The starbusting, nearby (D = 32.9 Mpc) spiral (Sc) galaxy NGC2276 belongs to the sparse group dominated by the elliptical galaxy NGC2300. NGC2276 is a remarkable galaxy, as it displays a disturbed morphology at many wavelengths. This is possibly due
to gravitational interaction with the central elliptical galaxy of the group. Previous ROSAT and XMM-Newton observations resulted in the detection of extended hot gas emission and of a single very bright (~1.e41 erg/s) ultraluminous X-ray source (ULX) candidate. Here we report on a study of the X-ray sources of NGC2276 based on CHANDRA data taken in 2004. CHANDRA was able to resolve 16 sources, 8 of which are ULXs, and to reveal that the previous ULX candidate is actually composed of a few distinct objects. We construct the luminosity function of NGC2276, which can be interpreted as dominated by high mass X-ray binaries, and estimate the star formation rate (SFR) to be ~5-15 Msun/yr, consistent with the values derived from optical and infrared observations. By means of numerical simulations, we show that both ram pressure and viscous transfer effects are necessary to produce the distorted morphology and the high SFR observed in NGC2276, while tidal interaction have a marginal effect.
A puzzling class of exotic objects, which have been known about for more than 30 years, is reaching a new era of understanding. We have discovered hundreds of Ultra Luminous X-ray sources (ULXs) - non-nuclear sources with X-ray luminosity in excess o
f the Eddington luminosity for normal size stellar Black Holes (BH) - and we are making progresses towards understanding their emission mechanisms. The current explanations imply either a peculiar state of accretion onto a stellar size BH or the presence of an intermediate mass BH, the long-sought link between stellar and supermassive BHs. Both models might co-exist and therefore studying this class of object will give insight into the realm of accretion in a variety of environments and at the same time find look-alikes of the primordial seed BHs that are thought to be at the origin of todays supermassive BHs at the centre of galaxies. The radio band has been exploited only scantily due to the relative faint fluxes of the sources, but we know a number of interesting sources exhibiting both extended emission (like bubbles and possibly jets) and cores, as well as observed transient behaviour. The new eras of the SKA will lead us to a major improvement of our insight of the extreme accretion within ULXs. We will both investigate in detail known sources and research new and fainter ones. When we have reached a thorough understanding of radio emission in ULX we could also use the SKA as a discovery instrument for new ULX candidates. The new array will give an enormous space to discovery: sources like the ones currently known will be detected in a snapshot up to 50 Mpc instead of at 5 Mpc with long, pointed observations.
We present results for X-ray point sources in the Sc galaxy NGC 2276, obtained by analyzing Chandra data. The galaxy is known to be very active in many wavelengths, possibly due to gravitational interaction with the central elliptical of the group, N
GC 2300. However, previous XMM-Newton observations resulted in the detection of only one bright ULX and extended hot gas emission. We present here the X-ray population in NGC 2276 which comprises 17 sources. We found that 6 of them are new ULX sources in this spiral galaxy resolved for the first time by Chandra. We constructed the Luminosity Function that can be interpreted as mainly due of High Mass X-ray binaries, and estimate the Star Formation rate (SFR) to be SFR ~ 5-10 M_sun/yr.
The extreme environment provided by the Cartwheel ring is analyzed to study its X-ray and optical-UV properties. We compare the Cartwheel with the other members of its group and study the system as a whole in the X-ray band. We analyze the data of th
e Cartwheel galaxy obtained with XMM-Newton in two different periods (December 2004 and May 2005). We focus on the X-ray properties of the system and use the OM data to obtain additional information in the optical and UV bands. We detect a total of 8 sources associated with the Cartwheel galaxy and three in its vicinity, including G1 and G2, all at L >= 10^39 erg/s, that is the Ultra Luminous X-ray (ULX) source range. The brightest ULX source has been already discussed elsewhere. The spectra of the next three brightest ULX are well fitted by a power-law model with a mean photon index of ~2. We compare the XMM-Newton and Chandra datasets to study the long-term variability of the sources. At least three sources vary in the 5 months between the two XMM-Newton observations and at least four in the 4-year timeframe between Chandra and XMM-Newton observations. One Chandra source disappears and a new one is detected by XMM-Newton in the ring. Optical-UV colors of the Cartwheel ring are consistent with a burst of star formation that is close to reaching its maximum, yielding a mean stellar age of about 40 Myr. The inferred variability and age suggest that high mass X-ray binaries are the counterparts to the ULX sources. The 3 companion galaxies have luminosities in the range 10^39-40 erg/s consistent with expectations. The hot gas of the Cartwheel galaxy is luminous and abundant (a few 10^8 Msol) and is found both in the outer ring, and in the inner part of the galaxy, behind the shock wave front. We also detect gas in the group with L_X ~10^40 erg/s.
We have observed 1ES 1426+428 with INTEGRAL detecting it up to $sim$150 keV. The spectrum is hard, confirming that this source is an extreme BL Lac object, with a synchrotron component peaking, in a $ u F_ u$ plot, at or above 100 keV, resembling the
hard states of Mkn 501 and 1ES 2344+514. All these three sources are TeV emitters, with 1ES 1426+428 lying at a larger redshift (z=0.129): for this source the absorption of high energy photons by the IR cosmic background is particularly relevant. The observed hard synchrotron tail helps the modeling of its spectral energy distribution, giving information on the expected intrinsic shape and flux in the TeV band. This in turn constrains the amount of the poorly known IR background.
