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IR brightening and possible appearance of the compact jet in XTE J1752-223 in the hard state

ATel #2549; M. Buxton (Yale University), Tolga Dincer, Emrah Kalemci (Sabanci University, Turkey), and John Tomsick (SSL, UC Berkeley)
on 12 Apr 2010; 23:23 UT
Credential Certification: Michelle Buxton (buxton@astro.yale.edu)

Subjects: Infra-Red, X-ray, Binary, Black Hole, Transient

Referred to by ATel #: 2573, 2775

We have been monitoring the black-hole candidate (ATel #2269) XTE J1752-223 using the ANDICAM instrument on the SMARTS 1.3m telescope in Cerro Tololo, Chile (IR) , and the PCA instrument on the Rossi X-ray Timing Explorer (RXTE, X-ray). XTE J1752-223 has made a gradual transition to the hard state since the transition started around 2010 March 27 (ATel#2518). Since then, the power spectrum as measured by the RXTE has shown an increase in the fractional rms from 10% (ATel#2518) to 25%+/-1.2% on 2010 April 12 (ObsID 95360-01-12-02). The power-law continues to dominate the 3-25 keV RXTE energy spectrum, and the power-law photon index has hardened from 2.4 to 1.6. As of April 12, the X-ray flux was 1.3e-9 ergs/cm2/s (3-25 keV, absorbed). Recent H-band observations show that between UT 06 April 2010 (JD 2455292.81289) and UT 11 April 2010 (JD 2455297.80768) XTE J1752-223 brightened by 0.45 mag which is likely due to the turn-on of a compact jet in this system. Therefore we strongly encourage observations to be made at other wavelengths, especially the radio, to study the evolution of a probable jet in this system.