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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"
  1. GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
  2. GRB 251002A: EP-FXT counterpart detection
  3. GRB 251003A: LCOGT Optical Detection
  4. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  5. GRB 251003A: 1.5m OSN afterglow candidate
  6. GRB 251003A: Prompt enhanced Swift-XRT position
  7. GRB 251003A: Swift detection of a burst
  8. GRB 251003A: Fermi GBM Final Real-time Localization
  9. Swift GRB251003A: Global MASTER-Net observations report
  10. Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
  11. GRB 251002A: BOOTES-6 early optical detection
  12. GRB 251002A: SAO RAS optical observations
  13. GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
  14. GRB 251002A: FRAM-ORM afterglow detection
  15. GRB 251002A: LCO optical observation
  16. GRB 251002A: SVOM/VT optical observation
  17. GRB 251002A: SVOM detection of a burst
  18. Fermi GRB 251002A: Global MASTER-Net observations report
  19. GRB 251001B: Swift-BAT refined analysis
  20. GRB 251001A: SVOM/GRM observation
  21. GRB 251001A: Insight-HXMT detection
  22. GRB 251001B: Swift/UVOT Detection
  23. GRB 251001B: COLIBRÍ optical observations
  24. GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
  25. GRB 251001B: Swift-XRT refined Analysis
  26. GRB 251001B: SVOM/VT optical observation
  27. GRB 251001B: NOT optical observations
  28. GRB 251001C: Glowbug gamma-ray detection
  29. Swift GRB 251001B: Global MASTER-Net observations report
  30. GRB 251001B: Fermi GBM Observation
  31. GRB 251001B: Further GOTO observations of optical counterpart.
  32. GRB 251001B: Enhanced Swift-XRT position
  33. GRB 250930A: Fermi GBM Final Localization
  34. GRB 251001B: LCOGT Optical Observations
  35. GRB 250930A: SVOM/GRM observation
  36. GRB 251001B: TRT optical afterglow detection and potential host galaxy
  37. GRB 251001B: GOTO optical counterpart detection
  38. GRB 251001B: Swift detection of a burst
  39. GRB 251001B: Fermi GBM Final Real-time Localization
  40. GRB 251001A: Fermi GBM Detection
  41. GRB 250910A / EP250910a: VLT limits on the possible associated supernova
  42. GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112)
  43. GRB 251001A: Fermi GBM Final Real-time Localization
  44. LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
  45. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  46. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  47. GRB 250925A: MAO/AZT-22 optical observations
  48. Fermi GRB 250929A: Global MASTER-Net observations report
  49. GRB 250929A: Fermi GBM Final Real-time Localization
  50. GRB 250926A: CALET Gamma-Ray Burst Monitor detection
  51. LIGO/Virgo/KAGRA S250929c: Updated Sky localization
  52. GRB 250925A: Mondy I-band optical observations
  53. GRB 250916A: SVOM/VT optical observation
  54. LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate
  55. LIGO/Virgo/KAGRA S250927cy: Updated Sky localization
  56. LIGO/Virgo/KAGRA S250927ck: Updated Sky localization
  57. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  58. GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM
  59. GRB 250924A: SVOM/GRM observation
  60. GRB 250925A: Swift-XRT refined Analysis
  61. LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
  62. LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
  63. IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
  64. GRB 250926A: Insight-HXMT detection
  65. GRB 250926B: Fermi GBM Final Localization
  66. Fermi trigger No 780609036: Global MASTER-Net observations report
  67. IceCube Alert 250926.52: Global MASTER-Net observations report
  68. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  69. GRB 250926A: AstroSat CZTI detection
  70. GRB 250925A: Swift/UVOT Upper Limits
  71. GRB 250925A: Swift-BAT refined analysis
  72. GRB 250925A: Mondy and AbAO optical observations
  73. GRB 250925A: COLIBRÍ photometric redshift
  74. IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
  75. GRB 250925A: SVOM/GWAC-F60A upper limit
  76. GRB 250925A/EP250925a: EP-WXT detection
  77. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  78. GRB 250925A : MITSuME Akeno optical upper limits
  79. GRB 250925A: JinShan optical observations
  80. GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
  81. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  82. GRB 250925A: COLIBRÍ optical photometry of the afterglow
  83. Fermi GRB 250926A: Global MASTER-Net observations report
  84. GRB 250926A: Fermi GBM Final Real-time Localization
  85. GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
  86. GRB250925A: Liverpool Telescope optical observations
  87. GRB 250925A: NOT optical afterglow candidate
  88. GRB 250925A: Leavitt Observatory optical upper limit
  89. GRB 250925A: Enhanced Swift-XRT position
  90. GRB 250924A: Swift-BAT refined analysis
  91. GRB 250925A: GROWTH-India Telescope Upper Limits
  92. GRB 250925A: Swift detection of a burst
  93. Swift GRB 250925A: Global MASTER-Net observations report
  94. GRB 250922A: SVOM/GRM observation
  95. GRB 250924A: 1.6m Mephisto optical upper limits
  96. GRB 250924A: SAO RAS optical observations
  97. GRB 250924A: NOT optical observations
  98. GRB 250924A: AstroSat CZTI detection
  99. GRB 250914A: AstroSat CZTI detection
  100. GRB 250920B: AstroSat CZTI detection

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