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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"

32495 results found.

  1. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  2. GRB 250322A: Swift/UVOT Upper Limits
  3. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  4. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  5. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  6. EP250321a: TNOT Observation of Optical Counterpart
  7. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  8. GRB 250322A: Gemini-North redshift of candidate host galaxy
  9. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  10. GRB 250322A: AstroSat CZTI detection of a short burst
  11. GRB250322A: STEP/T80S optical limits
  12. GRB 250322A: Gemini-South optical observations
  13. GRB 250322A: VLT optical observations
  14. GRB 250322A: VLT near-infrared observations
  15. FRB 250316A: DDOTI Continued Optical Observations
  16. GRB 250322A: NOT optical upper limits
  17. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  18. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  19. GRB 250322A: MASTER optical observation
  20. EP250321a: Liverpool Telescope optical follow-up
  21. EP250321a: Mondy AZT-33IK Optical Observations
  22. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  23. EP250321a: KAIT optical observations
  24. EP250321A: COLIBRÍ Continuing Optical Observations
  25. GRB 250225B: GECAM-A detection
  26. GRB 250312A: GECAM-A detection
  27. GRB 250321B: Swift ToO observations
  28. EP250321a: WFST optical observations
  29. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  30. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  31. GRB 250320B: Fermi GBM Observation
  32. EP250321a: Xinglong 216 decaying optical observations
  33. GRB 250321A: Swift-BAT refined analysis
  34. GRB 250320B: Fermi-LAT detection
  35. EP250321a: SVOM/VT optical observation
  36. EP 250321A: Optical counterpart detection by LCO.
  37. EP250321a: Kinder optical follow-up observations
  38. GRB 250321A: Swift/UVOT Upper Limits
  39. GRB 250320B: SVOM/GRM observation of a long burst
  40. EP250321a: LCO optical counterpart detection
  41. EP250321a: Swift-XRT detection of an X-ray source
  42. EP250321A: COLIBRÍ Optical Observations
  43. EP250321a: VLT/X-shooter redshift z = 4.368
  44. GRB 250320B: AstroSat CZTI detection
  45. EP250321a: REM optical/NIR afterglow detection
  46. Fermi GRB 250320B: Global MASTER-Net observations report
  47. EP250321a: TRT optical counterpart detection
  48. EP250321a: Global MASTER-Net observations report
  49. Swift GRB 250321A: Global MASTER-Net observations report
  50. Fermi GRB 250321A: Global MASTER-Net observations report
  51. GRB 250321A: GOTO optical upper limits
  52. GRB 250321A: Swift-XRT localisation
  53. GRB 250314A: Keck/NIRC2 J-band upper limit
  54. EP250226a/GRB 250226A: KAIT optical observations
  55. GRB 250321A: Fermi GBM Observation
  56. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  57. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  58. Fermi GRB 250319B: Global MASTER-Net observations report
  59. GRB 250313A: GRBAlpha detection
  60. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  61. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  62. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  63. GRB 250314A: ATCA radio upper limits
  64. EP250302a: VLA observations
  65. GRB 250317B: OHP/T193 continued follow-up
  66. LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
  67. GRB 250317C: SVOM/GRM observation of a long burst
  68. GRB 250317B: Leavitt Observatory optical upper limit
  69. GRB 250309B/AT2025dws: further ATCA observations
  70. GRB 250317B: Mondy AZT-33IK Optical Observations
  71. GRB 250317C: AstroSat CZTI detection
  72. GRB 250317B: NOT optical observations suggest an optical plateau phase
  73. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  74. GRB 250317B: OHP/T193 optical observations
  75. GRB250312A: Swift/UVOT Upper Limits
  76. GRB 250317B: REM optical/NIR observations
  77. GRB 250317B: Swift-XRT observations
  78. GRB 250316A: Swift/UVOT Upper Limits
  79. GRB 250314A: REM optical/NIR upper limits
  80. GRB 250316A: AbAO AS-32 Optical Upper Limit
  81. EP 250317B: Fading optical counterpart detection by LCO
  82. GRB 250317B: LCO detection of the fading optical afterglow
  83. GRB 250317B: refined SVOM/MXT analysis
  84. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  85. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  86. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  87. GRB 250316A: Fermi GBM Observation
  88. GRB 250316A: Swift-XRT observations
  89. Fermi GRB 250316A: Global MASTER-Net observations report
  90. GRB 250314A: SVOM/GRM analysis
  91. GRB 250316A: Swift ToO observations
  92. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  93. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  94. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  95. GRB 250314A: EP-FXT afterglow detection
  96. EP250315a: refined analysis of the EP-WXT and EP-FXT observations
  97. GRB 250314A: Swift/UVOT Upper Limits
  98. GRB 250312B: GRBAlpha detection
  99. GRB 250314A: Swift XRT Detection
  100. EP250315a: optical counterpart candidate detected by Gemini North

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