English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present two epochs of near-infrared spectroscopy of the candidate redsupergiant counterpart to RX~J004722.4-252051, a ULX in NGC 253. We measureradial velocities of the object and its approximate spectral type bycross-correlating our spectra with those of known red supergiants. OurVLT/X-shooter spectrum is best matched by that of early M-type supergiants,confirming the red supergiant nature of the candidate counterpart. The radialvelocity of the spectrum, taken on 2014, August 23, is $417 \pm 4$ km/s. Thisis consistent with the radial velocity measured in our spectrum taken withMagellan/MMIRS on 2013, June 28, of $410 \pm 70$ km/s, although the large erroron the latter implies that a radial velocity shift expected for a black hole oftens of $M_\odot$ can easily be hidden. Using nebular emission lines we findthat the radial velocity due to the rotation of NGC 253 is 351 $\pm$ 4 km/s atthe position of the ULX. Thus the radial velocity of the counterpart confirmsthat the source is located in NGC 253, but also shows an offset with respect tothe local bulk motion of the galaxy of 66 $\pm$ 6 km/s. We argue that the mostlikely origin for this displacement lies either in a SN kick, requiring asystem containing a $\gtrsim 50$ $M_\odot$ black hole, and/or in orbital radialvelocity variations in the ULX binary system, requiring a $\gtrsim 100$$M_\odot$ black hole. We therefore conclude that RX~J004722.4-252051 is astrong candidate for a ULX containing a massive stellar black hole.

Discovery of a red supergiant counterpart to RX~J004722.4-252051, a ULX in NGC 253