Identifications of faintChandrasources in the globular cluster M3

Abstract

We report a 30 ks Chandra ACIS-S survey of the globular cluster M3. Sixteen X-ray sources were detected within the half-light radius (2.3 ) with L X 2.3×10 31 erg s −1 . We used Hubble Space Telescope WFC3/UVIS and ACS/WFC images to find 10 plausible optical/UV counterparts.We fit the spectral energy distribution of the known cataclysmic variable 1E1339.8+2837 with a blue (T eff = 2.10 +1.96 −0.58 ×10 4 K, 90% conf.) spectral component from an accretion disc, plus a red component (T eff = 3.75 +1.05 −0.15 ×10 3 K) potentially from a subgiant donor. The second brightest source (CX2) has a soft blackbodylike spectrum suggesting a quiescent low-mass X-ray binary (qLMXB) containing a neutron star. Six new counterparts have obvious UV and/or blue excesses, suggesting a cataclysmic variable (CV) or background active galactic nucleus (AGN) nature. Two (CX6 and CX8) have proper motions indicating cluster membership, suggesting a CV nature. CX6 is blue in UV filters but red in V-I, which is difficult to interpret. Two CV candidates, CX7 and CX13, show blue excesses in B-V colour but were not detected in the UV. The other two CV candidates were only detected in the two UV bands (UV 275 and NUV 336 ), so do not have proper motion measurements, and may well be AGNs. One Chandra source can be confidently identified with a red straggler (a star redward of the giant branch). The observed X-ray source population of M3 appears consistent with its predicted stellar interaction rate.

A deep Chandra survey for faint X-ray sources in the Galactic globular cluster M30, and searches for optical and radio counterparts

“…The photometric criteria used for identifying optical counterparts depend on the type of the source. For example, we identify CVs with blue outliers on the UV CMDs, as CVs usually manifest strong UV emission thought to originate from a shock-heated region on the white dwarf surface (in the case of magnetic CVs) and/or from the accretion disc; whereas, when observed in optical bands like V 606 and I 814 , optical fluxes are dominated by the companion, which has a lower surface temperature, so they may appear to be consistent with, or even slightly redder than, the main sequence (e.g., Edmonds et al 2003a,b;Lugger et al 2017;Zhao et al 2019). On the other hand, ABs often manifest slight red excesses consistent with the binary sequence (BY Dra systems), or they have subgiant or red giant companions (RS CVn systems).…”

The MAVERIC Survey: Simultaneous Chandra and VLA observations of the transitional millisecond pulsar candidate NGC 6652B

“…ity and spectral hardness as NGC 6652B. However, that source is distinctly different from NGC 6652B in optical/UV bands, with a very bright blue UV counterpart (Edmonds et al 2004;Zhao et al 2019), and is not detected in the radio band (Shishkovsky et al 2020). Another population of X-ray bright CVs are intermediate polars (IPs), which radiate most of their accretion energy as X-rays at both low and high accretion rates (Patterson & Raymond 1985).…”

Two New Black Widow Millisecond Pulsars In M28

“…Such an excess is commonly observed in exotic binaries like cataclysmic variables and MSPs (e.g. Rivera Sandoval et al 2018;Zhao et al 2019Zhao et al , 2020, and it is usually related to the presence of an accretion disk and/or heating of the secondary star by the primary. Also in this case, no evidence of H α excess is detected.…”