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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

5814 results found.

  1. LIGO/Virgo/KAGRA S251112cm: Swift XRT observations, 20 X-ray sources
  2. LIGO/Virgo/KAGRA S251112cm: Candidates from the Zwicky Transient Facility
  3. Fermi Gamma-ray Burst Monitor trigger 784717756/251113381 is not a GRB
  4. GRB 251112A: Swift-XRT refined Analysis
  5. LIGO/Virgo/KAGRA S251112cm: Detection of two young transients by BlackGEM/MeerLICHT: AT2025adgp and AT2025adgq
  6. LIGO/Virgo/KAGRA S251112cm: Coverage and upper limits from MAXI/GSC observations
  7. LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations
  8. LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 3-Initial Localization Volume
  9. LIGO/Virgo/KAGRA S251112cm: Identification of a GW compact binary merger candidate
  10. GRB 251111A: Swift-XRT observations
  11. GRB 251013C: Chandra X-ray observations and jet break detection
  12. GRB 251111A: SVOM/COLIBRÍ (FM-GFT) optical counterpart detection
  13. SVOM GRB251108.54: Global MASTER-Net observations report
  14. SVOM GRB251106.83: Global MASTER-Net observations report
  15. GRB 250920C: TERI Gamma-ray detection
  16. Fermi GRB 251103A: Global MASTER-Net observations report
  17. GRB 251103B: GROWTH-India Telescope optical upper limits
  18. GRB 251103B: Swift detection of a burst
  19. GRB 251103A: BOOTES-2/TELMA optical afterglow
  20. GRB 251103A: NOT optical afterglow candidate
  21. Fermi GRB 251102A: Global MASTER-Net observations report
  22. GRB 250926B: VZLUSAT-2 detection
  23. GRB 250926A: VZLUSAT-2 detection
  24. GRB 250925A: VZLUSAT-2 detection
  25. GRB 251028A: MAXI/GSC detection
  26. Fermi-LAT Gamma-ray Observations of IceCube-251025A
  27. EP251027.145: COLIBRÍ optical upper limits
  28. GRB 251017A: Mondy AZT-33IK and Koshka Zeiss-1000 optical observations
  29. GRB 251017A: INASAN-Kislovodsk optical observations
  30. GRB 251026B: Tentative GOTO optical counterpart candidate
  31. GRB 251025B: MAO/AZT-22 optical observations
  32. Fermi GRB 251025C: Global MASTER-Net observations report
  33. GRB 251026A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  34. GRB 251025A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  35. EP251023b: Global MASTER-Net observations report
  36. EP251023a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm telescope at Teide Observatory
  37. IPN triangulation of GRB 251016B
  38. EP251023a: COLIBRÍ optical observations
  39. EP251021b/GRB 251021A: SVOM/VT optical candidate
  40. GRB 251023B / MAXI J0451+122: MAXI/GSC detection
  41. Fermi GRB 251023A: Global MASTER-Net observations report
  42. EP251023a: Einstein Probe detection of an X-ray transient
  43. LIGO/Virgo/KAGRA S251021u: Identification of a GW compact binary merger candidate
  44. Fermi-LAT gamma-ray observations of IceCube-251018A
  45. GRB 251013C: Leavitt Observatory optical photometry
  46. GRB 251017A: COLIBRÍ Early Afterglow Detection
  47. GRB 251017A: Swift detection of a burst with an optical counterpart
  48. sb25101602: Swift-XRT counterpart detection
  49. GRB 251011B: SVOM/VT optical upper limit
  50. LIGO/Virgo/KAGRA S251014cn: NED Galaxies in the 3-Initial Localization Volume
  51. GRB 251014A: DDOTI Upper Limit
  52. Fermi GRB 251013C: Global MASTER-Net observations report
  53. GRB 251011B inspection: MASTER orphan GRB detection
  54. GRB 251011B : MASTER optical observations
  55. GRB 251011B: Swift detection of a burst
  56. GRB 251009B (short): Glowbug gamma-ray detection
  57. GRB 251009A: Fermi GBM Final Localization
  58. GRB 250916A: TERI Gamma-ray detection
  59. GRB 250919A: TERI gamma-ray detection
  60. EP251006a: Global MASTER-Net observations report
  61. EP250911a: Koshka Zeiss-1000 Optical Upper Limit
  62. GRB 250902A: MSU cubesats detection
  63. Fermi GBM Sub-Threshold Detection of GRB 250910A
  64. GRB 251003A: Swift detection of a burst
  65. Fermi GRB 251002A: Global MASTER-Net observations report
  66. GRB 250930A: SVOM/GRM observation
  67. GRB 251001B: Swift detection of a burst
  68. LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
  69. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  70. GRB 250925A: MAO/AZT-22 optical observations
  71. Fermi GRB 250929A: Global MASTER-Net observations report
  72. GRB 250925A: Mondy I-band optical observations
  73. GRB 250916A: SVOM/VT optical observation
  74. LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate
  75. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  76. GRB 250924A: SVOM/GRM observation
  77. LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
  78. LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
  79. IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
  80. GRB 250926A: Insight-HXMT detection
  81. Fermi trigger No 780609036: Global MASTER-Net observations report
  82. IceCube Alert 250926.52: Global MASTER-Net observations report
  83. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  84. GRB 250926A: AstroSat CZTI detection
  85. GRB 250925A: Mondy and AbAO optical observations
  86. GRB 250925A: COLIBRÍ photometric redshift
  87. IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
  88. GRB 250925A: SVOM/GWAC-F60A upper limit
  89. GRB 250925A/EP250925a: EP-WXT detection
  90. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  91. GRB 250925A : MITSuME Akeno optical upper limits
  92. GRB 250925A: JinShan optical observations
  93. GRB 250925A: COLIBRÍ optical photometry of the afterglow
  94. Fermi GRB 250926A: Global MASTER-Net observations report
  95. GRB250925A: Liverpool Telescope optical observations
  96. GRB 250925A: Leavitt Observatory optical upper limit
  97. GRB 250925A: GROWTH-India Telescope Upper Limits
  98. Swift GRB 250925A: Global MASTER-Net observations report
  99. GRB 250922A: SVOM/GRM observation
  100. GRB 250924A: 1.6m Mephisto optical upper limits

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