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
Credential Certification: Rhaana Starling (rlcs1@star.le.ac.uk)
Subjects: Optical, X-ray, Transient
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.
