areas of stellar astrophysics. For example, Hyads have been used to test stellar models and to calibrate gyrochronology and metallicity scales. The X-ray picture, however, is far from satisfying: the X-ray census of Hyads is still woefully incomplete, consisting primarily of ROSAT observations of >1 M_solar stars. Given the wealth of new photometric data acquired by K2 and by TESS, the current limitations of the X-ray data are particularly galling, as we cannot fully exploit the cluster to place constraints on the still poorly understood age-rotation-activity relation. We therefore propose to target the Hyades as a Chandra CCT program. Every new X-ray observation of a Hyad can be matched to our extensive and growing database of complementary measurements to deepen our understanding of the connection between rotation and activity in low-mass stars.

PI: Marco Ajello

Title: X-Raying New Galactic Accelerators with Chandra


Very High Energy (VHE, >10 GeV) gamma rays provide a direct view of some of the most extreme environments in our Galaxy and are an excellent probe of non-thermal astrophysical processes. Studies of the non-thermal Galactic source population are essential to understand where and how the bulk of the cosmic rays are accelerated in our Galaxy. Fermi has recently produced a uniform survey of the Galactic plane at >10GeV, detecting more than 300 sources. We propose all the unassociated 3FHL sources in the Galactic plane as cool attitude targets for Chandra.

PI: David Alexander

Title: Chandra-NuSTAR synergy in the NuSTAR serendipitous survey


A great breakthrough in resolving the peak of the cosmic X-ray background (CXB) is NuSTAR. The NuSTAR extragalactic survey has resolved ~35% of the CXB at the >10 keV peak, provided the first measurements of the >10 keV AGN luminosity function at z>0.1, and identified extreme heavily obscured AGNs. The NuSTAR serendipitous survey is the largest component of the extragalactic survey program and provides the majority of the (~75-80%) NuSTAR-detected sources. Through a combination of deep and shallow wide-area coverage it fills out the X-ray luminosity-redshift plane of AGN and detects intrinsically rare source populations. However, the NuSTAR data alone are insufficient to fully understand the physical properties of the NuSTAR sources and Chandra CATS observations are required to (i) provide reliable sub-arcsec optical counterpart identification for spectroscopic observations to obtain redshifts and identify Galactic sources and (ii) broad-band X-ray spectral to characterize the X-ray emission of the NuSTAR sources down to ~0.5-3 keV, where NuSTAR has no sensitivity. The Chandra CATS observations will allow for (i) the robust identification of optical counterparts, (ii) the characterization of the 0.5-24 keV spectra, (iii) the detection of multiple Chandra counterparts in spatially complex systems and crowded fields, (iv) a broad suite of analyses to constrain the properties and evolution of AGN at >10 keV, and (v) long-term (>1 year timescale) X-ray variability analyses for the NuSTAR sources with existing X-ray coverage. The Chandra CATS target list includes all of the NuSTAR sources that lie within 40 degrees of the ecliptic within the serendipitous survey to date.

PI: Mark Birkinshaw

Title: X-ray observations of the southern part of a complete sample of extragalactic radio sources


We propose to combine the MS4 list of southern radio sources with the remaining 3CR sources not yet observed by Chandra to create a all-sky sample of extragalactic radio sources with Chandra-resolution imaging, suitable for joint radio/X-ray study into the 2030s. The unbiased sample of southern sources will allow proper statistical use to be made of existing Chandra observations of MS4 objects.

PI: Elizabeth Blanton

Title: Cool Targets from the COBRA Survey


We request observations of clusters in the redshift range z = 0.5 to 1.8 discovered with the COBRA (Clusters Occupied by Bent Radio AGN) survey. The clusters were found using bent, double-lobed (wide-angle-tail-like) radio galaxies selected from the VLA FIRST (Faint Images of the Radio Sky at Twenty cm) survey, as well as follow up observations in the infrared with Spitzer and the optical with the 4.3 m Discovery Channel Telescope. The survey is complementary to other methods in that it uses different search criteria and locates clusters and groups of galaxies with a wide range of masses. Given the nature of the selection technique, all of the clusters have extended radio sources associated with AGN and so are sites for studying AGN feedback.

PI: Nico Cappelluti

Title: Aiming at Stripe 82X Quasars as CATs: compelling targets while building area for the legacy survey


High luminosity AGN (i.e., quasars) have a powerful impact on their host galaxies, via winds, jets, or intense radiation that can regulate star formation, and they likely represent the phase when the majority of mass was accreted onto black holes. We propose a series of pre-selected source populations (mostly bright Quasars) in Stripe 82 to target with ACIS-I within the Chandra CAT program, which will build area in the Stripe 82 while obtaining useful results from each pointing. In particular we will aim to observe: Bright Herschel-selected quasars in Stripe 82, Red Quasars, z>4 Quasars and Candidate AGN in low mass galaxies.

PI: Igor Chilingarian



X-ray confirmation of a population of intermediate black holes (IMBHs) will allow us to solve one of the long-standing problems in modern astrophysics, the origin of supermassive black holes (SMBHs). Using dedicated analysis of 1 million optical spectra, we identified a sample of 305 IMBH candidates (3x10^4 < Mbh < 2x10^5 Msun), which reside in galaxy centers and appear as active galactic nuclei (AGN). They are evenly distributed across the SDSS DR7 footprint. With XMM- Newton and Chandra DDT observations in 2017 and mining X-ray data archives, we confirmed the AGN nature of ten candidates, thus validating our IMBH search approach. We propose 270 optically selected IMBH candidates as Chandra Cool Attitude Targets, with the aim to increase the number of X-ray confirmed accreting IMBHs by a factor of 10. Even if only 10% of the list gets observed, the sample of known IMBH will double. This will enable detailed statistical studies of the IMBH population and help to constrain the masses of 'seed' black holes in the early Universe.

PI: Francesca Civano

Title: Calibration of the quasar Hubble diagram with z ≤ 0.7 quasars as CATs


Quasars are among the most luminous sources in the sky and as such can be detected up to very high redshifts (z = 7.54). For these reasons, scientists have long chased the possibility of using quasars to constrain cosmological models in a completely unexplored redshift range (z > 1.4, beyond which Supernovae (SN) are rarely detected). Despite several attempts, most of the proposed methods are affected by a high dispersion in the observational relations used, preventing high precision distance measurements. A new method, recently proposed by Risaliti & Lusso 2015, overcomes this difficulty by taking advantage of the very large statistic provided by the quasar surveys currently available. Building upon this result and the latest improvements about it, the goal of this CAT project is to increase the sample of low-z (z<0.7) quasars with good quality X-ray data from pointed observations to decrease the dispersion in the quasar Hubble diagram and calibrate a zero-point for it.

PI: Harald Ebeling

Title: The most X-ray luminous clusters of galaxies in the Universe


Massive galaxy clusters are rare systems that allow us to tackle a vast range of topical science questions, from the physics of collisional and non-collisional matter in cluster mergers, through lensing-assisted probes of the era of ionization, to AGN-driven feedback processes governing the heating and cooling of the intra-cluster medium (ICM) in cluster cores. While samples of massive clusters have proven immensely powerful in statistical studies, they are equally valuable as individual laboratories, capable of revealing spectacular and often unexpected effects and insights, famous examples being Abell 370, the Bullet Cluster, or, more recently, MACSJ0717.5+3745 and MACSJ1149.5+2223 of Hubble Frontier Field fame. Since finding these rare systems (only a few hundred exist in the entire observable Universe) requires covering very large solid angles, most existing Chandra cluster surveys include too few truly massive clusters to characterize this extreme population and capitalize on the significant discovery potential of the associated observations. We here propose CAT observations of all CAT-eligible, extremely X-ray luminous clusters from a ROSAT All-Sky Survey-based sample compiled primarily from systems discovered by the eBCS, MACS, and eMACS surveys in the redshift range from z=0.2 to 0.9 that have not been observed with Chandra to date. The proposed observations will yield robust X-ray luminosities and global gas temperatures, allow the characterization of these systems ICM morphology (and hence relaxation state), and, in conjunction with our ongoing HST SNAPshot survey, permit us to identify the most promising targets for in-depth multi-wavelength follow-up studies.

PI: Felix Fuerst

Title: High-Mass X-ray Binaries with Chandra/HETG as CCTs


High-mass X-ray binaries (HMXBs) are formed by compact objects accreting from the stellar wind of an earlytype stellar companion. These winds are highly structured, both because of intrinsic clumping of the stellar wind and the influence of the compact object. Thanks to the strong X-ray source in the system we have the opportunity to study structure and physical conditions in the wind by measuring the variability of the fluorescence lines (mainly from iron) and the absorption column as function of orbital phase and time. Here we propose a sample of bright HMXBs with known iron lines as possible CCTs for Chandra .Chandra's HETG is ideally suited for this project, as its energy coverage reaches upto the crucial 6.4 keV region of FeK-alpha and provides the high spectral resolution necessary to measure the line width. In addition it covers lower energies, where lines from other metals like Si and Mg are present, allowing amore detailed study of the ionization state of the wind

PI: Elena Gallo



Cosmological volume simulations are fast approaching the resolution necessary to follow the assembly and evolution of galactic structure well below the knee of the galaxy mass function, where the black hole occupation fraction remains essentially unconstrained. In the low stellar mass regime (i.e. below ~1e10 solar masses), the black hole occupation fraction determines the black hole mass function, sets tidal disruption event rates, affects star formation quenching and may even depend on the black hole seeding mechanisms at high-z. This program will contribute to a high accuracy measurement of the local black hole occupation fraction in the low mass regime through imaging observations of nearby dwarf galaxies.

PI: Anthony Gonzalez



The Massive and Distant Clusters of WISE Survey (MaDCoWS) provides the first sample of galaxy clusters at z~1 spanning the full extragalactic sky. With over 2000 clusters visible at the ecliptic latitudes desired for Cool Attitude Targets (CATs), this catalog is well-suited for observations during the gaps between GO targets. From a scientific perspective, observations of this sample hold the promise of yielding the largest sample of X-ray detected clusters at z~1, which can be used for a range of scientific purposes including statistical studies of ICM astrophysics, identification of interestingly massive and merging systems for deeper future investigations, and characterization of the cluster population at this epoch to better inform future large surveys with facilities such as Euclid, LSST, and WFIRST. Additionally, this sample will be well-suited to investigating the dependence of the X-ray AGN population upon environment at high redshift for a statistical sample of clusters.

PI: Joel Kastner

Title: The Chandra Nearby Young Stars Cool Attitude Survey (NYSCATS)


Nearby (D < 50 pc), young (age <200 Myr) stars provide unique tests of pre-main sequence stellar evolution and the late stages of evolution of protoplanetary disks and represent the best targets for direct imaging searches for giant exoplanets. Gaia data is now providing the raw material for comprehensive studies of candidate nearby, young stars. The Nearby Young Stars Cool Attitude Targets Survey (NYSCATS) is designed to take advantage of this potential. The immediate objective of NYSCATS are to confirm young-star status for as many of our ~700 candidate nearby young stars as possible, by measuring X-ray luminosities and temperatures. These results will provide essential input to models describing the high-energy radiation environments endured by residual protoplanetary disks and young planets orbiting young, low-mass stars and will help constrain the early evolution of magnetic activity for late-type stars.

PI: Mike Koss

Title: C-BASS: A Chandra Legacy Survey of AGN at the Highest Spatial Resolutions


Chandra has conducted over 30 extragalactic surveys, at depths between 100 ks to 7 Ms that cumulatively add up to several years of observations. This has led to the discovery of thousands of distant black holes and hundreds of refereed papers that have defined our current understanding of the growth of SMBHs, their radiative outputs, and how these may be linked to their host galaxies. The Swift-BAT 105-month survey all sky survey has detected 1181 of the nearest and brightest AGN, which have similar luminosities to the distant AGN typically found in deep, pencil-beam Chandra surveys. We propose a Chandra cool attitude program to survey the 537 BAT AGN that have yet to be observed by Chandra, within the ecliptic plane constraints. This will enable a high-spatial resolution study on the scales of 100s of pc (~0.025, i.e. 0.5''=250 pc) for a large number of AGN with an unprecedented collection of ancillary multiwavelength data for the first time to study dual, recoiling, and offset AGN, and to resolve jets, study AGN feedback, and look for extended profiles of plasma (Fe Ka) emission.

PI: Gerardo Juan Manuel Luna



At least some symbiotic binaries, in which a white dwarf (WD) accretes from the wind of a red-giant companion, end their lives as type Ia supernovae (SNIa). But which ones and how many of them are in our Galaxy? Those symbiotics with the highest accretion rate should be the best candidates. During the last few years, our group has found that X-ray emission can be used to estimate the accretion rate onto the WD, a quantity that has been elusive to observations in other wavelengths. We propose that 300 of these objects, 130 already known as symbiotics and 170 new candidates, be used as Chandra Cool-Attitude targets. Because of its X-ray sensitivity and low X-ray background, Chandra can provide a comprehensive survey of the X-ray properties of symbiotic stars.

PI: Adam Mantz

Title: Enabling Dark Energy Constraints from Optically Selected Galaxy Clusters


One of the best current opportunities for cosmological tests using galaxy clusters is DES, which is revealing the cluster population to lower masses and with higher statistical power than any previous survey, and is paving the way for future programs like LSST. We propose a list of Chandra Cool-Attitude Targets selected from the DES cluster catalog, specifically focussing on redshifts z ~ 0.5 and relatively low richnesses (~30). This richness corresponds to a typical cluster in the DES cosmology sample, whereas all existing X-ray follow-up of optically selected clusters at these redshifts targets the most massive clusters, and is therefore not representative. X-ray mass proxies and centers would provide the first constraints on the richness-mass scatter and the optical mis-centering distribution at z ~ 0.5. Combined with existing Swift follow-up of similarly low richness clusters at z = 0.1, this would enable the first constraints on the evolution of the scatter and mis-centering, a key requirement for dark energy studies using DES and future optical cluster samples.

PI: Francesco Massaro



Surveying radio-loud active galaxies (AGNs) in the X-rays is a challenging task which difficulties are mainly driven by their low sky density (i.e. number of sources per square degree) in comparison with other AGN classes. On the other hand, discoveries achieved in the last two decades, based on Chandra observations, allowed us to study many aspects of their evolution. Given the observational evidence that radio-loud AGNs tend to live in galaxy-rich large-scale environments (i.e., galaxy groups or clusters), their X-ray observations are crucial to shed a light on the feedback mechanism. The main objective of this white paper is to highlight the importance of results achieved thanks to X-ray snapshot observations of radio-loud AGNs, in particular on the revised Third Cambridge catalog (3CR), to propose a selected sample of radio sources listed in the Bologna Sky Survey at 408 MHz (B2CAT), as cool-attitude targets for the Chandra mission. The 3CR Chandra snapshot survey represents a perfect example of how short-exposure X-ray observations can provide great discoveries.

PI: Koji Mukai

Title: X-ray Observations of Dwarf Novae Discovered by MASTER


We propose to obtain moderately deep Chandra ACIS observations of a large numberof optically faint cataclysmic variables (CVs) discovered as MASTER optical transients. Such observations, in conjunction with on-going ground-based follow-up works, will allow us to improve our understanding of the X-ray luminosity function of CVs on the low X-ray luminosity end, and, indirectly, of their space density and spatial distribution. This will help establish a more reliable estimate of teh CV contribution to the Galactic X-ray background.

PI: Ming Sun

Title: An random sub-sample of lambda=25-80 redMaPPer clusters


X-ray scaling relations of the intracluster medium are important for both cluster cosmology and baryon physics. There have already been a lot of data of galaxy clusters in the Chandra archive. However, the Chandra archive sample is not a representative sample of galaxy clusters, with many clusters selected for their X-ray properties. We propose to take advantage of the randomness of the Chandra Cool Attitude Target observations to obtain a sample of lambda = 25 - 80 redMaPPer clusters with the highest expected X-ray flux. Combined with the existing data in the Chandra archive, a large representative sample of lambda = 25 - 80 redMaPPer clusters will be constructed, which will provide important insights on the X-ray selection bias, cluster scaling relations and typical cluster core properties.

PI: Leisa Townsley

Title: Milky Way HEPCATs


With this white paper we recommend Milky Way HEPCATs (High Energy Panoramas of Cool Attitude Targets), a comprehensive Chandra/ACIS-I program to survey massive star-forming regions (MSFRs) in the Galactic Plane. HEPCATs will transform Chandra's operational necessity for cool attitude targets into a rich scientific legacy by X-raying the Galaxy's spiral arms. Its primary goal is to obtain ~2500 sharp X-ray snapshots of WISE and Spitzer bubbles, to reveal the massive stars driving these iconic structures and the wind-generated hot plasma that fills them. Over time, HEPCATs will build up wide-field X-ray mosaics of the vast giant molecular clouds that fuel the great MSFR complexes in the Milky Way, blazing a trail for future high-resolution X-ray missions.

PI: Dominic Walton

Title: ULX Science with Nearby Galaxies


The 703 nearby galaxies (D = 2.5-15 Mpc) in the RC3/CNG galaxy catalogues would make outstanding targets for the Chandra CCT program. These observations have the potential to significantly expand the known ultraluminous X-ray source (ULX) population, identifying individual sources of particular interest for detailed follow-up, and facilitating improved statistical studies of ULXs as a population. We also propose that known ULX host galaxies within this list be retained indefinitely as CATs to help build up multiple observations over a large temporal baseline, with the aim of searching for new ULX pulsar candidates through the identification of off-states similar to those seen from the known ULX pulsars.