17 research outputs found
X-Ray Flashes in Recurrent Novae: M31N 2008-12a and the Implications of the Swift Non-detection
Models of nova outbursts suggest that an X-ray flash should occur just after
hydrogen ignition. However, this X-ray flash has never been observationally
confirmed. We present four theoretical light curves of the X-ray flash for two
very massive white dwarfs (WDs) of 1.380 and 1.385 M_sun and for two recurrence
periods of 0.5 and 1 years. The duration of the X-ray flash is shorter for a
more massive WD and for a longer recurrence period. The shortest duration of 14
hours (0.6 days) among the four cases is obtained for the 1.385 M_sun WD with
one year recurrence period. In general, a nova explosion is relatively weak for
a very short recurrence period, which results in a rather slow evolution toward
the optical peak. This slow timescale and the predictability of very short
recurrence period novae give us a chance to observe X-ray flashes of recurrent
novae. In this context, we report the first attempt, using the Swift
observatory, to detect an X-ray flash of the recurrent nova M31N 2008-12a (0.5
or 1 year recurrence period), which resulted in the non-detection of X-ray
emission during the period of 8 days before the optical detection. We discuss
the impact of these observations on nova outburst theory. The X-ray flash is
one of the last frontiers of nova studies and its detection is essentially
important to understand the pre-optical-maximum phase. We encourage further
observations.Comment: 12 pages, including 9 figures and 3 tables. To appear in the
Astrophysical Journa
Discovery of the 2010 Eruption and the Pre-Eruption Light Curve for Recurrent Nova U Scorpii
We report the discovery by B. G. Harris and S. Dvorak on JD 2455224.9385
(2010 Jan 28.4385 UT) of the predicted eruption of the recurrent nova U Scorpii
(U Sco). We also report on 815 magnitudes (and 16 useful limits) on the
pre-eruption light curve in the UBVRI and Sloan r' and i' bands from 2000.4 up
to 9 hours before the peak of the January 2010 eruption. We found no
significant long-term variations, though we did find frequent fast variations
(flickering) with amplitudes up to 0.4 mag. We show that U Sco did not have any
rises or dips with amplitude greater than 0.2 mag on timescales from one day to
one year before the eruption. We find that the peak of this eruption occurred
at JD 2455224.69+-0.07 and the start of the rise was at JD 2455224.32+-0.12.
From our analysis of the average B-band flux between eruptions, we find that
the total mass accreted between eruptions is consistent with being a constant,
in agreement with a strong prediction of nova trigger theory. The date of the
next eruption can be anticipated with an accuracy of +-5 months by following
the average B-band magnitudes for the next ~10 years, although at this time we
can only predict that the next eruption will be in the year 2020+-2.Comment: Astronomical Journal submitted, 36 pages, 3 figures, full table
A 9-Month Hubble Space Telescope Near-UV Survey of M87. I. Light and Color Curves of 94 Novae, and a Re-determination of the Nova Rate
M87 has been monitored with a cadence of 5 days over a 9 month-long span
through the near-ultraviolet (NUV:F275W) and optical (F606W) filters of the
Wide Field Camera 3 (WFC3) of the . This
unprecedented dataset yields the NUV and optical light and color curves of 94
M87 novae, characterizing the outburst and decline properties of the largest
extragalactic nova dataset in the literature (after M31 and M81). We test and
confirm nova modelers' prediction that recurrent novae cannot erupt more
frequently that once every 45 days; show that there are zero rapidly recurring
novae in the central 1/3 of M87 with recurrence times 130 days;
demonstrate that novae closely follow the K-band light of M87 to within a few
arcsec of the galaxy nucleus; show that nova NUV light curves are as
heterogeneous as their optical counterparts, and usually peak 5 to 30 days
after visible light maximum; determine our observations' annual detection
completeness to be 71 - 77\%; and measure the rate Rnova of nova eruptions in
M87 as /yr. The corresponding luminosity-specific classical
nova rate for this galaxy is .
These rates confirm that ground-based observations of extragalactic novae miss
most faint, fast novae and those near the centers of galaxies. An annual M87
nova rate of 300 or more seems inescapable. A luminosity-specific nova rate of
in types of galaxies is
indicated by the data available in 2023.Comment: Accepted/In Press in ApJS; 3 Tables, 108 Figures, 180 page
Introducing the Condor Array Telescope: IV. A possible nova super-remnant surrounding the putative recurrent nova KT Eridani
Just 10 recurrent novae (RNe) - which erupt repeatedly on timescales shorter
than one century - are known in our Galaxy. The most extreme RN known (located
in the Andromeda galaxy), M31N 2008-12a, undergoes a nova eruption every year,
and is surrounded by a vast nova "super-remnant", 134 pc in extent. Simulations
predict that all RNe should be surrounded by similar vast shells, but previous
searches have failed to detect them. KT Eri has recently been suggested to be a
RN, and we have used the Condor Array Telescope to image its environs through
multiple narrowband filters. We report the existence of a large ( 50 pc
diameter), H-bright shell centered on KT Eri, exactly as predicted.
This strongly supports the claim that KT Eri is the 11th Galactic recurrent
nova, and only the second nova known to be surrounded by a super-remnant. SALT
spectra of the super-remnant demonstrate that its velocity width is consistent
with that of M31-2008-12a.Comment: 12 pages, 8 figure
Eclipses During the 2010 Eruption of the Recurrent Nova U Scorpii
The eruption of the recurrent nova U Scorpii on 28 January 2010 is now the
all-time best observed nova event. We report 36,776 magnitudes throughout its
67 day eruption, for an average of one measure every 2.6 minutes. This unique
and unprecedented coverage is the first time that a nova has any substantial
amount of fast photometry. With this, two new phenomena have been discovered:
the fast flares in the early light curve seen from days 9-15 (which have no
proposed explanation) and the optical dips seen out of eclipse from days 41-61
(likely caused by raised rims of the accretion disk occulting the bright inner
regions of the disk as seen over specific orbital phases). The expanding shell
and wind cleared enough from days 12-15 so that the inner binary system became
visible, resulting in the sudden onset of eclipses and the turn-on of the
supersoft X-ray source. On day 15, a strong asymmetry in the out-of-eclipse
light points to the existence of the accretion stream. The normal optical
flickering restarts on day 24.5. For days 15-26, eclipse mapping shows that the
optical source is spherically symmetric with a radius of 4.1 R_sun. For days
26-41, the optical light is coming from a rim-bright disk of radius 3.4 R_sun.
For days 41-67, the optical source is a center-bright disk of radius 2.2 R_sun.
Throughout the eruption, the colors remain essentially constant. We present 12
eclipse times during eruption plus five just after the eruption.Comment: ApJ in press. 60 pages, 17 figure