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Register a new userA search for optical bursts from RRAT J1819-1458: II. Simultaneous ULTRACAM-Lovell Telescope observations
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The Rotating RAdio Transient (RRAT) J1819-1458 exhibits ~3 ms bursts in the radio every ~3 min, implying that it is visible for only ~1 per day. Assuming that the optical light behaves in a similar manner, long exposures of the field would be relatively insensitive due to the accumulation of sky photons. A much better way of detecting optical emission from J1819-1458 would then be to observe with a high-speed optical camera simultaneously with radio observations, and co-add only those optical frames coincident with the dispersion-corrected radio bursts. We present the results of such a search, using simultaneous ULTRACAM and Lovell Telescope observations. We find no evidence for optical bursts in J1819-1458 at magnitudes brighter than i=19.3 (5-sigma limit). This is nearly 3 magnitudes fainter than the previous burst limit, which had no simultaneous radio observations.
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We derive the second and most stringent limit to date of the X-ray/radio flux ratio (F_x/F_R) for the radio bursts associated with the recently identified source class, the Rotating Radio Transients (RRATs). We analyze 20.1 hr of rxte/PCA observations of RRAT J1819-1458 -- a period during which 350ppm23 RRAT radio bursts occurred, based on the previously observed average radio burst rate. No X-ray bursts were detected, implying an upper-limit on the X-ray flux for RRAT-bursts of <1.5e-8 ergs cm-2 s-1 (2-10 keV) or a luminosity <2.3e37 (d/3.6kpc)^2 ergs s-1. The time-average burst flux is <2e-13 ergs cm-2 s-1 (0.5-8 keV) -- a factor of 10 below that of the previously identified persistent X-ray counterpart. Thus, X-ray bursts from the RRAT are energetically unimportant compared with the persistent X-ray emission. From the previously observed burst radio flux, we derive an upper-limit F_x/F_R< 4.2e-12 erg cm-2 s-1 mJy-1 for the radio bursts from this RRAT, the most stringent to date, due to the high radio flux of bursts from this source. The F_x/F_R ratio is a factor approximately 80 larger than that of the millisecond pulsar PSR B1821-24; thus emission processes of X-ray/radio efficiency comparable to MSP pulses cannot be ruled out. However, if the RRAT burst emission mechanism is identical to the msec bursts of magnetars, then the msec bursts of magnetars should be easily detected with radio instrumentation; yet none have been reported to date.
We present the results of simultaneous radio and X-ray observations of PSR J1819-1458. Our 94-ks XMM-Newton observation of the high magnetic field 5*10^13 G pulsar reveals a blackbody spectrum (kT~130 eV) with a broad absorption feature, possibly composed of two lines at ~1.0 and ~1.3 keV. We performed a correlation analysis of the X-ray photons with radio pulses detected in 16.2 hours of simultaneous observations at 1-2 GHz with the Green Bank, Effelsberg, and Parkes telescopes, respectively. Both the detected X-ray photons and radio pulses appear to be randomly distributed in time. We find tentative evidence for a correlation between the detected radio pulses and X-ray photons on timescales of less than 10 pulsar spin periods, with the probability of this occurring by chance being 0.46%. This suggests that the physical process producing the radio pulses may also heat the polar-cap.
We present an analysis of regular timing observations of the high-magnetic-field Rotating Radio Transient (RRAT) J1819$-$1458 obtained using the 64-m Parkes and 76-m Lovell radio telescopes over the past five years. During this time, the RRAT has suffered two significant glitches with fractional frequency changes of $0.6times10^{-6}$ and $0.1times10^{-6}$. Glitches of this magnitude are a phenomenon displayed by both radio pulsars and magnetars. However, the behaviour of J1819$-$1458 following these glitches is quite different to that which follows glitches in other neutron stars, since the glitch activity resulted in a significant long-term net decrease in the slow-down rate. If such glitches occur every 30 years, the spin-down rate, and by inference the magnetic dipole moment, will drop to zero on a timescale of a few thousand years. There are also significant increases in the rate of pulse detection and in the radio pulse energy immediately following the glitches.
FRB181228 was detected by the Molonglo Synthesis Radio Telescope (MOST) at a position and time coincident with Transiting Exoplanet Survey Satellite (TESS) observations, representing the first simultaneous multi-wavelength data collection for a Fast Radio Burst (FRB). The large imaged field-of-view of TESS allows a search over the uncertainty region produced by MOST. However, the TESS pixel scale of 21 and the Full Frame Image (FFI) cadence of 30 minutes is not optimal for the detection of an FOB with a possible millisecond duration. We search the TESS FFIs and find no events with a limiting TESS magnitude of 16, assuming a 30 minute event duration, corresponding to an optical flux density upper limit of approximately 2000 Jy for a ~ms signal duration, assuming no signal loss. In addition, the cosmic ray mitigation method for TESS significantly reduces its sensitivity to short timescale transients, which we quantify. We compare our results to the predictions of Yang, Zhang, and Wei (2019) and find that the upper limit is a factor of two thousand higher than the predicted maximum optical flux density. However, we find that if FRB181228 had occurred in the galaxy thought to host the nearest FRB detection to date (37 Mpc), an FOB may have been detectable by TESS. In the near future, when CHIME and ASKAP will detect hundreds to thousands of FRBs, TESS may be able to detect FOBs from those rare bright and nearby FRBs within this large population (if more sophisticated cosmic ray excision can be implemented).
We present sub-second, continuous-coverage photometry of three flares on the dM3.5e star, EQ Peg A, using custom continuum filters with WHT/ULTRACAM. These data provide a new view of flare continuum emission, with each flare exhibiting a very distinct light curve morphology. The spectral shape of flare emission for the two large-amplitude flares is compared with synthetic ULTRACAM measurements taken from the spectra during the large megaflare event on a similar type flare star. The white light shape during the impulsive phase of the EQ Peg flares is consistent with the range of colors derived from the megaflare continuum, which is known to contain a Hydrogen recombination component and compact, blackbody-like components. Tentative evidence in the ULTRACAM photometry is found for an anti-correlation between the emission of these components.
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