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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"

26504 results found.

  1. EP251130a: Mondy optical observations
  2. EP251130a: Optical detections with Kinder observations
  3. SVOM GRB251201.19: Global MASTER-Net observations report
  4. EP251130a: SAO RAS optical observations
  5. EP251130a: GTC OSIRIS+ redshift z = 4.035 and rebrightening
  6. EP251130A: Optical observation from 1.3m DFOT
  7. EP251130a: refined analysis of the EP-WXT and EP-FXT observations
  8. EP251130a: JinShan optical observations
  9. GRB 251201A: MAXI/GSC detection
  10. Fermi GRB 251130B: Global MASTER-Net observations report
  11. GRB 251127A: SVOM/GRM observation
  12. IceCube Alert 251130.75: Global MASTER-Net observations report
  13. EP251130a: Swift-XRT counterpart detection
  14. EP251130a: Global MASTER-Net observations report
  15. EP251130a: COLIBRÍ optical counterpart candidate
  16. EP251130a: Einstein Probe detection of an X-ray transient
  17. GRB 251129A / EP251129a: SAO RAS optical observations
  18. GRB 251126A: SAO RAS optical observations
  19. GRB 251128A: SVOM/GRM observation of a long burst
  20. SVOM GRB 251129A : MASTER optical counterpart detection
  21. GRB 251129A: Swift-XRT afterglow detection
  22. EP251129a: Global MASTER-Net observations report
  23. EP251129a/GRB 251129A : Einstein Probe detection of an X-ray transient
  24. GRB 251129A: SVOM/VT optical counterpart confirmation with VHF data
  25. GRB 251128A: Fermi GBM Observation
  26. GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  27. GRB 251129A: SVOM detection of a burst
  28. SVOM GRB251129A: Global MASTER-Net observations report
  29. GRB 251129A: SVOM detection of a burst
  30. GRB 251126A: Swift-BAT refined analysis
  31. GRB 251126A: TShAO, Mondy, and AbAO optical observations
  32. GRB 251128A: Swift/BAT-GUANO localization skymap of a burst
  33. Fermi GRB 251128A: Global MASTER-Net observations report
  34. GRB 251127A: Glowbug gamma-ray detection
  35. GRB 251126A: OHP/T193 optical observations and tentative spectroscopic redshift
  36. GRB 251126A: further SAO RAS optical observations
  37. GRB 251126A NUTTelA-TAO Early Measurements
  38. LIGO/Virgo/KAGRA S251112cm: GECKO/KMTNet tiling observations and transient candidates
  39. GRB251126A: MAO/AZT-22 optical observations
  40. GRB251126A: Continued optical observation from 1.3m DFOT
  41. GRB 251126A: Swift/UVOT Detection
  42. GRB 251126A: Mondy and SAO RAS optical observations
  43. GRB 251126A: Swift-XRT refined Analysis
  44. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  45. GRB 251126A: NOT optical observations
  46. GRB 251126A: 1.3m DFOT optical afterglow detection
  47. GRB 251126A: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 1-m telescope at McDonald Observatory
  48. GRB 251126A: COLIBRÍ photometric redshift z = 3.5
  49. Fermi GRB 251127A: Global MASTER-Net observations report
  50. GRB 251126A: Enhanced Swift-XRT position
  51. GRB 251126A: Kilonova-Catcher optical afterglow detection
  52. GRB 251126A: Nanshan/HMT optical afterglow detection
  53. Swift GRB 251126A: Global MASTER-Net observations report
  54. GRB 251121A: Fermi GBM Observation
  55. GRB 251126A: GIT discovery of the likely optical afterglow
  56. GRB 251126A: Swift detection of a burst
  57. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  58. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  59. EP251124b: NOT r- and z-band optical upper limits
  60. Fermi GRB 251125B : MASTER OT J155558.56+581224.1 optical counterpart discovery
  61. Fermi GRB 251125B: Global MASTER-Net observations report
  62. EP251124b: Global MASTER-Net observations report
  63. EP251124b: EP-WXT detection of a fast X-ray transient
  64. EP251124a: Xinglong GWAC-F60A optical observation
  65. Fermi GRB 251125A: Global MASTER-Net observations report
  66. EP251124a: NOT r- and z-band optical upper limits
  67. EP251124a: Global MASTER-Net observations report
  68. EP251124a: Swift-XRT observations
  69. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  70. EP251124a: Optical upper limit with Kinder observations
  71. Fermi GRB 251124a: Global MASTER-Net observations report
  72. LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901
  73. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  74. EP251124a: GROWTH-India Telescope optical upper limits
  75. EP251124a: Einstein Probe detection of an X-ray transient
  76. GRB 251116C: Swift-XRT confirmation of fading
  77. GRB 251122A/EP251122A: 1.3m DFOT optical detection
  78. GRB 251122A / EP251122a: Xinglong 2.16m optical observation
  79. EP251118A: 3.6m DOT optical afterglow detection
  80. GRB 251122A / EP251122a: EP-FXT counterpart detection
  81. EP251122a: refined analysis of the EP-WXT and EP-FXT observations
  82. GRB 251122A / EP251122a: WFST optical observations
  83. GRB 251122A/EP251122a: SVOM/VT optical observations with VHF data
  84. GRB 251122A/EP251122a: Additional, deeper LCO optical r band upper limit
  85. GRB 251122A / EP251122a: LCO optical upper limits
  86. EP251122a / GRB 251122A: optical counterpart candidate with Kinder observations
  87. EP251122a: Global MASTER-Net observations report
  88. GRB 251122A/EP251122a: SVOM/C-GFT upper limit
  89. GRB 251122A / EP251122a: SVOM detection of a long burst
  90. EP251122a: Einstein Probe detection of an X-ray transient
  91. EP251118a: Continued Optical Detection with Kinder observations
  92. LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search
  93. GRB 251121A: Swift/BAT-GUANO localization skymap of a short burst
  94. GRB 251121A: Glowbug gamma-ray detection of a likely short burst
  95. EP251118a: Xinglong-2.16m optical observation
  96. GRB 251115A: Fermi GBM Observation
  97. Fermi trigger No 785388351: Global MASTER-Net observations report
  98. EP251118A: 1.3m DFOT optical afterglow detection
  99. GRB 251118A: Swift/UVOT Detection
  100. EP251118a / GRB 251118C: SAO RAS optical observations

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