J/AJ/152/102 Flux conversion factors for the Swift/UVOT filters (Brown+, 2016)
Interpreting flux from broadband photometry.
Brown P.J., Breeveld A., Roming P.W.A., Siegel M.
<Astron. J., 152, 102-102 (2016)>
=2016AJ....152..102B 2016AJ....152..102B (SIMBAD/NED BibCode)
ADC_Keywords: Supernovae ; Spectra, ultraviolet
Keywords: instrumentation: photometers - methods: data analysis -
methods: observational - standards - supernovae: general -
techniques: photometric
Abstract:
We discuss the transformation of observed photometry into flux for the
creation of spectral energy distributions (SED) and the computation of
bolometric luminosities. We do this in the context of supernova
studies, particularly as observed with the Swift spacecraft, but the
concepts and techniques should be applicable to many other types of
sources and wavelength regimes. Traditional methods of converting
observed magnitudes to flux densities are not very accurate when
applied to UV photometry. Common methods for extinction and the
integration of pseudo-bolometric fluxes can also lead to inaccurate
results. The sources of inaccuracy, though, also apply to other
wavelengths. Because of the complicated nature of translating
broadband photometry into monochromatic flux densities, comparison
between observed photometry and a spectroscopic model is best done by
forward modeling the spectrum into the count rates or magnitudes of
the observations. We recommend that integrated flux measurements be
made using a spectrum or SED which is consistent with the multi-band
photometry rather than converting individual photometric measurements
to flux densities, linearly interpolating between the points, and
integrating. We also highlight some specific areas where the UV flux
can be mischaracterized.
Description:
The conversion of observed magnitudes (or the actual observed photon
or electron count rates) to a flux density is one of the most
fundamental calculations. The flux conversions factors for the six
Swift/UVOT filters are tabulated in Table1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 69 454 Flux conversion factors
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See also:
J/ApJ/805/74 : SN2014J Swift/UVOT light curves (Brown+, 2015)
J/ApJS/212/18 : An atlas of UV-to-MIR galaxy SEDs (Brown+, 2014)
J/ApJ/721/1608 : Absolute UV magnitudes of type Ia SNe (Brown+, 2010)
J/PASP/110/863 : A Stellar Spectral Flux Library: 1150 - 25000 A (Pickles 1998)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Spectrum Input spectrum
17- 18 I2 --- Ref Spectrum Reference (1)
20- 27 F8.5 aJ/m2/nm/ct uvw2 Swift Ultraviolet/Optical Telescope (UVOT)
uvw2 filter conversion factor (2)
29- 36 F8.5 aJ/m2/nm/ct uvm2 Swift/UVOT uvm2 filter conversion factor (2)
38- 45 F8.5 aJ/m2/nm/ct uvw1 Swift/UVOT uvw1 filter conversion factor (2)
47- 53 F7.5 aJ/m2/nm/ct u Swift/UVOT u filter conversion factor (2)
55- 61 F7.5 aJ/m2/nm/ct b Swift/UVOT b filter conversion factor (2)
63- 69 F7.5 aJ/m2/nm/ct v Swift/UVOT v filter conversion factor (2)
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Note (1): Spectrum references:
1 = Vega spectra from
ftp://ftp.stsci.edu/cdbs/calspec/alpha_lyr_stis_004.fits;
Bohlin & Gilliland (2004AJ....127.3508B 2004AJ....127.3508B);
2 = The value given is the average computed for a variety of GRB models
described in Poole et al. (2008MNRAS.383..627P 2008MNRAS.383..627P); This value is used in
the Swift CALDB products;
3 = The value given is the average computed for a variety of stellar
spectra Pickles 1998 (Cat. J/PASP/110/863) as described in Poole et
al. (2008MNRAS.383..627P 2008MNRAS.383..627P);
4 = This value is given in Swift/UVOT CALDB documentation for the AB
magnitude system as defined by Oke (1974ApJS...27...21O 1974ApJS...27...21O);
5 = The STMAG system is based on a spectrum with constant flux density per
unit wavelength as described by Koornneef et al.
(1986HiA.....7..833K 1986HiA.....7..833K);
6 = Blackbody spectrum calculated according to Planck & Masius (1914, The
Theory of Heat Radiation; New York, NY: Blakiston);
7 = Stellar spectra from Pickles 1998 (Cat. J/PASP/110/863);
8 = Galaxy spectra from Storchi-Bergmann et al. (1995ApJS...98..103S 1995ApJS...98..103S);
9 = Galaxy spectra from Brown et al. 2014 (Cat. J/ApJS/212/18);
10 = Average type Ia SN spectral series from Hsiao et al.
(2007ApJ...663.1187H 2007ApJ...663.1187H); The number indicates days from maximum light
(positive or negative).
11 = Theoretical spectra matched to Type IIP SN 2005cs from Dessart et al.
(2008ApJ...675..644D 2008ApJ...675..644D). The number indicates days from explosion;
12 = Type Ia SN2011fe spectra; Mazzali et al. (2014MNRAS.439.1959M 2014MNRAS.439.1959M);
13 = Type Ia SN1992A spectrum; Kirshner et al. (1993ApJ...415..589K 1993ApJ...415..589K);
14 = Type Ic SN1994I spectrum; Jeffery et al. (1994ApJ...421L..27J 1994ApJ...421L..27J);
15 = Type IIP SN1999em spectrum; Baron et al. (2000ApJ...545..444B 2000ApJ...545..444B).
Note (2): In units of 10-15erg/cm2/nm/ct. Conversion factors are multiplied
by the count rate to give the flux density in units of
10-16erg/s/cm2/Å.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 25-Oct-2016