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1

Constraints on the Formation of Double Neutron Stars from the Observed Eccentricities and Current Limits on Merger Rates

Chruslinska M., Belczynski K., Bulik T., Gladysz W.

Acta Astronomica

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2017

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Vol. 67, No. 1

37--50

EN

We employ population synthesis method to model the double neutron star (DNS) population and test various possibilities on natal kick velocities gained by neutron stars after their formation. We first choose natal kicks after standard core collapse supernovae (CCSN) from a Maxwellian distribution with velocity dispersion of σ = 265 km/s as proposed by Hobbs and then modify this distribution by changing σ toward smaller and larger kick values. We also take into account the possibility of NS formation through electron capture supernova. In this case we test two scenarios: zero natal kick or small natal kick, drawn from Maxwellian distribution with σ = 26.5 km/s. We calculate the present-day orbital parameters of binaries and compare the resulting eccentricities with those known for observed DNSs. As an additional test we calculate Galactic merger rates for our model populations and confront them with observational limits. We do not find any model unequivocally consistent with both observational constraints simultaneously. The models with low kicks after CCSN for binaries with the second NS forming through core collapse SN are marginally consistent with the observations. This means that either 14 observed DNSs are not representative of the intrinsic Galactic population, or that our modeling of DNS formation needs revision.

2

Discovery and Observations of the Unusually Luminous Type-Defying II-P/II-L Supernova ASASSN-13co

Holoien T. W.-S., Prieto J. L., Pejcha O., Stanek Z., Kochanek C. S., Shappee B. J., Grupe D., Morrell N., Thorstensen J. R., Basu U., Beacom J. F., Bersier D., Brimacombe J., Davis A. B., Pojmański G., Skowron D. M.

Acta Astronomica

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2016

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Vol. 66, No. 2

219--238

EN

We present photometric and spectroscopic observations of ASASSN-13co, an unusually luminous Type II supernova and the first core-collapse supernova discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN). First detection of the supernova was on UT 2013 August 29 and the data presented span roughly 3.5 months after discovery. We use the recently developed model by Pejcha and Prieto to model the multi-band light curves of ASASSN-13co and derive the bolometric luminosity curve. We compare ASASSN-13co to other Type II supernovae to show that it was unusually luminous for a Type II supernova and that it exhibited an atypical light curve shape that does not cleanly match that of either a standard Type II-L or Type II-P supernova.

3

OGLE-IV Real-Time Transient Search

Wyrzykowski Ł., Kostrzewa-Rutkowska Z., Kozłowski S., Udalski A., Poleski R., Skowron J., Blagorodnova N., Kubiak M., Szymański M. K., Pietrzyński G., Soszyński I., Ulaczyk K., Pietrukowicz P., Mróz Michał

Acta Astronomica

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2014

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Vol. 64, No. 3

197--232

EN

We present the design and first results of a real-time search for transients within the 650 sq. deg. area around the Magellanic Clouds, conducted as part of the OGLE-IV project and aimed at detecting supernovae, novae and other events. The average sampling of about four days from September to May, yielded a detection of 238 transients in 2012/2013 and 2013/2014 seasons. The superb photometric and astrometric quality of the OGLE data allows for numerous applications of the discovered transients. We use this sample to prepare and train a Machine Learning-based automated classifier for early light curves, which distinguishes major classes of transients with more than 80% of correct answers. Spectroscopically classified 49 supernovae Type Ia are used to construct a Hubble Diagram with statistical scatter of about 0.3 mag and fill the least populated region of the redshifts range in the Union sample. We investigate the influence of host galaxy environments on supernovae statistics and find the mean host extinction of AI=0.19±0.10 mag and AV=0.39±0.21 mag based on a subsample of supernovae Type Ia. We show that the positional accuracy of the survey is of the order of 0.5 pixels (0.13'') and that the OGLE-IV Transient Detection System is capable of detecting transients within the nuclei of galaxies. We present a few interesting cases of nuclear transients of unknown type. All data on the OGLE transients are made publicly available to the astronomical community via the OGLE website.

4

Supernovae and Other Transients in the OGLE-IV Magellanic Bridge Data

Kozłowski S., Udalski A., Wyrzykowski Ł., Poleski R., Pietrukowicz P., Skowron J., Szymański M. K., Kubiak M., Pietrzyński G., Soszyński I., Ulaczyk K.

Acta Astronomica

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2013

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Vol. 63, No. 1

1--19

EN

We analyze two years (mid-2010 to mid-2012) of OGLE-IV data covering ≈65 deg2 of the Magellanic Bridge (the area between the Magellanic Clouds) and find 130 transient events including 126 supernovae (SNe), two foreground dwarf novae and another two SNe-like transients that turned out to be active galactic nuclei (AGNs). We show our SNe detection efficiency as a function of SN peak magnitude based on available SNe rate estimates. It is 100% for SNe peak magnitudes I<18.8 mag and drops to 50% at I≈19.7 mag. With our current observing area between and around the Magellanic Clouds (≈600 deg2), we expect to find 24 SNe peaking above I<18 mag, 100 above I<19 mag, and 340 above I<20 mag, annually. We briefly introduce our on-line near-real-time detection system for SNe and other transients, the OGLE Transient Detection System.

5

Oxygen Issue in Core Collapse Supernovae

Elmhamdi A.

Acta Astronomica

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2011

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Vol. 61, No. 2

179--198

EN

We study the spectroscopic properties of a selected sample of 26 events within Core Collapse Supernovae (CCSNe) family. Special attention is paid to the nebular oxygen forbidden line [OI] 6300, 6364 Å doublet. We analyze the line flux ratio F6300/F6364 and infer information about the optical depth evolution, densities, volume-filling factors in the oxygen emitting zones. The line luminosity is measured for the sample events and its evolution is discussed on the basis of the bolometric light curve properties in type II and in type Ib-c SNe. The luminosities are then translated into oxygen abundances using two different methods. The results are combined with the determined 56Ni masses and compared with theoretical models by means of the [O/Fe] vs. Mms diagram. Two distinguishable and continuous populations, corresponding to Ib-c and type II SNe, are found. The higher mass nature of the ejecta in type II objects is also imprinted in the [CaII] 7291, 7324Å to [OI] 6300, 6364Å luminosity ratios. Our results may be used as input parameters for theoretical models studying the chemical enrichment of galaxies.

6

Gamma-Ray Bursts at Low Redshift

Paczyński B.

Acta Astronomica

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2001

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Vol. 51, No. 1

1--4

EN

Long duration gamma-ray bursts (GRBs) are at cosmological distance, they appear to be located near star forming regions and are likely associated with some type of supernovae. They are also likely to be strongly beamed, which lowers their energetics by several orders of magnitude and increases their rate by the same factor. Therefore, it is likely that one out of 100-1000 core collapse supernovae generates ultra-relativistic jets, which beam gamma-rays and all other early emission into two narrow cones. After a year or so, the jets are decelerated, become non-relativistic and their emission becomes more or less isotropic. At least two GRBs: 970508 (z=0.835) and 980703 (z=0.966) show strong radio emission from late and therefore non-relativistic afterglows. Such events should be readily detectable at low redshift, say z=0.03. A search for strong radio emitters among recent nearby supernovae should be done about one year after the explosion. If some of these explosions generated GRBs and their gamma-ray beam missed us the bipolar structure of the radio remnant should be resolvable with VLBA.