The NuSTAR and Chandra View of CL 0217+70 and Its Tell-tale Radio Halo

Abstract

Mergers of galaxy clusters are the most energetic events in the universe, driving shock and cold fronts, generating turbulence, and accelerating particles that create radio halos and relics. The galaxy cluster CL 0217+70 is a remarkable late-stage merger, with a double peripheral radio relic and a giant radio halo. Chandra detects surface brightness (SB) edges that correspond to radio features within the halo. In this work, we present a study of this cluster with Nuclear Spectroscopic Telescope Array and Chandra data using spectro-imaging methods. The global temperature is found to be kT = 9.1 keV. We set an upper limit for the inverse Compton (IC) flux of ∼2.7 × 10−12 erg s−1 cm−2, and a lower limit to the magnetic field of 0.08 μG. Our local IC search revealed a possibility that IC emission may have a significant contribution at the outskirts of the radio halo emission and on/near shock regions within ∼0.6 r 500 of clusters. We detected a “hot spot” feature in our temperature map coincident with an SB edge, but our investigation on its origin is inconclusive. If the “hot spot” is the downstream of a shock, we set a lower limit of kT > 21 keV to the plasma that corresponds to  ∼2. We found three shock fronts within 0.5 r 500. Multiple weak shocks within the cluster center hint at an ongoing merger activity and continued feeding of the giant radio halo. CL 0217+70 is the only example hosting these secondary shocks in multiple form.

The Hydrostatic Mass of A478: Discrepant Results from Chandra, NuSTAR, and XMM-Newton

“…NuSTAR is also less sensitive to absorption than Chandra and XMM-Newton due to its lack of sensitivity below 3 keV (Rojas Bolivar et al 2021), meaning the complicated absorption along the line of sight of A478 has less of an effect on temperature measurements. Tümer et al (2023) find that leaving the N H parameter free for a global NuSTAR fit of CL 0217 + 70 results in unphysical behavior, demonstrating NuSTAR's insensitivity to absorption.…”

“…This results in the XMM-Newton N H values being an average of ∼13% lower, with the maximum difference in the outermost region, where the XMM-Newton N H is ∼26% lower. This is an average difference between the Chandra and XMM-Newton N H of ∼5 × 10 20 cm −2 (see Table 2 temperature profile that results from fixing the Chandra N H to the XMM-Newton best-fit values, as well as the XMM-Newton spectra with N H fixed to the Chandra best-fit values can be seen in Appendix D. NuSTAR is less sensitive to absorption (Tümer et al 2023); in the central region, the inclusion of N H fixed to the best-fit Chandra value decreases the temperature by ∼1% compared to a fit without it.…”

“…Additionally, XMM-Newton has a greater effective area in the hard band, thus it more closely resembles NuSTAR images. How the nucrossarf code disentangles the cross talk is explained in detail by Tümer et al (2023).…”

ZWCL 1856.8: A Rare Double Radio Relic System Captured within NuSTAR and Chandra Field of View

“…A set of IDL routines created to account for this contamination that divorces the contamination and source emission is nucrossarf. 5 This method is explained, applied, and tested in detail by Tümer et al (2023).…”

The NuSTAR View of Perseus: The Intracluster Medium and a Peculiar Hard Excess

“…Unlike equipartition or Faraday rotation methods (see Govoni & Feretti 2004 for an overview of these topics), using IC to measure magnetic field strength is unambiguous and does not rely on assumptions (as in equipartition) or an incomplete knowledge of gas structure (as in Faraday rotation). However, previous searches for IC-which have largely focused on merging and disturbed clusters with bright radio structures-have been inconclusive, so only lower limits to magnetic field strength have been found so far (e.g., Nevalainen et al 2004;Wik et al 2009Wik et al , 2014Rojas Bolivar et al 2021Mirakhor et al 2022;Tümer et al 2023).…”