Dr Shubham Srivastav: Publications

The fast, luminous ultraviolet transient AT2018cow: extreme supernova, or disruption of a star by an intermediate-mass black hole?

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 484:1 (2019) 1031-1049

Authors:

Daniel A Perley, Paolo A Mazzali, Lin Yan, S Bradley Cenko, Suvi Gezari, Kirsty Taggart, Nadia Blagorodnova, Christoffer Fremling, Brenna Mockler, Avinash Singh, Nozomu Tominaga, Masaomi Tanaka, Alan M Watson, Tomás Ahumada, GC Anupama, Chris Ashall, Rosa L Becerra, David Bersier, Varun Bhalerao, Joshua S Bloom, Nathaniel R Butler, Chris Copperwheat, Michael W Coughlin, Kishalay De, Andrew J Drake, Dmitry A Duev, Sara Frederick, J Jesús González, Ariel Goobar, Marianne Heida, Anna YQ Ho, John Horst, Tiara Hung, Ryosuke Itoh, Jacob E Jencson, Mansi M Kasliwal, Nobuyuki Kawai, Tanazza Khanam, Shrinivas R Kulkarni, Brajesh Kumar, Harsh Kumar, Alexander S Kutyrev, William H Lee, Keiichi Maeda, Ashish Mahabal, Katsuhiro L Murata, James D Neill, Chow-Choong Ngeow, Bryan Penprase, Elena Pian, Robert Quimby, Enrico Ramirez-Ruiz, Michael G Richer, Carlos G Román-Zúñiga, DK Sahu, Shubham Srivastav, Quentin Socia, Jesper Sollerman, Yutaro Tachibana, Francesco Taddia, Samaporn Tinyanont, Eleonora Troja, Charlotte Ward, Jerrick Wee, Po-Chieh Yu

ASASSN-14dq: a fast-declining Type II-P supernova in a low-luminosity host galaxy

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 480:2 (2018) 2475-2500

Authors:

Avinash Singh, S Srivastav, Brajesh Kumar, GC Anupama, DK Sahu

SN 2015as: a low-luminosity Type IIb supernova without an early light-curve peak

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 476:3 (2018) 3611-3630

Authors:

Anjasha Gangopadhyay, Kuntal Misra, A Pastorello, DK Sahu, L Tomasella, L Tartaglia, Mridweeka Singh, Raya Dastidar, S Srivastav, P Ochner, Peter J Brown, GC Anupama, S Benetti, E Cappellaro, Brajesh Kumar, Brijesh Kumar, SB Pandey

Abstract:

AbstractWe present results of the photometric (from 3 to 509 d post-explosion) and spectroscopic (up to 230 d post-explosion) monitoring campaign of the He-rich Type IIb supernova (SN) 2015as. The (B − V) colour evolution of SN 2015as closely resemble those of SN 2008ax, suggesting that SN 2015as belongs to the SN IIb subgroup that does not show the early, short-duration photometric peak. The light curve of SN 2015as reaches the B-band maximum about 22 d after the explosion, at an absolute magnitude of −16.82 ± 0.18 mag. At ∼75 d after the explosion, its spectrum transitions from that of a SN II to a SN Ib. P Cygni features due to He i lines appear at around 30 d after explosion, indicating that the progenitor of SN 2015as was partially stripped. For SN 2015as, we estimate a 56Ni mass of ∼0.08 M⊙ and ejecta mass of 1.1–2.2 M⊙, which are similar to the values inferred for SN 2008ax. The quasi-bolometric analytical light-curve modelling suggests that the progenitor of SN 2015as has a modest mass (∼0.1 M⊙), a nearly compact (∼0.05 × 1013 cm) H envelope on top of a dense, compact (∼2 × 1011 cm) and a more massive (∼1.2 M⊙) He core. The analysis of the nebular phase spectra indicates that ∼0.44 M⊙ of O is ejected in the explosion. The intensity ratio of the [Ca ii]/[O i] nebular lines favours either a main-sequence progenitor mass of ∼15 M⊙ or a Wolf–Rayet star of 20 M⊙.

Broad-line Type Ic supernova SN 2014ad

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 475:2 (2018) 2591-2604

Authors:

DK Sahu, GC Anupama, NK Chakradhari, S Srivastav, Masaomi Tanaka, Keiichi Maeda, Ken'ichi Nomoto

Exploring the optical behaviour of a Type Iax supernova SN 2014dt

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 474:2 (2018) 2551-2563

Authors:

Mridweeka Singh, Kuntal Misra, DK Sahu, Raya Dastidar, Anjasha Gangopadhyay, Subhash Bose, Shubham Srivastav, GC Anupama, NK Chakradhari, Brajesh Kumar, Brijesh Kumar, SB Pandey

Abstract:

Abstract We present optical photometric (up to ∼410 d since Bmax) and spectroscopic (up to ∼157 d since Bmax) observations of a Type Iax supernova (SN) 2014dt located in M61. SN 2014dt is one of the brightest and closest (D ∼ 20 Mpc) discovered Type Iax SN. It best matches the light-curve evolution of SN 2005hk and reaches a peak magnitude of MB ∼ −18.13 ± 0.04 mag with Δm15 ∼ 1.35 ± 0.06 mag. The early spectra of SN 2014dt are similar to other Type Iax SNe, whereas the nebular spectrum at 157 d is dominated by narrow emission features with less blending as compared to SNe 2008ge and 2012Z. The ejecta velocities are between 5000 and 1000 km s−1, which also confirms the low-energy budget of Type Iax SN 2014dt compared to normal Type Ia SNe. Using the peak bolometric luminosity of SN 2005hk, we estimate the 56Ni mass of ∼0.14 M⊙. The striking similarity between SN 2014dt and SN 2005hk implies that a comparable amount of 56Ni would have been synthesized in the explosion of SN 2014dt.

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