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J/A+A/416/1037    BVRIK Photometry for the field of 4U 0142+61 (Hulleman+, 2004)

The anomalous X-ray pulsar 4U 0142+61: variability in the infrared and a spectral break in the optical. Hulleman F., van Kerkwijk M.H., Kulkarni S.R. <Astron. Astrophys. 416, 1037 (2004)> =2004A&A...416.1037H
ADC_Keywords: Pulsars ; X-ray sources ; Photometry, UBVRI ; Photometry, infrared ; Positional data Keywords: pulsars: individual: 4U 0142+61 - stars: neutron - stars: magnetic fields - X-rays: general Abstract: We present new optical and infrared observations of the counterpart to the Anomalous X-ray Pulsar (AXP) 4U 0142+61 taken with the Keck I telescope. The counterpart is found to be variable in the infrared. This contrasts with our optical observations, which do not show any evidence for variability. Apart from the variability the AXP shows a remarkable spectral energy distribution. In particular, we find a sudden drop in flux going from V to B, presumably due to a spectral feature. We compare our results to those obtained for the two other securely identified AXP counterparts, to 1E 2259+586 and 1E 1048.1-5937. 4U 0142+61 is very similar to the former source in its X-ray timing and spectral properties, and we find that this similarity extends to the quiescent infrared to X-ray flux ratio. For 1E 1048.1-5937, which has different X-ray properties, the situation is less clear: in one observation, the infrared to X-ray flux ratio was much larger, but another observation gave an upper limit which is consistent with that observed for 4U 0142+61. Assuming the quiescent ratios are all similar, we estimate the optical and infrared brightnesses for the three AXPs that remain to be identified as well as for the four Soft Gamma-ray Repeaters. We also discuss briefly how the observed optical and infrared emission might arise, in particular in the context of the magnetar model. Description: Infrared images in the K band were obtained on the nights of 1999 February 7 and 8 with the Near Infrared Camera, mounted on the Keck I telescope. Further images were obtained on 2001 October 31 in the Ks band. Finally, an additional set of 18 frames, each consisting of five co-added exposures of 10s, was obtained on 2002 December 18. Optical observations were obtained with the Low Resolution Imaging Spectrograph at either of the two Keck telescopes. For photometric calibration, we also used observations taken with the 60-inch telescope on Palomar mountain, using the direct imaging camera at the Cassegrain focus. Observations in the B band were made for us on 2000 September 3. On 2000 December 29, further LRIS observations were taken, in Band R. On 2000 July 23, V, R and I-band images were taken under photometric conditions. In order to verify the calibration, as well as to obtain a calibration for the B band, additional images were taken on 2000 November 18 (B, V, R and I) and 19 (B and V). Table3 contains photometry for 4U 0142+61 and objects in the field. The errors listed are measurement uncertainties, and do not include the zero-point uncertainty of 0.03mag in all bands. The astrometry is based on the K-band image. Measurement errors range from 0.02arcsec for objects as faint as 4U 0142+61, to 0.005arcsec for the brighter ones. The astrometry is on the USNO-A2.0 system to within 0.1arcsec; it should be on the International Celestial Reference Frame to about 0.2arcsec. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 100 43 BVRI photometry for objects in the field of AXP 4U 0142+61
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 2 I2 h RAh Right ascension (J2000.0) 4- 5 I2 min RAm Right ascension (J2000.0) 7- 12 F6.3 s RAs Right ascension (J2000.0) 14 A1 --- DE- Declination sign (J2000.0) 15- 16 I2 deg DEd Declination (J2000.0) 18- 19 I2 arcmin DEm Declination (J2000.0) 21- 25 F5.2 arcsec DEs Declination (J2000.0) 27- 32 F6.3 mag Bmag ? B band magnitude (1) 34- 38 F5.3 mag e_Bmag ? Error in B band magnitude 40- 45 F6.3 mag Vmag ? V band magnitude 47- 51 F5.3 mag e_Vmag ? Error in V band magnitude 53- 58 F6.3 mag Rmag ? R band magnitude 60- 64 F5.3 mag e_Rmag ? Error in R band magnitude 66- 71 F6.3 mag Imag ? I band magnitude 73- 77 F5.3 mag e_Imag ? Error in I band magnitude 79- 84 F6.3 mag Kmag ? K band magnitude (1), (2) 86- 90 F5.3 mag e_Kmag ? Error in K band magnitude 92- 94 A3 --- Ident Identification (3) 96- 97 A2 --- Other Previous identification (4) 99 A1 --- Flag [F] bad photometry flag (5)
Note (1): The B band magnitude for the AXP (A) is marginal detection, the 3σ limit is B>27.4, its K band magnitude varied between K=19.7 and K=20.2. Note (2): Average of K and Ks band magnitudes Note (3): Identificiations: A for 4U 0142+61 ([HVK2000] A, Hulleman et al., 2000Natur.408..689H) Numbers 102 to 143 for the field stars Note (4): Numbering scheme introduced by Reid et al. (1980AJ.....85.1062R) and subsequently followed and extended by White et al. (1987MNRAS.226..645W) and Coe & Pightling (1998MNRAS.299..223C). = [DAB78] 2S 0142+614 NNa in Simbad Note (5): Indicates that magnitudes are uncertain, because the object was saturated in (part of) the images.
Acknowledgements: Ferdi Hulleman
(End) Ferdi Hulleman [UU, Netherlands], Patricia Bauer [CDS] 12-Feb-2004
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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