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Swift observation of the nova candidate PNV J17452791-2305213 one day after discovery

ATel #4061; Kirill Sokolovsky (ASC Lebedev/SAI MSU), Stanislav Korotkiy (Ka-Dar Obs.), Leonid Elenin and Igor Molotov (ISON)
on 22 Apr 2012; 19:49 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

Subjects: Optical, Ultra-Violet, X-ray, Nova

Referred to by ATel #: 4088, 4094, 4110

The nova candidate PNV J17452791-2305213 (17:45:28.02 -23:05:23.1 +/-0.1", J2000) was discovered at V~9.6 by the authors (SK & KS) on 2012 April 21.0112 UT with a wide-field survey camera (F=135mm f/2.0 lens + ST8300M CCD) at Ka-Dar Observatory's TAU Station (Nizhny Arkhyz, Russia). Pre-discovery images from Xingming observatory (near Urumqi, China) reported through the CBAT "Transient Object Followup Reports" page ( http://www.cbat.eps.harvard.edu/unconf/followups/J17452791-2305213.html ) indicate that the outburst began as early as April 20.8403. Comparison with other observations reported through this page suggest that the nova candidate was discovered on the rising stage of its optical lightcurve.

The Swift satellite observation of PNV J17452791-2305213 started on April 21.9127 and lasted 1500 sec. Preliminary analysis of Swift/XRT data results in a non-detection of the X-ray counterpart with the 0.3-10 keV flux upper limit of >0.02 XRT counts per second. The nova candidate is clearly detected in the ultraviolet by Swift/UVOT with the magnitude of M2=13.90 +/-0.05 (Vega system).

X-ray emission from a classical nova is expected to arise at three phases (Orio 2004 RMxAC, 20, 182; Ness et al. 2007 ApJ, 665, 1334; Mukai et al. 2008, ApJ, 677, 1248): (1) thermal emission from the initial fireball, (2) emission from shocked material in the nova shell, and (3) the hot white dwarf surface (SSS phase). Our observation was conducted too late to catch the fireball phase and well too early for the SSS phase. We may conclude that the observable part of the nova shell is expanding rather uniformly with no shocks strong enough to produce bright X-ray emission. It cannot be excluded that detectable X-ray emission may appear later as the outburst develops.

We thank Neil Gehrels and the Swift team for rapidly approving and executing this ToO observation and Maria Mogilen for help in preparing the telegram. We used tools provided by the XRT Interactive Archive at ASI Science Data Center.