TY - JOUR
T1 - The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9
AU - Bahramian, Arash
AU - Heinke, Craig O.
AU - Tudor, Vlad
AU - Miller-Jones, James C.A.
AU - Bogdanov, Slavko
AU - Maccarone, Thomas J.
AU - Knigge, Christian
AU - Sivakoff, Gregory R.
AU - Chomiuk, Laura
AU - Strader, Jay
AU - Garcia, Javier A.
AU - Kallman, Timothy
N1 - Publisher Copyright:
© 2017 The Authors.
Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.
PY - 2017/5/11
Y1 - 2017/5/11
N2 - 47 Tuc X9 is a low-mass X-ray binary (LMXB) in the globular cluster 47 Tucanae, and was previously thought to be a cataclysmic variable. However, Miller-Jones et al. recently identified a radio counterpart to X9 (inferring a radio/X-ray luminosity ratio consistent with black hole LMXBs), and suggested that the donor star might be a white dwarf. We report simultaneous observations of X9 performed by Chandra, NuSTAR and Australia Telescope Compact Array. We find a clear 28.18 ± 0.02-min periodic modulation in the Chandra data, which we identify as the orbital period, confirming this system as an ultracompact X-ray binary. Our X-ray spectral fitting provides evidence for photoionized gas having a high oxygen abundance in this system, which indicates a C/O white dwarf donor. We also identify reflection features in the hard X-ray spectrum, making X9 the faintest LMXB to show X-ray reflection. We detect an ~6.8-d modulation in the X-ray brightness by a factor of 10, in archival Chandra, Swiftand ROSAT data. The simultaneous radio/X-ray flux ratio is consistent with either a black hole primary or a neutron star primary, if the neutron star is a transitional millisecond pulsar. Considering the measured orbital period (with other evidence of a white dwarf donor), and the lack of transitional millisecond pulsar features in the X-ray light curve, we suggest that this could be the first ultracompact black hole X-ray binary identified in our Galaxy.
AB - 47 Tuc X9 is a low-mass X-ray binary (LMXB) in the globular cluster 47 Tucanae, and was previously thought to be a cataclysmic variable. However, Miller-Jones et al. recently identified a radio counterpart to X9 (inferring a radio/X-ray luminosity ratio consistent with black hole LMXBs), and suggested that the donor star might be a white dwarf. We report simultaneous observations of X9 performed by Chandra, NuSTAR and Australia Telescope Compact Array. We find a clear 28.18 ± 0.02-min periodic modulation in the Chandra data, which we identify as the orbital period, confirming this system as an ultracompact X-ray binary. Our X-ray spectral fitting provides evidence for photoionized gas having a high oxygen abundance in this system, which indicates a C/O white dwarf donor. We also identify reflection features in the hard X-ray spectrum, making X9 the faintest LMXB to show X-ray reflection. We detect an ~6.8-d modulation in the X-ray brightness by a factor of 10, in archival Chandra, Swiftand ROSAT data. The simultaneous radio/X-ray flux ratio is consistent with either a black hole primary or a neutron star primary, if the neutron star is a transitional millisecond pulsar. Considering the measured orbital period (with other evidence of a white dwarf donor), and the lack of transitional millisecond pulsar features in the X-ray light curve, we suggest that this could be the first ultracompact black hole X-ray binary identified in our Galaxy.
KW - Accretion
KW - Accretion discs
KW - Globular clusters: individual: 47 Tuc
KW - Stars: Black holes
KW - Stars: neutron
KW - X-rays: binaries
UR - http://www.scopus.com/inward/record.url?scp=85018319591&partnerID=8YFLogxK
U2 - 10.1093/mnras/stx166
DO - 10.1093/mnras/stx166
M3 - Article
AN - SCOPUS:85018319591
VL - 467
SP - 2199
EP - 2216
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 2
ER -