This is a blog section of the site. However, I do not think that I will be able to write very often.
Thus, this is a place for scientific news which could be related to me and my comments on them. Enjoy!
July 19th, 2019 / Comments Off on Swift X-ray detection and ground-based observations of the new WZ Sge-type dwarf nova TCP J21040470+4631129 / by Vitaly
ATel #12947: K. Sokolovsky (MSU), V. Neustroev (U. Oulu), K. L. Page (U. Leicester), J. Leahy-McGregor, M. Bundas, H. Gallamore, C. Wicklund, B. McIntyre, C. Conner, E. Zobel, E. Aydi, L. Chomiuk, A. Kawash, J, Strader (MSU), K. Mukai (NASA/GSFC), N. P. M. Kuin (UCL-MSSL), J. P. Osborne (U. Leicester), C. Knigge (U. Southampton), D. Denisenko (SAI)
The 9.2 mag optical transient TCP J21040470+4631129 was discovered on 2019-07-12.49 UT by H. Nishimura on images obtained with a DSLR camera and a 200 mm telephoto lens. It was spectroscopically confirmed on 2019-07-12.9 as a dwarf nova outburst (ATel #12936). Swift observed TCP J21040470+4631129 for 5.1 ks between 2019-07-13 and 2019-07-17. During the first observation, Swift/XRT detected a relatively bright X-ray source at the position of the dwarf nova, with an XRT count rate of 0.64 +/- 0.03 cts/s. In the following days, the X-ray flux declined before stabilizing at an average level of 0.09 +/- 0.02 cts/s.
The total X-ray spectrum can be approximated by a combination of two optically thin emission components (the APEC model in XSPEC) having kT = 11.5 +13.8/-4.5 keV and 0.19 +/- 0.02 keV, respectively, and negligible absorption (n_H1 < 7e19 cm^-2). We note, however, that the spectra, extracted separately from the first and remaining observations are statistically different. While the lower APEC temperature component is consistent in both spectra (kT~0.2 keV), the hotter APEC component has cooled from >23.6 keV to 5.4 +4.6/-1.5 keV. The peak 0.3-10 keV flux of 1.5e-11 ergs/cm^2/s corresponds to the X-ray luminosity of 2.1e31 ergs/s at 109 pc (see below). The object is still too bright for UVOT photometry or spectroscopy.
We also observed TCP J21040470+4631129 with the 0.6 m telescope of the Michigan State University Campus Observatory (MPC code 766) on 2019-07-13, 15, 16 and 17 for ~7 h each night. The object declined from V=8.59 +/-0.01 on 2019-07-13.1145 to V=10.25 +/-0.01 on 2019-07-18.1111. The period search (after detrending) revealed the presence of superhumps with the period of 0.0535 +/-0.0003 d, close to the value reported by T. Vanmunster in vsnet-alert 23388, and shorter than the periods suggested by T. Kato in vsnet-alert 23396. The peak-to-peak amplitude of the superhumps is about 0.04 mag.
We used 10 best-seeing images to measure the position of TCP J21040470+4631129 relative to UCAC3 (Zacharias et al. 2010 AJ, 139, 2184) stars in the field: 21:04:04.691 +46:31:13.68 J2000 +/-0.05″; thus confirming the identification of Gaia DR2 2163612727665972096 (g=17.77, parallax 9.13 +/-0.12 mas) with the transient. The large outburst amplitude combined with the presence of superhumps suggests that TCP J21040470+4631129 is a WZ Sge-type dwarf nova. A dramatic increase in X-ray luminosity accompanying the optical outburst has been observed in other WZ Sge systems: GW Lib (Byckling et al. 2009, MNRAS, 399, 1576), SSS J122221.7-311525 (Neustroev et al. 2018, A&A, 611, 13), V805 Aur (ATel #4954), ASASSN-18fs (Parikh & Wijnands 2018, RNAAS, 2d, 201), TCP J06373299-0935420 (ATel #12531), ASASSN-19hl (ATel #12629).
Further Swift observations are planned to monitor this object. We thank the Swift PI, Brad Cenko, for approving the observations, and the Swift planning and operations teams for rapid scheduling of these ToO observations and for their ongoing support.
June 17th, 2019 / Comments Off on Multicolour Optical Photometry of Swift J1357.2-0933 just prior to the 2019 outburst rise / by Vitaly
ATel #12815: Vitaly Neustroev (University of Oulu), Elena Neustroeva (Oulu)
The black hole transient Swift J1357.2-0933 has recently been reported to be in a new outburst, less than 2 years after the previous one in 2017 (ATel #10297). The new outburst was first detected in the optical by the Zwicky Transient Facility (ATel #12796), and later confirmed in X-rays by NICER observations (ATel #12801). Russell et al. (ATel #12803) have reported the results of long-term optical monitoring of the transient. They found that Swift J1357.2-0933 has been in quiescence on 2019 March 19, but on March 21 its flux increase was detected. Thus, Russell et al. concluded that the optical outburst has started on MJD 58562.44 +/- 1.06.
On 2019 March 19 (MJD 58561.24+/-0.01), we observed the field of Swift J1357.2-0933 with the Nordic Optical Telescope (NOT) equipped with the STANcam imager. Observations were performed with the Bessel B, V, R, I, and sdss z’ filters. The observations gave the following magnitudes:
B=22.05+/-0.38, V=21.23+/-0.14, R=20.59+/-0.09, I=20.11+/-0.09, sdss z’=21.0+/-0.5.
Both the obtained spectral energy distribution (SED) and all the magnitudes are consistent with those found in the PanSTARRS catalog, allowing us to conclude that at the time of our observations (MJD 58561.24), the transient has not yet shown any sign of the forthcoming outburst.
May 13th, 2019 / Comments Off on A paper on the long cycle variability of the Algol OGLE-LMC-DPV-065 has been accepted in MNRAS / by Vitaly
The paper entitled “On the long cycle variability of the Algol OGLE-LMC-DPV-065 and its stellar, orbital and disk parameters” has been accepted for publication in MNRAS.
Preprint: ArXiv:1905.04231.
Mennickent R. E., …, Neustroev V. V., et al. Abstract:
OGLE-LMC-DPV-065 is an interacting binary whose double-hump long photometric cycle remains hitherto unexplained. We analyze photometric time series available in archive datasets spanning 124 years and present the analysis of new high-resolution spectra. A refined orbital period is found of 10\fd0316267 ± 0\fd0000056 without any evidence of variability. In spite of this constancy, small but significant changes in timings of the secondary eclipse are detected. We show that the long period continuously decreases from 350 to 218 days during 13 years, then remains almost constant for about 10 years. Our study of radial velocities indicates a circular orbit for the binary and yields a mass ratio of 0.203 ± 0.001. From the analysis of the orbital light curve we find that the system contains 13.8 and 2.81 \msun\ stars of radii 8.8 and 12.6 \rsun\ and absolute bolometric magnitudes -6.4 and -3.0, respectively. The orbit semi-major axis is 49.9 \rsun\ and the stellar temperatures are 25460 K and 9825 K. We find evidence for an optically and geometrically thick disk around the hotter star. According to our model, the disk has a radius of 25 \rsun, central and outer vertical thickness of 1.6 \rsun\ and 3.5 \rsun, and temperature of 9380 K at its outer edge. Two shock regions located at roughly opposite parts of the outer disk rim can explain the light curves asymmetries. The system is a member of the double periodic variables and its relatively high-mass and long photometric cycle make it similar in some aspects to β Lyrae.
April 1st, 2019 / Comments Off on A paper on a high-proper motion cataclysmic variable imbedded in a bow-shock nebula has been accepted in MNRAS / by Vitaly
The paper entitled “From outburst to quiescence: spectroscopic evolution of V1838 Aql imbedded in a bow-shock nebula” has been accepted for publication in MNRAS.
Preprint: ArXiv:1811.02349.
Hernandez Santisteban J. V., Echevarria J., Zharikov S., Neustroev V. V., et al. Abstract:
We analyse new optical spectroscopic, direct-image and X-ray observations of the recently discovered a high proper motion cataclysmic variable V1838 Aql. The data were obtained during its 2013 superoutburst and its subsequent quiescent state. An extended emission around the source was observed up to 30 days after the peak of the superoutburst, interpreted it as a bow–shock formed by a quasi-continuous outflow from the source in quiescence. The head of the bow–shock is coincident with the high-proper motion vector of the source (v⊥=123±5 km/s) at a distance of d=202±7 pc. The object was detected as a weak X-ray source (0.015±0.002 counts/s) in the plateau of the superoutburst, and its flux lowered by two times in quiescence (0.007±0.002 counts/s). Spectroscopic observations in quiescence we confirmed the orbital period value Porb=0.0545±0.0026 days, consistent with early-superhump estimates, and the following orbital parameters: γ=−21±3 km/s and K1=53±3 km/s. The white dwarf is revealed as the system approaches quiescence, which enables us to infer the effective temperature of the primary Teff=11600±400K. The donor temperature is estimated ≲2200K and suggestive of a system approaching the period minimum. Doppler maps in quiescence show the presence of the hot spot in HeI line at the expected accretion disc-stream shock position and an unusual structure of the accretion disc in Hα.
The Astronomy research unit of the University of Oulu is the northernmost department of astronomy in the world at a mere one degree south of the Polar Circle. We are a small but scientifically active research group consisting of 4 senior researchers (1 permanent, 3 fixed-term) and externally funded postdocs (3) and PhD students (4). According to all measures, we are proud to count ourselves among the best research units of our university. However, despite our success in attracting external funding (currently in excess of 300k€ per year), a strong publication track record (99 papers in 2016-2018, including 4 in Science and Nature) and a well-developed teaching curriculum, the Astronomy research unit is now in serious danger.
Without any preliminary consultations with the staff or the unit leader, the university board has decided to start a process that aims at terminating the main subject status of Astronomy, and converting two of the current astronomy researcher positions to teaching positions in Physics. This would be a serious blow for us, but it is in line with other actions taken previously by the faculty of science against the Astronomy unit, like a series of budget cuts, and the denial by the dean to approve our suggestions for continuation contracts of key personnel of the unit. The loss of the main subject status may sound like a harmless thing. But it is not: the process (called YT-negotiations), initiated by the dean of the faculty of science, is usually used by employers in Finland to terminate work contracts “efficiently” in a situation of economic difficulties. It is a heavy cannon, and it is surprising that this heavy measure is used for this purpose, in particular since the Astronomy unit is producing positive net income to the university, via the bonus university receives from the Ministry of Education and Culture based on the unit’s research output. We are afraid that the process will permit the faculty to take away positions from our unit. This will endanger the unit as a whole, because our budget is directly related to the research output, and a reduction in research staff would lead to a downward spiral and eventual termination of our research unit within a few forthcoming years.
The YT-committee will probably support the plans pursued by the faculty. However, the final decision will be made by the rector of the university (prof. Jouko Niinimaki), after discussion with the head of the university board (Dr. Risto Murto). There is no formal way for us to even raise our voice or formulate an appeal against the recommendation by the committee. In this situation, our only hope is the international astronomy community. We hope that supporting statements from international astronomy departments and institutes could be sent directly to the Rector’s office. Of course you cannot directly comment on the quality and quantity of teaching in our unit, having not seen it in person. But if you decide to support us, you could express your worry on the consequences of a reduction in staff on the research output of the unit and the international collaborations. For instance, during the last 2 years our researchers have been awarded 40% of all accepted ESO proposals with a Finland-based PI, with only 15% of the astronomy personnel in Finland. The Finnish investment in ESO is the largest scientific investment for astronomy in the country. Taking away positions from the group in Oulu would significantly decrease the science return for Finland.
If you decide to support us or you have any questions, please write me a message at vitaly@neustroev.net and I will then send you the addresses, to which you can send your statement.
Thank you for your consideration,
Dr. Vitaly Neustroev
on behalf of the members of the Astronomy research unit
January 15th, 2019 / Comments Off on First time detection of a GRB at sub-TeV energies: MAGIC detected the GRB 190114C / by Vitaly
After 15 years of dreaming about the GRB detection, tonight it became reality: MAGIC detected a GRB at a red-shift of 0.42 with > 20 sigma in 20 minutes observation time! We have already issued an ATel #12390 on this very hot topic:
“The MAGIC telescopes performed a rapid follow-up observation of GRB 190114C (Gropp et al., GCN 23688; Tyurina et al., GCN 23690, de Ugarte Postigo et al., GCN 23692, Lipunov et al. GCN 23693, Selsing et al. GCN 23695). This observation was triggered by the Swift-BAT alert; we started observing at about 50s after Swift T0: 20:57:03.19. The MAGIC real-time analysis shows a significance >20 sigma in the first 20 min of observations (starting at T0+50s) for energies >300GeV. The relatively high detection threshold is due to the large zenith angle of observations (>60 degrees) and the presence of partial Moon. Given the brightness of the event, MAGIC will continue the observation of GRB 190114C until it is observable tonight and also in the next days.”
July 12th, 2018 / Comments Off on A press conference announcing astrophysics breakthrough / by Vitaly
Today there will be a press conference announcing recent multi-messenger astrophysics findings led by the NSF’s IceCube Neutrino Observatory at the South Pole and the MAGIC collaboration. The briefing will feature leading astrophysicists from across the globe.
July 10th, 2018 / Comments Off on MAGIC celebrates its 15th anniversary! / by Vitaly
MAGIC (Major Atmospheric Gamma Imaging Cherenkov) is a system of two 17-m Imaging Atmospheric Cherenkov Telescopes. The MAGIC collaboration consists of about 165 astrophysicists from 24 institutions and consortia from 11 countries. I’m a member of MAGIC since 2013. This year, MAGIC celebrates its 15th anniversary! Our colleagues had produced a nice MAGIC 15th birthday celebration movie. Enjoy!
July 6th, 2018 / Comments Off on Another MAGIC paper accepted by MNRAS / by Vitaly
Another MAGIC paper entitled “The broad-band properties of the intermediate synchrotron peaked BL Lac S2 0109+22 from radio to VHE gamma rays” has been accepted for publication in MNRAS: arXiv:1807.02095
