X-ray, UV and millimeter observations of ASASSN-14du
ATel #6313; R. Margutti (CfA), P. J. Brown (Texas A&M, Mitchell Institute), A. Zauderer, A. M. Soderberg, A. Kamble, D. Milisavljevic, J. Parrent (CfA), report on behalf of the CARMA Key Project "A Millimeter View of the Transient Universe"
on 15 Jul 2014; 17:09 UT
Credential Certification: Raffaella Margutti (rmargutti@cfa.harvard.edu)
Subjects: Millimeter, Ultra-Violet, X-ray, Cataclysmic Variable, Nova, Star, Supernovae, Transient, Variables
Swift started observing the possible extreme luminosity transient ASASSN-14du (ATEL#6308) at 2014-07-13 00:43:43 UT.
From the Ultraviolet/Optical Telescope (UVOT) observations during that first epoch the following magnitudes were measured: uvw2 = 14.81 +\- 0.05 (649 s), uvm2 = 14.81 +\- 0.06 (488 s), uvw1 = 15.1 +\- 0.06 (814 s), u = 15.44 +\- 0.06 (314 s), b = 16.51 +\- 0.06 (315 s), v = 16.56 +\-0.06 (315 s). A later observation beginning 2014-07-15 02:17:24 shows marginal fading to uvw1 = 15.25 +\- 0.06 (814 s). These magnitudes are on the updated UVOT photometric system (Breeveld et al. 2011, in AIP Conf. Ser. 1358, p. 373). The photometry has not been corrected for extinction.
Two observations have been obtained with the X-Ray Telescope (XRT). An X-ray source is blindly detected at the position of the optical transient during the first observation (PI Brown), with limited significance of 2.6 sigma (total exposure time of 3 ks). The measured count-rate is (3.4 +/- 1.3)1E-3 c/s (0.3-10 keV). Assuming a spectral photon index ~2, the count-rate above translates into an absorbed flux of 1.2d-13 erg/s/cm2. The Galactic hydrogen column density in the direction of ASASSN-14du is 1.09E+20 cm-2 (Kalberla 2005). The corresponding luminosity is Lx~1E43 erg/s at z=0.18 (ATEL#6308) or Lx~1E32 erg/s if the transient is not extra-Galactic (ATel #6311) and at the distance of a few kpc.
The X-ray source is not blindly detected in the second X-ray observation that started at 2014-07-15 02:17:19 UT (total exposure time of 6 ks, PI Margutti), with a measured count-rate of ~1E-3 c/s. Further observations are planned to monitor the evolution of the possible X-ray source.
We observed ASASSN-14du beginning July 15, 2014 at 01:57:23 UT (or 2014 July 15.08 UT) with the Combined Array for Research in Millimeter Astronomy (CARMA) at a mean frequency of 85 GHz. In 117.7 minutes integration, we did not detect any significant radio emission at the position of ASASSN-14du to a 3-sigma level of 0.9 mJy/bm.
We thank the Swift team for scheduling these ToO observations. We thank the CARMA staff and observers for their support of these rapid-response observations.
