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Swift observations of the unidentified optical transient PQT 070519

ATEL # 1088; R. Starling, J.P. Osborne, P.T. O'Brien, M.R. Goad and P.A. Evans (University of Leicester)
on 30 May 2007; 18:14 UT
Password Certification: Rhaana Starling (rlcs1@star.le.ac.uk)

Subjects: Optical, X-ray, Transients

The unidentified optical transient PQT 070519 reported in ATel #1083 has been observed with Swift for a total of 9.8 ks over 3 epochs on 2007 May 24, 2007 May 27 and 2007 May 28.

The source is not detected in the 0.3-10 keV X-ray band down to a 3-sigma limiting flux of 3E-13 erg/cm2/s (assuming a nearby Gamma = 2 intrinsically unabsorbed power law source, and taking into account the Galactic absorption at this position of nH = 1.5E20 cm-2).

The source is marginally detected in the UVOT V-band filter with the following magnitudes:
Date-obs Texp (s) mag detection significance
2007-05-24 1240 20.70+/-0.53 2.2-sigma
2007-05-27 2301 20.75+/-0.41 2.8-sigma
2007-05-28 1619 20.79+/-0.50 2.3-sigma
There is no evidence of fading in our observations.

The nearby galaxy (RA, Dec (J2000) = 218.26674,+15.12142 deg, 11.3 arcsec from the transient source) is clearly detected with the following V-band magnitudes:
Date-obs Texp (s) mag
2007-05-24 1240 18.16+/-0.06
2007-05-27 2301 18.19+/-0.05
2007-05-28 1619 18.11+/-0.05
Magnitudes are not corrected for the Galactic extinction of E(B-V) = 0.018 mag. Quoted errors do not include the error in the zeropoint.


The long duration optical transient (>9 days), together with the X-ray non-detection suggests that this is not a Gamma-ray Burst or AGN, while the large distance between the source and the nearby galaxy does not favour a stellar capture event, ULX or supernova origin.

The faint pre-outburst limit suggests that any Galactic object must be in the halo or of very late spectral type. The duration and the >3 magnitude amplitude suggest a stellar flare is unlikely. Rather, we propose that a distant nova or dwarf nova eruption is consistent with the data to hand.

No further Swift observations are planned. We thank the Swift team for performing this ToO observation.


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