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ATEL # 1706; H. A. Krimm (CRESST/GSFC/USRA), J. L. Racusin (PSU), C. B. Markwardt (CRESST/GSFC/UMD) on behalf of the Swift BAT and XRT teams
on 8 Sep 2008; 21:29 UT
Password Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)
Subjects: X-ray, Request for Observations, Transients
Referred to by ATEL #: 1716
The Swift Burst Alert Telescope (BAT) triggered on a flux increase from the recently discovered galactic source Swift J1842.5-1124 (Krimm et al, ATel #1610). The first trigger was at 05:37:16 UT on 8 September, 2008 (Racusin et al, GCN 8199) and the source was observed by the Swift X-ray Telescope (XRT) for a total of 600 seconds and by the Swift/BAT for a total of 4150 seconds (Krimm et al, GCN 8200, 8201).
The BAT flux (15-50 keV) during this period averaged (0.016 ± 0.003) cts/sec/cm^2 (70 mcrab). The BAT event data is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.01 +- 0.37 (chisq/dof = 0.95 for 57 dof). The fluence in the 15-150 keV band is 7.2 +- 1.7 x 10^-7 erg/cm^2. The flux was constant to within errors during this period.
The XRT data for the first 300 seconds is best fit by a blackbody plus absorbed power law with fit parameters: nH = (4.4 ± 1.0) x 10^21 cm^-2, kT = 0.15 ± 0.02 keV, photon index = 1.71 ± 0.1, observed flux (0.3-10 keV) = (9.3 +0.3 -0.6) x 10^-10 erg/cm^2/s, unabsorbed flux = 1.9 x 10^-9 erg/cm^2/s, chisq/dof = 1.2 (dof=213). The fit to the second time interval is consistent.
Shortly after the discovery of Swift J1842.5-1124 on July 2, 2008, the flux from the source began to fall, becoming undetectable in the BAT monitor by July 15. The flux became detectable again on July 29 has been rising steadily ever since.
RXTE PCA scans of the galactic ridge region first detected the source on 27 July, 2008, after a period of time since 14 June when scans were not possible. The 2-10 keV fluxes ranged from 4-14 mCrab, and reached an intermediate minimum of about 7 mCrab on 28 August. Since then, the flux has been increasing (with a highest 2-10 keV flux of 36 mCrab on 7 September).
Swift/BAT Transient Monitor light curves for Swift J1842.5-1124