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EVLA Radio Detection of Swift J1357.2-0933

ATel #3147; G. R. Sivakoff (U Virginia), J. C.A. Miller-Jones (ICRAR), H. A. Krimm (CRESST/GSFC/USRA), and the JACPOT XRB collaboration
on 4 Feb 2011; 16:27 UT
Credential Certification: Gregory R Sivakoff (grs8g@virginia.edu)

Subjects: Radio, X-ray, Neutron Star, Transient, Variables

The JACPOT XRB project reports a radio detection of the newly detected transient Swift J1357.2-0933 (Krimm et al 2010, ATEL #3138) with the EVLA. EVLA observations on 4 Feb 2011 (MJD = 55596.35856 +/- 0.00448) detected a source at 245 +/- 54 microJy, stacking data at 4.6 and 7.9 GHz (nominal center frequency of 6.249 GHz).
 
The radio source is located at:
RA (J2000)  13:57:16.818 +/- 0.017 s (0.255 arcsec)
DEC (J2000) -09.32.38.550 +/- 0.164 arcsec.
 
The radio detection is consistent with the Swift localization of the source (Krimm et al. 2011, ATEL #3142). We note that the high noise level of the image is due to unseasonably cold weather in New Mexico and RFI in the 4.5-4.7 GHz bandwidth.
 
Given the detected X-ray flux in the 3-9 keV band, 2e-10 erg/s/cm-2, the radio flux, and potential distances of between 1 and 10 kpc, we note that Swift J1357.2-0933 is subluminous in the radio band compared to typical black hole X-ray binaries by a factor of >~10. While there is a chance that the source may be in transition between radiative inefficient and radiative efficient accretion flows like the black hole candidate H1743-322 (Coriat et al. 2011, arXiv:1101.5159), it is more likely that the source is an atoll neutron star X-ray binary. If the source is at 1.5 kpc as suggested by Rau et al. (ATEL # 3140), we note the source may be in an early stage of its evolution that has not been well studied in other atoll neutron star X-ray binaries.
 
Further observations at all wavelengths are encouraged.
 
We thank the EVLA for rapidly scheduling the observation.