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XTE J1752-223 in transition from a soft to a hard state

ATel #2518; T. Muñoz Darias, S. Motta, T. Belloni (INAF - Brera Observatory), J. Homan (MIT)
on 28 Mar 2010; 00:03 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Jeroen Homan (jeroen@space.mit.edu)

Subjects: X-ray, Black Hole, Transient

Referred to by ATel #: 2530, 2549, 2775

Recent RXTE observations of the X-ray transient XTE J1752-223 suggest that the source is currently in transition from a spectrally soft to a spectrally hard state. The system was discovered by RXTE last Oct 23 (#ATEL 2258) and showed spectral and timing properties consistent with a black hole transient during the canonical low/hard state (Muñoz-Darias et al. 2010). A transition to the high/soft state was observed on Jan 23 (#ATEL 2387). After ~two months in the soft state, during which the X-ray flux dropped by more than one order of magnitude, the latest RXTE observation (27 March 2010, 13:15 UT) shows the system in an intermediate state. The energy spectrum can be fitted with a disc black body component (Tin~0.4 keV) plus a power law (photon index~2.4) with an edge at 7.5 keV. Compared to the previous observation (26 March 2010 16:53 UT) the 3-25 keV flux of the power-law component increased by a factor of ~2.5 and contributes ~70% of the flux in that band. The power density spectrum can be fitted with a zero-centered Lorentzian with a fractional rms of ~10% (0.1-64 Hz). These properties are consistent with those observed in other black hole transients during transitions from the soft state to the hard state. We also notice an increase in hard X-ray flux (15-50 keV) detected by the Swift/BAT monitor during it latest pointing. Multiwavelength observations covering this soft-hard transition are encouraged.