Research

I am a postdoctoral researcher at the Oskar Klein Centre, Department of Astronomy, Stockholm University, working on the observational study of core-collapse supernovae (CCSNe) and explosive transients. My research combines high-cadence optical, ultraviolet, and near-infrared follow-up with hydrodynamical modelling to probe how massive stars lose mass, explode, illuminate their surroundings with circumstellar dust and enrich the interstellar medium with freshly formed dust and heavy elements.

A central thread of my current work is the interaction between the exploding ejecta and the circumstellar material (CSM) shed by the progenitor in the years to decades before core collapse. I lead multi-wavelength campaigns on flash-ionised and interacting Type II supernovae, most recently with the nearby SN 2023ixf in M101 to investigative the explosion properties, infer CSM and ejecta geometries, and trace the onset of in situ dust formation in the nebular phase. I am also active in the electromagnetic follow-up of gravitational-wave events and in estimating volumetric rates of rare transient classes such as superluminous supernovae.

I received my Ph.D. from the Joint Astronomy Program at the Indian Institute of Science / Indian Institute of Astrophysics, Bengaluru, working with Prof. G. C. Anupama on observational studies of Type II supernovae. Before joining Stockholm in 2024, I held a Fixed-Term Assistant Professor position at the Hiroshima Astrophysical Science Center, Japan, and a Research Associate–I position at ARIES, Nainital, India. Alongside my research, I develop open-source data-reduction and observation-planning pipelines, including RedPipe and NightSkyPlan.

For a full list of my refereed papers see my Publications page or my records on NASA ADS and ORCID. A current copy of my CV is available here.

Research Interests

  • Circumstellar material around progenitors of core-collapse supernovae (CCSNe)
  • Explosion and CSM geometry constraints through polarimetric and spectroscopic observations
  • Dust formation and its time-resolved evolution in interacting CCSNe
  • Hydrodynamical light-curve modelling of hydrogen-rich CCSNe
  • Nebular-phase investigation of CCSNe
  • Volumetric rate measurements of transients, including SLSNe-I and SLSNe-II
  • Electromagnetic follow-up of gravitational-wave events
  • Host environments of CCSNe, in particular 1987A-like explosions from blue supergiants
  • Development of reduction and candidate-vetting pipelines for real-time transient follow-up

Infrared Echoes and New Dust in hydrogen-rich SN 2023ixf

In my most recent lead-author paper (Singh et al. 2026, Nebular Phase Evolution of SN 2023ixf I), I follow SN 2023ixf from roughly 200 days to beyond 600 days after explosion in the optical and near-infrared. The near-IR excess is first explained by a circumstellar IR echo from pre-existing dust, and then by the onset of in situ dust formation in the cooling, clumpy ejecta. Combined with blue-shifted line profiles, the data place SN 2023ixf among a growing population of hydrogen-rich events where interaction-driven grain growth begins surprisingly early, with implications for the contribution of CCSNe to the cosmic dust budget.

Asphericities and a Multi-faceted CSM in SN 2023ixf

SN 2023ixf in M101 was the second-nearest core-collapse event of the millennium and offered a once-in-a-decade dataset to dissect the immediate environment of a Type II supernova. In Singh et al. (2024, ApJ 975, 132) I combined high-cadence UBVRI photometry, optical spectroscopy, and spectropolarimetry to show that the flash-ionisation signatures, the early light-curve excess, and the evolving polarisation signal are all jointly explained by an asymmetric, disk-like confined CSM plus an extended low-density wind. The analysis constrains mass-loss episodes in the final one to a few years before explosion and reveals ejecta-CSM geometry inconsistent with a single, spherical wind.

Circumstellar Interaction and 56Ni Mixing in Type II SN 2016gfy

SN 2016gfy is a luminous, slow-declining Type II supernova whose host HII-region spectrum yielded a sub-solar oxygen abundance (12+log(O/H) = 8.50±0.11). Early-time spectra showed a boxy Hα emission indicating a recent episode of enhanced mass loss 30–80 years before explosion, and a late-plateau bump in the VRI light curves required a combination of continued CSM interaction and partial mixing of radioactive 56Ni in the outer ejecta. Hydrodynamical modelling preferred a confined CSM of ~0.15 M☉ spread out to ~70 AU (Singh et al. 2019, ApJ 882, 68).

An 1987A-like Event Caught Early: SN 2018hna

The nearest naked-eye supernova of the modern era, SN 1987A, revealed that blue supergiants can also be progenitors of Type II supernovae. SN 2018hna is only the second 1987A-like event caught within a few days of explosion. Our high-cadence UVOIR observations clearly captured the adiabatic cooling of the shock-heated ejecta following shock breakout; hydrodynamical modelling of the cooling emission favoured a compact progenitor of radius ~50 R☉, confirming its BSG nature. The sub-solar host metallicity (~0.3 Z☉) is consistent with the low-metallicity environments typical of 1987A-like events (Singh et al. 2019, ApJL 882, L15).

Volumetric Rates of Superluminous Supernovae from ZTF

Volumetric rates of rare transients encode the physics of their progenitor channels — from magnetar spin-down to pair-instability explosions — but require a careful accounting of survey completeness. In collaboration with Dr. Lin Yan and Dr. Christoffer Fremling at Caltech, I used the untargeted, high-cadence Zwicky Transient Facility (ZTF) survey and the simsurvey forward-modelling framework to derive the first ZTF-based luminosity function and volumetric rate of hydrogen-poor superluminous supernovae, with clear implications for magnetar-driven formation scenarios.

Electromagnetic Follow-up of Gravitational-Wave Events

As part of the GROWTH, ENGRAVE, and J-GEM collaborations I have contributed to searches for optical/near-infrared counterparts to LIGO/Virgo/KAGRA binary neutron-star and neutron-star–black-hole candidates, including GW190425, S190426c, the kilonova luminosity-function constraints of Kasliwal et al. (2020), and the recent ZTF follow-up of S250206dm (Ahumada et al. 2026, PASP) and the subthreshold candidate superkilonova AT2025ulz / S250818k (Kasliwal et al. 2025, ApJL).

Active Collaborations

I am a member of several international collaborations active in time-domain and multi-messenger astronomy:

  • GROWTH — Global Relay of Observatories Watching Transients Happen (2018–2021, 2024–present)
  • ZTF — Zwicky Transient Facility (2024–present)
  • ePESSTO+ — extended Public ESO Spectroscopic Survey of Transient Objects (2024–present)
  • ENGRAVE — Electromagnetic counterparts of Gravitational-Wave sources at the VLT (2024–present)
  • LS4 — La Silla Schmidt Southern Survey (2025–present)
  • J-GEM — Japanese collaboration for Gravitational-wave ElectroMagnetic follow-up (2022–2024)

Observing Facilities & Recent Proposals

I regularly lead and co-lead time proposals across a range of northern- and southern-hemisphere facilities. Selected recent PI programs include:

  • Gemini N/S - GMOS, GNIRS, FLAMINGOS-2 — Probing Ejecta Composition, Mixing, and Asymmetries in CCSNe (Large and Long Program GN/GS-2025B-LP-209 — 96 hr)
  • CTIO/NEWFIRM — Probing Dust Formation Channels in Flash Supernovae with Multi-Epoch NIR Observations (2026A-165518 — 22.5 hr)
  • VLT/X-Shooter — Ejecta composition and mixing in CCSNe (P117.ALD, 7 hr); DDT on Type I SN 2024vcn (P114.28HJ, 2.1 hr)
  • VLT/MUSE — Host environments of 1987A-like Type II supernovae (P112 — 10 hr)
  • 3.6m DOT, India — Nebular-phase imaging of flash SNe; near-IR follow-up of SN 2023ixf (2024C1–2025B.1 — 12 hr)
  • 3.8m Seimei Telescope, Japan — Host-environment metallicities of CCSNe (2022B–2023A — 30 hr)
  • 2m HCT, India — Multi-year nebular-phase and ToO follow-up of low-redshift (2017C2, 2017C3; 2018C1, 2018C2, 2018C3: 2019C1 — 300 hr)

Grants & Funding

  • Royal Swedish Academy of Sciences Grant — 50,000 SEK (2026–2027)
  • Royal Swedish Academy of Sciences Grant — 17,000 SEK (2026–2027)
  • Dahlmark Grant 2026 — 9,700 SEK (2026)
  • Dahlmark Grant 2025 — 8,000 SEK (2025)
  • Royal Swedish Academy of Sciences Grant — 45,000 SEK (2025–2026)

Selected Recent Talks

  • Infrared Echoes and New Dust in SN 2023ixf — Multi-Messenger Astrophysics in the Dynamic Universe, Yukawa Institute of Theoretical Physics, Kyoto (Feb 2026)
  • SN 2023ixf: Shock-Powered Excess, Dust Formation and Emerging Asymmetries from Nebular-Phase Observations — An Extraordinary Journey into the Transient Sky, Padova, Italy (Apr 2025)
  • SN 2022ffg: An Interacting Type II SN with an Ultraviolet Plateau — Celebrating 20 Years of Swift Discoveries, Florence, Italy (Mar 2025)
  • Heterogeneity of Type II Supernovae — OKC Seminar, Stockholm, Sweden (Oct 2024)
  • Unravelling the Asphericity and Multi-faceted CSM in SN 2023ixf — OKC Extreme Objects Seminar, Stockholm (Sep 2024)
  • Multi-wavelength Analysis of SN 2023ixf — Transients Down Under 2024, Melbourne, Australia (Jan 2024)
  • Invited Talk: Investigation of Core-Collapse and Superluminous SNe — Supernova Workshop 2021 (Online, Dec 2021)
  • Invited Talk: Follow-up of Core-Collapse Supernovae from HCT — 20 Years of the Himalayan Chandra Telescope, Bengaluru, India (Sep 2020)
Page last updated April 2026 — more projects and highlights will be added soon.