Multi-epoch spectroscopy of the globular cluster black hole in NGC 4472

Abstract

We present a study of the X-ray spectral properties of the highly variable X-ray emitting black hole in a globular cluster in the elliptical galaxy NGC 4472. The XMM-Newton spectrum of the source in its bright epoch is well described by a multiple blackbody model with a characteristic temperature $kT_{in}\approx$ 0.2 keV. The spectrum of an archival Chandra observation of the source obtained 3.5 years before the XMM data gives similar estimates for the blackbody parameters. We confirm that the fainter interval of the XMM-Newton observation has a spectrum that is consistent with the brighter epoch, except for an additional level of foreground absorption. We also consider other possible mechanisms for the variability. Based on the timescale of the X-ray flux decline and the estimated size of the X-ray emission region we argue that an eclipsing companion is highly unlikely. We find the most likely means of producing the absorption changes on the observed timescale is through partial obscuration by a precessing warped accretion disk.Comment: Accepted for publication in MNRA

Deep Chandra observations of the NGC 4472 globular cluster black hole XMMU 122939.7+075333: short-term variability from the first globular cluster black hole binary

“…Shih et al (2008) also found that the spectral changes between the faint and bright phases in XMM04 were due to a lack of soft photons in the faint phase, which is consistent with our result for Obs ID 12888. . The diskbb plus PL model has fit the apparent hard excess much better than the previous models that only include one continuum component (see Fig.…”

“…Both the Obs ID 12889 and 12888 spectra show suggestive evidence for a hard (>2 keV) excess. Shih et al (2008) also report a hard excess in their spectral analysis of the source. This feature may require an additional continuum component in order to fit properly.…”

“…tana@ast.uct.ac.za; thomas.maccarone@ttu.edu; kraft@head.cfa.harvard.edu; sivakoff@ualberta.ca Shih et al (2008) carried out spectroscopic analysis of XMMU 122939.7+075333 using XMM-Newton data and Chandra data. They found that the spectra were well fit by a multicolour disk blackbody model and had an inner disk temperature of about k Tin= 0.15 keV with the same underlying continuum whether the source was in a bright or faint phase, but with varying absorption column density.…”

“…The flux for the 2004 XMM observation was taken from the bright phase spectrum (count rate 0.04 counts/s) of XMM04 only and calculated in ISIS using the spectral parameters found in Shih et al (2008). This was done to be consistent with the work of Shih et al (2008) and Maccarone et al (2010). The 2002 XMM (values taken from the 2XMM catalogue of Watson et al 2009) and 2010 Chandra (Maccarone et al 2010) fluxes and errors were calculated from their respective count rate or flux errors using the w3pimms tool, assuming a Γ= 1.7 power law spectral model.…”

X-ray spectral variability of ultraluminous X-ray sources in extragalactic globular clusters

“…One other difference between these ULX populations is that those in star forming regions have hydrogen emission present in their optical spectra (e.g., Fabrika et al 2015), while at least three of the globular cluster ULXs have no hydrogen emission Irwin et al 2010;Roberts et al 2012). The most well studied GC ULX, RZ2109, also has very different X-ray behaviour from ULXs in star forming regions; it varies by more than an order of magnitude in X-ray luminosity between many different observations, but exhibits little or no variation in kT over those same observations (Shih et al 2008;Dage et al 2018). Several studies have considered the nature of the GC ULX sources and their optical emission, although most of them tend to focus on the source RZ2109 (e.g., Zepf et al 2008;Steele et al 2011a;Peacock et al 2012a,b;Steele et al 2014).…”