GRB 090126A
GCN Circular 8854
Subject
GRB 090126A: Swift-XRT Refined Analysis
Date
2009-01-27T01:23:41Z (16 years ago)
From
Michael Stroh at PSU/Swift <stroh@astroh.org>
M. C. Stroh (PSU) reports on behalf of the Swift-XRT team:
We have analyzed the first 3.1 ks of XRT data for GRB 090126A
(Evangelista et al., GCN Circ. 8852), from T+48 ks to T+60 ks after
the trigger. The data is all taken in Photon Counting (PC) mode.
Using 1435 s of XRT Photon Counting mode data and 2 UVOT images, we
find an astrometrically corrected X-ray position (using the XRT-UVOT
alignment and matching to the USNO-B1 catalogue): RA, Dec = 3.6577,
81.3733 which is equivalent to:
RA (J2000): 00 14 37.85
Dec (J2000): +81 22 24.0
with an uncertainty of 2.2 arcsec (90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions.
Position enhancement is described by Goad et al. (2007, A&A, 476, 1401 http://www.swift.ac.uk/xrt_positions/Goad.pdf)
, the current algorithm is an extension of this method.
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.8 (+0.6, -0.4). The best-
fitting absorption column is 1.8 (+/- 1.8) x 10^21 cm^-2, which is
consistent with the Galactic value of 1.4 x 10^21 cm^-2 (Kalberla et
al. 2005). The observed (unabsorbed) flux in the 0.3-10.0 keV band is
1.49 (1.9) x 10^-12 erg cm^-2 s^-1.
The light curve shows a potentially decaying source which can be fit
using a single power-law decay with a slope, alpha = 1.2 (+/- 1.1).
Assuming the light curve decays at the current rate, we predict count
rates at T+24 and T+48 hours to be 1.6 x 10^-2 and 7.0 x 10^-3
respectively.
This is an official product of the Swift-XRT team.
GCN Circular 8864
Subject
GRB 090126A: Swift/UVOT Upper Limits
Date
2009-01-30T18:03:40Z (16 years ago)
From
Stephen Holland at USRA/NASA/GSFC/SSC <Stephen.T.Holland@nasa.gov>
S. T. Holland (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC), and
M. C. Stroh (PSU) report, on the behalf of the Swift/UVOT team:
The Swift/UVOT observed the field of GRB 090126A (Evangelista
et al. 2009, GCN Circ. 8852) starting approximately 48 ks after the
SuperAGILE detection. We find no new source, relative to the DSS or
USNO-B1.0 catalogue, or a variable source, inside the UVOT-enhanced
XRT error circle (Stroh et al. 2009, GCN Circ. 8854). Preliminary
3-sigma upper limits for detecting a source in the co-added images,
using an aperture-corrected 2.5 arcsecond radius circular aperture,
are
Filter T_start T_stop Exp(s) Mag
------------------------------------------
v 49,398 55,302 208 >20.1
b 48,033 71,752 3256 >22.7
u 47,960 71,155 333 >21.0
white 48,713 66,162 2022 >23.1
------------------------------------------
The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.20 mag (Schlegel et al., 1998, ApJS, 500,
525). All photometry is on the UVOT photometry system described in
Poole et al. (2008, MNRAS, 383, 627).
Please update my e-mail address in your Address Book to <Stephen.T.Holland@nasa.gov
>.
/
\
/
GCN Circular 8880
Subject
GRB 090126A: Swift-XRT afterglow confirmation
Date
2009-02-03T16:43:33Z (16 years ago)
From
Michael Stroh at PSU/Swift <stroh@astroh.org>
M. C. Stroh (PSU) reports on behalf of the Swift-XRT team:
Swift took an additional 7.6ks observation of GRB 090126A centered at T
+29ks after the trigger. The single uncatalogued X-ray source
previously reported by Stroh et al. (GCN Circ. 8854) shows fading
flux, confirming its afterglow nature.
The 0.3-10 keV light curve can be fit using a simple power law model
with decay index alpha = 1.42 +/- 0.13.
This is an official product of the Swift-XRT team.