Rubin-LSST

Abstract:

We present optical, X-ray and radio observations of the black hole transient (BHT) XTE J1752-223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752-223 is fainter than 24.4mag in the i′ band. A comparison with measurements of the source during its 2009-2010 outburst shows that the outburst amplitude is more than 8 mag in the i′ band. Known X-ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital-period system (Porb≲ 6.8h) with an M type (or later) mass donor, at a distance of 3.5 ≲d≲ 8kpc. Simultaneous X-ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X-ray and radio flux of XTE J1752-223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low-luminosity end of the X-ray-radio correlation for this source and compared it with other BHTs. We found that XTE J1752-223 adds to the number of outliers with respect to the 'standard' X-ray-radio luminosity relation. Furthermore, XTE J1752-223 is the second source, after the BHT H1743-322, that shows a transition from the region of the outliers towards the 'standard' correlation at low luminosity. Finally, we report on a faint, variable X-ray source we discovered with Chandra at an angular distance of ~2.9arcsec to XTE J1752-223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X-ray emission associated with a jet from XTE J1752-223. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Abstract:

We present the first resolved imaging of the milliarcsecond-scale jets in the neutron star X-ray binary Circinus X-1, made using the Australian Long Baseline Array. The angular extent of the resolved jets is ∼20mas, corresponding to a physical scale of ∼150au at the assumed distance of 7.8kpc. The jet position angle is relatively consistent with previous arcsecond-scale imaging with the Australia Telescope Compact Array. The radio emission is symmetric about the peak, and is unresolved along the minor axis, constraining the opening angle to be <20°. We observe evidence for outward motion of the components between the two halves of the observation. Constraints on the proper motion of the radio-emitting components suggest that they are only mildly relativistic, although we cannot definitively rule out the presence of the unseen, ultrarelativistic (Γ > 15) flow previously inferred to exist in this system. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

The search for transient phenomena in the Universe has entered a new era. In the next decade new all-sky surveys will provide a vast amount of astronomical survey data. These data will address issues in many of the astronomical fields. In the Supernova field, we will have for the first time the possibility to discover SNe without most of the observational bias present in the previous SN searches. Here we report the status of the transients study in one of the new on-going all-sky surveys: the Panoramic Survey Telescope & Rapid Response System-1 (PanStarrs-1).

Abstract:

We present a statistical observational study of the tidal dwarf (TD) population in the nearby Universe by exploiting a large, homogeneous catalogue of galaxy mergers compiled from the Sloan Digital Sky Survey. 95percent of TD-producing mergers involve two spiral progenitors (typically both in the blue cloud), while most remaining systems have at least one spiral progenitor. The fraction of TD-producing mergers where both parents are early-type galaxies is less than 2percent, suggesting that TDs are unlikely to form in such mergers. The bulk of TD-producing mergers inhabit a field environment and have mass ratios greater than ~1:7 (the median value is 1:2.5). TDs forming at the tidal-tail tips are ~4 times more massive than those forming at the base of the tails. TD stellar masses are less than 10percent of the stellar masses of their parents (the median is 0.6percent) and lie within 15 optical half-light radii of their parent galaxies. The TD population is typically bluer than the parents, with a median offset of ~0.3mag in the (g-r) colour and the TD colours are not affected by the presence of active galactic nuclei (AGN) activity in their parents. An analysis of their star formation histories indicates that TDs contain both newly formed stars (with a median age of ~30Myr) and old stars drawn from the parent discs, each component probably contributing roughly equally to the stellar mass of the object. Thus TDs are not formed purely through gas condensation in tidal tails but host a significant component of old stars from the parent discs. Finally, an analysis of the TD contribution to the observed dwarf-to-massive galaxy ratio in the local Universe indicates that ~6percent of dwarfs in nearby clusters may have a tidal origin, if TD production rates in nearby mergers are representative of those in the high-redshift Universe. Even if TD production rates at high redshift were several factors higher, it seems unlikely that the entire dwarf galaxy population today is a result of merger activity over the lifetime of the Universe. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.