Swift observations of CSS 081007 030559 054715 Andy Beardmore

Swift observations of CSS 081007: 030559+054715 Andy Beardmore along with Julian Osborne, Kim Page (U. Leicester), Greg Schwarz (West Chester University), Sumner Starrfield (Arizona State University) Solen Balman (Middle East Technical University) Pasi Hakala (U. Turku) Jan-Uwe Ness (ESAC, Madrid) ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 1)

Discovery • Discovered by the Catalina Realtime Transient Survey (CRTS) → brightened by ~4 mag over a year (Pejcha et al. ATel#1825) • All Sky Automated Survey data → V = 14. 3 on MJD 54664 (Prieto et al. Atel#1835) • Outburst max assumed to occur during seasonal gap. • Pre-outburst shows variability > 1 mag on timescales of ~11 days (Drake et al. ATel#1940) ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 2) * ASAS

Spectroscopy Initial red spectrum (ATel # 1825) revealed broad, structured lines at Hα, [OIII] (4959, 5007Å), He II (4686Å) blended with [Ne IV] (4721Å) ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 3)

Spectroscopy Hα close-up shows at least 3 well separated components at 1740, -160, 1580 km/s HWZI ~ 3000 km/s → high velocity flows ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 4)

Spectroscopy Blue spectrum (ATel #1835) → strong, double peaked [Ne V] 3426Å, at -1700, 1100 km/s Suggestive of fast neon nova, like V 838 Her or V 4160 Sgr (e. g. Schwarz et al 2007) ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 5)

Swift TOO Optical spectroscopy suggested the hot, nuclear burning, WD would already be visible so a Swift TOO was requested Initial observation on 2008 -Nov-10 (day 34) was hindered by observing constraints → only 530 s of data Sufficient to give 75 counts, all below 1 ke. V. Observation was rescheduled on 2008 -Nov-14 (3. 5 ks) Blackbody spectral fit → k. TBB = 38+/- 6 e. V, LBB = 0. 9 -14. x 10^37 erg/s (for D = 2. 5 – 6. 4 kpc)* Both XRT and UVOT uvw 2 (λc=1928Å) showed slight variability (~ few %) (Schwarz et al ATel#1847) ( * D estimated indirectly from the pre-outburst V mag. Places object z > 1. 7 kpc – well out of Galactic plane. ) ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 6)

Swift-XRT & UVOT uvw 2 light curves 2008 -Nov 10 to 2008 -Nov-21 ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 7)

Swift TOO Following a 8 day hiatus, Swift observation resumed on 2008 -Nov-30 until 2008 -Dec-09 Revealed highly variable soft X-ray source, ranging from 0. 2 -2. 2 count/s. ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 8)

Swift-XRT & UVOT uvw 2 light curves 2008 -Nov 10 to 2008 -Dec-09 ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 9)

Swift high cadence campaigns Following a 8 day hiatus, Swift observation resumed on 2008 -Nov-30 until 2008 -Dec-09 Revealed highly variable soft X-ray source, ranging from 0. 2 -2. 2 count/s. Lomb-Scargle periodogram → 1. 77 day perodicity UVOT uvw 2 data varied from 14. 6 to 14. 0 mag also on 1. 77 day period. (Beardmore et al. ATel#1873) Following the 1. 77 day modulation discovery, a high cadence Swift observation campaign was initiated from 2008 -Dec-12 until 2008 -Dec-24, 500 s of data were taken every Swift orbit (GRBs permittiing) ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 10)

Swift high cadence campaigns 2008 -Nov 10 to 2008 -Dec-24 ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 11)

Swift high cadence campaigns High cadence data confirmed the 1. 77 day periodicity XRT peak count rate slowly decreased over time, though the minimum stayed at the same level UVOT uvw 2 mean magnitude decreased while its modulation amplitude increased This led to a 2 nd high cadence campaign → 500 s every orbit every 4 days from 2009 -Jan-18 to 2009 -Feb-09 ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 12)

Swift high cadence campaigns 2008 -Nov 10 to 2009 -Feb-09 ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 13)

Swift high cadence campaigns The 1. 77 day periodicity remained visible Soft X-ray peak count rate and uvw 2 mean mag recover slightly. UVOT uvw 2 light curve show an apparent longer modulation on a timescale ~50 days – poss. precessing disk. On 2009 -Feb-14 returned to lower cadence observations (1 ks per day) We expected the UVOT data would increase in brightness if it followed a 50 day timescale. However. . . Both UVOT and XRT data started to fade gradually over the next month until target was lost to Sun 1. 77 day modulation still evident in UVOT data ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 14)

Swift final XRT/uvw 2 light curves 2008 -Nov 10 to 2009 -Mar-20 ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 15)

1. 77 day periodicity AAVSO V day 70. 6 -83. 8 XRT UVOT uvw 2 ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 16)

UVOT minima O-C Tmin = MJD 54812. 4899 +/- 0. 0198 + E (1. 7718 +/- 0. 0010) ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 17)

Phase folded light curves V day 70. 6 -83. uvw 2 all data XRT Modulation in phase in optical → X-ray Day : 52. 1 -63. 7 -69. 9 -120. 0 wavebands ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 18)

XRT spectrum (< 0. 25 count/s) 0. 165 count/s for 175 ks → 29000 counts ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 19)

Spectral evolution Assume uv and X-ray arise from same component Fit uvw 2 & XRT together → lowers k. TBB Spectral evolution seen through outburst Temperature rather than radius change day 54 -70 Temperature/radius/ luminosity decrease beyond day ~140 → shrinking atmosphere → end of nuclear burning ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 20)

Nature of CSS 081007 X-ray lc has very similar morphology to AM Her – modulation caused by WD self-occultation of an accreting hot spot. 1. 77 day period → highly magnetic (>few hundred MG) WD to ensure synchronisation NOT circular polarisation limits: U < 0. 3 %, V < 0. 07 %. Suggests not strongly magnetic. No high-T bremss-like emission → AM Her type unlikely. Are we dealing with a persistent SSS ? Not really : ROSAT All-Sky Survey non-detection → XRT upper limit of 1. 6 e-4 count/s – much less than observed. X-ray source fades away after day 150. ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 21)

Nature of CSS 081007 Nova whose initial outburst was missed during the ground based telescopes seasonal gap. Optical spectroscopy and X-ray decline after day 140 suggest we have a fast neon nova Origin of 1. 77 day period : Such a coherent modulation must be orbital period 1. 77 day period is long for a nova but not unusual – e. g. GK Per Nova orbital variations are usually attributed to obscuration of the WD by material (eg disk) in high inclination systems Optical spectroscopy → radial velocity studies will hopefully confirm the binary nature of system. ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 22)

Summary CSS 081007 was a probable neon nova, whose peak outburst was missed Swift-XRT observations revealed a supersoft source spectrum from the initial observation (day 34). Further intensive monitoring with Swift revealed a variable UV and X-ray source, modulated with a 1. 77 day periodicity → binary orbital period Swift followed the source out to 160 days after the outburst, revealing a fading SSS beyond day 140. ESAC SSS Workshop – May 18 th - 20 th, 2009 (Page 23)