The Ultraluminous X‐Ray Sources Near the Center of M82

Abstract

We report the identification of a recurrent ultraluminous X-ray source (ULX), a highly absorbed X-ray source (possibly a background AGN), and a young supernova remnant near the center of the starburst galaxy M82. From a series of Chandra observations taken from 1999 to 2005, we found that the transient ULX first appeared in 1999 October. The source turned off in 2000 January, but later reappeared and has been active since then. The X-ray luminosity of this source varies from below the detection level ($2:5 ; 10 38 ergs s À1 ) to its active state between $7 ; 10 39 and 1:3 ; 10 40 ergs s À1 (in the 0.5Y10 keV energy band) and shows unusual spectral changes. The X-ray spectra of some Chandra observations are best fitted with an absorbed power-law model with photon index ranging from 1.3 to 1.7. These spectra are similar to those of Galactic black hole binary candidates seen in the low/hard state, except that a very hard spectrum was seen in one of the observations. By comparing with near-infrared images taken with the Hubble Space Telescope, the ULX is found to be located within a young star cluster. Radio imaging indicates that it is associated with a H ii region. We suggest that the ULX is likely to be a >100 M intermediate-mass black hole in the low/hard state. In addition to the transient ULX, we also found a highly absorbed hard X-ray source which is likely to be an AGN and an ultraluminous X-ray-emitting young supernova remnant which may be related to a 100 yr old gamma-ray burst event, within 2 00 of the transient ULX.

Discovery of a bright radio transient in M 82: a new radio supernova?

“…They do not find a counterpart to our new radio source. Neither do Kong et al (2007) Camera and Multi-Object Spectrometer (NICMOS) that, again, does not show a counterpart to our variable radio source. Körding et al (2005) …”

Ultraluminous X‐ray sources: Three exciting years

“…In 2014, two remarkable discoveries came out of the Cigar Galaxy, M82, that harbors three known ULXs (Matsumoto et al 2001;Kaaret et al 2001;Feng and Kaaret 2007;Kong et al 2007;Jin et al 2010). The first was the observation of quasi-periodic oscillations from a known eULX, M82 X-1, also known as M82 X41.4+60…”

“…This source was a wellknown ULX, showing very strong luminosity variations on timescales of ∼weeks and up to 3·10 40 ergs s −1 (Kong et al 2007;Feng and Kaaret 2007). The presence of mHz QPOs had been used to model it as an IMBH above 10000M .…”

A possible 55-d X-ray period of the ultraluminous accreting pulsar M82 X–2

“…Furthermore, this modulation is contaminated by signals generated from the two nearby variable ULXs (X-2 and X-3) because of the poor spatial resolution of RXTE. For instance, M82 X-2 and X-3 can be as luminous as 10 40 erg s −1 (Kong et al 2007), which are comparable to M82 X-1 (Chiang & Kong 2011). Following the method used in Qiu et al (2015), we extracted the light curves of the four ULXs using Swift/XRT data with small extraction regions centred at each ULX.…”

“…In addition to the population of black holes, the ULX M82 X-2 is recently confirmed as a neutron star system (Bachetti et al 2014). Furthermore, some young X-ray supernova remnants can also be ultralu-⋆ E-mail: akong@phys.nthu.edu.tw minous and M82 X-4 is one of the examples (Kong et al 2007). …”