Discovery of 3:2 ratio High-Frequency QPOs from a ULX: A ... · source in galaxy M82 suggests that,...
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Ultraluminous X-ray sources (ULXs) are X-ray point sources in nearby galaxies with isotropic luminosities exceeding the Eddington value of a 25 solar mass black hole, i.e, ≥ 3×10 39 erg/sec. A long-standing debate is whether they are hyper-accreting stellar-mass black holes or intermediate-mass black holes (a few 100-1000 solar masses) accreting at sub-Eddington rates. M82 X-1 is an extreme ULX with an average X-ray luminosity of 5×10 40 ergs s -1 and a strong intermediate-mass black hole candidate 1-6 . “ Context ” Discovery of 3:2 ratio High-Frequency QPOs from a ULX: A 400 solar mass black hole in M82 Dheeraj R. Pasham aka DJ (UMD/NASA), Tod E. Strohmayer (NASA), Richard F. Mushotzky (UMD) In addition to the low-frequency quasi-periodic oscillations (0.2-15 Hz; QPOs), three confirmed stellar- mass black holes exhibit high-frequency QPO pairs (100-450 Hz) in a frequency ratio of 3:2 (see power spectra on the right) 7 . These frequencies are fast, comparable to their Keplerian orbital values in the inner few gravitational radii of the accretion disk and appear to be frequency-invariant when the sources change their luminosities. Such stable, general relativity induced oscillations should scale inversely with the black hole mass if they arise from orbital motion near the innermost stable circular orbit in the accretion disk and there is observational support that they do for stellar-mass black holes 7 . References : [1] Casella et al. 2008, MNRAS, 387,1701-1011. [2] Dewangan et al. 06, ApJ, 637, L21-L24. [3] Feng & Kaaret 2010 ApJ, 712, L169-L173. [4] Mucciarelli et al. 06, MNRAS, 365, 1123-1130. [5] Patruno et al. 2006, MNRAS, 370, L6-L9. [6] Zhou et al. 2010, ApJ, 710, 16-23. [7] McClintock & Remillard 2006, Compact Stellar X-ray Sources, 157-213. [8] Kaaret et al. 06, ApJ, 646, 174-183. [9] Middleton et al. 2011, MNRAS, 411, 644-652. [10] Pasham & Strohmayer 2013, ApJ, 771, 101. [11] Abramowicz et al. 2004, ApJ, 609, L63-L65. [12] Stella et al. 1999, ApJ, 524, L63-L66. [13] Beer & Podsiadlowski 2002, MNRAS, 331, 351-360. [14] Orosz et al. 2011, ApJ, 730, 75-88. [15] Steeghs et al. 2013, ApJ, 768, 185-192. M82 X-1's high luminosity 8 and the identification of its 30-200 mHz X-ray QPOs as the analogs of the low-frequency QPOs of stellar-mass black holes suggests that it may contain an intermediate-mass black hole with mass in the range of 25-1300 solar masses 1-6 . But, there were two uncertainties with such scaling: first, it was unclear--until now--whether these mHz QPOs are indeed the low-frequency analogs of stellar-mass systems 9,10 and, second, both the low-frequency and the mHz oscillations are variable, resulting in a large dispersion in the measured mass. The simultaneous detection of a stable, 3:2-ratio, high-frequency periodicity and low-frequency mHz oscillations allows one to set the overall frequency scale of the power spectrum and has been proposed to be the smoking gun evidence for an intermediate-mass black hole in a ULX 11 . Power density spectra of M82 (a) Six-year average X-ray (3–13 keV) power density spectrum of M82 using 7,362 individual 128 s RXTE/PCA light curves. The frequency resolution is 0.125 Hz. The two strongest features in the power spectrum occur at 3.32±0.06 (3.7σ) and 5.07±0.06 Hz (2.75σ), consistent with a 3:2 frequency ratio. The combined statistical significance of the detection is greater than 4.7σ and is > 5σ considering a search for 3:2 ration pair. (b) Averaged power density spectrum of all (363) 1,024 s segments with RXTE/PCA. The frequency resolution is 0.0625 Hz. The strongest feature is at 5 Hz (3.8σ). (c) For a direct comparison with stellar-mass black holes, we show the broadband power density spectrum of M82 (using 100 ks of XMM-Newton/EPIC data) showing the low-frequency quasi-periodic oscillation at 120 mHz in addition to the high-frequency quasi-periodic oscillation pair in (a) and (b). Power spectra are Leahy-normalized to a value of 2. Mass, spin and radius measurements using inverse-mass scaling and relativistic precession modeling 12 (a) Contours (90% confidence) of M82 X-1’s mass as a function of the spin parameter, that is, the ratio of the black hole’s angular momentum to its mass. The three contours correspond to the three low frequency values (37, 120 and 210 mHz), with the mass increasing as the low-frequency oscillation frequency increases. (b) Contours of M82 X-1’s mass as a function of the radius of the origin of these oscillations (in units of rg = GM/c 2 , where G, M and c are the gravitational constant, the black hole mass and the speed of light, respectively). In (a) and (b), the vertical lines (solid, solution; dashed, upper and lower limits) represent M82 X-1’s mass estimates assuming a simple inverse-mass scaling for the high- frequency QPOs. The three colours correspond to scalings using the masses of the microquasars GRO J1655-40 13 (green), XTE J1550-64 14 (blue) and GRS 1915+105 15 (black). “ In Stellar-mass Black Holes …. ” The discovery of two stable peaks at frequencies with a ratio of 3:2 (3.3 and 5 Hz) in the power spectrum of X-ray emission from the brightest X-ray source in galaxy M82 suggests that, if the relationship between frequency and mass that holds for stellar-mass black holes can be extended to intermediate masses, the black hole believed to be the source of the emission has a mass approximately 400 times that of the Sun. “One sentence summary” “ Result: Evidence for stable, 3:2 frequency ratio high-frequency QPOs from ULX M82 X-1” This work will be published online 17th August 2014 and can be found using its digital object identifier (DOI) at http://dx.doi.org/10.1038/nature13710 For additional details see http://www.astro.umd.edu/~dheeraj/
Transcript of Discovery of 3:2 ratio High-Frequency QPOs from a ULX: A ... · source in galaxy M82 suggests that,...
Ultraluminous X-ray sources (ULXs) are X-ray point sources in nearby galaxies with isotropic luminosities exceeding the Eddington value of a 25 solar mass black hole, i.e, ≥ 3×1039 erg/sec. A long-standing debate is whether they are hyper-accreting stellar-mass black holes or intermediate-mass black holes (a few 100-1000 solar masses) accreting at sub-Eddington rates. M82 X-1 is an extreme ULX with an average X-ray luminosity of 5×1040 ergs s-1 and a strong intermediate-mass black hole candidate1-6.
“ Context ”
Discovery of 3:2 ratio High-Frequency QPOs from a ULX:A 400 solar mass black hole in M82
Dheeraj R. Pasham aka DJ (UMD/NASA), Tod E. Strohmayer (NASA), Richard F. Mushotzky (UMD)
In addition to the low-frequency quasi-periodic oscillations (0.2-15 Hz; QPOs), three confirmed stellar-mass black holes exhibit high-frequency QPO pairs (100-450 Hz) in a frequency ratio of 3:2 (see power spectra on the right)7. These frequencies are fast, comparable to their Keplerian orbital values in the inner few gravitational radii of the accretion disk and appear to be frequency-invariant when the sources change their luminosities. Such stable, general relativity induced oscillations should scale inversely with the black hole mass if they arise from orbital motion near the innermost stable circular orbit in the accretion disk and there is observational support that they do for stellar-mass black holes7.
References : [1] Casella et al. 2008, MNRAS, 387,1701-1011. [2] Dewangan et al. 06, ApJ, 637, L21-L24. [3] Feng & Kaaret 2010 ApJ, 712, L169-L173. [4] Mucciarelli et al. 06, MNRAS, 365, 1123-1130. [5] Patruno et al. 2006, MNRAS, 370, L6-L9. [6] Zhou et al. 2010, ApJ, 710, 16-23. [7] McClintock & Remillard 2006, Compact Stellar X-ray Sources, 157-213. [8] Kaaret et al. 06, ApJ, 646, 174-183. [9] Middleton et al. 2011, MNRAS, 411, 644-652. [10] Pasham & Strohmayer 2013, ApJ, 771, 101. [11] Abramowicz et al. 2004, ApJ, 609, L63-L65. [12] Stella et al. 1999, ApJ, 524, L63-L66. [13] Beer & Podsiadlowski 2002, MNRAS, 331, 351-360. [14] Orosz et al. 2011, ApJ, 730, 75-88. [15] Steeghs et al. 2013, ApJ, 768, 185-192.
M82 X-1's high luminosity8 and the identification of its 30-200 mHz X-ray QPOs as the analogs of the low-frequency QPOs of stellar-mass black holes suggests that it may contain an intermediate-mass black hole with mass in the range of 25-1300 solar masses1-6. But, there were two uncertainties with such scaling: first, it was unclear--until now--whether these mHz QPOs are indeed the low-frequency analogs of stellar-mass systems9,10 and, second, both the low-frequency and the mHz oscillations are variable, resulting in a large dispersion in the measured mass. The simultaneous detection of a stable, 3:2-ratio, high-frequency periodicity and low-frequency mHz oscillations allows one to set the overall frequency scale of the power spectrum and has been proposed to be the smoking gun evidence for an intermediate-mass black hole in a ULX 11.
Power density spectra of M82 (a) Six-year average X-ray (3–13 keV) power density spectrum of M82 using 7,362 individual 128 s RXTE/PCA light curves. The frequency resolution is 0.125 Hz. The two strongest features in the power spectrum occur at 3.32±0.06 (3.7σ) and 5.07±0.06 Hz (2.75σ), consistent with a 3:2 frequency ratio. The combined statistical significance of the detection is greater than 4.7σ and is > 5σ considering a search for 3:2 ration pair. (b) Averaged power density spectrum of all (363) 1,024 s segments with RXTE/PCA. The frequency resolution is 0.0625 Hz. The strongest feature is at 5 Hz (3.8σ). (c) For a direct comparison with stellar-mass black holes, we show the broadband power density spectrum of M82 (using 100 ks of XMM-Newton/EPIC data) showing the low-frequency quasi-periodic oscillation at 120 mHz in addition to the high-frequency quasi-periodic oscillation pair in (a) and (b). Power spectra are Leahy-normalized to a value of 2.
Mass, spin and radius measurements using inverse-mass scaling and relativistic precession modeling12 (a) Contours (90% confidence) of M82 X-1’s mass as a function of the spin parameter, that is, the ratio of the black hole’s angular momentum to its mass. The three contours correspond to the three low frequency values (37, 120 and 210 mHz), with the mass increasing as the low-frequency oscillation frequency increases. (b) Contours of M82 X-1’s mass as a function of the radius of the origin of these oscillations (in units of rg = GM/c2, where G, M and c are the gravitational constant, the black hole mass and the speed of light, respectively). In (a) and (b), the vertical lines (solid, solution; dashed, upper and lower limits) represent M82 X-1’s mass estimates assuming a simple inverse-mass scaling for the high-frequency QPOs. The three colours correspond to scalings using the masses of the microquasars GRO J1655-4013 (green), XTE J1550-6414 (blue) and GRS 1915+10515 (black).
“ In Stellar-mass Black Holes …. ”
The discovery of two stable peaks at frequencies with a ratio of 3:2 (3.3 and 5 Hz) in the power spectrum of X-ray emission from the brightest X-ray source in galaxy M82 suggests that, if the relationship between frequency and mass that holds for stellar-mass black holes can be extended to intermediate masses, the black hole believed to be the source of the emission has a mass approximately 400 times that of the Sun.
“One sentence summary”
“ Result: Evidence for stable, 3:2 frequency ratio high-frequency QPOs from ULX M82 X-1”
This work will be published online 17th August 2014 and can be found using its digital object identifier (DOI) at http://dx.doi.org/10.1038/nature13710For additional details see http://www.astro.umd.edu/~dheeraj/
