A variable Quasi-Periodic Oscillation in M82 X-1. Timing and spectral analysis of XMM-Newton and RossiXTE observations

Abstract

We report results from a spectral and timing analysis of M82 X‐1, one of the brightest known ultraluminous X‐ray sources. Data from a new 105‐ks XMM–Newton observation of M82 X‐1, performed in 2004 April, and of archival RossiXTE observations are presented. A very soft thermal component is present in the XMM spectrum. Although it is not possible to rule out a residual contamination from the host galaxy, modelling it with a standard accretion disc would imply a black hole (BH) mass of ≈103 M⊙. An emission line was also detected at an energy typical for fluorescent Fe emission. The power density spectrum of the XMM observation shows a variable Quasi‐Periodic Oscillation (QPO) at frequency of 113 mHz with properties similar to those discovered by Strohmayer and Mushotzky. The QPO was also found in seven archival RXTE observations, that include those analysed by Strohmayer and Mushotzky, and Fiorito and Titarchuk. A comparison of the properties of this QPO with those of the various types of QPOs observed in Galactic black hole candidates strongly suggests an association with the type‐C, low‐frequency QPOs. Scaling the frequency inversely to the BH mass, the observed QPO frequency range (from 50 to 166 mHz) would yield a BH mass anywhere in the interval few tens to 1000 M⊙.

X-ray observations of ultraluminous X-ray sources

“…Similarly, simple photon counting arguments for high-excitation optical line emission regions near ULXs make the same argument (Pakull & Mirioni 2002;Kaaret et al 2004). The source for which most evidence stacks up is M82 X-1, which through a combination of its extreme luminosity (L X,peak ∼ 10 41 erg s −1 ), co-location with the young, dense stellar cluster MGG 11, and QPO detections is the best known candidate for an IMBH (Kaaret et al 2001;Strohmayer & Mushotzky 2003;Portegies Zwart et al 2004;Mucciarelli et al 2006). However, it is possible this source is an atypical ULX; it may be the nucleus of an accreted dwarf galaxy (King & Dehnen 2005).…”

“…In fact, the detection of 3:2 ratio twin-peak high-frequency QPOs at ∼ 1 Hz would be strong evidence for the presence of an IMBH (Abramowicz et al 2004) (though scaling from Galactic systems implies such a measurement is unlikely even in the medium term). Low frequency QPOs, on the other hand, have now been detected in a handful of ULXs (Strohmayer & Mushotzky 2003;Dewangan, Griffiths & Rao 2006;Mucciarelli et al 2006;Strohmayer et al 2007). However, this type of QPO does not provide a clear, unambiguous mass estimate.…”

Ultraluminous X‐ray sources: Three exciting years

“…It was observed to undergo spectral transitions reminiscent of standard BH spectral states (transition to "thermal-dominant" , and this pointed strongly towards the IMBH interpretation. It's one of the few ULXs known to show strong quasi-periodic oscillations, detected by RXTE and XMM in the range 50 − 100 Hz (Mucciarelli et al 2006). In 2014, the IMBH hypothesis gained strong support when a timing analysis including all RXTE observations of M82 X-1 showed a new pair of quasi-periodic oscillations, at ∼ 3 and ∼ 5 Hz (Pasham et al 2014, see Figure 2).…”

A 400-solar-mass black hole in the galaxy M82

“…M82 X-1's previous mass estimates of a few hundred solar masses combined with the Type-C identification 2,4,9 of its mHz X-ray quasi-periodic oscillations suggest that 3:2 ratio, twin-peak, high-frequency oscillations analogous to those seen in stellar-mass black holes, if present, should be detectable in the frequency range of a few Hz 16 . We accordingly searched Rossi X-ray Timing Explorer's (RXTE's) proportional counter array archival data to look for 3:2 oscillation pairs in the frequency range of [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Hz which corresponds to a black hole mass range of 50-2000 M ⊙ .…”