Faint Radio Emission from the X-ray Transient, XTE J1748-288
ATel #14369; S. D. Hyman (Sweet Briar College), N. E. Kassim (NRL), S. Giacintucci (NRL), T. J. W. Lazio (JPL-Caltech), D. A. Frail (NRAO), J. E. Kooi (NRL), E. J. Polisensky (NRL), W. M. Peters (NRL)
on 5 Feb 2021; 03:32 UT
Credential Certification: Scott Hyman (shyman@sbc.edu)
Subjects: Radio, X-ray, Black Hole, Transient
Our recent radio observations with the VLA L-band (1-2 GHz) of a candidate pulsar in the Galactic center reveal nearby faint emission from the location of the black hole X-ray transient, XTE J1748-288 (Hjellming, R. M. et al. 1998, IAUC # 6934 , # 6937 ). On 2021 January 15 and 25, the measured peak flux densities at the 1.53 GHz central frequency are 0.109 +- 0.016 mJy/bm and 0.080 +- 0.012 mJy/bm (both 6.5 sigma), respectively. An image made from the combined observations yields a flux density of 0.096 +- 0.011 mJy/bm (9 sigma). Archival VLA L-band and GMRT Band 5 (1-1.5 GHz) observations from 2017 January and 2019 December are inconclusive, but a weighted average of the images yields a 3-sigma upper limit of 0.11 mJy/bm. The current detection could therefore be indicative of either an active state or a steady quiescent flux reached sometime after the ~600 mJy (1.5 GHz) outburst in 1998 that declined significantly over a period of months to, e.g., ~100 mJy in 1998 September (Hyman, S. D. et al. 2002, AJ, 123, 1497). Simultaneous 2021 January observations obtained by the commensal P-band system, VLITE (Polisensky, E. et al. 2016, ApJ, 832, 60), yield a 3-sigma upper limit of 7.5 mJy at 335 MHz, far below the ~300 mJy P-band measurement obtained in 1998 September. Further analysis of the 1998 activity revealed a resolved source with a 0.25'' E-W elongation (Rupen, M. P. et al. 1998 IAUC # 6938 ), later determined to be a highly polarized jet (Brocksopp, C. et al. 2007, MNRAS, 378, 3, 1111). The resolution of our images is 2'' x 1'', and the position of the peak pixel of the source is (J2000) RA 17 48 05.06, DEC -28 28 25.9. We note that while we report peak pixel flux densities here, the source does appear marginally resolved in the SE-NW direction, although this could be due to confusion with background noise. We encourage further monitoring, especially at high energy, to determine if XTE J1748-288 is currently in an active state.
