RXTE Observations of IGR J16283-4838 and IGR J16493-4348

ATel #465; C. B. Markwardt (U. Maryland & NASA/GSFC), J. H. Swank, E. Smith (NASA/GSFC)
on 16 Apr 2005; 21:36 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

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RXTE has observed two recently reported INTEGRAL transients, IGR J16493-4348 and IGR J16283-4838.

IGR J16493-4348 was reported to be associated with the pulsar PSR J1649-4349 (Grebenev et al, ATEL #457). RXTE observed on Apr 14 at 02:20 for 3.5 ks, and on Apr 15 at 14:33 for 2.6 ks. Because of the Proportional Counter Array's (PCA) large field of view (2 deg at FWZM), the count rates are contaminated by significant amounts of galactic emission. On April 14, the count rate was variable on time scales of 100 to 1000 seconds; on April 15, the count rate was lower and flat. Assuming the second observation approximately represents quiescence, the variations on April 14 are from 0 to 3.6 ct/s/PCU (2-10 keV). No significant pulsations are detected from IGR J1649-4348 at any period, including the 0.871 second pulse period of PSR J1649-4349 (Manchester et all, 2001, MNRAS, 328, 17).

The background subtracted mean spectrum of IGR J16493-4348 is consistent with a heavily absorbed power law (with n_H of ~1 x 10E23 cmE-2 and photon index 1.4). The fluxes in the 2-10, 10-20 and 20-40 keV bands are 1.0, 1.3 and 2.1 (units of 10E-11 erg cmE-2 sE-1). No significant line emission is required.

IGR J16283-4838 was reported as a rising X-ray transient (ATEL #456, #458), was localized by the Swift XRT (ATEL #459), and may have an IR counterpart (ATEL #460). RXTE observed on April 14 at 00:46 for 3.6 ks, and on April 15 at 16:07 for 2.9 ks. Like J16493, J16283 is contaminated by galactic emission. Taking a best estimate of the background, the source is again well modeled by an absorbed power law (with n_H of ~4-5 x 10E22 and photon index 0.8 - 1.1). On April 14 the fluxes in the 2-10, 10-20 and 20-40 keV bands were 7.6, 11 and 21 (units of 10E-11 erg cmE-2 sE-1). On April 15, the fluxes were 3.8, 7.0 and 16 (same bands and units). No pulsations were detected.

The highly absorbed spectrum of J16283 is consistent with that reported by Kennea et al (ATEL #459). It appears that both sources have declined significantly since the last INTEGRAL reports. However if an imaging instrument observes J16493, it too should have a highly absorbed spectrum.