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Pre-discovery detection of the nova candidate M33N 2010-07a in XMM-Newton OM observations

ATEL # 2760; W. Pietsch, F. Haberl (Max-Planck-Institut fuer extraterrestrische Physik, MPE), B.F. Williams (University of Washington), W.P. Blair (John Hopkins University), T.J. Gaetz (Harvard-Smithonian Center for Astrophysics, CFA), K.S. Long (Space Telescope Science Institute), T.G. Pannuti (Morehead State University), P.P. Plucinsky (CFA), P.F. Winkler (Middlebury College) as part of the XMM-Newton M33 Large Program collaboration
on 27 Jul 2010; 13:09 UT
Password Certification: Wolfgang Pietsch (

Subjects: Optical, X-ray, Nova

Nishiyama and Kabashima discovered the nova candidate M33N 2010-07a on unfiltered images taken around 2010-07-17.798 UT (see CBET #2375). No source was present in their images taken on 2010-03-18.44 UT, in their earlier images and other deep optical images.

The "Deep XMM-Newton Legacy survey of M 33" (PI Williams) will cover the entire D25 isophote of the galaxy with a total of seven contiguous 100 ks exposures. The first two observations (ObsID 0650510101 and 0650510201) started on 2010-07-09.30 UT and 2010-07-11.29 UT, respectively.

M33N 2010-07a was in the field of view of the XMM-Newton Optical Monitor OM during ObsID 0650510101. We detect a source at RA = 01h33m36.84s, Dec = +30d46'22.6" (J2000, accuracy of 0.3", comparing to USNO B1 catalogue, Monet et al. 2003, AJ 125, 984) consistent with the position of the nova candidate. We determined the source brightness in the U, B, UVW1 and UVM2 filters as mag 19.7(1), 19.1(1), 20.4(1), and >21.0, respectively. The magnitudes are given in the AB system (see Oke 1974, ApJS 27, 21). The detection of a new source in the OM coincident with the nova candidate indicates that the outburst must have occurred already more than 8 days before the original nova discovery.

In X-rays, no source was detected within 56.4" and 19.9" in the XMM-Newton observatory survey (observations from 2000-2003, 0.2-4.5 keV, limiting luminosity 1x1035 erg s-1; Pietsch et al. 2004, A&A 426, 11) and in the Chandra observatory ChASeM33 survey (2000-2006, 0.35-8.0 keV, 2.1x1034 erg s-1, Tuellmann et al. 2010, in preparation), respectively. M33N 2010-07a was in the field of view of the EPIC pn instrument during both XMM-Newton large project observations. We do not detect X-ray emission from the nova candidate (3 sigma upper limits of 0.42x10-3 ct s-1 and 3.0x10-3 ct s-1 in the 0.2-1 keV band). Assuming an energy conversion factor of 1.04x10-11 erg cm-2 ct-1 for the EPIC pn thin filter observations (black body spectrum and Galactic foreground absorption of 6.66x1020 cm-2, see Pietsch et al. 2005, A&A 442, 925) leads to unabsorbed fluxes and luminosities in M 33 (assumed distance 817 kpc) of 4.4x10-15, 3.1x10-14 erg cm-2 s-1 and 3.5x1035, 2.5x1036 erg s-1, respectively. These upper limits are well below the luminosities reported for the supersoft source phase of novae, which however mostly is detected weeks to months after the optical outburst.

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