THE ABSENCE OF RADIO EMISSION FROM THE GLOBULAR CLUSTER G1

Journal Article · Fri Aug 10 00:00:00 EDT 2012 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/755/1/L1· OSTI ID:22047625

Miller-Jones, J C. A. ^[1]; Wrobel, J M ^[2]; Sivakoff, G R; Heinke, C O; Miller, R E ^[3]; Plotkin, R M ^[4]; Di Stefano, R ^[5]; Greene, J E ^[6]; Ho, L C ^[7]; Joseph, T D; Maccarone, T J ^[8]; Kong, A K. H., ^[9]

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1. International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, WA 6845 (Australia)
2. NRAO Domenici Science Operations Center, 1003 Lopezville Road, Socorro, NM 87801 (United States)
3. Department of Physics, University of Alberta, Room 238 CEB, Edmonton, AB T6G 2G7 (Canada)
4. Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)
5. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
6. Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 71712 (United States)
7. The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
8. School of Physics and Astronomy, University of Southampton, Highfield SO17 IBJ (United Kingdom)
9. Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

The detections of both X-ray and radio emission from the cluster G1 in M31 have provided strong support for existing dynamical evidence for an intermediate-mass black hole (IMBH) of mass (1.8 {+-} 0.5) Multiplication-Sign 10{sup 4} M{sub Sun} at the cluster center. However, given the relatively low significance and astrometric accuracy of the radio detection, and the non-simultaneity of the X-ray and radio measurements, this identification required further confirmation. Here we present deep, high angular resolution, strictly simultaneous X-ray and radio observations of G1. While the X-ray emission (L{sub X} = 1.74{sup +0.53}{sub -0.44} Multiplication-Sign 10{sup 36} (d/750 kpc){sup 2} erg s{sup -1} in the 0.5-10 keV band) remained fully consistent with previous observations, we detected no radio emission from the cluster center down to a 3{sigma} upper limit of 4.7 {mu}Jy beam{sup -1}. Our favored explanation for the previous radio detection is flaring activity from a black hole low-mass X-ray binary (LMXB). We performed a new regression of the 'Fundamental Plane' of black hole activity, valid for determining black hole mass from radio and X-ray observations of sub-Eddington black holes, finding log M{sub BH} = (1.638 {+-} 0.070)log L{sub R} - (1.136 {+-} 0.077)log L{sub X} - (6.863 {+-} 0.790), with an empirically determined uncertainty of 0.44 dex. This constrains the mass of the X-ray source in G1, if a black hole, to be <9.7 Multiplication-Sign 10{sup 3} M{sub Sun} at 95% confidence, suggesting that it is a persistent LMXB. This annuls what was previously the most convincing evidence from radiation for an IMBH in the Local Group, though the evidence for an IMBH in G1 from velocity dispersion measurements remains unaffected by these results.

• OSTI ID: 22047625
• Journal Information: Astrophysical Journal Letters, Vol. 755, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
ACCURACY
ASTROPHYSICS
BLACK HOLES
COSMIC RADIO SOURCES
COSMIC X-RAY SOURCES
DETECTION
FLARING
GALAXIES
GAMMA ASTRONOMY
KEV RANGE
MASS
RESOLUTION
STAR CLUSTERS
VELOCITY
X RADIATION