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Swift X-ray, UV and optical observations of MAXI J0637-430

ATel #13295; C. Knigge, A. Rao, P. Gandhi, D. Altamirano (University of Southampton)
on 18 Nov 2019; 13:55 UT
Credential Certification: Christian Knigge (christian@astro.soton.ac.uk)

Subjects: Optical, Ultra-Violet, X-ray, Binary, Black Hole, Transient, Variables

Referred to by ATel #: 13296

We report on Swift observations of MAXI J0637-430 carried out on 2019-11-07. Our main goal was to establish the near-UV through optical SED of the source by cycling through all of the UVOT filters (except for white light) in a single visit. The source was clearly detected in all bands, at the following flux levels:

Filter  Effective Wavelength   Flux             Error 
        (Angstrom)             (erg/s/cm2/A)    (erg/s/cm2/A) 
UVW2	2085.73	               1.794e-14	2.206e-16	 
UVM2	2245.78	               1.382e-14	2.367e-16	 
UVW1	2684.14	               9.358e-15	1.786e-16	 
U	3520.95	               4.221e-15	9.540e-17	 
B	4346.25	               2.012e-15	6.603e-17	 
V	5411.43	               9.294e-16	6.588e-17	 
We have used VOSA (http://svo2.cab.inta-csic.es/theory/vosa) to obtain an approximate blackbody fit to this data set, adopting a reddening of E(B-V) = 0.064, as suggested by the line-of-sight Hydrogen column density. We find that the data are reasonably well described by a blackbody with T_eff = 45,000 K and a luminosity of L = 2.6e34 (d/1kpc)^2 erg/s. The XRT X-ray spectrum obtained during our observations can be modelled (reduced chi-squared = 1.4) as an absorbed blackbody disk (phabs*diskbb) with inner disk temperature T_in = 0.675 +/- 0.003 keV and luminosity (2-10 keV) = 8.3e34 (d/1kpc)^2 erg/s. Residuals around this model remain at energies >5 keV and near 0.6 keV. The mean XRT count rate was 46 counts/s (0.3-10 keV).