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Detection of GRS 1915+105 and SS 433 at 7.2 GHz and 21.4 GHz with the Sardinia Radio Telescope

ATel #8921; E. Egron (INAF-OAC), A. Pellizzoni (INAF-OAC), M. Bachetti (INAF-OAC), A. Navarrini (INAF-OAC), A. Trois (INAF-OAC), M. Pilia (INAF-OAC), M. N. Iacolina (INAF-OAC), A. Melis (INAF-OAC), R. Concu (INAF-OAC), S. Loru (INAF-OAC), R. Ballhausen (Remeis/FAU/ECAP), S. Corbel (AIM/CEA), W. Eikmann (Remeis/FAU/ECAP), F. Fuerst (CalTech), V. Grinberg (MIT), I. Kreykenbohm (Remeis/FAU/ECAP), M. Marongiu (INAF-OAC), M. Nowak (MIT), A. Possenti (INAF-OAC), K. Pottschmidt (CRESST/GSFC/UMBC), J. Rodriguez (AIM/CEA), J. Wilms (Remeis/FAU/ECAP)
on 7 Apr 2016; 13:47 UT
Credential Certification: Elise Egron (egron@oa-cagliari.inaf.it)

Subjects: Radio, Binary, Black Hole, Neutron Star, Transient

In the frame of radio monitoring of Galactic NS/BH X-ray binaries with the Sardinia Radio Telescope (www.srt.inaf.it), we detected GRS 1915+105 and SS 433 in the C- and K-bands through single-dish on-the-fly mapping centered on the sources.

The observation of GRS 1915+105 was performed on 2016 April 5, 04:00-06:00 UTC (MJD 57483.2), about 2 weeks after one of the strongest hard X-ray flare registered by Swift so far (13 counts/cm2/s @ 15-50 keV, MJD 57468; http://swift.gsfc.nasa.gov/results/transients/GRS1915p105/ ). At the epoch of our observation, GRS 1915+105 is apparently performing a hard-to-soft state transition halving its hard X-ray flux with respect to the peak flux of the flare. We measured a flux density of 140+/-15 mJy at 7.2 GHz (with a band-width of 0.68 GHz), and 85+/-10 mJy at 21.4 GHz (1.2 GHz band-width), using both SRT Total Power and SARDARA (Roach2) digital back-end operated in piggy-back mode. The radio spectrum is softening significantly during the hard-to-soft transition (radio spectral index α=-0.5+/-0.1, where flux density is S∝να).

During the same observing session, the X-ray binary SS433 was also detected by SRT with high significance: 520+/-10 mJy at 7.2 GHz and 420+/-10 mJy at 21.4 GHz, indicating a radio spectral index α=-0.2+/-0.05.

Further radio monitoring of these sources with SRT is on-going on a weekly basis during the Early Science Program S0013 (PI Egron).