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J/ApJ/794/54    Polarization and photometry for blazar W Comae   (Sorcia+, 2014)

Rotation of the optical polarization angle associated with the 2008 γ-ray flare of blazar W Comae. Sorcia M., Benitez E., Hiriart D., Lopez J.M., Cabrera J.I., Mujica R. <Astrophys. J., 794, 54 (2014)> =2014ApJ...794...54S (SIMBAD/NED BibCode)
ADC_Keywords: BL Lac objects ; Accretion ; Polarization ; Photometry Keywords: BL Lacertae objects: individual: ON231, W Comae - galaxies: jets - galaxies: photometry - polarization Abstract: An R-band photopolarimetric variability analysis of the TeV bright blazar W Comae between 2008 February 28 and 2013 May 17 is presented. The source showed a gradual tendency to decrease its mean flux level with a total change of 3 mJy. A maximum and minimum brightness states in the R band of 14.25±0.04 and 16.52±0.1 mag, respectively, were observed, corresponding to a maximum variation of ΔF=5.40 mJy. We estimated a minimum variability timescale of Δt=3.3 days. A maximum polarization degree P=33.8%±1.6%, with a maximum variation of ΔP=33.2%, was found. One of our main results is the detection of a large rotation of the polarization angle from 78° to 315° (Δθ∼237°) that coincides in time with the γ-ray flare observed in 2008 June. This result indicates that both optical and γ-ray emission regions could be co-spatial. During this flare, a correlation between the R-band flux and polarization degree was found with a correlation coefficient of rF-p =0.93±0.11. From the Stokes parameters, we infer the existence of two optically thin synchrotron components that contribute to the polarized flux. One of them is stable with a constant polarization degree of 11%. Assuming a shock-in jet model during the 2008 flare, we estimated a maximum Doppler factor δD∼27 and a minimum of δD∼16; a minimum viewing angle of the jet ∼2.0°; and a magnetic field B∼0.12 G. Description: The observations were carried out with the 0.84 m f/15 Ritchey-Chretien telescope at the Observatorio Astronomico Nacional of San Pedro Martir (OAN-SPM) in Baja California, Mexico and the instrument POLIMA. The differential R-band magnitudes of W Comae were calculated using the standard star A distant about ∼1.2 arcminutes to the southeast from the studied object. The magnitude of the comparison star A in the R band is (11.72±0.04) mag (Fiorucci & Tosti 1996, J/A+AS/116/403). Because of the narrow field of view of the instrument, ∼4 arcminutes, this was the only standard star available for calibration with a reasonable flux level. The exposure time was 80 s per image for W Comae. Polarimetric calibrations were made using the polarized standard stars ViCyg12 and HD 155197 and the unpolarized standard stars GD319 and BD+332642 (Schmidt et al. 1992AJ....104.1563S). W Comae was observed between 2008 February 28 and 2013 May 17. During this period, 32 observing runs of 7 nights per run were carried out around the new moon phase; in total, we collected 141 data points. Objects: ---------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------- 12 21 31.69 +28 13 58.5 W Comae = QSO B1219+28 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 62 141 Polarization and Photometry in the R-Band for W Comae
See also: J/A+AS/116/403 : VRI photometry of stars in 12 BL Lac objects (Fiorucci+, 1996) J/A+AS/128/315 : BVRI photometry of blazars (Jia Guibin+ 1998) J/ApJ/833/77 : gamma-ray bright blazars optical polarization (Itoh+, 2016) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 3 A3 --- Cycle Cycle number 5- 15 A11 "Y/M/D" Date Date of the observation 17- 25 F9.4 d JD Julian Date of the observation (JD -2450000.00) 27- 30 F4.1 % p Polarization degree 32- 34 F3.1 % e_p Uncertainty in p 36- 38 I3 deg theta Orientation of electric vector position angle 40- 41 I2 deg e_theta Uncertainty in theta 43- 47 F5.2 mag Rmag R band magnitude 49- 52 F4.2 mag e_Rmag Uncertainty in Rmag 54- 57 F4.2 mJy RFlux R band flux density 59- 62 F4.2 mJy e_RFlux Uncertainty in RFlux
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 26-Apr-2017
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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